Hi All:

I need some help trying to diagnose a problem with my X2 spindle. Here's the story:

I bought an X2 in very lightly used condition off eBay and after less than an hour of running decided to put a belt drive on it. Everything went OK until I noticed that the spindle would heat up very quickly when running above 1000RPM or so.

I fiddled with the belt tension a bit without any change. The heating was definitely coming from the bearings.

Since then I have pulled and replaced the bearings with Nachi rubber-sealed bearings following the Little Machine Shop instructions for doing so (see here (http://www.littlemachineshop.com/Instructions/R8%20Spindle%20Kit.pdf)). The amount of force needed to budge anything felt pretty heavy to me and if the original bearings were not damaged, I suspect they were getting them out.

After pressing on the new bearings (which also took an enormous amount of force, or what felt like it to me--it was a stick-and-jerk process, not a smooth one--the problem seemed worse in that the spindle ran even hotter faster, though it did sound a little smoother.

Afterwards I pulled everything apart again and polished the spindle journals on my lathe with some fine sandpaper. This made the bearings press on a *little* smoother though still under substantial pressure. I reassmbled everything but no improvement seen.

One thing I am wondering about is whether there is any problem besides the bearing installation themselves that could cause this.

Right now I am kind of at a dead end and wondering if my only good choice is to buy a whole new spindle assembly. I suspect that the process of installing and removing the bearings several times was not kind to them. There are several steps that as best as I could tell had you pushing on the bearings the "wrong" way.

I've measured the bearings and spindle journals and they seem to be right on top of each other size-wise. Measuring with my caliper I get readings of between 35.02 and 34.99 mm on the lower section for instance, mostly right at 35.00. The bearing ID measures at 35.00 or less though to be honest I have a hard time reading consistently. I could polish this down farther but not sure how far I should go.

I can buy another pair of bearings for $20 but right now I have zero confidence it will turn out any better than the first time. Either there is something defective in the spindle assembly or in my technique but it is not clear how I would determine this.

The only other thread I saw about this problem seemed to be resolved with a bearing replacement without anything special. So I am escalating it here in hopes that something new is revealed or confirming that replacing the whole spindle head assembly is the wisest choice. Right now I'm down $30 or so of parts and two days of what was supposed to be productive time and I'm loathe to throw more at it without something new....

THANKS IN ADVANCE!

Common fault on these machines caused by the makers grinding both bearing journals the same.
The lower one can be tight and it's as well that it is, tight that is not super tight.

The upper one need to be a sliding fit, i.e. the bearing needs to be able to be tapped down the shaft but not fall down on it's own.

The reason for this is that when you assemble the spindle and fit the top bearing you press the bearing home with the adjusting nuts to get the preload but when you back the nuts off the bearing is that tight it stays where it is with too much preload on it.

One word of warning when polishing the spindle to get the correct fit. The spindle will heat up and expand when polishing, allow to cool before trying the bearing or you may get the bearing to fit nicely when warm and it's too loose when cool.

Not knowing what equipment or skills you have it's also possible to improve on these spindles in that you have two C spanner type nuts to adjust the bearings, one sets the preload and the second locks the first.
It's very hard to lock the second without moving the first. If you have the skills and equipment think about making one nut as deep as the two.
Then drill into the side, tap for a grub screw and fit a small brass pad to the bottom before fitting the screw so it doesn't mar the threads.

This way you have only one nut to worry about and tightening the grub screw will not affect the preset preload.

John S.

It will eventually cool down after hours of running. As long as the spindle runs smooth, and isnt in danger of catching on fire, I wouldn't worry about it.

I have 3 X2 spindles, and they all have their own quirks. One came with damaged bearings right out of the box. I agree that the press fit on the bearings is a little excessive. I pressed them in on a hydraulic jig with loadcells and measured the press force at 800 lbs! Oh well, they will never fall out.

Paul

fatal--thanks for the data points. FWIW, when I say "hot," I mean after 3-4 minutes at top speed it was almost too hot to touch. If it kept going I'd be afraid it would carry a lot of heat to the belt--those aluminum pulleys make great heat sinks!

Well, the game is up for now anyway I think. I managed to polish the spindle to exactly 0.01mm too small, giving a perfect slip fit. (nuts)

You know if I *tried* to do that I couldn't possibly hit it so well. I'm almost tempted to put it all back together just for giggles and see what happens. I figured the risk of exactly this happening was pretty high but since I was looking at the full replacement anyway, I figured it was worth a shot. Oh well, thanks for playing I guess!

Even if the journals are ground to the right size for the bearings, whether they are aligned perfectly is another issue as well. This can also cause excessive heat and binding problems from the uneven loading on the bearings. They have to be perfectly concentric to each other as well as sit exactly parallel. Any minor tilt is going to load the bearings unevenly and cause a crapload of heat. From what we have seen of Chinese QC it would be prudent not to assume one or both of those things to always be properly trued on every machine as shipped, so you might want to check that as well before you throw in the towel!

BTW, if the spindle is only .01mm undersize, there are several easy ways to 'grow' the shaft back up larger again for that small amount. So don't give up on it quite yet either!

Parallelism and concentricity were on my mind. Any suggestions on how to check for those? That said, it would seem like those would be even harder problems to fix than the bearings.

Oh, and about putting .01mm of metal back on, what would you suggest? I know about knurling but was doubtful that would work here. I also thought about something like a little loctite but that seemed to be asking for trouble. My hope is that a replacement assembly from LMS will, at worst, come with an exchange warranty.

Also one poster on a Yahoo board suggested making sure the lower edge of the pulley wasn't fouling the bearing shield--he said this happened to him and it just needed a little relieving of the pulley and all was well again. I'm well past that now (and I doubt that was the problem) but figured I'd post it here for the benefit of future readers.

im not sure what part you need to grow back, but doesnt heating it up red hot help?

Oh, and about putting .01mm of metal back on, what would you suggest? I know about knurling but was doubtful that would work here. I also thought about something like a little loctite but that seemed to be asking for trouble. My hope is that a replacement assembly from LMS will, at worst, come with an exchange warranty.

Knurling is certainly one of the options, a time-tested old way to do it. Depending on the type of knurl used, once it is turned back down to normal diameter after knurling, you can often get back to the vast majority of the surface area of the shaft at the right diameter. It often looks just like a bit of cross-hatching that doesn't lose more than a small percentage of the original surface area, and in this case it isn't necessary to have all of it there anyway. It should work just fine for this.
Another simple way to do it is to electroform. I have seen worn parts brought back up to spec by plating even up to 5 thou or so of Nickle onto the parts and resurfacing. On a round shaft that growth would of course be doubled as it would be applied evenly to all sides. In fact, when hard nickle plating new gun parts the dimensional growth can actually keep them from fitting properly. It is cheap, quick, and easily done, but then again I have that equipment around, so its easy for me to suggest. I don't know how easy it is for you to find a local shop for that if you don't know someone already with the right gear.

The part is probably too cheaply replaced for these other options to make sense, but in restoring old cars and vintage aircraft with irreplaceable parts there are other options I use too. Quick and dirty, you can turn the shaft down much smaller, swage a bushing on, and then turn it to correct size. Just make sure there is enough wall thickness for the bushing not to be too thin.
If the shaft is hollow or you can't get at the ends of it you can't do that, so you weld a spiral fillet of metal winding around it (like a screw thread) to build the surface back up, then turn it back down and re-heat treat it. That is the way we redo old crankshaft bearing journals.
You can fix anything with enough time, though in this case maybe not worth the effort, but its nice to know you can always 'grow' a part back up.

If you have the spindle torn down again, why not mount it between centers and measure the total run out. Both bearing journals can be measured in relationship to each other. Mark the highest spot on the journals. If they are high on different sides, but not too far out, perhaps you can take it to an auto machine shop for regrinding. Once reground, you can knurl, or plate your way back into spec. Actually you can add a few thou with DIY electroless nickel plating in your own shop. I do electroless nickel frequently. It is cheap and extremely easy to do.

A new spindle assembly is $100. Honestly, is hours of work and ordering a few dollars (or more) worth of parts several times better than dropping another $100? To me (and most people), no.

Guys,

Thanks for the ideas and help. As Stepper Monkey alluded to, $100 for a full semi-guaranteed replacement is going to be the cheapest option here if I place any value on my time as well as the downtime which is preventing me from moving on to the project which got this whole ball rolling in the first place. Order placed this morning and with any luck in hand by the weekend or so.

Still, I appreciate the suggestions as they may someday come in handy when a replacement is less economically feasible. The electroless nickel plating is a new technique for me and may come in handy for other purposes. Somewhere down the road I might try to make this spindle work again for the heck of it--somebody suggested building a small horizontal mill around it which I thought might be neat as I do have a spare X-Y table around. Besides, there's at least three square feet of basement space yet to be filled with junk, er, I mean future projects....

Good stuff. Be sure to update with the quality of the new spindle. Hopefully you aren't unlucky enough to get another lemon. If the new one is bad, LMS may be able to exchange it for you.

Good stuff. Be sure to update with the quality of the new spindle. Hopefully you aren't unlucky enough to get another lemon. If the new one is bad, LMS may be able to exchange it for you.

That is precisely the plan--their website says they give 30 days' exchange credit, and I've bought enough stuff from them the past 6 months that I'd hope they'd honor a genuinely flawed piece. That said I am going to take even more care installing this one just to be absolutely sure I'm not part of the problem....

The spindle assembly that I bought from LMS had shot bearings right out of the box. They were very rough. They seemed to be sliding rather than rolling. Maybe you'll get a good one.

This may sound sick, but I would rather go with tight and hot than loose and cold. What disadvantage is there other than increased power consumption? If the TIR is within spec, forget about the heat.

Beware....

Paul

Well UPS says the new spindle should arrive Friday so I'll get a look at it this week. If it runs the same as the last one then I'll probably call and ask LMS for their opinion. I'd be willing to try a bearing swap yet again if they'll accept an exchange if it doesn't work, otherwise it's going back. The only thing I'd see changing if I did this all again would be to get metal-shielded bearings rather than rubber-sealed ones because I think that is exacerbating if not causing the problem.

If I had the time I'd be tempted to put the old setup back together and run it for an hour or so to see where the temperature plateaus. Part of me thinks that it might be high enough to be dangerous to the belt. If all that happens is that the belt dies every 50-100 hours and the bearings every 500, I could live with that, even if it is in principle really excessive. OTOH if the belt or bearing life is more easily measured in minutes, it's not going to work. I don't really have an instinctive engineering feel for these things, all I know is that the spindle got HOT fast.

I think that's a good plan. Metal shielded bearings are a good choice as well. They automatically have a higher RPM limit because of the reduced drag. They are not as well sealed, but probably good enough for this application. Plus, that's what was originally installed.


[QUOTE=sansbury;473621]. The only thing I'd see changing if I did this all again would be to get metal-shielded bearings rather than rubber-sealed ones because I think that is exacerbating if not causing the problem.

Hi Sansbury,

To much preload is probably the most common cause of overheating spindles. I don't see much discussion on this thread regarding this subject. If it requires excessive force to assemble the spindle then it is not possible to adjust the preload. The clue was given by John S in post number 2 but seems to have been ignored. At least one of the inner or outer journals needs to be able to move when you loosen the adjusting nut. It matters which one so you will need to study this for your particular spindle. If you follow the LMS assembly procedure you will automatically end up with to much prelaod if the bearings do not have the necessary freedom to move.

Phil

Phil,

I did read John's post and it has been discussed. In fact I sort-of ruined my spindle trying to resolve things down that path.

Anyway, I guess that the part which is confusing me a little is that if the design and manufacturing process is all wrong, then shouldn't the problem be a lot more common? I'm not the first or the hundredth guy to put a belt drive on an X2 and run it at 4000rpm for 5 minutes. Plenty of people have replaced bearings using the LMS instructions.

I get that the design in principle cuts a very large corner, but it seems to work well enough for the vast majority of cases, no? That's why I wonder if there isn't a manufacturing defect or something like that which is coming into play.

Phil,

How is preload properly calculated and set?

The preload adjustment on the X2 is accomplished entirely by moving the inner race of the upper bearing with a left hand threaded spindle nut that begs to "snugged up". I'm sure bearings are regularly ruined by Mini Mill owners. Assuming that the inner race will slide on the journal, how much is too much? If the head gets hot, back off a tiny increment?

Hi Sansbury,

To much preload is probably the most common cause of overheating spindles. I don't see much discussion on this thread regarding this subject. If it requires excessive force to assemble the spindle then it is not possible to adjust the preload. The clue was given by John S in post number 2 but seems to have been ignored. At least one of the inner or outer journals needs to be able to move when you loosen the adjusting nut. It matters which one so you will need to study this for your particular spindle. If you follow the LMS assembly procedure you will automatically end up with to much prelaod if the bearings do not have the necessary freedom to move.

Phil

I don't see that. If the bearing journal is to tight on the shaft or in the housing then isn't that a manufacturing fault. This is a very common with both Chinese mills and lathes and is discussed regularly on a number of forums.

If you have freed up the correct journal seat by 0.01mm then reassemble it and try it. If it is the incorrect seat you can buy a Loctite grade (or similar) especially for bearing seats. It's semi-permanent but will allow disassembled if necessary. Its not clear to me that you have ruined anything, yet.

I'm not saying the LMS instructions are wrong, providing the correct bearing journal is free enough to allow movement. If it is not then you will apply to much preload.

Did you remove material from the "correct" journal seat. You have to work that out by studying the assembly.

Sorry if you have already been through all of this but I don't see it in the posts. The only mention of preload I can find is in the post by John S.

Phil

Phil,

I did read John's post and it has been discussed. In fact I sort-of ruined my spindle trying to resolve things down that path.

Anyway, I guess that the part which is confusing me a little is that if the design and manufacturing process is all wrong, then shouldn't the problem be a lot more common? I'm not the first or the hundredth guy to put a belt drive on an X2 and run it at 4000rpm for 5 minutes. Plenty of people have replaced bearings using the LMS instructions.

I get that the design in principle cuts a very large corner, but it seems to work well enough for the vast majority of cases, no? That's why I wonder if there isn't a manufacturing defect or something like that which is coming into play.

"Proper" preloading of bearing assemblies is done by measurement on a surface plate, with the correct axial load applied, then by the use of the correct precision shims that match the measurements taken on the surface plate. I suspect that not many of us hobby types use this method, me included.

Backing off on the "adjusting" nut will only relieve the preload if the corresponding bearing journal is capable of backing of against the adjusting nut. If it is very tight on the shaft then it will stay where it is even if you remove the "adjusting" nut altogether.

Or quite possibly I missed something.

Just trying to help.
Phil

Phil,

How is preload properly calculated and set?

The preload adjustment on the X2 is accomplished entirely by moving the inner race of the upper bearing with a left hand threaded spindle nut that begs to "snugged up". I'm sure bearings are regularly ruined by Mini Mill owners. Assuming that the inner race will slide on the journal, how much is too much? If the head gets hot, back off a tiny increment?

Phil,

I polished both top and bottom journals, but left the bottom as a fairly tight press fit--really just smoothed it down. The top I relieved more (too) significantly.

Based on the spindle nut being at the top it would seem that you would want the sliding fit on the top at least. This would allow you to tighten the nut and pull the bearing races in towards each other and thus accomplish a preload. Have I got it so far?

I am now really interested to see what my second spindle looks like and whether it too has a super-tight fit. I would agree that it is a mfg. fault but I was curious because unlike you I had not seen that many mentions of it here or elsewhere. If it was common then like I said I would expect a lot more complaints like mine when belt drives go on. Then again maybe I am wrong and most guys put them on just to reduce the noise and keep running their mills way too slow. It seemed to me like below 2000RPM the heat buildup was a lot slower and in many cases perhaps might not happen. I don't know how much variance there is in these.

This should be quite easy to test.

Follow the LMS assembly procedure and measure the end float on the spindle. Now back off the adjusting nut by say half a turn. Re-measure the end float. Now run the spindle at full speed for a few minutes and re-measure the end float. If the bearing is not to tight here should now be significant end float and therefore no preload (if there is no endfloat then the bearing is to tight on the shaft). Now run the spindle at full speed to see what the equalibrium temperature is. If the spindle still overheats with no preload I concede that the problem is elsewhere. Obviously you can't use the spindle with excessive endfloat but it is a way of determining if preload is the problem.

Phil

Based on the spindle nut being at the top it would seem that you would want the sliding fit on the top at least. This would allow you to tighten the nut and pull the bearing races in towards each other and thus accomplish a preload. Have I got it so far?

The correct preload is accomplished when you back off the nut (as per the LMS procedure) not when you tighten it.

Phil

This would allow you to tighten the nut and pull the bearing races in towards each other and thus accomplish a preload. Have I got it so far?

Hi again Sansbury,

you said.

"Well, the game is up for now anyway I think. I managed to polish the spindle to exactly 0.01mm too small, giving a perfect slip fit.

You know if I *tried* to do that I couldn't possibly hit it so well. I'm almost tempted to put it all back together just for giggles and see what happens."

A "perfect" slip fit is much better than to tight. I don't understand why you don't put it back togther. Just nip the preload up, then back off a touch, check that the spindle runs freely and that there is minimal end float and Bobs your uncle.

Phil

Phil,

Thanks. I will try putting it back together at some point for forensic purposes. I think the issue was that I felt like I was starting to shave a yak with this and I have tried to learn from that.

In other words, the spindle was noisy so I put on a belt drive, the belt drive ran hot so I replaced the bearings, the bearings ran hot so I polished the spindle, I polished the spindle too far so I needed to wrap it in some yak hair to bring it back up, now all I need to do is go shave a yak so I can get my nice quiet spindle up and running! Yak-shaving costs a lot in time and often it ends up costing money, too, sometimes more than calling a halt at the start and changing your approach.

Now it may turn out that I need some yak hair to shim the replacement spindle assembly, but I will cross that bridge when I come to it :)

I agree that after a point you have to realize chasing something down isn't worth it, and solving one problem only gets you to solving the next one that comes of it. Sounds like you are there, and so a new spindle does indeed seem the safest plan.

That being said, since you have gone past the point of getting what you have to work, and are looking at an entire headstock replacement anyway, why do you necessarily want to go with another identical X2 headstock?
It's a blank slate now, so at this point any new headstock is effectively an option. Is there something less problematic or better performing out there to try? Question is, are there any other good viable options from, say, other brands of import mill or something? An awesome option would be a good servo/vfd setup scrounged from Ebay, but that takes some luck and a lot of watching to get cheaply.
I don't know what would best work or anything for that specific application, or even what your budget is, but if you were ever thinking of going to a different headstock or spindle option now would clearly be the logical time to swap it out for something different!

Yak shaving is the name of the game with low end Chinese machinery.;)

If you are going to buy your way out you probably shouldn't have bought you way in in the first place.(chair)

Tormach, IH and a few others run pretty good straight out of the box or if you are looking for a smallish manual machine how about a Wabeco.:)

Oh well, good luck anyway.
Phil

PS: I have to say I don't understand the reference to "forensic purposes". You go to the trouble of freeing up the bearing but don't even bother to put it back together and adjust it to see if it works. I call that weird.

By the way did you check the belt tension, this can also cause hot running bearings.

Phil,

Thanks. I will try putting it back together at some point for forensic purposes. I think the issue was that I felt like I was starting to shave a yak with this and I have tried to learn from that.

In other words, the spindle was noisy so I put on a belt drive, the belt drive ran hot so I replaced the bearings, the bearings ran hot so I polished the spindle, I polished the spindle too far so I needed to wrap it in some yak hair to bring it back up, now all I need to do is go shave a yak so I can get my nice quiet spindle up and running! Yak-shaving costs a lot in time and often it ends up costing money, too, sometimes more than calling a halt at the start and changing your approach.

Now it may turn out that I need some yak hair to shim the replacement spindle assembly, but I will cross that bridge when I come to it :)

Yak shaving is the name of the game with low end Chinese machinery.;)

If you are going to buy your way out you probably shouldn't have bought you way in in the first place.(chair)

Tormach, IH and a few others run pretty good straight out of the box or if you are looking for a smallish manual machine how about a Wabeco.:)


If you have a spare $5000 you'd like to loan me at no interest with very flexible payment terms I'd be more than happy to :withstupi

Seriously, I'm not expecting Tormach/IH/Wabeco quality here, just something that works. I've bought two other Sieg machines and while both had many areas where they could be improved, they also operated properly as soon as the red grease was cleaned off.


PS: I have to say I don't understand the reference to "forensic purposes". You go to the trouble of freeing up the bearing but don't even bother to put it back together and adjust it to see if it works. I call that weird.

By the way did you check the belt tension, this can also cause hot running bearings.

Belt tension: checked, yes, many times. Tried tighter, looser, everything in between.

I didn't put it back together because the spindle was sliding slightly (slipping when I turned it that is) in the bearing, and my understanding is that's no good either. So it was going to need Yet More Work. As I said, I spent a couple hours on a couple of nights last week, and a large part of Friday and Saturday on this. I didn't enjoy it. It wasn't fun. None of my planned work involves rebuilding spindles. In other words, it was like work. If I want to do that I can go to the office and get paid for it. Which I do regularly, partly to have money to spend on fun. So, I decided to call it quits, which in hindsight wouldn't have been a bad idea two days sooner!

That being said, since you have gone past the point of getting what you have to work, and are looking at an entire headstock replacement anyway, why do you necessarily want to go with another identical X2 headstock?


Oh for the love of all that is shiny and metallic tell me you are kidding. Forget shaving the yak, that's finding a mate and breeding a herd of the hairy buggers :)

There are of course degrees of "not good". Many would argue that a X2 is "not good" full stop. On a scale of 1 to 10 for things that are not good about cheap Chinese machinery 0.01mm undersize on the spindle bearing seat probably ranks a lowly 1.1.

Wait till you get to alignment/traming, gib sorting, under powered motors, flexible coumns etc, etc. You are in for a lot more fun yet.

There is one school of thought that says this quality of equipment is basically a kit of DIY parts that has been pre-assemble for shipping purposes only.

Phil



I didn't put it back together because the spindle was sliding slightly (slipping when I turned it that is) in the bearing, and my understanding is that's no good either. So it was going to need Yet More Work.

.

Hey, welcome to the discussion, Hoss!

Oops.

I think you have misunderstood my points.:)

1st point was that he should not bin the spindle because of the 0.01mm undersize.

2nd point was that if he is worried about that 0.01mm then he has a lot more worries to come.

3rd point was that if he really wants the machine to work well he will need to consider a complete strip down and rebuild.

I was not degrading the mill just pointing out some realities with respect to a 500 USD mill. All of my machine tools and major workshop equipment was made in the Far East. Some of it has run for twenty years and some got binned within a week. All of the machine tools have had significant work to make then function satisfactorily. :wave:

Phil

PS: Note that at no time did I make a personal attack.:nono:


typical arrogance common on this site from the silver spoon crowd that
have to put people down that can't afford the same high end equipment as them.
really pathetic behavior.
some people are willing to work for what they get.
a little elbow grease never hurt anyone.
$500 is plenty to spend on a hobby mill, i'll feed my kids with the other 4500.

barack, easy man. philbur wasn't kidding when he said the x2 is a kit. The quality is in there, it just takes some fine tuning, scraping, and lapping to get it out. This is part of the reason it's cheap. 4500 hun to tune it? yeah probably, if you are measuring your time. If you want a solution out of a box, the X2 probably isnt the way to go. if you want to explore the hobby, your machining skills (in light of the poorly tuned machine), and increase the accuracy and value of the machine, by all means, buy one. Dont complain when you get what you paid for, like I said, the quality is in there, you just have to unleash it. The only part of the machine that I care that should be reasonable quality is the spindle, and out of 3 that I have only 2 were good 'out of the box'.

If anyone thinks they can do good work on an X2 right out of the crate, I will personally fly to where you live and watch you make your first part. Ony time will show you where you need to improve your X2. CNC'ing it will only complicate the mechanical issues, especially if you are new to machining. I know, I was there.

Paul

Sansbury,
You should come over to the GrizHFMinimill yahoo group.
http://groups.yahoo.com/group/GrizHFMinimill/messages
you can get some real useful info from other guys with experience
with the minimill and won't have to wade through constant X2 putdowns
from the elite.
it's a much more x2 friendly site.

Lots of inuendo and personal attacks but very little advice. As for "constant" X2 putdowns, perhaps you should reread the whole thread.

What's your take on Sansburys spindle problem and how would you fix it.

Phil

Sansbury,
You should come over to the GrizHFMinimill yahoo group.
http://groups.yahoo.com/group/GrizHFMinimill/messages
you can get some real useful info from other guys with experience
with the minimill and won't have to wade through constant X2 putdowns
from the elite.
it's a much more x2 friendly site.

Nice how barack deleted his previous post with only a period.

I guess if you dont strive to be better, goto the yahoo group, like bareback.

Regardless of your outlook on them, and they aren't my thing, but I thought that the X2's basic nature of being "basically a kit of DIY parts" was pretty well accepted by all, and the primary reason they were so loved by many in the first place.

For better or worse, you get into them expecting a lot of work. To say any different is dishonest in the extreme. This isn't necessarily a bad thing, as they can open the opportunity for ownership to people to get a machine they otherwise couldn't justify the cost for, if they are only willing to deal with some hassle and headache. The thing you can't just gloss over about the deal is that there is going to be some hassle and headache. You can't have it both ways!
The decision comes down to whether you can better afford to either spend the extra money on a machine that makes chips right away and more reliably, or spend the extra time and delay in getting one of these to a state that makes chips and then living with it's limitations.

Either can be equally valid depending on the individuals needs.

Those involved in the partisan ego trips trying to paint only one of these options as correct and somehow superior in every aspect, and extending that to the moral and intellectual superiority of their owners, serves no positive purpose at all. Especially when the misinformation leads new people into buying them, without the experience or skills to modify them, fully expecting them to work right out of the crate and it proved too big of a hurdle for them to overcome. I have seen a number of promising people frustrated out of this hobby that way, never knowing why they couldn't get machining to work for them, as they trusted the equipment implicitly due to these glaring omissions and just assumed they were doing something wrong.
By the same token, for those that made the choice to get one WITH THEIR EYES OPEN, it has made available opportunities to get into machining to those who would not have otherwise been able to do so. Open discussion accomplishes that, not ego trips.

Don't worry, philbur, your points were solid. Most of us can see them as simply machines to work with - not extensions of our ego, id, weenie, self-worth, anti-intellectual sentiments, or some form of subtle class warfare. To mention any shortcoming of a product they own, no matter how trivial or well-known of fault, IS construed as a personal attack to some types of mentality. Besides, he makes money from selling parts for the things and just doesn't like bad press, and especially even-handed press.

Lots of inuendo and personal attacks but very little advice. As for "constant" X2 putdowns, perhaps you should reread the whole thread.

What's your take on Sansburys spindle problem and how would you fix it.

Phil

My advice was to join a friendly group that have EXPERIENCE with the minimill
because as usual,
someone starts putting down the x2 (philbur)
and the others smell blood in the water and have to chime in, it never fails.
The useful advice goes out the door and then it's a bashing fest.
It so boring.
Come on over sans, barry and dave don't tolerate this kind of garbage.

Come on over sans, barry and dave don't tolerate this kind of garbage.

I see the only negative garbage and personal attacks bent on destroying any productive discussion could most simply be removed by you going back over there. Please do. If it was unwelcome under some of your previous, now banned handles, why do you think it will be any better accepted under this new one, 'barack'?

Now, I believe we were talking about options to get Sansbury's machine running again, correct? Where were we?

seeing as you only have 4 (negative charged) posts, why dont you go back to your yahoo groups and leave us alone? I can guarantee that there's many X2 owners here with plenty of experience, but are man enough to admit the shortcommings of the machine, not to mention, how to overcome those shortcommings.

Did you help the spindle bearing problem at all?

I was breaking out some of my auto related tools today, and I spotted my cylinder hones - you know, those three-armed spring loaded things that chuck in a hand drill or drill press and have what look to be small pivoting whetstones attached to each arm. The smallest sizes of them are tiny, for brake slave cylinders and the like. You spin them up and the force opens them to hone out the inside of a bore.
Certainly not high precision instruments by any stretch, but maybe just perfect for opening up the upper bearing seat a Yak hair for proper clearance to do preload adjustment?
Certainly beats trying to buy a reamer that size just for this one job, that would cost as much as a new headstock. The hassle to properly line bore it is right out, too, even if you had the equipment. These hones are self-centering and could be used with a hand drill right in place, cheaply and in minutes. It may not sound like it, but it would actually be relatively quite precise, at least way more precise than the tolerances needed for this, and also far more so than any other rough and ready solution I can think of. Rather a Rube Goldberg solution I know, but I really can't find any fault with the results in this case. Any thoughts?

Getting uniformly right down to the bearing seat shoulder might be difficult.

Phil

I was breaking out some of my auto related tools today, and I spotted my cylinder hones - you know, those three-armed spring loaded things that chuck in a hand drill or drill press and have what look to be small pivoting whetstones attached to each arm. The smallest sizes of them are tiny, for brake slave cylinders and the like. You spin them up and the force opens them to hone out the inside of a bore.
Certainly not high precision instruments by any stretch, but maybe just perfect for opening up the upper bearing seat a Yak hair for proper clearance to do preload adjustment?
Certainly beats trying to buy a reamer that size just for this one job, that would cost as much as a new headstock. The hassle to properly line bore it is right out, too, even if you had the equipment. These hones are self-centering and could be used with a hand drill right in place, cheaply and in minutes. It may not sound like it, but it would actually be relatively quite precise, at least way more precise than the tolerances needed for this, and also far more so than any other rough and ready solution I can think of. Rather a Rube Goldberg solution I know, but I really can't find any fault with the results in this case. Any thoughts?

Ah, very good point. I did not know the upper seat had a fixed shoulder. I haven't opened one of these up. If the two weren't line bored together I can see why these problems might come up as often as it appears to!

Actually, align boring would yield really excellent results if the shoulders could replaced with bolt on flanges to retain the bearings.

Geez, something get in the water supply on the Zone recently?

I don't think anyone was being excessively negative, just opinionated. Nothing wrong with that.

My work is more sculptural than mechanical, and both my x1 and 7x10 worked well enough where it mattered. So my expectations here are I think fairly low. I can often do just ducky with parts made to within +/- 0.010" tolerances so long as the repeatability is there. I upgraded to the X2 because I got a sweet deal on eBay and because I had never really been happy with the X1's Z-axis in terms of CNC driving it and I liked the options I saw for the X2.

Anyway I do appreciate the suggestions and ideas (the cylinder hone is a good one) and when the new spindle assembly shows up we'll see whether I need a comb, a razor, or a pair of shears for my yak.

I don't think anyone was being excessively negative, just opinionated. Nothing wrong with that.

Opinionated is great, it does definitely get lively around here sometimes! Nobody minds that part, really. That particular individual just has a very well known pattern, and he often gets very vulgar and childish very quick. Trust us, better to cut it off quickly while it was still coherent, and still coming from only one fake user account at a time.
Sorry you had to see that, it isn't always perfect around here but the vast majority of users really are on the whole a set of very decent, together people.

Anyway, good luck with the new headstock, and I would definitely like to hear what luck you have with the old one.
As you don't have anything to risk now by trying unorthodox things on it, you may well discover something very useful to optimize these spindles, as you can try things none would dare to try with their working spindle!

Well, the new headstock arrived and went on the machine today.

NO DIFFERENCE. Heated up just the same as the other ones.

What I am going to do now is put the gear drive back on with the new headstock and see what happens. If it doesn't get warm at full speed then the belt drive is clearly implicated.

If it does get warm then the old pile of parts comes back out again and I am putting a call into LMS and asking their advice. There is no question here that the heat is excessive.

One thing I did notice this time around is that the pulley on the spindle side of the drive seems like it might be not quite perpendicular to the spindle. I put an indicator on the face and got a max of .007 on the outer ring and .004 on the inner one.

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Don't know if that is normal for this or if it could be the cause of my woes.

http://project-himalaya.com/i-kanch-02/yak-cresting-moraine.jpg

Yakity Yak!

That's some backyard you've got there Sansbury! If the pulley misalignment is warping the bearing, it could certainly be a cause of friction and heat. Can you hear any scraping type noises at low speed?

CR.

CR: No obvious scraping noises. It doesn't sound perfectly smooth though, about the same as the original one. Oh, and my backyard is Logan Airport in the wilds of East Boston. No yaks but plenty of alien wildlife.

Anyway, I just tried running it with the gear drive back on. I ran it at full speed to compare to about half speed with the belt on the high range. I don't have a tach so it's approximate. The top bearing did start to warm up. The bottom seemed to run cooler. I want to say that the top heated up more slowly but it is hard to say so for sure without a timer and thermometer.

Given what I've seen so far, the question is whether the pulley could really be the culprit in this?

Also it seems like this spindle is put together even tighter than the last one. Removing the sleeve that goes under the spindle nut required me to jerry-rig a bushing with a pin so I could use a gear puller on it and then I had to press it (and the pulley for the belt drive) back on. On the other one everything came off and went on by hand alone. So needless to say I will bet the spindle nut tightness has very little effect on preload.

Story so far:

Chris at LMS suggested I give the old spindle assembly another try. Since I didn't like the way the bearings had gone on last time I made some extra bushings to try to make sure they went in correctly. I also bought new bearings with metal instead of rubber shields.

After pressing in the lower bearing, I noticed that there was a significant amount of axial play when I turned the spindle by hand. I took the spindle and bearing apart again (yes I am getting good at this or so I think) and if I held the bearing inner and outer races in my hands and pushed on the outer race, I could see a little play. Also, I could hear the dreaded scraping and clicking souds and feeling of a lump or two when turning it indicative of a shot bearing.

I passed frustration long ago and am now entirely in the land of bewilderment. Two questions:

1. AFAICT the bearing was OK out of the box and I took great pains pressing it together to follow the instructions carefully and avoid damage. I am befuddled as to whether it is in fact damaged or if what I reported is normal. The other bearing for the top which I only took out of the box does not make any sounds or any clicks or anything of that sort...

2. Checking all the bearings I have (now quite a collection) I notice there is a bit of mostly axial wobble in all of them, though the original ones seem to have the least. Is this normal for this bearing type and is it not relevant in this use? For reference the P/N on the latest bearings is as follows:

Nachi Quest
6007ZZE C3 XM * 080221
6206ZZE C3 XM * 080123

These cost about $8 each from a local bearing supplier. As others have reported spending a bit more I am wondering if these are of a lower grade than I should be using?

All this time you are using junk bearings for a spindle? Not even a motor type bearing (Abec 1) ? See McMaster Carr #2349k671. All cheap bearings have play in them. ALL bearings with metal cages sound like junk out of the box. All bearings need some friction heat to expand the race to take up the gap that is engineered in them. Testing a bearing out of the box by hand is useless. Read some of the posts on bearings. For your problem now, you could use bearing retainer by Locktite to take up that.010 gap. Throughout your post I didn't see one professional machine tech post anything. If you had iced the shaft and heated the inner race of the bearing to 250 deg. , it would have slipped on. I suspect you do not have a bearing warmer. You can make one by using an electric fry pan set to 250 and using aluminum to prop up the bearing above the pan at the center race. Be prepared to quickly slide that bearing on or you will get stuck.

Your bearings are deep groove bearings. An individual DG bearing will have axial play by design. It is not until you put a pair together on a spindle and apply preload that it is possible to remove the axial play. Put the original spindle back together, apply the preload correctly (it must run freely by hand) and run the bloody thing.

You are trying to build a precision spindle with none precision parts. It is not possible. However it is possible to make it run, but you may have to accept a little bit of axial play in order to get it to run freely and not over heat.

Phil

Story so far:

Chris at LMS suggested I give the old spindle assembly another try. Since I didn't like the way the bearings had gone on last time I made some extra bushings to try to make sure they went in correctly. I also bought new bearings with metal instead of rubber shields.

After pressing in the lower bearing, I noticed that there was a significant amount of axial play when I turned the spindle by hand. I took the spindle and bearing apart again (yes I am getting good at this or so I think) and if I held the bearing inner and outer races in my hands and pushed on the outer race, I could see a little play. Also, I could hear the dreaded scraping and clicking souds and feeling of a lump or two when turning it indicative of a shot bearing.

I passed frustration long ago and am now entirely in the land of bewilderment. Two questions:

1. AFAICT the bearing was OK out of the box and I took great pains pressing it together to follow the instructions carefully and avoid damage. I am befuddled as to whether it is in fact damaged or if what I reported is normal. The other bearing for the top which I only took out of the box does not make any sounds or any clicks or anything of that sort...

2. Checking all the bearings I have (now quite a collection) I notice there is a bit of mostly axial wobble in all of them, though the original ones seem to have the least. Is this normal for this bearing type and is it not relevant in this use? For reference the P/N on the latest bearings is as follows:

Nachi Quest
6007ZZE C3 XM * 080221
6206ZZE C3 XM * 080123

These cost about $8 each from a local bearing supplier. As others have reported spending a bit more I am wondering if these are of a lower grade than I should be using?

You are trying to build a precision spindle with none precision parts. It is not possible. However it is possible to make it run, but you may have to accept a little bit of axial play in order to get it to run freely and not over heat.

Phil,

I appreciate the suggestions. I am not trying to do anything other than make the bloody spindle run properly. I think my posts have made pretty clear that I know I am nothing more than a rank beginner in this area :)

All this time you are using junk bearings for a spindle? Not even a motor type bearing (Abec 1) ? See McMaster Carr #2349k671. All cheap bearings have play in them. ALL bearings with metal cages sound like junk out of the box. All bearings need some friction heat to expand the race to take up the gap that is engineered in them. Testing a bearing out of the box by hand is useless.

OK, now I know! I picked the bearings based on the replacements sold by Little Machine Shop. Thanks also for the suggestion about how to heat the inner race to do a slide-fit. At this point the only fit that is taking substantial pressure is the one seating the bearings in the spindle housing. It seemed reasonable but was trying to figure out if I was wrong and had managed to muck up the bearing while installing it. Next time around I will use the hot/cold method.

That tight fit on the outer race may be the problem. That may be warping the outer part of the bearing. When the bearing heats up it is out of round and trouble starts. Philbur is right about these bearings not made for precision work. You can help your problem by asking your bearing supplier for Abec 3 or Abec 5 for the bottom bearing. Or you could go pro and buy an Abec 7 ceramic balled bearing from VBX Bearing for $140 and end the problem of heat. Ceramic bearings are used on high speed spindles (24,000+ rpm) and are not affected by heat. Preloading thrust bearings is a no no. That type of bearing is designed to have the balls centered in the race. When you add any preload you drive the balls toward the sides of the race causing heat and low bearing life. The idea that you can make accurate spindles in these chinese machines by forcing the bearings under preload is bogus. That low hour machine probably was at it's end in bearing life and the owner knew it.

Well I put it all back together and ran it again. The first time it made a little noise but after a couple minutes smoothed out. I ran it for about two minutes and checked and saw that both upper and lower bearings were warming up. Then I ran it for five minutes. Afterwards the spindle was warm enough that I could touch it and hold for maybe 2-3 seconds and then had to let go. I backed off the nut a little and ran it again, this time it started making a lot of noise. I tried adjusting the nut to the original slightly tighter setting and a little looser but it kept making a moderate amount of noise and seemed to be getting worse. I stopped and will let the spindle cool down and try again.

NWREPAIR- I appreciate the suggestions of alternate bearings though not sure I see the wisdom in putting $140 bearings in a $600 mill. To be honest I am starting to lean towards selling this off as a project for someone else and buying a Taig. My original goal was that I had an X1 I had CNCd that needed a lot of fiddling. I thought something a little larger with ball screws might be an improvement. I was mostly OK with the X1 work envelope otherwise. So far I've done nothing but throw time and money at this thing with very little to show for it but the receipts!

EDIT: Just to be clear I was testing with the spindle running at full speed, ~4000RPM. After it cools down I will test it again at closer to the maximum speed of the gear drive, 2500 or so. If it runs OK at that speed I might just leave it at that for the time being. But I'm afraid there's something going wrong here (probably pilot error!?) that is going to cause me to eat bearings.

EDIT2: The outer race fit seems to be a lot smoother now, presumably from the number of times I've pressed things in and out. It's still a press fit but there's none of the stick and jump there was the first time.

How about some positive news for a change?

I reassembled everything for a run at lower speed and used an old bearing that had the seals pulled out (I thought it was shot and wanted to look at it). The noise I had last night appears to have been due to the spindle nut not being sufficiently tight due to some schmutz making me think things were tight just a hair too soon. After cleaning and lubing everything I reassembled and got no bad noise.

Anyway, I gave it a run with the speed set between 5 and 6 to get a speed comparable to the gear drive's top speed, and after a total of 20 minutes with a couple brief stops, the spindle and housing were warm, but not hot, and the heat buildup seemed to be fairly slow throughout. I then took a few quick cuts in some 6061 using a 1/4" endmill just for kicks, and the surface finish was good and smooth, and nothing weird happened.

One thing I did notice is that the heating was definitely coming more from the lower than the upper bearing. I don't know if that tells anyone anything interesting, but thought I'd mention it. Anyway, at this point I'm starting to feel like this might be a sustainable configuration--though I will need to swap the lower bearing with a sealed one. Still, it does seem like this is a setup that ought to work for a while, as I can deal with the speed limit.

Sansbury,

If I were you, I would invest $20 apiece on ABEC 3 bearings. I bet they would solve your problems.

Bill

the c3 part of the bearing number means that the internal clearance is one step looser than standard (c0).
this is called electric motor fit, high speed spindles often will use a c2 fit (one step tighter than standard). You might also have better luck with nylon cage bearing and a p6 precision(abec 3) which is not that much more expensive. Also look for VV seals which are light contact and will produce less heat. Go to a bearing distributor and explain to the oldest guy there your problem and I'll bet he will have a solution.

nwrepair1 wrote:
"Preloading thrust bearings is a no no. That type of bearing is designed to have the balls centered in the race. When you add any preload you drive the balls toward the sides of the race causing heat and low bearing life. The idea that you can make accurate spindles in these chinese machines by forcing the bearings under preload is bogus. That low hour machine probably was at it's end in bearing life and the owner knew it."

Yes, you do preload thrust bearings-- I assume you meant deep groove ball bearings, but you can preload those,too. That is what the factory does on the X2. In fact, I have sold deep groove bearings that were flush ground for light preload when mounted in pairs, just like angular contact bearings.

also, I would go with NSK rather than Nachi, just a little better quality. On the other hand aren't the vxb from the same place that makes the mill?

Yes, my mistake. Now that I see that this thread is going in the direction of a pissing match, I'll drop out now. I'm surprised NC Cams isn't chiming in on your deep groove bearings used in place of angular contact bearings. You know that preloading deep groove bearings to save money is a cheap trick.

If yo read any bearing manufacturers literature you will see that this is not correct. It is quite acceptable to preload deep groove bearings. The maximum allowable preload however is of course less.

It's a pity you think that different opinions equals a pissing contest.

Phil

You know that preloading deep groove bearings to save money is a cheap trick.

I stand corrected. Does that help? My 30 some years of seeing duplex, triplex, and even quad deep groove bearings used as a cheaper way to avoid angular contact bearings has obviously jaded my opinion to the point that I've forgotten my basic bearing knowledge. As to the pissing comment, you saw fit to chastise me already.

Don't make me stop this car!

Seriously--I really appreciate all the opinions, even the wrong ones (just kidding). Everyone's input has kept me moving forward and taught me more than I expected I was going to need to learn about this. nwrepair, philbur, bill, and bearingman have all given fast and very specific input which has been helpful so please don't fight!

I think it's pretty obvious the X2 design has plenty of compromises to manage the price point, and the choice of bearing is one of the big ones. However it is a compromise that seems to be OK given the other parameters. The 4k rpm belt drive conversion is very common and my impression has been that most people just bolt it on and go with a lot less fuss. Most of this thread has been about trying to make sense of why my experience has been very different. Possible answers include:

1. Most people don't pay attention to the heat: given that it rapidly achieved finger-singeing levels I would be surprised if that's true, or maybe very few people actually run wide open.

2. My original spindle is seriously defective: Perhaps, but the most obvious defect (too tight spindle-bearing fit) is the same or worse on the replacement I bought, which leads me to conclude this is by design. As someone noted, that's a bad design, but that brings us back to the question of "then why do they work for everyone else!?"

3. Something is wrong with my belt drive that is causing this (seems v. unlikely, but it is the only common element between the spindles)

4. Everybody who runs the belt drive has upgraded to better bearings than I bought, but doesn't talk about it much. If I buy better bearings the problem will go away.

5. I'm a doofus and went through the right motions but performed them incorrectly and thus failed to fix the problem. I don't think this is the issue at this point, but then everyone thinks they have a good sense of humor and are a good driver.

Right now I am going to get a price check on an ABEC 3 bearing in line with Bill & Bearingman's suggestions--if it's around $20 I will try it, otherwise I will probably stick with what I've got for a little while since it's workable and I am getting a bit of wallet fatigue. That said I feel a lot better about knowing what I'm doing and not as worried about ruining expensive parts.

Beyond this I have a spare spindle assembly which I may hang onto since it would cost me $20 to ship it back to LMS. I have two ideas for what to do with this:

1. Build a heavy-duty 4th axis for indexing and turn-milling (since it's the same casting as the 7x10 lathe headstock this might only require a few new parts)

2. Take it to my friend who owns a large machine shop and see about modifying it to take AC bearings. They are 10mm larger diameter so don't know if it can be made to fit, but might give a chance to do some sort of more precise setup. This might be an interesting exercise but at present not sure it's worth the payoff if the regular spindle works OK. My guess is that when all is said and done it will not be the limiting factor in the machine's performance.

Sansbury,

I'm in the same boat as you, belt kit = lots of heat.

I bought the bearings recommended by bilinghm - even more heat when I put it back together.

So I don't think its as simple as "expensive" vs "cheap" bearings.

I ended up sanding down the upper bearing area on the spindle, nice slip fit, then snugged up the nut until it ran fairly quiet and didn't produce lots of heat, so far so good.

Good lord, you mean to tell me I'm not crazy? Sorry to hear you're here in yak country with me but it feels better knowing I'm not alone.

I am going to experiment a little more with the loading and see how far I can back off before things start to get noisy and then make a smoke run that way. It may be that in some cases this needs a lot more fiddling to yield proper results. Or good dumb luck. Maybe some runs of the spindle are a lot looser and easier to set properly, or come with a better preload and thus never exhibit the problem to begin with.

Besides that I am going to swap an enclosed bearing back in to try out, and see if that aggravates the situation. If so then the light contact option Bearingman recommended might be the key. Not sure how long an unenclosed bearing would last before some chips get in there and kill it. I can live with <3000RPM but if I could get full speed I'd be happy since most of my work runs well on a 1/4" endmill or less in 6061. I use a cobalt rougher (mostly for 2.5D profiles) and it seems to work better the faster I go with it.

I think Dogwood has the right idea. I still think the outside ring of the bearing is getting deformed by too tight a fit. Gear drive would allow a lot of slop and no tension on the spindle. Tight belt would add stress to the bearing. Try less tension on belt. Anything over 90 deg. bearing heat would be trouble. You don't want to spend your time constantly changing bearings.

Ok. I've read the whole thread again. Watched the belt conversion on YouTube. I also read Syil America site. In that site's FAQ Syil mentions switching out the bearings for precision bearings if you need more speed aka 4,000rpm. To me that indicates they know it needs better bearings. McMaster-Carr has precision plus Abec 1 bearings that are built to Abec 3 standards that work up to 7800rpm. Your 6206 bearing is $17.10 . There are also other types of bearings that allow for more error in alignment. One thing that bothers me is that it looks like the belt is not cogged but flat. Is it?

Assuming you mean 90 deg F I think that is a bit low, it's less than body temperature. From memory upto 140 - 150 deg F should normally not be a problem.

However none sealed bearings are going to have a tendency to leak their lubrication if they run hot and will require more frequent lubrication.

Phil

I think Dogwood has the right idea. I still think the outside ring of the bearing is getting deformed by too tight a fit. Gear drive would allow a lot of slop and no tension on the spindle. Tight belt would add stress to the bearing. Try less tension on belt. Anything over 90 deg. bearing heat would be trouble. You don't want to spend your time constantly changing bearings.

nwrepair--not sure if you caught this above but I did sand my spindle journals down. I sanded the bottom to a light press fit and the top to a almost-slip fit. It is 29.99mm and it's a slip with one bearing I have and a light interference with another. I suppose I could take a little more off the lower journal. Just afraid of going too far!

The belt is a simple V-belt. I will try running it loose tonight for kicks--obviously you don't want it slipping but I want to test your suspicion.

Possible answers include:

1. Most people don't pay attention to the heat: given that it rapidly achieved finger-singeing levels I would be surprised if that's true, or maybe very few people actually run wide open.
Just did the belt update. Checked the heat ... a bit hot so I loosened the preload (won't admit to my brain dead move ;)) and loosened the belt tension ... all better.
3. Something is wrong with my belt drive that is causing this (seems v. unlikely, but it is the only common element between the spindles)
Or you have installed it with too much preload (ie you turned the spindle nut too tight) which I found surprisingly easy when you have a 6" arm of leverage ;) Also, the belt does not need to be tight ... hell try to run it loose first. Also, did you check the spindle movement (turn it with your hand with the belt off) to see if you felt any binding?
4. Everybody who runs the belt drive has upgraded to better bearings than I bought, but doesn't talk about it much. If I buy better bearings the problem will go away.
Hell no. If I have to do that, I'll try to sell of this mill. Way too much work.
5. I'm a doofus and went through the right motions but performed them incorrectly and thus failed to fix the problem. I don't think this is the issue at this point, but then everyone thinks they have a good sense of humor and are a good driver.
Only you know what you did and what order, but with some many people making the belt conversion I think it could be operator error ... it was on my end :) (ahem left-threaded nut ... DOH!)

FWIW, from one non-expert to another
Jay

PS: I meant to thank you and the others for increasing my working knowledge of this mill. If it weren't for this thread I never would have looked at the "preload" due to the tightness of the spindle nut. Also, my belt is the Harrisson.biz one. recent tests of runout show that I can get 2500 RPM with 0 runout but anything higher and resonance shakes the needle as much as .01" :eek: But I got my requirement of "quiet" so I'm not complaining too much ;)

I'm confused. I thought you were turning down the shaft to allow an easier fit for the bearing. I've never seen a mill with bearing journals for the spindle shaft. Usually spindles are mounted in cast iron,aluminum or some type of steel collar. I was thinking that you should sand out more space for the outer race. I have had 2 cases of bearings not working properly on router retrofits I'm doing.. The cause was deformation of the outer bearing ring. Sorry, I can only tell you that human body temperature has nothing to do with acceptable bearing temperature. We check bearing temps with IR thermometers .

I have 3 of these mini mill/lathe spindle heads. They are very simple, yet sturdy little head stocks. For some reason the factory that makes these head stocks likes to keep tolerances on the tight side!:eek:.
I have had trouble using a 12 ton press to remove a bearing on one of these head stocks the bearing fit was so tight.

If you are doing a rebuild on one of these, I find it best to carefully inspect the bearing bores for the outer races for nicks, burrs or debris. Sometimes I don't think they are assembled in the cleanest environment and this will distort the bearing.
A little light hand finishing of the casting may be needed if the outer race is to tight in the casting. After cleaning them up I boil the casting in TSP and water to remove all traces of grit.

You'll definitely need to lightly sand down the rear end of the spindle shaft to allow the rear bearing to have a close sliding fit. Otherwise proper preload adjustment will be impossible.

As has already been said, ice the shaft and heat the bearing and it should drop on. The rear bearing should slide on tightly by hand IMHO.

Once setup with a decent 6206 series bearing, these head stocks will run at 5000rpm for 8 hours straight and should only be warm to the touch.
Steve

I also own a couple of X2 heads, one MT3, one R8. Thankfully they are running okay so far. The R8 head was purchased from another member here and came with a Ron Steele belt drive but no assembly instructions. I used the LMS spindle kit pdf for a reference.

According to LMS the spindle nut is snugged up and then backed off to slightly loosen it, followed by tightening the set screw. Replace the words "set screw" with "cotter pin" and this sounds much like adjusting the tapered roller bearings used in the wheels of my old car. Then it goes on to read "there should be a small amount of preload on the bearings". Is this a contradiction ? Maybe I don't understand the term "preload" or what exactly creates the preload. When adjusting the car's wheel bearings this procedure allows a small bit of necessary play.

edit/ off topic but...
The term preload is also used for the selective fitting of balls in a ballnut. Surely the balls aren't chosen for an interference (pressure) fit? Otoh preload also describes the use of 2 ballnuts with an opposing spring, a case where the term makes more sense. Preload is a term that doesn't always make intuitive sense to me. Just a 4 a.m rant.

Wit respect to that type of ballscrews it is exactly that, the balls are selected to provide an interference fit. The amount of oversize then dictates the degree of preload.

Preload basically means that the balls are in compression within the elastic limit of the ball/race. Preload reduces bearing life, so you can have a stiff assembly with relatively short bearing life or less stiff and longer bearing life. Car wheel bearings with negative preload will give the longest life. You have to also consider how temperature will change the preload under operating conditions.

Implicit in "Snugging up" is that you have created excessive preload (compression of the balls). Backing of then reduces the preload to an acceptable level with respect to bearing life. In high precision systems the preload would be measured directly, however for us hobbiests a subjective method is usually employed. Correct preload (for the hobbiest) is defined as tight enough that you cannot measure any axial float. The spindle will freely rotate without binding and when running the assembly does not get hotter than what you can hold your hand on. This is about as precise as you can get with a subjective, eyeball type procedure. The primary test is the temperature when running as this effectively tells you the preload under operating conditions, the initial adjustments are really just to get you in the ball park.

Phil


The term preload is also used for the selective fitting of balls in a ballnut. Surely the balls aren't chosen for an interference (pressure) fit? Otoh preload also describes the use of 2 ballnuts with an opposing spring, a case where the term makes more sense. Preload is a term that doesn't always make intuitive sense to me. Just a 4 a.m rant.

Ahhh, LMS is assuming we'll over tighten the nut initially and some preload is needed, just not that much. Given that most of us are amateurs their concern is understandable. From what you've written, some trial and error might be needed.

Interesting regarding the ballscrews. The preload on mine (single nut Nooks) allow near zero play. Hard to measure in some spots. Measurable in others. Suspect some longevity has been sacrificed to attain this.

Getting back to the car example, setting up the spindle would be closer to adjusting the pinion gear in a differential where some preload is desirable. Car repairs are more my comfort zone :)

I think the snugging up is to make sure the bearings are fully seated etc. otherwise you could be confused as to whether the resistance to movement was actually the onset of preload or just frictional resistance as you pull the whole assembly together.

I would say that light preload on a ballscrew is probably the best compromise for the average hobby machine with repsect to stiffness vs component life. If the rest of the machine is super stiff it might be worth some additional preload. On a hobby machine a ball-srew with light preload will probably out-last the rest of the machine if not you.:)

Phil

Ahhh, LMS is assuming we'll over tighten the nut initially. Given that most of us are amateurs their concern is understandable. From what you've written, some trial and error might be needed.

Interesting regarding the ballscrews. The preload on mine (single nut) allow near zero play. Hard to measure in some spots. Measurable in others. Suspect some longevity has been sacrificed to attain this.

OK, here is the latest... I did a lot more experimenting with this. First, with the open bearing and a lot of fiddling with the preload, I was able to get it to run wide open with low heat buildup. After I was sure of this I pulled it apart and put on a sealed bearing. No matter how much I adjusted it, I could not get it to run cool. Even at 50% speed it was warming up very noticeably after less than a minute. I then pulled the bottom seal off the bearing and tried running it again. This time it built up almost no heat at 50% and only moderately at full speed. So the seal contributed a lot to the heat buildup.

Unless the wise men think this is bad, at this point I am leaning towards sticking with this configuration for a while. When I put the plastic cover back on the bearing will be protected from most chips and if I have to lube it every so often no big deal. Otherwise I guess it's off to the bearing house to try and get some Light Contact bearings.