Hi, I have a CNC'ed X1 (CNCFusion kit :) ) with the standard ACME screws. I was making some tooling at the weekend and all of my circular pockets are distinctly deformed at the point the X-axis changes direction. Right to left seems worse than left to right - could this be down to an interaction with the direction of tool rotation?

Anyway, is there anything I can do about it? I am running Mach 3 - it has software backlash correction, but that seems like a last-resort from the manual. I'd also need to know what the backlash actually is - any ideas how I measure it?

I believe the X1's ACME nuts are adjustable, is it possible to adjust it without removing the table by cranking the table all the way over to the right and then using a long screwdriver to adjust the set-screws?

Cheers.

Backlash compensation won't do much to help you machine round circles.
The only way to do it right is to remove backlash - as much as possible.

Yes, you can adjust the leadscrew nuts some amount by changing the pressure on the nut split screws.
(make sure they are well lubed & also the ways)

Long term, the best solution is get ball screws -as accurate as you can afford to buy.

Checking backlash is covered in many other posts - just search for them.

To me, the "acid test" of any mills accuracy is how round it can machine a circle.

Good luck,
Pres

Backlash is basically the amount of "non-movement" you have in your machine axis when you reverse direction. Simply measured by using an indicator.

Even IF you upgrade to ball lead screws, you could still have backlash and quadrant marks, just to a lesser degree. You may also have an issue with your settings. How much error are we talking about?? How much error can you live with?? How much are you willing to spend to get "perfect circles"??

In any case, measure your backlash and add the compensation amount. It should help and you will also find your point to point operations will be more accurate as well.

Backlash compensation won't do much to help you machine round circles.
The only way to do it right is to remove backlash - as much as possible.

Yes, you can adjust the leadscrew nuts some amount by changing the pressure on the nut split screws.
(make sure they are well lubed & also the ways)

Long term, the best solution is get ball screws -as accurate as you can afford to buy.

Checking backlash is covered in many other posts - just search for them.

To me, the "acid test" of any mills accuracy is how round it can machine a circle.

Good luck,
Pres


Thanks - I am looking to upgrade from my X-1 to something larger and faster, but I do need it to make some parts right now. I will have a play with the split nuts.

Backlash is basically the amount of "non-movement" you have in your machine axis when you reverse direction. Simply measured by using an indicator.

Even IF you upgrade to ball lead screws, you could still have backlash and quadrant marks, just to a lesser degree. You may also have an issue with your settings. How much error are we talking about?? How much error can you live with?? How much are you willing to spend to get "perfect circles"??

In any case, measure your backlash and add the compensation amount. It should help and you will also find your point to point operations will be more accurate as well.


Thanks - I don't expect perfection, but I would expect circles to 'look' round even if measurements indicate otherwise. I would estimate that I have about 0.5mm of error - which looks awful. I will have a go at actually measuring it tonight though.

I would certainly expect much better than .5 mm even with acme screws.
Yes, adjust the split nut first as that is where the bulk of your backlash is probably coming from. Then, measure and tweak the backlash comp to see if you can get more improvement. FYI - In my experiences, you will probably always see the quadrant marks though.

Good luck!!

You should not have to remove the table to adjust teh antibacklash nuts on your X1. Just crank it over as far as possible as you've described.
There is not enough room to fit the standard, low cost, 5/8"-.2 ballscrew in the X1. But You can get a 3/8" ballscrew in there just fine, get two nuts and preload them. I suspect it will be around 100 dollars, but it will be well worth it. Call Roton for prices that are not a guess!

This is not my page but shows how it can be done.
http://www.aonx97.dsl.pipex.com/WS-page/X1CNC/X1CNC.htm

You can fit the 5/8" ball screws with the extended axis kits but you need to do a fair amount of cutting.


Aaron

I would certainly expect much better than .5 mm even with acme screws.
Yes, adjust the split nut first as that is where the bulk of your backlash is probably coming from. Then, measure and tweak the backlash comp to see if you can get more improvement. FYI - In my experiences, you will probably always see the quadrant marks though.

Good luck!!


I didn't adjust anything, but cut some more pockets last night at a much lower feedrate - 50mm/min 4mm slot mill, 0.5mm/pass - it was much rounder, so I guess either the machine or the endmill were flexing when I was cutting at 250mm/min.

I will have a play with the split nuts and see if that improves things.

You should not have to remove the table to adjust teh antibacklash nuts on your X1. Just crank it over as far as possible as you've described.
There is not enough room to fit the standard, low cost, 5/8"-.2 ballscrew in the X1. But You can get a 3/8" ballscrew in there just fine, get two nuts and preload them. I suspect it will be around 100 dollars, but it will be well worth it. Call Roton for prices that are not a guess!

I think I'd be looking at well over £100 in the UK - $100 might buy me 3/4 of a ball nut! I can't even fall back on eBay as eBay in the UK is useless!

This is not my page but shows how it can be done.
http://www.aonx97.dsl.pipex.com/WS-page/X1CNC/X1CNC.htm

You can fit the 5/8" ball screws with the extended axis kits but you need to do a fair amount of cutting.


Aaron

Thanks - that is a good site. I am beginning to think that I should have bought a pair of mills so that I'd have one to use to modify the first ;)

If you get the extended axis kits you can use the old parts to machine the new ones.

Aaron

If you get the extended axis kits you can use the old parts to machine the new ones.

Aaron


Mine is a Super X1-L so it has both the extensions and the stupid tilting column out of the box! I suppose I could order spare parts and mill those, but I'd rather use my X-1 to build a whole new, bigger machine! It's just a shame that that's the hard way round ;)

Right now, I'm trying to make some tooling to allow me to make a motor plate to mount the X3 motor on my X2-head. I have some nice contours on that plate, so I'm hoping I can dial some of the backlash out with a tweak to those split nuts.

I had also hoped to use the X-1 to cnc out a motor pulley, but right now I just don't think it would be round enough :(

How about making some Delrin nuts? You would only need a length of leadscrew to make a homebrew tap (or a lathe).

Aaron

How about making some Delrin nuts? You would only need a length of leadscrew to make a homebrew tap (or a lathe).

Aaron

Dumpster CNC mentioned that delrin nuts will flex too much for use on milling machines. He specifically mentioned the Sieg X2.
"Friction is one variable that can cause backlash with these lead nuts, I've tried these on a Sieg X2 mini-mill and with the gibs tightened, the backlash was .003-.005 due to the natural flexing of the Delrin... the tighter the gibs, the more the Delrin flexed. The high friction of the mini-mill gibs makes these a poor choice for that type of machine."

I saw some anti-backlash projects here:

http://www.billsbest.com/thatlasacme.html
http://www.cnczone.com/forums/showthread.php?t=20527

And a delrin/acetel gib project here.
http://www.fignoggle.com/machines/x2mill/howTo-gibsAcetal.htm

This X1 looks like it has ballscrews (see page bottom):
http://www.embeddedtronics.com/micromill.html

I also wonder if you can make some kind of anti-backlash situation using a heavy preload spring, such as a car valve spring. I would guess you would want just enough preload to negate the linear force, but not so much to add additional resistance to already inefficient acme screws.

It would seem that even the lubricant used on acme threads would have some effect on the backlash: Do you expect the grease to take the slack out, or should you worry that it would give a false preload inidication.

I assume that sometimes the choice of tool path can have a bearing on the amount of backlash; in other words, taking up the backlash before making a cut, though that may not help you make a circle.

[It seems to make a case for optical encoded servo motors.]

I was cutting a motor mount last night, after having adjusted the X-axis split nut, and the results were much better, though perhaps that's just because the circle I was milling was far larger than before.

It's just a shame that I now have nice round chunks gouged out of the clamps I spent a week making because my toolpath was slightly larger than I'd realised - D'oh!

I still think some of the problems are down to machine and endmill rigidity - slower cuts are much cleaner, and I don't think speed wouldn't affect backlash, unless the cutting force is actually compensating for or making it worse.

I went to the London Model Engineering Exhibition on Saturday - and saw some stunning 3D milling from a ball-screwed X3. I am now convinced that ball-screws are a must for my next machine!

..... . I am now convinced that ball-screws are a must for my next machine!

Yes, and your EXISTING machine also! :)

X1's love having balls too

Yes, and your EXISTING machine also! :)

X1's love having balls too

Yes, but unfortunately ballscrews cost real money in the UK - I'm looking at over £200/$400 per screw/nut/bearings in my next machine, and I've got more than 3 screws to save up for!

Just buy them from the US then. Even with import charges, you are looking at a huge saving compared with anything available here. That's what I did for the ballscrews for my X2.

digits

thats not the case with ball screws in the uk. you just don't use the uk you buy in the usa and ship it here. i bought two 40" 5/8 ball screws with 4 nuts and end machining for under £150 with tax and duty paid. Then bought a speciel tape for the mounting flange for £15 shipped.

digits

thats not the case with ball screws in the uk. you just don't use the uk you buy in the usa and ship it here. i bought two 40" 5/8 ball screws with 4 nuts and end machining for under £150 with tax and duty paid. Then bought a speciel tape for the mounting flange for £15 shipped.

Which US suppliers did you guys use then? I'd be a bit worried about screws getting damaged in 3,500 miles of transit, and all the pain and tedium involved in returning anything. But with the pound worth $2, it might be worth a punt!

me and longrat used homeshopcnc

me and longrat used homeshopcnc

Thanks - do you know how much the end machining costs, and what did you do for bearings?

Looking at their prices, it is about 30% cheaper than I've been quoted here, but I imagine that the shipping would errode some of those savings.

The £200/screw in the UK I stated works out roughly as:

Screw (600mm) ~£36
Screw machining ~£40
Ballnut ~£50
Ballnut holder ~£25
Bearings ~£70
------
~£220 and all of that is ex-VAT.

well the screw would be £16.40
2 ball nuts £28.20 (zero baklash)
flange £16.66
and i think machining was it was £33
Postage might be £30

total would be £124.66

vat and duty on £94.26 would be around £24

Grand total £148

that is assuming machining is 60 dollars, longrat machined his own. I have the tap for the ballscrew nut so you could machine a flange as you could borrow the tap. matt

well the screw would be £16.40
2 ball nuts £28.20 (zero baklash)
flange £16.66
and i think machining was it was £33
Postage might be £30

total would be £124.66

vat and duty on £94.26 would be around £24

Grand total £148

that is assuming machining is 60 dollars, longrat machined his own. I have the tap for the ballscrew nut so you could machine a flange as you could borrow the tap. matt

Thanks - that is a lot cheaper (though you pay VAT + Duty on shipping too!).

I don't know I'd be up to machining my own screws - I am seriously considering getting a lathe, but I don't think cutting hardened ball-screws should be my first project!

So are there any issues in fitting 16mm screws to an X1 then? And what did you do for bearings?

Cheers.

no you should not as that is deemed to be a service. also i did the calculation based on a 1.8 exchange rate not the 1.98 at the moment.

from others you can put the 5/8th screws on the y and z axis but would require modifcation on the X.

no you should not as that is deemed to be a service. also i did the calculation based on a 1.8 exchange rate not the 1.98 at the moment.

from others you can put the 5/8th screws on the y and z axis but would require modifcation on the X.

Thanks again for the info.

TBH, I think needing to modify the table for the X-axis probably rules this out for me - I'd need another mill to do it! That said, the X-2 clone from Warco really does seem to have 300mm X and Y travel and a 550W motor ;)

??
Warco's X2 clone has nothing like 300mm travel last time I looked. If it does, please enlighten me as it would require an elongated base which I would definitely be buying from them. For reference, I'm getting 89mm Y travel out of my ballscrew converted X2, which is a little bit less than the manual machine. It's the no.1 limitation on this machine. I bought mine from Chester.
I strongly recommend the homeshopcnc screws and services. Your best bet would seem to be 5/8" screws on Y and Z, and sourcing a more tricky to find 3/8" ballscrew for the X. If you do go for homeshopcnc, even if you had a lathe, seriously consider his machining service. It is very good value and I can personally confirm machining hardened screws is no fun.
For info, here's a picture of my first anti-backlash solution before I went over to ballscrews. It's a self-cut delrin nut pairing. I got the backlash in the 40-60µm region before friction got too high, but it wouldn't stay that way for long and it isn't the most rigid setup. Ballscrews are in a whole different league.
http://pic16.picturetrail.com:80/VOL660/2777486/6910876/160599194.jpg

??
Warco's X2 clone has nothing like 300mm travel last time I looked. If it does, please enlighten me as it would require an elongated base which I would definitely be buying from them. For reference, I'm getting 89mm Y travel out of my ballscrew converted X2, which is a little bit less than the manual machine. It's the no.1 limitation on this machine. I bought mine from Chester.
I strongly recommend the homeshopcnc screws and services. Your best bet would seem to be 5/8" screws on Y and Z, and sourcing a more tricky to find 3/8" ballscrew for the X. If you do go for homeshopcnc, even if you had a lathe, seriously consider his machining service. It is very good value and I can personally confirm machining hardened screws is no fun.
For info, here's a picture of my first anti-backlash solution before I went over to ballscrews. It's a self-cut delrin nut pairing. I got the backlash in the 40-60µm region before friction got too high, but it wouldn't stay that way for long and it isn't the most rigid setup. Ballscrews are in a whole different league.
http://pic16.picturetrail.com:80/VOL660/2777486/6910876/160599194.jpg

I went to the London Model Engineering Exhibition on Saturday and had a very quick play with Warco's X-2 clone and the WM-14. The X-2 clone really does seem to have a sqaure base, with a lot of Y-travel. I didn't crank it all the way back and forth though and I didn't have a ruler to measure the throat - perhaps a lot of the travel isn't actually usable...

I will do some investigation of homeshop CNC's screws etc - but I still need to find some decent fixed and floating bearings at reduced prices - any ideas would be welcome!

Cheers.

On the X2 I used a duplex arrangement of axial thrust bearings on the driven end of each screw - nothing on the ends of any of my 3 screws. This works very nicely, I got the thrust bearings from Arc Euro, they are not expensive.
I was also at the show on Saturday, and looked at the same machine. The X2 clone certainly doesn't have any more travel than mine, but the machine they had set up as a CNC (WM-14?) has what seems to be more all around, I would have to check the catalogue. Looks like a nice machine, but their CNC conversion at over £3k is way overpriced, esp as you don't even get ballscrews.

On the X2 I used a duplex arrangement of axial thrust bearings on the driven end of each screw - nothing on the ends of any of my 3 screws. This works very nicely, I got the thrust bearings from Arc Euro, they are not expensive.
I was also at the show on Saturday, and looked at the same machine. The X2 clone certainly doesn't have any more travel than mine, but the machine they had set up as a CNC (WM-14?) has what seems to be more all around, I would have to check the catalogue. Looks like a nice machine, but their CNC conversion at over £3k is way overpriced, esp as you don't even get ballscrews.

Cheers - I guess 300mm of Y would really need about 500mm of base and a 300mm throat to work properly!

I had a quick look at the WM-14 - but didn't see the CNC'ed one - D'oh. It looked a lot like a little X-3 to me - but TBH I'd rather not have the quill - it's just a source of wobble IMHO - my drilling is all hands off and better for it! The travels are also less than my Super X-1L : 220 long, 160 wide, 220 vertical! It's also MT-2 which rules out all that nice Tormach tooling...

Did you see the X3-CNC on the Arc Euro stand? Very nice looking 3D-parts which convinced me ballscrews really are worth the cash! I didn't get a chance to ask them how long it had taken though - the lack of a live demo suggested it was a very long time ;)

To be honest, the demo parts on the Arc X3 did not impress me much. The finish you could get is far superior. I would not be surprised if that part was not hogged out quickly based on the way it looked. That is, if we are talking about the same demo object (plate alu filled with misc parts, con rods etc). Also, I think they were mostly 2.5D parts, if not all, so cheap CAD and CAM would sort it easily.

To be honest, the demo parts on the Arc X3 did not impress me much. The finish you could get is far superior. I would not be surprised if that part was not hogged out quickly based on the way it looked. That is, if we are talking about the same demo object (plate alu filled with misc parts, con rods etc). Also, I think they were mostly 2.5D parts, if not all, so cheap CAD and CAM would sort it easily.

You're probably right - I only gave it a quick glance, I was too busy queueing to try and buy things they didn't have at the show :(