Milling spindle collaboration project

[pstockley]

Thanks for the feedback dpuch, I will be hardening the gripper assembly for sure.

NC, I wasn't aware of the requirement to preload the rear bearing, however, it makes sense. I will add provision for a spring washer. Like I said, I understand making spacers is out of my capabilities due to the reasons you state. My bearings are DUL so I think I may just double up the bearings at the front and remove the spacers. I think spacers will cost more than my bearings.

Mcgyver, a lot of spindles I have looked at use spacers to increase the overturning moment (I wrongly quoted stiffness before as pointed out by NC). I know they use spacers on the small Setco spindles for two bearing arrangements. For four bearings I don't think they do.

On high speed spindles they don't normally use contact seals and rely entirely on labyrinth seals, sometimes in conjunction with compressed air purge. From what I have read the labyrinth seals work pretty well by a combination of convoluted path for the contaminant to get in and pressure drops. You can't really see the details, but I will post a close up when I have finished dimensioning them.

Regarding the front bearing cover, duplex pairs of precision bearings are designed to be clamped firmly together (they give torque specs for bearing cover bolts). The inner and outer races are ground in such a way to apply the correct amount of preload once clamped together. There is no provision for adjustment typically. To change the preload you get a different set of bearings (or have them ground).

Last night, I made a decision to go with my own taper. A 30 taper was just too big and was compromising the design. So I will use custom holders which are 1.125" reference diameter (30 tapers are 1.25") with the same taper (3.5" in 12"). I have modelled a holder and adjusted the spindle, retention knob and gripper to match. I am much happier with the cross section of the spindle now. Making the holders will be a good test of my Hardinge CNC conversion when it is complete. I will post an updated design in a few days once I have added some more detail.

[pstockley]

So here is the second iteration of my design







As I mentioned above, I decided on a custom sized taper. This has allowed me to beef up the spindle and reduce the overhang. I have also decided to double up the front bearings, as spacers would cost more than I paid for the bearings. The housing has been increased in diameter from 3" to just under 3.5". At the rear I have added two belleville washers to give some preload to the rear bearing. Once I determine the rear bearing I will calculate the preload required etc.

The next step is to finalize the calculations for the pulley, belleville washers for the draw bar and rear bearing specs.

[WhiteTiger]

Looks like a winner

Much better proportions on the taper cross section, and a nice mass distribution through the three front zones.


Tiger

[NC Cams]

Only comments would be to watch fits and tolerance stacks....

especially on the top bearing with respect to concentricity with bottom so that it slides properly and does not create a moment in the lower bearing.....

With that much bearing stiffness in the lower bearing, concentricity is going to be VERY critical to prevent moment loading....

[Carel]

You could remove the balls from the two inner bearings (remove cage and slide balls to one side) and voila, 2 inner spacers and two outer spacers.

Carel

[NC Cams]

NOT really, Carel.

The inner bearing is ground with a load applied to obtain an offset with the matching outer. THis takes into consideration the raceway offset, the bearing flex and other tolearance stacks.

Making spacers is not that big of a deal IF you have access to a blanchard or decent surface grinder. Machine the rings, preferrably harden them and then grind them as a matched assembly (inner and outer set). As long as they are same width (inner and outer for that set), the preload is contained in the bearings.

Tubing or billet will work fine as would the inner and outer rings for a set of regular deep groove ball bearings with the balls removed. I would NOT tear apart some M/T grade A/C's to make spacers. If you do use a generic bearing to make spacers, you'll still need to surface grind the rings to make them parallel and equal width.

The Quad set of bearings will give TREMENDOUS capacity (radial and axial). Theoretical failure potential is higher - more moving parts = higher probability of failure but OH the capacity....

BTW, to take apart an A/C bearings, the inner ring will literally fall out as long as you orient it properly and heat and support the outer ring ONLY. A propane torch works fine for heating it....

[Carel]

NcCams,

We keep crossing swords over different objects. I don't like the stacked bearing design, because if you view an axle from a flexible point of view, you will see that the outer bearings of the stack take the load. The inners will float. The OP stated in post #18 that he had no way of getting spacers. If I look in my catalog i see that spindle bearings can be used in X and O configurations. That's a claim for axial finish. Your story applies also to the 4-bearing design as I only took out the balls of the middle bearings. Taking a bearing apart requires no violence. In the past I needed non available bearings. Assembled them out of two. Won the championship.

Carel

[miljnor]

Sometimes knowing something can't be done, Keeps you from doing it!

[NC Cams]

Prior to my prior post, I looked to see what kind of loads might be involved - I don't recall seeing any.

I also recall that the original design had a spacer included. It wasn't until later that the issue of not wanting to build spacers but to use bearings to fill the hole became an option. I wasn't following the thread on a word by word basis, I did chime in when I felt my technical experience would be of benefit.

Quad bearings mounted in tandem provide additional axial and radial capacity. Hence, it is a quite viable way to add capacity to a spindle.

The reason for suggesting the use of regular bearings for spacers was simple - I hate to see someone tear up a set of ABEC 7's just to make up some spacers. No more, no less.

Rather than "pop out the cage" as I believe was suggested, I pointed out an industry accepted way to disassemble the bearing if the user wanted to make spacers.

I have no qualms with folks being "creative" with regard to their use of bearings. However, since this is a DIY site with a lot of folks who merely read and do, I feel it is more appropriate to provide the technically accepted method for doing something. This provides the highest probability of success.

People can, will and do ignore well intended advice - usually at their own peril. And, yes, I too have taken short cuts with regard to bearings. Some have worked and others were unmitigated disasters (as outlined in a different spindle thread re: ABEC 7's).

To clarify, yes you can disassemble bearings to make spacers - I'd merely used generic ones instead of ABEC 7's - just my style and attitude towards the use of expensive bearings versus generic ones to serve as space fillers.

The user can also install quads for a very robust cutting end of the spindle - the user's call.

I don't see the exchange we've had a as a crossing of swords but rather merely a cross polination of ideas that can create something synergistically better than the ideas taken individually.

[miljnor]

Well stated!

My 2cents is that if you don't have the money or the know-how to do to industry standards, don't let that stop you. Some of the best inventions were thrown together just to see what would happen. Some without regard for longevity some with.

And as I am sure you can put something together under perfect conditions and have it fail miserably, you can also put something together under the worst conditions and have it exceed your wildest dreams.

It’s been my experience that if you "overbuild something" you better do it right (as NC Cams points out) or you will have some severe headaches. Or you build it a little looser and make it work as best you can and be highly rewarded.

NC Cam (correct me if i am wrong) builds Race car Camshafts and used to be in the bearing industry, so he speaks from experience, Take head of his advice especially if your using all the high end stuff.

On the other hand, a friend of mind asked if I knew why I opened my own business? I said yes "I wanted to make more money and be my own boss" He said "NO". He had me hooked so I said, "Well then why did I?" He said, "Because you didn't know it was impossible!"

While obviously not true, you get the point! I would have never attempted it knowing the pitfalls ahead of time. Although as I become more successful I will regret it less and less.

Here are some interesting points:

1. a bearing has a "rated" life span.
Deviating from operating parameters shorts this time period, usually depending on how for you deviated.

2. A looser bearing is rated for a specific amount of run out.
If you don't get the class "7" bearings in Perfect they will Most likely blow up.
If you don't get the looser class bearing in perfect they won't last as long but they will work and you may even get them to run truer than spec (this is what has happened to the spindles I have made, sure the bearing life might not get the 10k hour listed but they still run fine for me after 3years of intermittent use)

3. If you buy the expensive stuff and don't follow the bearing wizards advice don't expect to get you moneys worth! But On the other hand if you buy cheaper bearings for you experiment and you suck wind, well you’re only out a little time and money.

Just my 2cents.

[NC Cams]

Generally speaking, mechanical devices follow a rule I call "the perverse nature of inanimate objects". That is, stuff that should work often doesn't and for some reason stuff that shouldn't, does - only God knows why. If you know what IS needed to make it work, it is often easier to understand why it doesn't or how to get by if you don't have what you need.

Engineers are theoretically taught how to solve problems - some are better than others and some are more creative than others. We tend to follow a logical path dictated by rhyme, reason and technical principles. Thus, when folks ask for information, I try to provide the best info that will provide for the most reasonable degree of success.

The points made by miljnr are absolutely correct (with some teeny tiny opinion differences regarding semantics but correct enough even for my overly sensitive tastes). You simply CAN'T expect to have good results if you make bad compromises (2 wrongs don't make a right kind of deal).

The lowly Chevy small block engine that was designed for 190hp in 1955 is, in today's trim, capable of nearly 800 in full NASCAR trim. How? Surely NOT "abec 1 parts and lots of luck" but truly "abec 9's or better parts" plus LOTS AND LOTS of TLC and research.

I learned bearings as it was a job. I did the cam thing because I wanted to learn how to do it. The ego part kicked in when I thought I could offer a better service that wasn't being offered by the name cam companies. wanted to sell the engineering service but couldn't do it without a grinder to make them. Bought a grinder and learned to use it to sell engineering services. Left handed logic but it's how I got into the busines.

It takes a LOT of work, thought and knowledge to make simple parts do extravagant things - you create luck when preparation coincides with an opportunity.

To the budding DIY'er, the worst thing the veterans could do would be to give them the impression that you simply "bolt this stuff together" and "if it was machined wrong, Loctite will fix it".

I feel the veterans should teach them the GOOD and proper technical skill (not wives tales or tricks)- they'll pick up the bad ones (and learn the wives tales) on their own in due time ....

[gotis]

Originally Posted by NC Cams There are several philosophies to consider: Make a precisiong spindle, use precision bearings, assemble it and grind the ID to get the axis of the spindle to run tru to the axis established by the bearings. or Make semi precision spindle, use semi precision bearings, selectively assemble (move them around until you get axis to run true) then "lock it down" and grind the ID. Make whatever for a spindle, use whatever for bearings, grind after selective fit but don't be surprised if you end up with something that is oversize and doesn't holed tolerance. Whenever you talk high speed, you want the cutter running true. Otherwise, finish, chatter and size control become concurrent problems. Thus, precision machining and bearings become more critical as speeds mount. Like we tell our racing customers, "Speed costs money - how fast do you want to go and how long do you want to go that fast???" I bought an import mill and it ran well as is. Since I worked for a bearings supplier, I figured I"d "tune it up" with some surplus ABEC7's that were being tossed. Result: Disaster Reason: the housing and spindle were selectively fit (cheap labor enables you to assemble/reassemble sloppy stuff until you get it to work much cheaper than buying expensive bearings and holding tite tolerances when grinding). Yes, you can buy the spindle as a "core" and then via grinding, plating and selective fitting, you can blueprint the part to do what you want. However, it will cost time and/or money. Do you have either/both to spare????

These are probably too large but I got them "cheap".
Was thinking of using them for a lathe but got something wrong, the bearings in the lathe was imperial and the bearings I got was metric, ended up buying a used lathe instead of rebuilding the old one.

You seem to know what you´re talking about, is this too cheap?

http://www.cnczone.com/classifieds/s...&cat=6&page=13