Millrite MVI spindle bearing repair - first report

This is a continuation of the thread "Millrite MVI spindle bearings may need replacement" first posted on 31 July 2010.

I now have the spindle out of the quill and the taper roller bearings off the quill. I made (from a cast iron pipe fitting) a special pusher to avoid crushing the grease slinger, and (lacking a press) used a piece of 1/2-13 allthread passed through the drawbar hole to generate the needed force. Greasing the spindle just ahead of the sliding bearing race also helped.

The taper roller bearings are not in that bad condition, given that the grease had turned into some kind of chalky cake. However, the absence of grease had allowed coolant to enter and corrode the bearing "cup" (the outer race) of the lower bearing assembly in a few places. I assume that the area weakened by corrosion will soon fail. The rollers are not yet clean enough to tell if they have been compromised, but one assumes that there has been damage.

It is not obvious how one would grease these bearings without removing spindle from quill (which isn't that hard, but still). I have heard of people instead using DTE24 or heavier hydraulic oil fed in through the plug in the side of the quill, and letting it drip out of the bottom of the quill. This may be a better approach. What experience do people have with this?

For the record, the two outer races ("cups") are each Timken 19268; and thetwo assemblies of inner races ("cones"), rollers, and cages are each Timken 19150. The stated ID of a 19150 cone is 1.5000".

The quill shaft is about 0.0011" larger than the stated cone ID, so it was a light press fit. As others have noted , this cripples the running preload adjustment by turning a ring nut on the spindle, and press fits are too hard to get exactly correct.

Is there a standard solution? I'm tempted to polish the spindle shaft down until the (new?) bearings are a (hand) push fit. Has anyone done this?

Joe Gwinn

Reply to
Joseph Gwinn
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That's near the high end of the recommended shaft diameter, which is .0007 to .0012 (+18 to +30 microns) over nominal. The ID of a class 0 precision cone is nominal +13/+0 microns, with a resulting 5 to 30 micron interference. Personally, I wouldn't mess with the bearing seats. Even if you can maintain cylindricity, you're risking fretting of the seat if the fit is not tight enough.

Be aware that the specs on standard tapered rollers are very loose compared to inexpensive ball bearings, and precision class bearings are quite expensive. Expect to pay around $270 for each cup/cone ass'y in class 0 vs. $45 for a standard bearing.

BTW, the first thousand or so J-head Bridgeports used tapered rollers on the spindle; the subsequent couple hundred thousand have angular contact bearings.

Reply to
Ned Simmons

There are people probably a lot more knowledgeable on this subject, but here=92s my two cents. When you=92re pressing the bearing into place, you=92re putting the load on the outer race. When you tighten the ring nut, it preloads the inner race and rollers. The force used getting the bearing set in the bottom of bushing shouldn=92t come into play. (If the bushing was too tight, I suppose that you might crack the bushing or outer bearing race.)

I=92ve put in a grease-fitting in the rod end of an old Keller power hacksaw that I=92ve refurbished and it seems to have worked well. I think that my repair will make it last much longer, but what you probably have to guess is the level of stresses in the area supporting the bearing. If you drill there to put an oil cup or grease fitting, you could possibly cause a stress riser. If the bearing support is low-stressed, you=92re probably safe to drill & tap it to add a lubrication fitting.

Reply to
Denis G.

Yep.

D.C.Morrison says that if one just puts the grease in at the quill side port, it will work itself into the roller bearings (which are open). No harm in trying.

Joe Gwinn

Reply to
Joseph Gwinn

D.C.Morrison says that the bearings should be a "tap fit" on the spindle, not a press fit, and endorsed my plan to polish the quill down a bit to achieve a tap fit.

What class is needed for a MVI anyway?

Burke used taper roller bearings for the standard R8 spindle, and ball bearings for the high-speed spindle. Taper roller bearings are more robust than ball bearings under shock loads (like interrupted cuts).

Joe Gwinn

Reply to
Joseph Gwinn

I dunno who DC Morrison is so can't decide whether their opinion should carry more weight than that of Timken's engineers in this case. "Tap fit" is a rather subjective way to characterize a bearing fit, depending on who's doing the tapping and the size of the tapper, but I assume it means a transitional fit with minimal interference. The ID of your cones can vary by 5 tenths, so a tap fit on one bearing may result in excessive clearance on another.

Class TIR

4 .0020 2 .0015 3 .0003 0 .00015 00 .000075

The runout of Class 0 roller bearings is approximately the same as the ABEC 7 angular contact bearings typically found in machine tool spindles.

True, but BP spindle bearings will take a lot of abuse if they're lubricated properly and kept clean. Tapered rollers will carry a substantially heavier load than angular contact bearings in a given volume. But there are tradeoffs, such as added complexity, expense, and less tolerance of contamination.

Reply to
Ned Simmons

By the way, the interference may be half that. I found the the zero of the micrometer (B&S 84) I am using is off by about 0.0005". This will be fixed over the weekend.

DC Morrison is the company that supports Millrites, having bought the wreakage of Burke. You must call for Millrite manuals and parts.

The issue is to ensure that the preload can be set accurately enough. This is impossible if the bearing closest to the preload ring nut cannot move because it's too tight a press fit.

Does Timken mention alignment of high spots and low spots to reduce runout?

This may be what is happening. And things may have corroded and so grown a bit over the years. I think I'll do most of the polishing on the bearing ID, rather than the shaft OD, although I'll clean corrosion off the shaft.

Which class is a "standard bearing"? I'd guess 4, for wheel bearings.

What are "airplane bearings", like from skygeek.com? They are priced at the $45 level for the cup and another $45 for the cone et al.

What is a typical price for Class 3 set of one 19268 and one 19150?

DC Morrison says that Timken Class 3 are what was specified for the Millrite spindle, and the existing bearings are in fact marked 3.

All true, and Burke apparently valued robust more than Bridgeport. Perhaps the intended audiences were different. Not that I've heard of Bridgeport spindles being so fragile. But I don't know why Burke didn't provide more protection against the entry of dirt and coolants.

Joe Gwinn

Reply to
Joseph Gwinn

That's one of the complications of tapered rollers. Angular contact bearings can use equal length ID and OD spacers to control preload, and the same spacers will work with a new bearing pair. Not so with roller bearings.

Not that I see in the literature I have, but "Timken Bearings for Machine Tools" is mentioned in the section on precision bearings, and may have more info if you can find a copy online.

I certainly wouldn't hesitate to cautiously remove any corrosion or high spots you find.

Yes.

I don't know what "airplane bearings" are, but Motion Industries also references "aircraft bearings" in their database, with no indication of what distinguishes them from standard bearings. But they are listed as "standard precision."

Looks like about $125 for the cone and $68 for the cup. Those are my approx prices from Motion Industries.

BP spindles are not especially well protected, either. The nose pair is protected only by a labyrinth formed by close clearances between the various parts of the spindle and quill. Indiscriminate use of air to clear chips can force crud up into the bearings.

Reply to
Ned Simmons

Generally means that they've jumped through the hoops to get the part FAA approved for repairs of certificated aircraft.

Reply to
J. Clarke

Guys..when pricing bearings....a hint and an offer Ive made before...

Contact Alpine Bearing and Thompson Industrial Bearing

Tell them you are with Rapid Turn..and ask for pricing. If they ask about John..tell them he is doing fine.

If you prefer, when calling Thompson...tell them you are with Coyote Engineering, (my company) and get a price.

Period.

You will get FAR better pricing quotes than a cold call to Motion Industries.

We do this with GREAT regularlity for our customers and its quite common.

As long as they have a name with regular bearing sales..they give 3rd column pricing..and the differences in pricing is often staggering.

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Gunner

Reply to
Gunner Asch

[snip]

So the tap fit is the compromise.

I'm not finding anything by this name; perhaps this was an earlier version and/or name.

What I did find is "Timken Super Precision Bearings for Machine Tool Applications", file "5918_09-09-29.pdf", 259 pages. The pages are all marked "TIMKEN MACHINE TOOL CATALOG" at the bottom. This is a very useful document, from the look of it.

On page 100, they start to talk about aligning the high spots in exactly the same terms as I have been hearing, and later there is a picture showing what the high-spot marks look like. I found such marks on the bearings in my mill. Well, I'm short one mark (on a cup), which mark seems to have been abraded off.

Yes. This weekend.

Another poster (J.Clarke) said that it meant only that the maker had jumped the hoops to become FAA certified for airplane repair.

Oof. That's a total of 2(125+68)= 386= $400. I was leaning towards letting it be for now, and this is pushing me that direction. There is only one corroded spot, about 0.25" in diameter.

The Millrite also has a labyrinth of sorts, being three ~square cross section grooves in the quill nut through which the spindle nose protrudes. It's a tight fit. Sounds like the BP approach. The grooves were packed full of crud, now removed.

Yet another reason for the tradition to forbid use of compressed air on machine tools.

Joe Gwinn

Reply to
Joseph Gwinn

As an interested onlooker. How much of the TIR is eccentricity and how much is "out of round".

For instance. If we fitted class 2 set of bearings and then finish ground the spindle nose and bore in situ, would we have a class 00 sytem?

Jim

Reply to
pentagrid

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I have no way to measure out of round better than measuring the spindle diameter in various places around the circle, and I get the same answer all around.

The spindle appears to have been ground. What I had thought were are longitudinal ripples from some kind of chatter in the grinder upon cleaning, polishing, and inspection with a 10x magnifier are scratches, apparently from dirt caught between spindle and cup when the cups were pulled off the spindle. Given the design, it was difficult to clean this area before disassembly, a Catch-22.

The inside of the quill is bored, and so is likely quite round.

If the two bearing cones (or cups respectively) can be depended on not to rotate with respect to one another over time, it could work I would think.

The cones (inner races) are too tight on the spindle shaft to rotate unless a bearing completely jams. Even then, a more likely outcome is rollers skidding. In any event, a repair must immediately follow.

Both cup (outer race) faces are scuffed, apparently by the spacer tube, but the cup OD cylinder surfaces show no signs of having rotated in the quill. So, the cups may stay put well enough. The movement of the spacer tube may indicate that the preload wasn't quite enough.

At least at low rotation rates, where the resulting slight imbalance is without effect. Given the maximum of ~3000 rpm for a Millrite spindle, I would doubt that a little spindle imbalance would be noticed. After all, we are likely talking about a few times 0.0001" of decentering, which we probably already have.

Joe Gwinn

Reply to
Joseph Gwinn

Just stay away from 'Acme' brand bearings and anvils ;-)

Reply to
Michael A. Terrell

I've had an OEM account with MI for about 25 years, since the ME branches were a family owned business. I'll bet the prices I gave are pretty close to the best you can do in small quantities, but a thrifty man will shop around.

For curiosity's sake, I sent an RFQ on the bearings to Thompson Industrial last Wed. They didn't reply.

Reply to
Ned Simmons

Unless you have a vendor within walking distance, "face to face" implies driving around. Or do you take the bus?

Reply to
Ned Simmons

All that because I prefer to submit purchase orders by email. Imagine if we disagreed on something substantive, like the 4th Amendment or brands of cat kibble.

Reply to
Ned Simmons

Maybe he got a parking-lot ding in the door of his truck.

Reply to
Ed Huntress

And the other poor bastards who have emailed companies and have gotten no responses?

Whats the matter boys..afraid to use the phone these days? You two gotten some additional wierd Leftwing mental illness about using the phone?

At least it keeps you from calling little kids.

Hummm..or..does it have something to do with a court order?

Gunner

I am the Sword of my Family and the Shield of my Nation. If sent, I will crush everything you have built, burn everything you love, and kill every one of you. (Hebrew quote)

Reply to
Gunner Asch

And we know who's responsible. I have it on good authority that the incidence of door dings is 2-1/2x the national average in Home Depot parking lots frequented by illegal day laborers.

Reply to
Ned Simmons

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