DIYbanter - View Single Post - Millrite MVI spindle bearing repair

Joseph Gwinn

In article ,
wrote:

On Wed, 18 Aug 2010 23:27:22 -0400, Joseph Gwinn
wrote:

In article ,
Ned Simmons wrote:

On Wed, 18 Aug 2010 00:02:45 -0400, Joseph Gwinn
wrote:

In article ,
Ned Simmons wrote:

On Mon, 16 Aug 2010 23:28:56 -0400, Joseph Gwinn
wrote:

In article ,
Ned Simmons wrote:

On Mon, 16 Aug 2010 09:55:27 -0400, Joseph Gwinn
wrote:

[snip]

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

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'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.

[snip]

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.

[snip]

What class is needed for a MVI anyway?

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.

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

[snip]

Joe Gwinn

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

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.

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?

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