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]

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.

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.

So the tap fit is the compromise.


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.


"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.

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.

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

Yes. This weekend.


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.

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

Yes.


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.


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."

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


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

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

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.


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.


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

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).

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.

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.

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.

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.


Indiscriminate use of air
to clear chips can force crud up into the bearings.

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


Joe Gwinn