Millrite MVI spindle bearing repair - Second report


This is a followup to "Millrite MVI spindle bearing repair - first report"
posted on 16 August 2010.
The Millrite is back together, and was improved by the experience, although the
runout is unchanged.
For all the discussion of tapping bearings onto the spindle, I never could get
it to work, and ended up using a length of 1/2-13 allthread, some black iron
pipe and machined cast-iron pipe fittings, and various washers (some shopmade)
to push the bearings back onto the spindle, and to fully seat the spindle plus
taper roller bearings assembly back into the quill, which was still in the MVI.
I also slightly reduced (by perhaps a tenth) the spindle diameter under the
upper bearing (farthest from the spindle nose) by careful manual sanding and
polishing, using sandpaper and crocus cloth backed with a piece of 0.125" thick
stiff red rubber gasket material from the local hardware store. The backing is
intended to ensure that sanding and polishing preferentially flattens any
scratch ridges and other peaks. Roughing the surface slightly also helps with
grease retention, making for easier sliding while pushing bearings into place.
It is now possible to adjust the preload by turning the round nut on the spindle.
I suppose that tapping might work if the quill were on a bench, but proved
hopelessly awkward with quill in the mill. I've certainly installed plenty of
automobile wheel bearings by tapping, but for the spindle I was not able to keep
the bearing race from cocking and jamming, and gave up.
A big arbor press would also have worked, had the quill been removed.
I didn't want to remove the quill because I would have to disassemble and later
reassemble the quill DRO assembly.
The spindle now runs very quietly - the funny noises that started this exercise
are now gone. Only the two taper roller bearings were touched, so their lack of
lubrication and contamination with grit were the cause. The races and rollers
all look OK, despite the abuse.
Milling finishes are much improved, especially when climb milling, probably
because the dirt is gone and the preload is now correct, so the spindle cannot
squirm around so much any more.
Also, there was some axial play that is now gone, as the big quill nut is now
fully tight.
Runout is unchanged. Near the spindle, with a drill blank clamped into a fancy
3-jaw chuck, I measure 0.001" total runout, and 0.002" runout about 6" from the
chuck. This is essentially what I measured before taking the spindle apart.
For the record, the specs are 0.0005" total runout near the spindle nose, and
0.001" at 8" from the spindle nose, using a test bar. A machine made in 1965
need not apologize for having only twice the runout it had in its youth.
Part of the problem is that I get (and got) different answers with each chuck,
and have no way to know which to believe, if any. Sometimes I get very low
runout values (in the tenths), sometimes large values (a few mils). Test bars
work, but are expensive, so I'm looking for an alternative. Until this is
figured out, I won't attempt to high-spot align the bearing races.
The existing Timken bearings were high-spot marked, but the marks had been
rubbed off both outer races, probably because the quill nut was not tight
enough, allowing things to move.
Anyway, when I have an adequate way to measure spindle runout, I will simply try
different outer race orientations and keep the best, as removing and replacing
the spindle with bearings is actually fairly easy.
The trick to getting the spindle assembly out is to use a bit of allthread
passing through the spindle, one end screwed into a T-Nut in a table slot, the
other end with washer and nut bearing on the top of the spindle, then crank the
table down and/or the quill up to extract the spindle from the quill. A piece
of wood between spindle and table will prevent loose spindle hitting table. An
extra washer and nut just under the spindle would also work.
Joe Gwinn
Reply to
Joseph Gwinn
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For testing chucks, I've always used selected dowel pins, 1/4" ones are fairly easy to come by if not really, really long. May not be good enough if you're trying to reduce runout to fractions of tenths.
Stan
Reply to
stans4
Yes, I've done that too, but using drill blanks.
But, now we are trying to measure the spindle runout, not chuck runout.
Joe Gwinn
Reply to
Joseph Gwinn
Not familiar with this machine but assuming it's an Int 40 taper or similar can you not clock the inside of the taper. One set of measurements close to the spindle nose should show eccentricity and out of round. A second carefully centred set further up the bore should show up residual tilt.
It's a bit fiddly even with a small sensitive lever type clock. I use a home brew capacitative sensor which has the business end on the side at the end of a short length of 1/4" tubing.
Jim
Reply to
pentagrid
[snip]
[snip]
I did consider using the inside taper, but it's R8, so there really isn't enough space for a dial test indicator to reach the back cylinder and still be able to see the dial. Unless one can get a really long-armed unit, which isn't impossible.
Capacitative sensor. Now there's a thought. I certainly can easily build such a thing, especially the diode-bridge kind with guard ring, and it would have the advantage of ignoring the surface roughness and dings of an old and well-used spindle.
Joe Gwinn
Reply to
Joseph Gwinn
I actually already have such a sensor circuit that I built in the 1970s to track rats. (Yes, rodents, for pharmacological research.) But I have to find the circuit board.
Another good idea was suggested by Jim B on 2 September 2010 in a posting to the Burke Mills (Millrite and others) reflector ( snipped-for-privacy@yahoogroups.com):
Use Rollie's Dad's Method , originally for aligning lathes, but ought to work for a vertical mill as well.
I'll use some shafting held in a R8 collet, as a collet is simpler and more repeatable than any reasonable 3-jaw chuck.
Joe Gwinn
Reply to
Joseph Gwinn

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