Bearing question re:Spindle/Quill

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wally318
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Joined: Sun Jun 05, 2011 1:06 am
Location: Kelowna, British Columbia

Bearing question re:Spindle/Quill

Post by wally318 »

Hello all. I'm at the point in my rebuild of the vertical head.
Rockwell 21-100 vertical head.
Specifically the quill. I went to clean and repack the bearings
and found 1 of the lower bearings to feel rough after flushing
the dirt/old grease. A bearing place recommended 6008-2ZC3
as a relacement for the MRC 108 KSF. They yeilded horrible runout
results even after playing with shims etc.
So I ordered a duplex angular contact bearing Abec#7 and that
got me thinking. Would a higher tolerance bearing also give benefit
for the top bearing? THey gave me a R16-2Z as a relacement for
the Norma S10RPP. Its only a abec#1 rating.
Was thinking something in an Abec#5 might improve the runout
even more? Any members have an experience with this?
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Bill Shields
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Re: Bearing question re:Spindle/Quill

Post by Bill Shields »

To what end?

Calculate the existing runout using the standard top bearing and how that translates to actual possible motion at the tool tip.

If it ends up with a measurable difference, and your collets and tools and measuring equipment are up to it, then go for it.

Question -> where were the 'horrible runout' bearings made?

The general eccentricity specs of a #1 bearing (.0003") should be quite acceptable for your mill when properly loaded.

I have personally owned a mill where the quill itself was more crooked than the bearing runout, and ate bearings.

I suspected that it had been crashed hard with a big cutter by a prior owner. $ more to fix than it was worth and I sold it off for parts and purchased something else.

R8 are not the most stout of quills.

Any greater than that and I would blame the manufacturer not the bearing spec.

There are certain manufacturers from whom I prefer not to purchase bearings, even for what I call junk applications.
Too many things going on to bother listing them.
wally318
Posts: 260
Joined: Sun Jun 05, 2011 1:06 am
Location: Kelowna, British Columbia

Re: Bearing question re:Spindle/Quill

Post by wally318 »

The bearings in question are an SKF 6008-2Z/C3 made in Italy.
I tried to preload the bearing with a ring shim between the inner races.
That yeilded the worst runout.
First I read off the R8 taper but several small pits prevented a good reading.
Even after a good clean-up on the lathe.
So I installed a collet chuck rated @ .0001" or 2, and read off the taper and
also housing circumference was getting .002/.003" runout.
So I decided to shim between the outer races and got about .001" runout.
A far cry from the .0001" runout that I've seen on test reports of the new machines.
Thats when I decided I was beating a dead horse and ordered the NSK abec#7
angular contact bearings.
As an afterthought I decided to repack the original bearings and install them for a comparison test
and got a runout of .0005" in the R8 taper (a bit higher up in a fairly clean area) as well as
in the taper and circumference of the collet chuck. And that without any preload what soever.
I just installed them the way they came out. They have no preload built in the races. Both inner
and outer races are the same width to the tenth. In comparison the pulley bearings are a matched set
with inner races about .008" narrower for the pair.

The bearing I'm asking about is an RBL-made in china R16 ZZ.
My logic is this: If I'm minimizing runout down at the spindle taper by going to a high tolerance(minimal runout) bearings
then I could minimize runout even more by controlling any runout at the top end of the spindle.
Could I acheive even some gains by going to a better R16 bearing than the RBL?
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Bill Shields
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Re: Bearing question re:Spindle/Quill

Post by Bill Shields »

The math is easy to work out

Take the runout and work the triangle.

.003 runout I'd a nasty, out of spec bearing if I read your post correctly
Too many things going on to bother listing them.
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