Drill / Mill Spindle-to-Pulley Spline Fit

You're thinking like this is an ideal world- it isn't. Belts are not perfect, motors pulsate as they turn, machined parts have eccentricity and imbalance.
Add to that the spline issue and you get rattle from all the dynamic rotational effects
 
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Haha, me? I work in metal with hobby grade machines: no time for ideal in that world.

Just trying to wrap my head around the mechanics because it’s interesting. Think I might try to get some super slo-mo on the iPhone. Not sure why I didn’t think of that earlier.

Will update if/when it’s all back to ‘good-nuff’.
 
I misunderstood some of the things you posted, I’m glad it looks like the bearing is fine and you don’t get the play like I thought you were getting. Mark is correct, there are many things that can cause torsional vibration, if it doesn't affect the operation of the machine while you are machining, I wouldn’t worry about it.
 
installed the new pulley bearing. same chatter. new pulley from LMS arrives on Thursday.

To your point @Ischgl99, the surface finish is fine, but eventually that chatter / vibration is going to break something. My videos may not do it justice but it is quite loud and my top speed is about 500rpm lower than before the refurb.
 
It's apparent to me that the pulley and the spindle need to be precisely coaxial. How is the pulley support structure keyed to achieve that position?
Please provide pictures rather than only text.
 
Yeah, it didn’t sound that bad in the videos, at least on my iPad, and if you can’t reach top speed any longer, then it does need to be solved. Are you saying at full speed it is now 500 rpm less than before, or you can’t run it at full speed because of the vibration?

If you can’t reach full speed any longer, then it could be a drive problem. A drive problem can cause a torsional vibration problem that would give you symptoms like you are seeing. I would still check the following to make sure there are not any mechanical issues.

Take the belt off and spin the spindle by hand, does it spin smoothly without any indication of chatter or pulsating resistance? If the bearings are not seated squarely to the shoulders, you could be getting binding during the rotation, but since you said the surface finish is good, I don’t think this is it, but should be checked to eliminate it as a possibility.
Measure the runout of the spindle pulley and motor pulley in the grooves, as well as axially. If either do not look good, take the pulley off and see if it is the pulley, or the shaft. You want to measure in the grooves since that is where the belts are running.

If you run the motor without the belt on, does it give any indication it is pulsating? Since you mentioned earlier that it doesn’t do this on the low speed setting, but does on the high speed, then I would think this is probably ok, but should be checked anyway.

I wish you lived nearby, troubleshooting is much easier in person than 3,000 miles away.
 
  • I can only reach 4500 rpm now. Used to get 5000.
  • I chucked the spindle/quill assembly into my lathe using a four jaw and ran it at 2000 rpm. It sounded great and didn't heat up. runout was pretty low, 10 microns (.0004")
  • Will measure the pulleys tomorrow, that's a good idea
  • Motor sounds good
I think @extropic has a good point about axial alignment. I'll add some photos tomorrow but the pulley housing is a clearance fit into the column. interesting point to consider...

I would say that the PNW is beautiful this time of year but so is Connecticut! I grew up not far New Milford actually.
 
@extropic here ya go!
  • The pulley housing fits into the spindle housing with a clearance fit
  • the pulley housing is fixed to the spindle housing with 4x m5 SHCS
    • the clearance holes for the capscrews are nominal
Happy to add any more detail and you can find the exploded diagram on LMS here

20240911_5921.jpg
 
@Ischgl99 measured runout on the following:
  • spindle pulley: less than 5 micron
  • spindle pulley v-belt grooves: 10 micron
  • motor pulley: 5 micron
chatter is most pronounced when the quill is fully retracted (ie top of its travel, no downfeed displacement, etc).

This chatter wasn't there before I started digging around. I wonder if the pulley was fit to the spindle at the factory with a specific clocking? Will try that now.
 
well, there are indeed two positions of the pulley relative to the spindle that all but eliminate the chatter....and they are clocked 180 degrees from each other.

I *think* this confirms the hypothesis that the tolerance between splines is the culprit. happy to take objections if you have them
 
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