Drill / Mill Spindle-to-Pulley Spline Fit

[extropic]

@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

View attachment 502410

I have no idea what you mean by a "clearance fit". Can you define it in terms of actual dimensions?
In the picture (reply #28) I see two small holes, opposite the flat on the circumference of the pulley support/bearing housing.
On the main body casting, faying surface, I think I see very slight (.03"?) protrusion of two C-pins (spring pins?) that are probably intended to precisely locate the pulley assembly. The pins are protruding so little as to be ineffective at precise indexing. Apparently, someone has tried to install the pulley assembly without paying proper attention to the pins and has driven them into a depth that renders them inadequate.
I suspect that the resulting misalignment is at the core of your noise problem.
I suggest you remove those and start over with fresh pins. If it were my machine, I would try substituting solid dowel pins and Loctite them them into the pully support housing, with about 2 x D protrusion for engagement into the main casting. The hole diameters would have to be compatible with that approach.

If the existing pins are C-type (hollow) as I suspect, I would try using an easy-out to turn and pull them out enough to get some Vise-Grips to finish the job.

 

[jdeng]

• I'd ballpark an RC5 fit if you're looking to be technical. I think it's sufficient to share that it slides in easily with no noticeable play, but I'll grab dimensions next time I pull the assembly (tomorrow, when the new pulley arrives).
• Those are holes for mounting the speed sensor, not for alignment. edit: The dimples you're seeing are grease blobs.

The exploded diagram I linked is helpful if my descriptions are not working for you.

 

[Janderso]

My concern is the movement of the pulley you showed in the video,

That movement is a problem!
I would address that first.

 

[jdeng]

Well extropic got me curious, the fit between the pulley housing shaft (75.10mm) and the spindle housing bore (75.35mm) is .25mm. Quite loose for sure.

Will get the new pulley from LMS installed tomorrow.

 

[extropic]

• I'd ballpark an RC5 fit if you're looking to be technical. I think it's sufficient to share that it slides in easily with no noticeable play, but I'll grab dimensions next time I pull the assembly (tomorrow, when the new pulley arrives).
• Those are holes for mounting the speed sensor, not for alignment. edit: The dimples you're seeing are grease blobs.

The exploded diagram I linked is helpful if my descriptions are not working for you.

Grease blobs! Foiled again.

It seems that I'm contributing more heat than light here.
If I wasn't interested in specific quantities and units of measure, I would spend my time on a "Hobby-Cat-Herding" forum.

 

[Ischgl99]

The pulley bearing housing doesn’t need any more than a sliding locational fit, a clearance of 0.25mm is a lot more than I would expect. The screws holding it in place should be able to hold it reasonable well, but it is possible that is contributing to the noise you are getting.

 

[jdeng]

unfortunate update. Installed new pulley and new belt. no change.

I ran at top speed (which is now 4500 rpm, 10% less than before the refurb) for 20 minutes. The spindle gets warm (100F) but the pulley get hot (140F). I can't explain it but clearly the chatter is coming from the pulley, whatever it is is causing it to heat up, and I'm losing power at the tool.

Beyond getting a new spindle (with the assumption that the splines are somehow at fault), I am out of ideas.

 

[jdeng]

@Ischgl99 I agree the fit between bearing housing and spindle housing is quite sloppy. the clamping force from the four screws is very high and I can all-but-guarantee the rattle isn't from that part moving around.

However, given the slop, I can't guarantee that the pulley is coaxial with the spindle shaft. The splines line up...and that's probably the best gauge I can get.

 

[Ischgl99]

Do you have feeler gages to check how much clearance between the spindle splines and the pulley shaft? I would check that at several points and also see if it varies as the pulley is rotated by hand.

How tight are you tensioning the belt?

 

[jdeng]

Do you have feeler gages

I do. None narrow enough to give me a good reading though.

How tight are you tensioning the belt?

I've tensioned from loose and flopping around to crowbar tight and everything in between. If the spindle / pulley is spinning, it will chatter regardless of the tension.

I'm still dumbfounded about why the chatter is reduced or eliminated when using the low-speed belt. the moment arm on the pulley and pulley-bearing is greater (for a given belt tension) on that setting. It's really confusing.