Wiggle in the spindle - are my bearings toast?

[cobrakai]

Hey all,

It has been a while since I've visited the forum. My 1100 Series 2 has sat idle for many months, and I'm finally working on a project again. I recently tightened the gibs, balanced the spindle motor fan, and trammed it. All of those aspects are awesome!

Back story: During a lot of stock removal, I found my TTS tooling slowly walking out. I was profiling with a 1/2" 3-flute end mill, 5000RPM, 45IPM, 0.5" DOC, 0.1" WOC. This was fine, until I went into an internal radius momentarily, effectively increasing the WOC to 0.2" (4.5cu-in/min MMR) The spindle bogged down for this brief second and the holder walked out about .002". It actually sounded amazing, super smooth and the chips were FLYING.

Anyway - I thought I'd double check the PDB adjustment and re-lube the R8 adapter, when decided to grab a hold of the end mill and holder with a glove on and wiggle it hard (20-30lbs back and forth). There is a noticeable wiggle, looseness that can be felt at certain clock positions. I'd say .001" or .002" of total wiggle. I instantly thought the R8-TTS collet is to blame, and probably needs a fine hone to get better contact. I took the collet out, and grabbed a hold of the spindle nose to do the same test. It also wiggled.


TL;DR
If my spindle has minor radial play, but feels smooth and quiet, can I simply re-preload it, or do my bearings need replacement? I probably have 300 hours on the machine and the spindle has never been serviced. Thank you

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[cobrakai]

Welp - to answer my own question. There is a reason the bearing developed radial play! I adjusted the preload on the spindle nut and heard crunching. Time to order up a new set.

[wildwhl]

I recommend building one of the preload disc springs like Keen did. There's a thread here with a picture somewhere. Helps a ton. Also, you can use a combination of heat and cold, and very little force, to put the bearings in place. Use good grease. Break them in and they last.

WW

[cobrakai]

Upon disassembly, I have found that the very top bearing has spun its outer race in the bore. The lower top bearing also seems to have spun, but maybe only a couple times, as it still has its arrow marking and was not shiny. Both bearings have 1 or 2 spots where a notch can be felt. The lower (tool end) bearings are both smooth, but are devoid of grease.

There is a slight burnishing on the spindle housing, but no ledge or roughness can be felt with my finger nail or sharp scribe. The bearings are a slip fit into the housing when everything is at room temperature. It's a very slight slip fit, as no wiggle can be felt even with both surfaces clean and dry, and they give that "whoosh" draggy feeling coming in and out. I really don't want to buy a whole new spindle housing for $550. So I am going to try using new bearings with Loctite 638 high strength retaining compound. It can fill gaps well beyond this and will keep them from spinning in the future.

I saw the preload ring that Keen made. I think it's a great idea. I'm not sure I have the capability to make such a thing. It's essentially a giant belleville washer, right?

[IMT]

I've rebuilt two spindles and the bearings were not a slip fit into the housing on either one. The last one I did (about 2 weeks ago) I heated the housing to 200F in an oven. Both sets of bearings just dropped in. I packed the spindle shaft in dry ice (~-110F) and it slipped right through the bearings with no force. If your bearings slip into the housing at room temperature then I expect the housing bore is out of spec, nonetheless the retaining compound should work. Good luck.

[cobrakai]

After fiddling with my spindle enough, I concluded that the design and/or manufacturing on my spindle is flawed. The upper bearings were a (very precise) slip fit into the housing, and the spindle shaft was a press fit on both upper and lower bearings. I believe the upper bearings should be press fit into the housing and the spindle shaft should slip into the upper bearing inner races. I ran into the problem of the entire system basically binding or becoming loose due to the inability of the preload collar to maintain a preload - instead being overpowered by the the friction of the inner bearing races.

What I did was chuck the spindle in the lathe and carefully hone the upper spindle shaft where it slips into the upper bearings until it just slipped in with a tiny bit of force (This was a trial and error thing about 10 times). I left the lower bearing interface alone, with just a quick polish to clean it up. The assembly now spins silently and smoothly, whereas before it was making some pretty horrific noises. No doubt I took some life off the bearings due to that abuse. I will need to still run a project and see how it does long-term, but it sounds and feels promising. Hope this helps someone.

[GLCarlson]

I've rebuilt two spindles and the bearings were not a slip fit into the housing on either one. The last one I did (about 2 weeks ago) I heated the housing to 200F in an oven. Both sets of bearings just dropped in. I packed the spindle shaft in dry ice (~-110F) and it slipped right through the bearings with no force. If your bearings slip into the housing at room temperature then I expect the housing bore is out of spec, nonetheless the retaining compound should work. Good luck.

Absolutely right. Dry ice in the bore makes this dead easy.