Tearing Apart an HSD Spindle for Maintenance

Is it worth doing your own spindle bearing replacements? June 17, 2009

Has anyone taking apart an HSD Spindle to clean the bearings?

Forum Responses
(CNC Forum)
From contributor K:
If you go to the trouble to take apart a spindle just install new bearings. Don't try to clean the old ones - they are worn out.

From contributor D:
We've been faced with the task before and have opted to drop the entire router and send down to HSD in FLA for a rebuild. Unless you're real good and balancing, running it in, and keeping everything clean it seems like a worthwhile investment to let them do it.

From contributor W:
I had to take mine apart this year to replace the cartridge. Not too bad of a job, the only problem I have, the db level seems to be higher with the new spindle. I liked the noise level of the old one but the bearings had started making a little noise.

From contributor N:
I recently (several months ago) replaced the bearings on my Rover 23. The first time an upper bearing failed within two days. I gave it a second go as the bearings were cheap enough and it only takes 1hr to do. I had already made a tool to hold the collet clamp in place to remove the release shaft. I had read on the bearing website that the bearings need to be broken in. I didn't do this the first time. I made a program that started the spindle speed at 5,000 rpm and increased it by 2,000 every 15 minutes until it reached 20,000. It didn't like going under 5,000 for more than a few minutes. I also used grease by Dow Corning made for high speed spindles. Itís worked great since then and has been screaming its head off all day with no troubles so far and is quieter than ever before. It was to be a $6,000 plus exercise to exchange it so I thought I'd give it a go myself. It is after all just a motor, not a space shuttle. If it fails again, I'd probably give it one more try before passing it on.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
To anyone thinking about having a go, I say do it. There are a bunch of companies out there that no doubt do a good job, but in my humble opinion may have been slightly exaggerating the difficulty. They talk at length about how they will check it, polish it, re-balance it, test the windings, read it a bedtime story and tuck it up in bed. Actually, I'd rather they just changed the bearings and saved me a few dollars.

Anyway, after a short lived and expensive rebuild we decided to do it ourselves. This was a 6.8KW, HSD with an ISO30 toolholder.

Here's what we found: The upper bearings are generally fine, it's the lower bearings that seem to go first. The one nearest the nose in particular is more prone to dust (especially if the professional rebuild you had done forgets to open up the air bleed control, misses out the grub screw in the cross-drill, etc.).

You'll need to remove the cover off the top. There is an HSD booklet on how to strip out the spindle cartridge, but before you get that far it is easier to remove the outer bearing retainer while the cartridge is still attached to the motor as it is nicely held. There is a cross-drilling in the front bearing holder where the air is bled in to keep the spindle nose bearing clean. On the other side is a drilling with a grub-screw deep in a hole. Loosen that grub-screw and remove it. Without this, you wonít be able to remove the retainer collar.

Next, undo the front bearing retaining collar. Itís the collar with four pin holes around the spindle nose. We had a tool made with four hardened pins and a 10mm plate with a hole that matched the spindle nose.


It is tight too, so be prepared to put a bit of pressure on.

When it is loose remove the retaining collar. Now set about removing the cartridge from the motor. You will find instructions in the HSD handbook on the web. Basically you unscrew the six bolts in the front bearing holder and use them in the alternate holes to push the bearing holder off the motor. You may need to use some bolts to hold the two retainer plates at the top of the spindle out of the way.

So the cartridge is out - now remove the inner bearing retainer. If you slide the outer bearing holder back up the shaft you will see the four holes around the spindle nose. I used the tool we made, put four hardened pins in the side holes and let them engage the hardened pins on the tool. This is a normal RIGHT HAND thread, just unscrew it.

There you go - bearings out, and the rebuild is a reverse of the disassembly process, as indicated in all the best manuals.

The bearings in ours are SKF 7007 CE/P4ADGB 15 degree angular contact bearings which are about $200- $300 a set. They are an opposed pair so be sure to mount them with the engraved faces facing towards each other in a back to back configuration. Clean up the labyrinth seals in thinners, clean the bearing spacer, drop your new bearings in and away you go. We actually have put in some standard 7007 CDUP4 bearings. These are a lower spec, but still a very high quality precision bearing pair. They are rated to 20,000 RPM so they should be ok as we rarely run that fast. They are only about $60- $100 a pair, so if they fail early I'm not that bothered. Do get a precision matched pair though, not just a couple of regular angular contact bearings. In theory, you are supposed to clock them in, adjusting their relative rotation for the position that runs truest. Not sure if itís going to make a big difference here.

All in all itís about an hour to strip it down, not exactly the worldís worst problem to solve. We were charged $1850 last time and they left the air bleed system closed down and a grubscrew missing, so the front bearing got dust contaminated. I feel that not only have I saved money, I may have even done a better job!