Spindle bearings

**chrisb691** · 2nd May 2012, 07:29 PM

I have a Chinese 800wt air cooled spindle, which has been doing the job for me okay. However, on Monday, whilst machining pockets, I pushed things a tad too far. The end result was a stepper stall, and lost steps. The problem was, that the stepper started up again, and the 6.4mm straight bit tried (successfully) to make a 19mm deep cut at 2400 mm/min. Naturally, this buggered up the piece I was working on, but worse still the spindle developed a real 'growl'. Hmmm, says I, I think I just stuffed the bearings. Oh bugga me (or words to that effect).

I pulled the spindle down, and checked the bearings, which seemed okay. But I figured that since I wasn't spinning them at 24000 rpm, that how they "felt" was probably irrelevant. Down to the local bearing shop, where I was informed that they weren't in stock, but that a set of high spec Nachi ones could be got in for the sum of $160.

Thought about it a little, then told him to get them for me. The rationale was, that even if I could get a replacement spindle somewhat close to that cost, it would come fitted with Chinese bearings.

Sorry, I didn't think to get pics of the disassembled spindle. But it is of simple construction, with a top bearing, and a bottom bearing. Both of these are angular contact bearings. The top bearing is simply floating in it's pocket, and takes no thrust at all. Whilst the bottom bearing (collet end), is contained within a housing, and is loaded via a screw-down aluminium piece. If this bearing is put in upside down, then the spindle will still growl. GO ON.....ask me how I know.

The purpose of this post, is to point this out to anyone that might think about replacing bearings on one of these cheap air cooled jobs, and maybe save them a bit of grief.

If you look at the 2 bearings in the pic, you will see that the one on the left has lettering showing around the rim, and that it's wall is thicker than the one on the right. These are actually identical bearings, but show the 2 sides. The side with the thinner wall, is the side that takes the thrust. ie when assembled in the housing, the thrust side will point towards the collet, and is what the aluminium piece screws down onto. I can't see how it matters which way the top bearing faces, as there is know thrust load on it.

All good now, and the spindle is running sweetly again.

**Bob Willson** · 3rd May 2012, 02:00 AM

Hi Chris

That growl you were getting may have been from the powdered bearing bits that seem to be strewn through the old bearings.

While $160 may seem to be a little expensive I think you may have made a good decision. On another thread here somewhere, someone said that they had bearings that they could file. Not hardened at all. How are your balls? Can you file them? Is there enough of then left to even get a file onto?

It is an interesting way to go. Please let us know how the bearings last and sound.

PS thanks for the grief saving. If it were possible to put something in back to front or upside down then I would almost certainly do so.

**rodm** · 3rd May 2012, 02:41 AM

Hi Chris,
It worries me a bit about the top bearing not taking any load. Usually a pair of angular contact bearing require slight end load to pinch the bearing together so that it takes the play out. Is the bottom bearing held in any way that prevents end play along the spindle shaft?
I will go take a look at the photos in the other thread.
I agree with Bob that there looks to be a lot of metal shavings around the bearings you took out.

Update
Ok still not sure what is going on as their spindle had two angular contacts on the bottom.

**chrisb691** · 3rd May 2012, 10:42 AM

Bob, what you are seeing in the photo is sawdust, not metal.

Rod, the pre-load is got by screwing down a stepped cylindrical piece of aluminium down onto the bearing. There's no play along the axis of the shaft, when the cylinder is locked down. However, that will change if it comes loose. As far as the top goes, it's all a bit under designed. There is a 6mm (approx) plastic plate screwed down over the top of the bearing. But there is at least 6mm clearance between the plastic, and the top of the bearing, so the bearing would be able to float in it's housing.

It's an ugly piece of design, but it is working okay again so I'm not going to stress about it. I'll pull the spindle out later, and take a pic of the pre-load feature.

**rodm** · 3rd May 2012, 03:29 PM

Thanks Chris,
Don't pul it down on my count - if it ain't broke don't fix it.

I am having trouble visualizing one angular contact bearing tensioned up to take out end float. A double row angular contact will work but a single row on it's own just doesn't do it for me.
I have a spindle with shot bearings so will pull it apart when the mood takes me and investigate.
Thanks for the post.

**PsychoPig7** · 3rd May 2012, 04:19 PM

Hi Guys
long time no post.

Chris - you are spot on aboput the bearings - the top one has no real adjustment for float or anything else.
I have attached a set of photos I took when I pulled a brand new spindle down to see how they were constructed. -Amazing - talk about simplified engineering.

I think the surprising thing about these Chinese spindles is that they not only work pretty well, but last for a considerable time.

I also went down the replacement bearing road, and a "well-known" bearing supplier here in Australia charged me a similar fortune for bearings, however, I have found that cheap (only a couple of dollars) bearings seem to work equally well and for the same sort of time.

Actually got a lot of very good advice about bearings from "Bazza Broomhall" another forum members - and what he doesn't know about bearings probably isn't important anyway.

If in doubt, I would strongly urge you to talk to him - he really is a fount of knowledge, about a lot of things mechanical.

The other point is that you can get a replacement spindle for just a little more than the price of a quality set of bearings - and saves you mucking about getting the thrust force correct - if you can on the spindles anyway.

When one of my 1.5kw spindles ran a bearing reasonably shortly after purchase (about three months from memory) the supplier "LoveHappy" came to the party with a new one, and also paid for the postage - couldn't ask for better than that.

anyway - happy cutting

Cheers

Noel

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