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Bearings, Spindles, and Tolerences
Hello everyone. I've been having some issues with the spindle on my PM30 and I need some advice on how to proceed.
When I first got the mill, it worked OK, but I had always planned on going to a belt drive, so I didn't test it a whole lot.. The mill was making some noise in the spindle and was getting warm after only 15-20 minutes of use. I decided it was time to mess with the spindle. I replaced the lower 2 bearings with angular contact bearings and the noise went away, and it runs a LOT better. Before, I wasn't able to run at full speed for very long, it would just get too hot. Now, I can run at ~1500-2k RPM without excessive heat or noise.
HOWEVER, when I go above ~1500 RPM (my high speed pulley maxes our around 5k), I get a LOT of heat, and quickly. After only 15 minutes, the top bearing (the one visible from the top of the head) gets up to around 140 F. I've stripped everything down on the head and ran some tests and all the heat is generating from that one spot. After 15 minutes, the top bearing will be at 140F, the bottom bearing is only around 100-110, the quill housing is just a few degrees above ambient, etc.
When it heats up, the whole assembly is VERY tight and although it spins smoothly (no grinding or tight spots), there is a lot of resistance. This is without the belt attached, and the whole quill mechanism OUT of the mill. The top two bearings with the gear part between them, that whole thing has a lot of resistance to it. When it heats up, it gets significantly worse, and it gets very hard to turn. Of course, when this starts happening, my motor starts getting really warm because of the added load.
So, that's the back story.
I tried to remove the bearing assembly with a mallet. Then I tried using a jig I made using a long 3/4" bolt and a 0.5" plate of aluminum to pull it out. The aluminum bent under the force and the bearings didn't budge (yes, I removed the snap rings :-) ). I ended up using a 12 ton shop press and it finally came out with a huge BANG after nearly 3 full pumps on the handle. It was in there good.
With everything removed, the bearings actually move pretty freely and as expected. I bought new bearings, but they feel about the same honestly. I'm wondering if the hole for the bearing(s) are too small in diamter and it was just pressed in there too hard? I measured the top, and it was about 0.06mm too small, or ~0.0025". Also, would misalignment of the top and bottom holes cause this?
At this point, I'm wondering what to do. I don't want to just swap the bearings with the new ones and press it all back together, that doesn't seem like it would solve the problems.
Here's a video to try and give an idea of the resistance of the spindle:
https://www.youtube.com/watch?v=abq18iMqenM
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Re: Bearings, Spindles, and Tolerences
Heat comes from friction. My best guesses are:
- Too tight pre load
- Misaligned bearings (either not collinear and/or not parallel)
Maybe pre load I think? Since heating up makes it worse.. The shaft will expand when heated up and further tighten the pre load.
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Re: Bearings, Spindles, and Tolerences
Yep, that's kinda what I was thinking (and hoping). I hope it's just too much pre-load. Mis-alignment could also be an issue, but I would think heat wouldn't affect this as much. They should expand at roughly the same rate, and therefore not become MORE out of alignment? Also, based on how much force it took to pop them out, I'm guessing that everything is just way too tight.
I have a bore indicator, so I can get centered over the hole and open it up a bit. How do I go about calculating pre-load? These bearings are just to stabilize the top portion of the spindle and really don't do much else, so could the pre-load be a bit less? For example, could they just be a simple press-fit and still function well?
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Re: Bearings, Spindles, and Tolerences
cowanrg
That's way to tight for a bearing like this ( - .0025 ) you only want around ( - .0002 ) the preload is a big problem on these spindles, they are a very poor design, you really need a set of spacers, between the bearing, then you adjust the spacer length to get the right preload, once set it is good for ever
The top bearings don't need any preload, post a photo of the spindle parts, this will give a better idea of what you need to do, to fix the preload
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1 Attachment(s)
Re: Bearings, Spindles, and Tolerences
Cool. I think I'll try opening up the bore a bit, and also seeing if the two holes are aligned properly. Here's an exploded diagram of the head. This is from a G0704, but the setup is the same, the part sizes are just a bit bigger on my mill:
Attachment 278114
I've been talking about 205, 206, and 207. Really, they just stabilize the top part of the spline of the spindle (246) which has the belt drive pulley bolted to the top. I was thinking it didn't need a whole lot of pre-load either, as most of the cutting force is supported by 296 and 248. Those were replaced with angular contact bearings and are doing great.
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
cowanrg
Cool. I think I'll try opening up the bore a bit, and also seeing if the two holes are aligned properly. Here's an exploded diagram of the head. This is from a G0704, but the setup is the same, the part sizes are just a bit bigger on my mill:
Attachment 278114
I've been talking about 205, 206, and 207. Really, they just stabilize the top part of the spline of the spindle (246) which has the belt drive pulley bolted to the top. I was thinking it didn't need a whole lot of pre-load either, as most of the cutting force is supported by 296 and 248. Those were replaced with angular contact bearings and are doing great.
If I understood the diagram correctly, to upper bearings (205 207) are just plain roller bearings, the should not be any pre-load on them. There should be pre-load between the AC bearings 248 & 296, but not too much or they will heat up.
I can't figure out from the diagram how the pre-load is adjusted..?
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Re: Bearings, Spindles, and Tolerences
cowanrg
Is 251 the locknut ?
What is 250 & 247?
Does the outside dia of the 2 AC Bearings, both go against a shoulder in the quill housing ( 1 ) in the top ( 1 ) in the bottom, if so then all you need, to make to control a better preload, is a tube spacer for the ( 2 ) inside Bearing face's to be locked up, it will take you some time to set it up, but once made/setup you will have at least a good bottom end, the spacer will need to be made from steel, a slide fit on the spindle & the same OD as what the inside diameter of the Bearings are, there won't be much preload needed, should be around 4lb
If ( 1 ) of the washers ( 250 ) is a wavey washer you will make the spacer length so this wavey washer will be compressed by just over half it's compressed height, this will set the preload, this is still not ideal but is better than what is there now, you can then just lock the lock not tight, & your preload will stay the same all the time
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Re: Bearings, Spindles, and Tolerences
hub - sorry, I was using the wrong term and confusing you. I was just talking about the bore diameter for the bearings. They are just normal bearings, so no preload between them. I was using the term 'preload' to refer to the undersized hole. Ignore that ;-)
The preload for the AC bearings in the bottom of the spindle (248 and 296) is adjusted by 251. There's also another one of these at the BOTTOM of the spindle too. I think I have that part figured out. I rebuilt that a few months back and it works really well. It's very smooth without any run out.
mactec54,
250 and 247 are spacers. When I rebuilt the spindle with AC bearings, I got some spacers from mcmaster and got everything snugged up according to what I've seen on here, and Hoss' plans. As I said above, there is another ring (like 251) at the bottom of the spindle which is used to adjust preload on the bottom AC bearing (296).
I just got done messing with the spindle today and here's where I'm at:
I went to my office and use the knee mill there. I got the head as level as I could on the table, and trammed the head to the top face of the PM30 head. I used a coaxial bore indicator to center over the bore for the bearings. Both were pretty well aligned actually. I didn't have to make any adjustments from the top to bottom bearing (205 and 207). I used a boring head to take off a tiny bit on the bores. Now they are a tight slip fit (or very light press fit), needing a dead blow to get them in place. It feels a LOT better and the gear spacer (206) moves a lot more freely.
But...
I'm still getting a good amount of heat. At ~2k RPM, there isn't any noticeable heat, but above that, it gets very warm. It's not nearly as bad as before, but it's still not fixed. Also, I'm getting some noise when running at high speeds (sounds like a bad bearing, or a intermittent rattling sound). However, when things heat up, they don't bind, which is good? I was able to run it at full speed (~5k RPM) and it gets warm, maybe 110F (as opposed to 150+ F) and when I stop the motor, the spindle is still very loose and nothing is bound up.
I did a little experiment. I'm trying to determine if the AC bearings are good and the preload is appropriate, so I just completely removed 205, 206, and 207. The quill (249) houses the spindle and is locked in place, and the spline (246V2) comes up through the head of the head, unsupported. I attached my spindle pulley and turned it on. It's smooth and quiet. It runs like a dream. Seriously, after 15-20 minutes at top speed, it's cool and nothing is getting hot. There's no noise, no heat, etc. I know that the 205, 206, and 207 were originally intended to drive the spindle with the original gear drive, and also for the quill mechanism, but I'm not using any of that now. It's a fixed spindle. Do I even need those? Do I need to support the drive pulley?
I'm wondering if I can just make a spacer for 205, so that it supports the spline near the pulley...
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Re: Bearings, Spindles, and Tolerences
cowanrg
Yes you need to support the drive pulley at the top, there is something wrong also with your 2 AC Bearings, you can only have ( 1 ) nut to do a preload, as you have just said,you have ( 2 ) may be the front/bottom nut, is & should be just a locking nut for the outer bearing race, this is not for doing any preload, it is to lock the bearing in place against the shoulder, which it has to do, you don't want this nut to loose in any way, your preload can only be from the nut on the spindle behind the top AC Bearing
You don't need the other parts that are not doing anything, now that you have modified it
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
mactec54
cowanrg
Yes you need to support the drive pulley at the top, there is something wrong also with your 2 AC Bearings, you can only have ( 1 ) nut to do a preload, as you have just said,you have ( 2 ) may be the front/bottom nut, is & should be just a locking nut for the outer bearing race, this is not for doing any preload, it is to lock the bearing in place against the shoulder, which it has to do, you don't want this nut to loose in any way, your preload can only be from the nut on the spindle behind the top AC Bearing
You don't need the other parts that are not doing anything, now that you have modified it
I'm probably explaining it wrong, but you might be right. The bottom part doesn't necessarily add pre-load I guess, but the top certainly does. It's the same way everyone else has rebuilt their spindle. That part took me awhile to get right and get the right spacers and shims, but it runs VERY well. Before it would get really warm too and there was a lot of noise, but now it's very quiet and runs cool, even at 5k RPM.
What is the purpose of the top bearings in my current configuration? Sure, it supports the pulley, but how much force is being exerted on that pulley? Wouldn't it just be the force of the tension of the belt? The bottom half is fully supported by the AC bearings. I know it's just anecdotal, but I tried pulling on the top of the spindle where the pulley sits, and it's pretty damn stiff. I didn't put an indicator on it, but there's no detectable deflection.
If I do absolutely need some support up top, I'm trying to think of a way to use just the top bearing for support, with some sort of flanged insert. At the very least, the bottom bearing seems redundant in this case.
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Re: Bearings, Spindles, and Tolerences
cowanrg
Your top AC Bearing as it is now, is taking what ever tension you have on your belt, it should not be seeing anything from above
It would be simple to just use the top bearing with a bushing that will fit the bearing & the shaft, a flange on the bush, so it can't go down through the bearing
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
mactec54
cowanrg
Your top AC Bearing as it is now, is taking what ever tension you have on your belt, it should not be seeing anything from above
It would be simple to just use the top bearing with a bushing that will fit the bearing & the shaft, a flange on the bush, so it can't go down through the bearing
This was my thinking. Sure, I might get a bit of deflection on the unsupported shaft up top, but it won't go any further than past the top AC bearing, and it's only the force of the belt tension.
Unfortunately, the top bearing is normally supported from the top by a snap ring, so I'll have to figure out how to secure it so it can't slip down. But a flanged piece to support the shaft through the top bearing sounds like an easy fix.
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Re: Bearings, Spindles, and Tolerences
Try this, run the spindle at mid rpm, say 4000 for 10-15 min. Then adjust the pre-load. (I did a mistake recently and adjusted pre-load when all parts were cold (2C ~ 35F).. It didn't run well when warm. Noise & heat... )
Then before a job run the spindle for ~10min before cutting.
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Re: Bearings, Spindles, and Tolerences
hub, without the top bearing assembly, it runs like a dream :-) There is no pre-load in the top bearings, they're just basic ball bearings. The noise and heat is coming from there, so I'm not sure adjusting the preload on those would help anything?
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
cowanrg
hub, without the top bearing assembly, it runs like a dream :-) There is no pre-load in the top bearings, they're just basic ball bearings. The noise and heat is coming from there, so I'm not sure adjusting the preload on those would help anything?
Ok so pre-load is ok then :)
1) What is the ball bearings RPM rating? (Maybe it can't do high RPM)
2) Maybe misalignment
3) ?
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
hub
Ok so pre-load is ok then :)
1) What is the ball bearings RPM rating? (Maybe it can't do high RPM)
2) Maybe misalignment
3) ?
good questions!
1) the top one has the lowest rating, and it's rated to 6400. So, 5k is near the upper limit, but still within tolerance. The bottom one is like 8k or something.
2) that's KINDA what I'm thinking, but when I bored out the holes for the bearings I locked the table and the knee and bored them with the quill, after tramming the head top of the PM30 head, so they SHOULD be lined up now.
3) yep.
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
cowanrg
good questions!
1) the top one has the lowest rating, and it's rated to 6400. So, 5k is near the upper limit, but still within tolerance. The bottom one is like 8k or something.
2) that's KINDA what I'm thinking, but when I bored out the holes for the bearings I locked the table and the knee and bored them with the quill, after tramming the head top of the PM30 head, so they SHOULD be lined up now.
3) yep.
I'm betting on misalignment (best guess). It only takes a very tiny bit and it starts to heat up, but in that case I would expect there would be some resistance when turning by hand.
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2 Attachment(s)
Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
cowanrg
This was my thinking. Sure, I might get a bit of deflection on the unsupported shaft up top, but it won't go any further than past the top AC bearing, and it's only the force of the belt tension.
That is correct, but that bearing is not designed to work like that, so should not see anything from above
Quote:
Originally Posted by
cowanrg
Unfortunately, the top bearing is normally supported from the top by a snap ring, so I'll have to figure out how to secure it so it can't slip down. But a flanged piece to support the shaft through the top bearing sounds like an easy fix.
You can get Bearings with a flange, or with a snap ring groove, you could also just loctite it in place, even drill & tap 4 holes close to the edge of the Bearing bore & attach a ring underneath
Those Bearings that were in the top are most likely junk, so you would need a new one anyway, make sure when you get one it is sealed 2RS on the end of the Bearing number is what you want for rubber sealed
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Re: Bearings, Spindles, and Tolerences
I actually did get a replacement bearing, but I thought I wanted to stay away from rubber-sealed, as they typically have a much lower RPM rating?
I was thinking about doing what you said, attaching a ring underneath. I have a couple ideas of how to fix the bearing in place. Loctite might be a solution too...
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Re: Bearings, Spindles, and Tolerences
Quote:
Originally Posted by
cowanrg
I actually did get a replacement bearing, but I thought I wanted to stay away from rubber-sealed, as they typically have a much lower RPM rating?
Not sure what you are saying about the rubber-sealed Bearing, having a much lower RPM, as they will do more than your machine will ever run at, most that size will be good for around 7.500 to 12,000 RPM, depending on the brand/quality of the bearing, what are the dimensions of the top Bearing
The only difference is either having oil lubrication, or grease, Grease has a lower RPM but still more than you will ever need for your machine
An open bearing is not suitable for that position, as you have no way to lubricate it, & keep the junk out of it