X2 spindle bearing upgrade
I just finished replacing the spindle bearings for the first time, and it made the shortcomings of the current system very clear. The mill currently uses 6206 deep groove radial bearings both on top and bottom. The bearings are a press fit both on the spindle and the housing. Bearing preload is set via a nut on the end of the spindle.
The problems I see are:
1. Since the top bearing is a press fit on the spindle it makes preload difficult to set.
2. Deep groove radial bearings, while adequate, aren't ideal for a mill spindle.
3. Having a press fit on both the spindle and housing makes it more difficult to replace bearings.
After researching and reading a lot of the NSK and SKF catalogs, I think my best option would be:
1. Sand/polish the top bearing seat on the spindle to take it from a press fit to a tight slip fit.
2. Use Belleville washers to to exactly set my bearing preload. My only concern is a heavy cut might overpower the Belleville washers and pull the spindle down, but I doubt the actual forces at play in my mini mill could excert that much force. Alternatively, I could continue to set the preload using just the nut.
3. Upgrade both bearings to angular contact. I'd need to find a way to seal the bearings or re-grease them on a schedule. I did find sealed angular contact bearings online, but they're generic Chinese: Angular Contact Ball Bearings - Arc Euro Trade
I was wondering what you thought of my plan, and if you had any suggestions or advice. Thanks!
Re: X2 spindle bearing upgrade
I will take a shot at this.
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Originally Posted by
zoltank
I just finished replacing the spindle bearings for the first time, and it made the shortcomings of the current system very clear. The mill currently uses 6206 deep groove radial bearings both on top and bottom. The bearings are a press fit both on the spindle and the housing. Bearing preload is set via a nut on the end of the spindle.
The press fit at the top end is less than ideal. In this case it makes getting the preload difficult.
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The problems I see are:
1. Since the top bearing is a press fit on the spindle it makes preload difficult to set.
Or to adjust.
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2. Deep groove radial bearings, while adequate, aren't ideal for a mill spindle.
While this is true, such bearings are used in all sorts of spindles as a low cost solution. It isn't like these mills are heavy duty production machines.
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3. Having a press fit on both the spindle and housing makes it more difficult to replace bearings.
There is a flip side here, bearings that are too loose on a spindle can spin the inner race resulting in a damaged spindle. I would certainly prefer a press or shrunk fit for the nose bearing over something that was loose on the shaft.
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After researching and reading a lot of the NSK and SKF catalogs, I think my best option would be:
1. Sand/polish the top bearing seat on the spindle to take it from a press fit to a tight slip fit.
This is tricky work and can lead to problems with eccentricity. You might want to consider having the spindle professionally ground. If not at the very least chuck the spindle in a lathe and carefully work the surface.
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2. Use Belleville washers to to exactly set my bearing preload. My only concern is a heavy cut might overpower the Belleville washers and pull the spindle down, but I doubt the actual forces at play in my mini mill could excert that much force. Alternatively, I could continue to set the preload using just the nut.
There are many possible arrangements of the bearings but you need to consider the potential of running into problems adapting new features into the spindle. Further the spindle doesn't run at a high enough speed in my estimation to need spring loaded bearings. Further I don't se how belleville washers will lead to an exact preload.
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3. Upgrade both bearings to angular contact. I'd need to find a way to seal the bearings or re-grease them on a schedule. I did find sealed angular contact bearings online, but they're generic Chinese:
Angular Contact Ball Bearings - Arc Euro Trade
This is the easiest option beyond simply replacing the ball bearings with newer hopefully higher quality bearings. You don't specifically need sealed bearings but you would need to add slingers and possibly additional sealing. Going this route you would absolutely need to address the far end of the spindle to loosen the fit of the bearing to allow precise preload adjustment.
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I was wondering what you thought of my plan, and if you had any suggestions or advice. Thanks!
So which is your plan? 1, 2 or 3 or all of the above? More so are you currently having problems? It isn't unheard of for these spindles to have problems right out of the box and that in my opinion is due to the tight fit of the top bearing which makes preload setting so difficult. I'd tackle the problem of preloading the bearings first, to the extent of using the old bearings. If the old bearings get damaged from improper preload, or the exercise of fitting them up to the spindle, you will not be out money. Beyond that a proper preload might give acceptable performance.
Re: X2 spindle bearing upgrade
I just replaced the stock bearings with SKF 6206 sealed bearings and they're running well right now. They definitely run hotter than the stock bearings, but still within allowable temperatures. Setting the preload on them was a debacle, and I'm still not sure if I have too much or not enough. I'm not planning on replacing the bearings right now, but I'd like to have a plan ready to go for when they'll need replacing again.
The plan is to do 1, 2, and 3.
I figured Belleville washers would give me an exact preload since I can measure how far they compress, which in turns tells me the force they're exerting. They should be exact and repeatable.
Regarding sanding/polishing the spindle, I'd throw it in my lathe, do a pass with fine sandpaper, and then check the bearing fit. I've already tested the procedure with an old spindle I had and it worked pretty well. I only need to remove less then 0.02mm,
Re: X2 spindle bearing upgrade
I did some more testing to try and correlate how loose the bearing fit can be before the bearing will spin on the spindle, and my results were no encouraging at all. Basically, the stock press fit on the spindle is the loosest it can be without risking spinning the bearing. I then looked around for a bearing with a keyed inner race, but I haven't found anything like that.
