# New bearings for mini mill



## zoltan (Mar 16, 2015)

Since I'm already replacing my mini mill's spindle, I figured I'd replace the bearings as well. The stock bearings were painted over and are cheap no-names. I'd like to install good Japanese bearings like NSK or SFK. My questions are:

1. Do I need to get ABEC-3 or ABEC-5 bearings? Almost everything available I see if ABEC-1.
2. What internal clearance do I need? From researching I think I just need normal clearance (CN) though a lot of aftermarket bearings are C3.


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## velocette (Mar 16, 2015)

Hi zoltan
Angular contact bearings will give superior service than deep groove ball bearings

available at

http://www.arceurotrade.co.uk/Catalogue/Bearings/Angular-Contact-Ball-Bearings.

Full instructions also from Arceurotrade

http://www.arceurotrade.co.uk/projects.aspx

I Have no connection to this company other than by what I read from from other satisfied customers on many forums.

Eric


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## zoltan (Mar 16, 2015)

I've considered it. However, getting a shielded or sealed high quality angular contact bearing is pretty expensive, and I think a high quality radial bearing will do better than a questionable quality angular contact bearing. Considering the orientation of the bearings on the mini mill, I think getting shielded or sealed bearings is a must for grease retention.


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## velocette (Mar 16, 2015)

Hi zoltan 
Regardless of what bearing you use in an X2 mill the clearance is of no great importance as they require that they are "Preloaded" to take up any clearance-endfloat.

Read the attached PDF file by Neil Wyatt of MEW on bearing replacement on X2 mills for more info.

Taper Roller Bearing will give the best possible performance in spindle rigidity and smooth cutting on an X2 mill.

Edit this is NOT a straight swap

Some modifications will be required to fit taper rollers to to replace the original bearings as there is a size difference.

1) Machine the two headstock outer race pockets 1.25 mm deeper plus the thickness of the shim that you need to fabricate for a grease shield.

2) Remove 1.25 mm plus shim thickness from the inner race with a Precision Toolroom Grinder.

Added a JPG file to clarify the difference in sizes.


Eric 

View attachment MEW201_p52_58_X2_Mill.pdf


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## zoltan (Mar 18, 2015)

Well, I just found a supply of SKF 7206 ABEC-3 angular contact bearings for a decent price, so they're definitely a player now.

The question is, how do you deal with grease retention when the bearing is on a vertical shaft? It seems like gravity would slowly pull the grease out of the bearing over time.


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## velocette (Mar 18, 2015)

Hi zoltan
Grease shields can be fabricated from brass shim just make sure that it does not rub on the inner race of the bearing.
The spacers on the inside of the housing will need to be shimmed the same thickness as the shield or new spacing collars made.
Good luck with the angular contact bearing choice you will be pleased with the improved performance.
No leakage on my X2 with fabricated brass shim shields in over two years of use with taper roller bearings fitted.
Use a good quality bearing grease the SKF supplier can advise you.

Attached JPG File  

Eric


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## Cogsy (Mar 18, 2015)

If you have the room, you can purchase loose 'shields' from bearing suppliers in sizes to match normal bearings. These shields do not fit into the bearings but rest on the outside and provide some help in keeping grease in. When I was in bearings we called them Z Shields but there are many names for them I think.


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## zoltan (Jan 9, 2017)

velocette said:


> Hi zoltan
> Grease shields can be fabricated from brass shim just make sure that it does not rub on the inner race of the bearing.
> The spacers on the inside of the housing will need to be shimmed the same thickness as the shield or new spacing collars made.
> Good luck with the angular contact bearing choice you will be pleased with the improved performance.
> ...



How did you machine something only 0.1mm thick?

It looks like I'm going to be doing something like this now, but I have no idea how to actually do it.


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## XD351 (Jan 9, 2017)

zoltan said:


> How did you machine something only 0.1mm thick?
> 
> 
> 
> It looks like I'm going to be doing something like this now, but I have no idea how to actually do it.




Joe pieczynski  did a video on youtube about machining thin shims , it may give you some guidance  .


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## velocette (Jan 9, 2017)

Hi
You can cut shim with a Trammel bar with tool sharpened to  a curved knife or dividers with  a curved knife shape.
Cut the larger Diameter First  
See attachment

Eric 

View attachment shim cutter.pdf


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## Wizard69 (Jan 11, 2017)

zoltan said:


> Well, I just found a supply of SKF 7206 ABEC-3 angular contact bearings for a decent price, so they're definitely a player now.


That is good because you would be wasting your time by using radial ball bearings.   Angular contact bearings are needed to better handle trusts from the cutter and to minimize axial play.   They will function far longer than standard bearings due to the ability to handle the thrusts.


> The question is, how do you deal with grease retention when the bearing is on a vertical shaft?


Depends upon the grease.   Looking at my import drill press, that leaks oil and grease, I'd have to say retention of grease wasn't on their mind.

Here is the thing though, too much grease isn't a good thing at all.   This is sometimes hard for people to grasp but it can be as bad as no grease.


> It seems like gravity would slowly pull the grease out of the bearing over time.



There are all sorts of greases out there many are far more sticky than #2.  Generally the manufacture of the machine tool will be very specific about the grease to be used in the spindle bearings.   Doing an upgrade like this you become the manufacture so you need to seek out the best grease for the job.  SKF has a nice little chart: http://www.skf.com/binary/21-99598/13238EN_GreaseSelectionChart.pdf, that really doesn't go into a lot of detail but might help.   I'd look for greases recommended for spindle bearings, but do realize that what you are creating here is a very low end spindle, so SKF's point of view might not match yours.

You can buy Nilos Rings: http://www.skf.com/binary/30-228382/950-710-Nilos_08.pdf to help protect the bearings.   Not these are really for keeping stuff out of the bearings not so much for keeping grease in.   Still as a shield they will help a bit.   In any event putting effort into keeping stuff out of the bearings is a good idea.   I'm not sure about this spindles construction but kilos rings or a shop made slinger can be a big help in this regard.


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