How to mount thrust bearings

[Spitfire]

Hi
I want to us thrust bearings on my ball screws and was wondering if any one could tell me how to mount them and at what end they should be mounted,
by this i mean at the drive end or at the other end of the ball screw, the races come in three parts so i would like to know what type of a cage should be made for them and what would be the best way to do it, any advice would be appreaciated.
Thanks Bill

[RICHARD ZASTROW]

Bill, Personally I'd use paired angular contact bearings. If you choose to use thrust bearings, remember to account for both directions of axial displacement. Screws (ball or otherwise) "push" and "pull" the nut axially. Strictly thrust bearings do not stop radial displacement so you will also require radial bearings. On the end opposite the drive, you should allow the radial supporting bearing to "float" to accomodate screw length expansion. FAG even makes a "floating displacement bearing" for this type of application.

Just my opinion, Good Luck.

[NC Cams]

You wan't/need HIGH contact angle, HEAVY preloaded A/C's.

The least expensive would be 30 deg versions although there are higher angle versions that are SPECIFICALLY for ball screws but these are pricey. These are superb in comparison to 30, 25 or 15 deg more "generic" A/C bearings.


You have two choices of mounting and either has compromises.

Putting the preloaed bearings on one end and simply supporting the other end simplifies things a bit as it gets you away from "stretching screws" and/or thermal growth issue.

Putting the screw into tension by preloading the end bearings with a "stretched screw" helps keep the screw from stretching more the farther you get from the single supported end. However, this tensioning of the screw is a PITA to do as it ultimately compresses everything inbetween.

You can safely mount the ball screw thrust bearings on one end as you'd essentially be duplicating a lot of mills as many mills are done this way, including Bridgeport.

[Oldmanandhistoy]

Originally Posted by Spitfire Hi I want to us thrust bearings on my ball screws and was wondering if any one could tell me how to mount them and at what end they should be mounted, by this i mean at the drive end or at the other end of the ball screw, the races come in three parts so i would like to know what type of a cage should be made for them and what would be the best way to do it, any advice would be appreaciated. Thanks Bill

Hi Bill,

You may like to have a look at this thread to see how Steve aka S J H did it. He used thrust bearing but also included 2 deep groove bearing to take the radial loads. My X3 conversion.It's alive!

NC Cams is without doubt the bearing guru on this site and I read somewhere he was quite impressed with Steve’s set up and it is a method I plan to use on my mill conversion.

Good luck,
John

[Rube]

These are the ones I bought to test on my setup. They are inexpensive and thus prbably cheap as well. There is no info on the VBX site as to contact angle, but I looked up the 7200B number on a manufacturer site, and it says 40*

[NC Cams]

7200B's should take quite a bit of axial thrust. Once you get them properly preloaded, they should be QUITE stiff axially while still being relatively low in friction. You'd be surprised how much preload an A/C can take and still spin relatively freely.

For example, we have some 500+lb preloaded 20TAC47's on our Bridgeport mill. These are 60 deg true ball screw bearings. They have much heavier preload than the kluged up 6204's that Bridgeport axially preloaded with only 75 to 125 lbs preload. Yet, they have NO axial deflection (unlike the OEM's) and actually rotate with LESS torque than the OEM's as well

It all has to do with how the bearings are actually taking load in true A/C format as opposed to the psuedo A/C's that the factory crafted up.

IN reality, most 7200B's are used in other than ball screw applications - they're sort of a generic bearing that is/was used in a lot of motor applications that saw lots of axial thrust. They, however, also see use in true situations that need/want an A/C bearing.

They should work fine in your case as a ball screw support with some decent preload - I"d try 25 to 50lbs initially and perhaps more if you have the nerve.