[15mgtar]

I've got a 25mm ballscrew with bk/bf17 setup my question is do I need thrust bearings for this setup especially on the Z axis?

[jhowelb]

The short answer is "yes!"

Neither steppers nor servos can long tolerate the push/pull as they have only radial bearings.

[15mgtar]

But I saw on the ballscrew's manufucturer setup it doesn't use thrust bearings it just use bk/bf to hold both ends.

[jhowelb]

BF Type Ballscrew Support Unit
This BF type ball screw support bearings are manufactured with poly amide so that bearing stiffness is greater than conventional bearings. These bearings have a 60 contact angle so that radial and thrust load combination can be sustained. We also provide our clients with flush ground set combination bearings which are also available with suffix U. This permits the use of random combination where two or more bearings are mounted. These are used at actuators of high precision and high speed machines, precision measurement equipment, robots etc.

[Glacern]

BF Type Ballscrew Support Unit
This BF type ball screw support bearings are manufactured with poly amide so that bearing stiffness is greater than conventional bearings. These bearings have a 60 contact angle so that radial and thrust load combination can be sustained. We also provide our clients with flush ground set combination bearings which are also available with suffix U. This permits the use of random combination where two or more bearings are mounted. These are used at actuators of high precision and high speed machines, precision measurement equipment, robots etc.

That's actually a misprint. The BF block is the "free" end. It cannot handle axial load. In fact, the bearing is loose within the bore.

[15mgtar]

So in short the answer in "no" I do not need thrust bearings since I have the bk/bf support unit mount for ballscrew? They should be fine to use in Z axis right? I just want to make sure because I am new to these stuff.

[Glacern]

So in short the answer in "no" I do not need thrust bearings since I have the bk/bf support unit mount for ballscrew? They should be fine to use in Z axis right? I just want to make sure because I am new to these stuff.

You are correct, you don't need additional thrust bearings because the BK unit already contains the thrust bearings.

The BK block contains two preloaded angular-contact bearings. These bearings can handle both thrust and radial loads. By having two bearings mounted face to face, the BK unit can handle thrust in both axial directions. The BK is known as the "fixed" block, because the ballscrew is rigidly fixed to the support block with a locknut.

The BF block contains a single radial bearing. Its only purpose is to reduce ballscrew whip. The bearing is loose withiin the bore to allow the ballscrew to lengthen and shorten with changes in temperature. A circlip on the ballscrew journal prevents the bearing from falling out.

Make sure you mount the the BK fixed end on the same side as your stepper/servo motor.

[15mgtar]

Ok well noted and thank you guys!