end blocks for ball screws

[senor J.]

hello All, I read alot here on the zone about people who make there own end blocks for their screws Its usually for the 5/8 in ball screws that they turn down to fit there taperbearing { dont know exactly what that is } my question is what are the advantages of going that route over and against using a flange type pillow block bearing such as the type that you can buy from the surplus center

http://www.surpluscenter.com/sort.as...ange%20bearing

[Evodyne]

The reason is axial thrust. As hard as the machine is pushing whatever is attached to the axis, the axis is pushing back against the lead screw. The tapered bearings are designed to eliminate any resulting axial motion in one direction. So to get stiffness in both directions two bearings are used back to back and facing in opposite directions.
You could use a pillow block, but it defeats the purpose of using a precision ground screw and ball nuts if the whole assembly has any play.

[DESERT RAT]

Evodyne

Are you saying to use two taper bearings on each end of the ball screw?


Rich

[Torsten]

They are both mounted on one side of the screw.
Temperature changes make the screw expand and retrackt so mounting
one on each end would be a bad idea.
The bearings you have linked to would work for the other side wich just
has to hold the screw radialy.
Good Luck

[Evodyne]

To add to what Torsten said the two tapered bearings go on one end and are either back to back in direct contact or have a spacer that keeps them a distance x apart. The bearing-bearing or bearing-spacer-bearing stack is usually a skant couple of thousandths taller than the holder. This way the whole enchilada has a slight crush when the end plates are tightened down-and is immoveable.
I have one in the other room. Hold on. (Magic time delay while Lance takes a picture or two). Bingo. Take a look. The first is from a big, long screw. The others are from a small slide. On these others note how the assembly on the motor end checks lateral movement while the far end (the thin plate) just has a straight roller bearing that's pressed in. Same effect, different approach.

[WoodSnarfer]

I noticed that most of these have a set screw which they claim "to lock the shaft". Would this be enough to prevent axial movement?

Here's an example:

http://www.surpluscenter.com/item.as...tem=1-201-08-2

-Chris

[Evodyne]

I'll be honest, I haven't seen that type used before. It would probably be O.K. depending on your machine use. For milling metal to close tolerances I wouldn't go that route. But if doing engraving on laminates (low force) or wood, say for moldings, etc. (lower precision tolerable) it might be O.K. In that sense you need to look at your intended use and go from there.

[Torsten]

Originally Posted by WoodSnarfer I noticed that most of these have a set screw which they claim "to lock the shaft". Would this be enough to prevent axial movement? Here's an example: http://www.surpluscenter.com/item.as...tem=1-201-08-2 -Chris

Some of them do have some thrust load capability but generaly much
less then real thrustbearings.
Its hard to tell without any supplied spec's on them.
You may check out http://www.mcmaster.com/
and look up some similar bearings there, they do provide
very good spec's and usage articles on the items they sell.
This may give you a ballpark figure what the loadrating may be.
Good Luck