[thewoodnerd]

I'm a little unclear on how ballscrews are supported on each end.

I understand that each end has a bearing that sits in a support, then the screw has a machined end that goes into the bearing. What I'm not clear on is what's holding the bearing in the support and how the screw ties to the bearing. Is there a threaded section on the screw where a nut goes and snugs down on the bearing race? Pictures or drawings would be nice

[pete from TN]

From what I am seeing a lot and also the way mine is made on all three axes is like this. Basically the end of the ballscrew has a short length of a precisely machined or ground smooth round portion. The start of the smooth portion has a shoulder that accepts the two angular contact bearings in their proper orientation. The machined mounting plate of this captured end of the ballscrew has a precisely machined pocket that accepts the depth and width of both of these bearings back to back but allows a little of them to protrude out of the pocket. Then there is another small part that has the same size pocket machined into it yet a much shallower depth and this part usually either screws down with several screws or some other way of tightening down the preload between the two angular contact bearingscapturing them into the pocket in the mounting plate . The remaining portion of the end of the ballscrew then has a short threaded length and then either a flat or some other way to attatch the drive pulley in the case of a belt drive or I suppose a coupler for a stepper setup. Basically the two angular contacts are sandwiched between the shoulder on the screw and the washer and nut that threads onto the threaded portion after the bearings. I initially machined some keyways into my screws but found out that they did not allow for zero backlash the way I wanted and since then I have actually gone to pinning all three of the pulleys to the shafts with some heavy roll pins. I have since had no problems and this was much easier to do. The pulleys also have setscrews in them as they came that way so i just tighten them down.

It is much easier to do actually than describe. Some guys actually just machine the bearing pockets into the factory leadscrew end mounts and machine them to accept the drive system.


Now the other end of the ballscrew that is not the driven end usually is set into another single plain bearing that has a slip fit of the end of the ballscrew shank which is machined smooth and round. The purpose of this is to allow the ballscrew to expand and contract with heat and allow it to spin without binding or whipping around. There are certain lengths and applications where this is not necessary and personally on my RF45 the only screw that is actually supported at both ends is the X axis. The Z is vertical and driven from the top so no need for the bearing at the bottom there and the Y axis is not very long and all three axes are double nut ballnut applications mounted on either side of a mounting block so the actual unsupported Y length is negligible and thus far I have not noticed any issues with whipping or undue wear. The most important thing about ballscrews is that you MUST have full travel without any binding and ideally Zero or as close to it as possible backlash in the movements. Good luck and peace

Pete

[kawazuki]

They say a picture saves a thousand words- try this?

[pete from TN]

More like precisely.... peace

Pete