Lead screw setup is binding...need a new design

[ssbowtie1]

Hi guys, I was presented with the current lead screw setup, which raises and lowers a platform with high precision. However, as you can see in the attached pictures, if the tolerances aren't exact, the mechanism easily binds. Assembly requires shimming, and the motor powering the mechanism is not very powerful, so it is easy to bind it.

I am looking for a way to make assembly easier and end any chance of binding. A complete redesign can be done if needed.

Thanks for your suggestions!

http://i51.tinypic.com/2hmh94i.jpg

http://i55.tinypic.com/28bza8j.jpg

http://i56.tinypic.com/33nf6uo.jpg

 

[asimpson]

Misumi have a good range of re-configurable ready made solutions.

http://us.misumi-ec.com/mech/

Parallel linear bearings really need to be perfectly alligned. I few microns out and they wont run. The trick is to build some compliance into system. One rail fixed to give linear guidance. the other which allows relative movement between the carriage and bearing to compensate for out of parallel running.

Ball bushings are more tolerant.

Crossed roller slides allow easier adjustment.

Leadscrew offset looks too high for trouble free running. Closer to slides would reduce twisting loading of carriage. Also some compliance should be allowed between carriage and nut.

I would still favor a ready made over custom build.

 

[Tmoose]

http://www.mini-lathe.com/m4/C4/bed02.jpg

One flat "way" and one V "way" for the carriage, and another pair for the tailstock. The V does all the lateral guiding. If your "flat" way is vertical you'd need something to preload the carriage against it

The V (or equivalent) benefits from being long ( minimum 5 or 6) relative to its width.

Some of those roller/ball tracks come with slotted holes, and installation procedure includes locking them only when the carriage is near the screws to be tightened, thus ensuring the center to center is pretty close to the same.

 

[Compositepro]

It seems to me that your basic problem is that you have many rigidly fixed elements that are only free to move in one axis. This is a common beginner design error. It would work if everything were perfectly aligned and stayed that way under load changes. You might be able to get what you have to work but one of the main problems is the method of alignment. Without set screws for making adjustments it becomes a nightmare, because every time you loosen a clamp screw you lose alignment and cannot make small and controlled changes. You might try replacing shims with a group of three set screws.