[dneisler]

Hello,
Been using my CNC Fusion Deluxe X3 ballscrew conversion for a while, and love it. I have ignored some Z axis issues as it was not important for what I was doing. Now it is....Imagine that!

I have about .030" backlash in my Z axis. It appears to be coming from the bottom of the screw where the collar and pulley are. I have retightened the collar several several times, and .009" is about the best I can get it. What is the trick to get better accuracy on the Z axis. My X & Y are great, normally less than 001".

[Crevice Reamer]

Do you have a threaded nut on the bottom of the screw? Make sure the set screws in the pulleys are very tight. Also, a loose timing belt can cause backlash. The BELT tension needs to be very tight.

CR.

[dneisler]

It is not the belt or pulley. I only have a collar at the bottom, no nut.
I can see the actual ballscrew moving up and down when I change directions a slight bit. I know it is there and the collar is loose, but how do I tighten it more....It would be nice if it had a nut like the X & Y do.

[Bamber]

It might help if you over counter balance the head so that it has a permanent upward thrust of about 5 lbs. This will make it look like a cut is actually on so that the head cannot drop.

Dave

[dneisler]

I have my gibs tight and I cannot hardly any movement in the actual head. I can SEE movement in the bottom bearing hold where the collar is. I have lifted the collar with a screwdriver and tightened it and got it down from .030" to .009" but I can still see the actual screw going up and down when I change the direction of the head movment.

[cadmonkey]

a) does the kit use AC bearings or the stock thrust bearings? (I'm not intimately familiar with their kit)
b) can you thread the screw to accept a nut?

I run a tight gibb on the Z axis with AC bearings and a nut for preload in my conversion and the only backlash I get is induced by the fact that I skimped and only used a single nut on the Z axis. Tax return this year might get me a preloaded nut to replace the simple nut currently on there if the economy doesn't kill me first.

My backlash is between .001 and .002 on a full column move with EMC2's BL compensation running and I haven't touched the preload on the screw since the day I installed the screw.

edit -
Another idea - try locking the head in place (if you still have the gibb lock installed) and jogging the head up till the stepper stalls, then jack up the collar and tighten it. That might put enough downforce on the top of the bearing to give you more preload. Worth a shot?
/edit

Greg

[Crevice Reamer]

Hi Donald. The newer CNC kits come with a nut instead of a collar. I'm sure Michael made the change for this reason. If you email him and explain the problem, maybe he would be willing to exchange your z ball screw for a newer type with a nut.

CR.