A few questions about backlash

[Dwane]

Hi, I'm new to this forum,
I have a knee mill that was factory retrofitted with ball screws and cnc control. I notice that the flats on the transition moves when doing circles look large. I put an indicator on the vise, and turn the handle clockwise zeroing the dial. I reverse the dial until the indicator moves. The dial shows .005 consistently when done in different places on the travel. This shows about the same on x or y. These are supposed to be ground ball screws. The machine is a Bridgeport series 1 made in the mid 80's. Is this unusually excessive? What are others getting on their machines? Can anything be done about this, short of replacement? Does any control software help minimize this? Maybe I should just learn to live with it, sounds expensive to replace the screws.
Any replies are appreciated.

Dwane

[JimBoyce]

Check the thrust bearings on the ball screws. There is probably a parameter that compensates for backlass on each axis.

[Al_The_Man]

Also depends on whether they are pre-loaded ball nuts and if so, can they be adjusted.
Al.

[Dwane]

Jim,
Thanks for replying I will check the thrust bearings. What I was getting at when I asked about control software minimizing this, was that I'm considering upgrading the control, and was wondering if Mach or Emc2 has compensation for backlash? The current econtrol is from Southwestern Industries. The control is from the 80's, and not very sophisticated.

Dwane

[Dwane]

I'm encouraged. I did a quick check by mounting an indicator base to the table with the needle on the end of the shaft (ball screw). Then I tried moving the table back and forth by hand. When the table was moved, the needle showed movement also, (about .005"). I don't think that this would happen if the thrust bearings were tight and the movement was between the screw and the nut. It must be a thrust bearing issue, I will look further into it when I have time.
Much Thanks

Dwane