Bridgeport Series 1 CNC backlash ??

[dansawyer]

I am bringing a Bridgeport Series 1 CNC back on line and have one access working. I have set up 1 inch dial meter and tested the 'jog' function. The good news is the movement in one direction is very accurate and consistant. The bad news is there is .003 backlash.
Is there anything that can account for this beyond ware?
Are there any adjustments that can be made on ball screw backlash?
3 thou is a small tolarance. Is it possible this is from the gearing / drive mechanism? Is there a way to isolate backlash from the drive versus the ball screws?

 

[derf]

There is a backlash compensation adjustment in the software,depending on the OS. Mine has been retro fitted with an Anilam controller and there is a place in the parameters were you can set the backlash compensation down to the tenth of a thou.

 

[hwelecrepair]

3 thou slop in a ballscrew is typically going to be the wear in the screw. If it was something else like the bearings or something is loose, you would be looking at a more odd/outrageous backlash number like 15 thou or something like that.
+1 to derfs comment, most controllers have a backlash comp setting to take that out.

Give Rockford a call, you can typically get a ballscrew rebuilt for about $300-$600, depending on how bad it is.

Jon

 

[dansawyer]

Is an alternative to implement a closed loop system, i.e. to add linear encoders?

 

[dansawyer]

I subsequently tested the Y axis, it was spot on. I found a great Youtube video

that shows alternative sources for backlash. Does anyone have any documentation on the the construction of the Bridgeport BOSS machines? The mechanisms are sufficiently different that manual machine docs do not help.

 

[dansawyer]

Follow up: The X backlash was due to drive belt adjustment. The ball screw is driven by a pulley cog belt mechanism. I loosened the motor holding bolts and tiensioned the belt by hand. I then retighted the motor holding bolts. The mechanism now has on the order of half a thou. That is well within my expectations for the moment.
Lesson learned: Sometimes it is the simple things. In this case it was an adjustment that may not been made since the machine was built.