I checked my back lash on the X and Y axis of my mill. The X axis seems to not have any backlash. Or if there is, I cannot measure it with my dial indicator. When I move the table .001, the DRO shows .001. I come back to 0 and the DRO reads 0.

The Y axis, however, is a different story. I have .020 backlash. What do I need to do to get the out? The gibs seem to adjested OK. At least I cannot feel any play in the bed by trying to move it by hand. I would think I could feel .020 movement if the gibs was not adjusted correctly.

I'm running the cncfusion ballscrews with preloaded ballnuts.

Any ideas?
Mike

Take a close look at the y coupler and also how well the alignment was done when you reassembled the mill. Especially the coupler. Cncfusion did a very nice job preloading my ballnuts. Hard to believe they would have messed up the preload that bad, and frankly I don't believe it..

yep 0.02 backlash on ballscrew is pretty weird honnestly i have 0.004x and 0.0055y of backlash with acme screw

I feel stupid now.
You guys got me on the right track anyway.

One of the set screws on the Y coupler was loose and I forgot to tighten a collar thing right behind the ballnut.

I got it down to .006. I was hoping to get it down to .004 or less though. But it is a heck of a lot better than .020.

Thanks
Mike

0.006 is still alot for a ball screw was it preloaded

Yes,
It is a preloaded ballnut. I'm going to take another look at it today.

The thing is, if I have the mill tilted back and run the Y axis, I do not have any backlash. I guess that makes sense as having the mill leaning back must put just enough pressure on *something* to keep the backlash down. I think I have something loose that I missed.

Mike

Could it be in the screw bearing or ballnut mount? It may or may not be hard to check. If you can get an indicator on the end of the screw, or even on a thread, and push/pull on the table without turning the screw it should not move. But don't over tighten the bearing.

I just had a DUH moment last night on the new Y on my IH mill. Self built conversion and I not only forgot to tighten the ballnut mounting block, but my AC bearing spacer ring was too short to allow the screws to lock them together. I was tired :tired: and that was my excuse. I only hope I didn't screw anything up more than the thread and nuts trying to tighten the wrong things.:(

Nook screws are are marginal for precision work but .006 sounds much to high for a preloaded. I've read Michael of cncfusion throwing around different numbers for a preloaded screw. It's possible he has had to adjust this estimate depending on the quality of the screws the supplier ships to him. If it's more than .003 the source will be something other than the screw for a near certainty.

Go over the assembly again and think through how the parts work together. Bolts bottoming, whatever. A bit of a long shot, but I do recall this thread
http://www.cnczone.com/forums/showthread.php?t=43634

Could it be in the screw bearing or ballnut mount? It may or may not be hard to check. If you can get an indicator on the end of the screw, or even on a thread, and push/pull on the table without turning the screw it should not move. But don't over tighten the bearing.



Got it! This was the problem. I pulled the motor off and the connectors and put the indiciator on the end of the shaft. Surprise, surprise, .006 of play.
I did not have the nut on the end of the ballscrew *quite* tight enough. I tightened it down around a half turn or so and that took care of it.

I ran the table back and forth a few thousandth either way and the indicator and DRO matched.

Yay!

Mike

good glad you found what was the problem