PM 833-T Backlash

[Bill Kirkley]

I am having problems correcting the Y axis backlash. PM tech support suggested tightening the split-nut screw and tightening the split-nut mounting bolts.

After a lot of trial and error I was able to tighten the split nut screw to the point that it was hard to turn the crank handle. There was no affect on the backlash.

Getting to that screw was difficult to say the least. I used a 1/4" drive ratchet, a mirror, and a flashlight. String was attached to the flashlight and wrench.

The mounting bolts for the split nut could not be tightened any further.

For all my effort the backlash is a little worse than when I started.

Does anyone have any suggestions?
Below is a link to a YouTube video:

 

[benmychree]

Could the screw be moving axially in its mounting bearings?

 

[Bill Kirkley]

I think correcting axial movement in the split nut is what tightening the split nut screw corrects. When I tightened it enough to cause more resistance to turning the Y axis handle it didn't decrease the backlash.

I got an email from the PM tech folks. They are going to look into it further.

Any other suggestions would be appreciated

 

[davidpbest]

Kind of a stupid question perhaps, but are you sure the lead screw is turning over that range of backlash? From the video it looks like the handle is loose on the lead screw shaft.

 

[Bill Kirkley]

The handle is tight. There is a key between the handle and the dial. There is a second key between the dial and lead screw. The keys prevent circular motion between the handle and lead screw.

 

[benmychree]

My comment on axial movement was directed to looseness in the thrust bearings that connect the screw to the table; if you've tightened the screw until it binds, that is about the only other possibility.

 

[Bill Kirkley]

Benmychree, I'm not sure I follow. What is the part number on the attached diagram you are referring to?

 

[davidpbest]

Same as on my PM935. Just thought I’d ask.

 

[jaek]

You say you have backlash - what is moving relative to what? .081 is more than a sixteenth - this should be readily visible. Leadscrew relative to splitnut? Splitnut relative to saddle? Leadscrew relative to bearing mounting to base? Dro readhead?

 

[mksj]

Per above, take off the handle and see if there is any back/forward movement of the Y-axis leadscrew with your hand and also rotational. Make sure the gibs are adjusted and not binding. Also at the end of the video, there seems to be a M5x5 set screw that is missing from the handle dial. Check if the handle to leadscrew key is is present. Not sure if this makes a difference, but if may effect movement of the hand wheel/leadscrew. Need to determine what is loose. Can't imagine the leadscrew nut having that much play when new, part diagram does not show it as being adjustable (split nut), you have tightened it to the saddle so there should be no movement at the nut.