PM 833-T Backlash

Mksj- I checked and there is no back and forth motion to the lead screw.

As it turns out PM's tech support suggesting the split nut is moving back and forth is the answer.

I pushed a ruler against the split nut and moved the handle back and forth. The ruler, and therefore the split nut, is sliding back and forth. I have to find a way to tighten the mounting bolts more. I attached a video to show this. I also uploaded another YouTube video

PM tech says to move the table back to visualize the bolts. I tried once and the table would not move far enough back. I'll tackle it again later.

FOR SOME REASON THE VIDEO WON'T WORK. MAYBE THE SIGHT'S ADMINISTRATOR CAN GET IT WORKING
 

Attachments

  • 2BDB7341-D749-4334-976F-F42CB730C584.MOV
    8.1 MB
I deleted the original YouTube video. Here is a link to the updated video:

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Jaek, if you rotate the Y axis handle counterclockwise about two revolutions until you zero out the dial, then rotate it clockwise to a dial reading of .081, the table doesn't move. It turns out the Y axis split nut is sliding on its mount.
 
Based on what your have indicated, the 4 retaining bolts (50) are the same for the X axis leadscrew nut (51) and the Y axis leadscrew nut (62, see diagram). It would seem the only way to assess the problem and tighten the screws would be to remove the mill table.
833T.jpg
 
MKSJ, you are right. Sadly, I suppose to make a little more money, there are only 2 bolts (50), not four. In the four bolt configuration the base of the split nut would likely have more surface area, so more friction. There would also be twice the clamping force.

I don't think you have to completely remove the table. It just needs to be backed off enough to expose the bolts. I also think it is important to keep one of the two X axis handles attached to insure the X axis lead screw is lined up. The table needs to be properly aligned as well.
 
Good news that you found the split nut moving relative to the table.

Putting the table back on shouldn't be too bad. Realigning to the saddle is automatic - the ways and the gib locate it precisely. Leadscrew alignment is done by brackets 55 and 46, you should just be able to run the table to each side and tighten down the screws for the corresponding bracket.

This video link ought to work:
 
It's fixed! There is a third "magic" screw PM tech said I had to tighten. They slid a table to photograph it and told me the steps for doing the same. Their photo is the last one.

Not wanting to remove the table I came up with a way to tighten it with the table on.

The third screw was loose. Tightening it about 3/4 turn did the trick! The Y backlash is now four thousands.

I used a craftsman 6mm ratcheting wrench, a cut off 6mm hex wrench peened at one end, and a screw driver. See the photos and, a video. (The third photo is before I cut a new hex insert). The video is the end of the tightening process.

D5A41C59-2487-4E6F-9BCD-7A0C7F86EF87.jpeg


D700320D-554A-4E14-9C8A-47AD003D6ABC.jpeg
 
Sweet! Don't forget to back off the split nut screw so you don't wear it completely away and need a new one...
 
Thanks Jaek, I had backed off the split nut screw before tightening the third screw.
 
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