REPAIRS: Broken Feed Nut


REPAIR Crossslide Feed Nut
06/22/1999
Just received a couple spare parts from Harbor Freight & started to go about fixing a problem I discovered with my cross slide. I could not figure out whymy cross slide was impossible to adjust. I removed the cross slide to check for junk on the lead screw or in the brass nut. What I found was that the two 4mm screws that adjust the nut were completely stripped. Or so I thought. Most set screws or adjustments on the 7x10 rarely need more than finger tight on the allen wrench. This is because they almost all have a locking device ( a nut or another set screw ). I thought it was weird that both screws on my brass nut would spin forever with the tiniest amount of friction.
What I found as the cause, was that both screws had been tightened so much that the screw holes had cracked clear through to the side and left one with a giant pit, where the top of the nut had popped out. I temporarily drilled & re-threaded that one for a 10-32 screw. This allowed some grip in the small amount of brass left in the hole. the other one I left alone as it had a crack through the hole extending to the side of the nut. I re-installed the nut hoping that the new one I ordered would arrive soon. On the tenth day after ordering the parts UPS arrived with the package. It contained the brass nut but not the 80 tooth gear I ordered ( another story! Involving a ringing phone during a moment with the carriage moving to the left under power). To my suprise the nut did not have either of the two mounting holes. Well this left me with the task of measuring the old nut & drilling the new one. What thread to use? I opted for, yep you guessed it, 10-32. Why? Well to be honest I only have one metric tap a 3mm ( for my R/C heli's ). I felt 3mm was too small & decided that 10-32 would work better. So I placed the two nuts side by side in the Mill vice. I used a pointed shaft to locate the center of each hole on the old nut & then used the cross slide on the mill to drag the pointer across the brass scoring the center line of the hole on the new nut.
Next I scored a line along the threaded axis for center. Center drilled the two holes. Threaded the holes for 10-32 screws and did a test fit. Everything fit smoothly so I re-installed the nut in the cross slide & mounted the cross slide.
The head on the 10-32 screws was just bigger than the counter sunk holes on the cross slide, so I turned the cap screw heads down with the 3-jaw chuck & a file. Just a few passes & they were a perfect fit.
I followed Mike's instructions on Adjusting backlash out of your cross slide to adjust the cross slide & it worked perfectly, or at least, alot better than it did out of the crate.

Here are a couple of pictures of the broken feed nut.


End view showing crack through to the end of the nut.

Top View showing the crack on the RIGHT &
Broken out area on the LEFT



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For more information email me at:
pth3k@virginia.edu


All above images Copyright (c)1999
Ty Hoeffer