South Bend 10K cross slide feed screw thread size

[twooldvolvos]

Forum,

I am working on improving the cross slide feed screw threads on my 1975ish 10K.

This is the dial side of my cross slide.



The dial is held on by this split nut.



The threads on the feed screw have been damaged to the point that the nut does not thread on the whole way. Looks like Bubba didn't have a split screw driver blade so he wacked the general area with a chisel. So before I proceeded, I made a proper screw driver.



You can see the very end of the damaged screw here.



My plan is to carefully run a die onto the injured threads. Does anyone know what size die I should use? By screwing a tap into the nut, I came up with 7/32-24. Does anyone agree? Turns out that this is not a very popular die size and has been a little tricky to get my hands on as it has been backordered. So confirmation that 7/32-24 is in fact the correct die to use would be appreciated. Thanks much.

 

[piper184]

I had to repair the end of the cross slide screw on my '70's vintage 10K. If I remember correctly it is a #12 screw with 24 TPI.

Mine was actually broken and the end was bent. I parted off the bent area and drilled it out. Then turned a replacement part with the threaded end and a "stub" that was a close fit into the existing end where I drilled it. I used Loc-tite retaining compound (648?) to hold it together. I had left it a bit oversize and was able to then turn it down to match the lead screw where the two connected. It is barely perceivable and is hidden from view.
It worked fine.
I also had to turn a new nut and tapped it 12-24. I then threaded it onto a mandrel with the same thread and used a file to get it turned to shape. I ground a special bit to cut the screw driver slot. Locked the back gear and drove the compound slide (set perpendicular to the spindle) by hand. Advancing a thou or two with the carriage for each pass until I had a slot the proper depth. Then I turned it around on the mandrel and faced it off to final depth.

I didn't think to take any pictures of the lead screw repair, but here is the nut and the tool to cut the slot. It was made from a broken tap.

 

[twooldvolvos]

Thanks for the reply. That was an impressive repair!

I now see that 12-24 and 7/32-24 are pretty much the same thing. Since I had a 7/32-24 tap that fit the nut, I just assumed that I needed to find a 7/32-24 die to repair the threads. I have a 12-24 die so I guess I can use that. I find it confusing that we have more than one designation for the same thread sizes.

 

[twooldvolvos]

So I guess my question to the forum is what is the best die to repair the threads on my cross slide feed screw? Should I use a 7-32-24 or a 12-24 or something different? I know these 2 sizes are close but is that good enough?

 

[brandon428]

I'm pretty sure it's a 12-24, so go with that.

 

[twooldvolvos]

Here is an update. I did some more research on my question. 7/64 is .1094 inches. A guage conversion table I found shows that a #12 is .109". So it looks like we are talking a difference of .0004. That's good enough for the girls I go with.