3 tries and 3 fails to make a 1/4 20 thread

[benmychree]

You need to reset the thread dial so that the lines line up with the half nuts is engaged, and then try to engage the half nuts when threading just slightly before the lines line up with the witness mark. No need to use the same mark for even threads, numbered or plain lines are all fair game, for odd numbered threads use any numbered line, opposite numbers for half threads, the same number for quarter threads; this works on every lathe that I have ever run.

 

[RJSakowski]

Like someone mentioned the sharpie mark on the dial works for me but if the TDI bolts to the right side of the carriage you may be able to shim it with a washer or 2.
All the above posts are good but mainly the practice till you got it.
Aaron

A good point! Registration is determined by the distance from the half nut engagement to the thread dial gear engagement with the lead screw. If there is no other adjustment for a misaligned dial on the South Bend, a shim on the pivot pin will work. The maximum thichness required won't be more than the lead screw pitch.

 

[martik777]

Are you backing off enough with the crossfeed before each pass and returning to zero correctly? I'm assuming you are only advancing the compound.

 

[Mini Cooper S]

I always use the same lime on the threading dial to engage the half nuts. You waste a little time waiting for your line to come around but it never fails, even number of threads or odd number, doesn't matter. The other thing that I do if there is room, I position the tool maybe a half of an inch or so to the right of my work piece, and start my cut there. This gives me some time to disengage the half nuts before the tool enters the part in case I missed my mark or the half nuts don't engage well.

Richard

 

[twooldvolvos]

I would expect some way of adjusting the disc relative to the mark. can you turn it by hand, twist the face?

There is a set screw near the face that is accessible from an oil hole on the side of the threading dial. I loosened it and tried to turn the face on the shaft but did not get it to budge. I may not have been using enough force.

 

[twooldvolvos]

A good practice you can try that i think alot of us do is try to stick to the same line when you engage. Are you going back to your zero everytime?

I was not using the same line every time. But yes, I did take my cross slide back to zero on each pass. All my advancement was done with the compound.

 

[twooldvolvos]

This may be a bad idea, but when I was first practicing cutting threads, it worked for me. 1/4-20 is a fairly fine thread to learn on. I started by trying much coarser threads like 12 or 14 TPI. I didn't even care what round stock I started from - I just wanted to see if I could cut the threads successfully. For me, it was lot easier to visually see what was happening with the coarse threads. And it was a lot easier to see if my subsequent tweaking was behaving as I anticipated.

Veterans, comment on this please. If it's a bad idea, I'd like to know that myself.

Regards

Good point. I used 1/4 20 because I use that size quite often and I had easy access to nuts for testing my threads.

 

[twooldvolvos]

Like someone mentioned the sharpie mark on the dial works for me but if the TDI bolts to the right side of the carriage you may be able to shim it with a washer or 2.
All the above posts are good but mainly the practice till you got it.
Aaron

Good idea. Shimming on the mount would be easy to do with washers.

 

[twooldvolvos]

Are you backing off enough with the crossfeed before each pass and returning to zero correctly? I'm assuming you are only advancing the compound.

Yes. I am pretty sure I am doing this correctly. Disengage the split nut. Back off the cross slide. Wind the carriage back beyond the starting point. Advance the compound. Engage the split nut.

 

[cathead]

Sometimes it helps to apply a slight down pressure just before the mark. That way you can time when the
half nuts engage with the exact position of the dial.(You can feel the half nuts engage just as the mark comes up) Also just
a dry run with the cutter close to the work but not touching it will allow you to verify that the cutter is tracking properly against the
previous threads. The slowest speed helps too till you get the hang of it. It won't be long and you will think it is easy. Good luck.