Problem threading 4.5 TPI on grizzley lathe

You should be able to use any number on the dial, just use the same number for each cut.

But you can always use the metric method::
A) in cut
B) stop
C) back out
D) reverse
E) back in
F) set cut
repeat at A never disengaging the half nut.

Yep, that's just about what I do.
 
edit: delete "I would agree that something is loose." While it is possible, I don't think you would have returned to the proper setting on the third pass.

Since you were able to successfully cut the thread by leaving the half nuts engaged, I would conclude that the problem isn't in the gear train. That leaves the thread dial indicator. Possibilities include having a misaligned dial, the thread dial gear not fully engaged with the lead screw, or a loose thread dial gear. Your 4-1/2 tpi is a .222" pitch. Being off by one thread on the lead screw would shift the cut by .125" which is close to a half thread.

I had a problem with my Grizzly G0602 where the thread dial was not concentric with the thread dial axle and in some positions, it would the half nits would engage slightly off the mark. This would result in a similar situation as yours. I made a new thread dial which solved the problem.
I made about 6 lite passes using asharpie between passes trying to see what was wrong; it appeared to be a 2 start thread it measured 9tpi with thread gage but alternated threads each pass. I will check thread dial thanks for the input. like I said I cut the thread leaving the half nut engaged and backing out but it bugs me when I cant figure out why.
 
Assuming you are leaving the feed reverse lever in place once you are ready to thread. You'll lose registration if you disengage the lever and rotate the spindle.

Bruce
 
Assuming you are leaving the feed reverse lever in place once you are ready to thread. You'll lose registration if you disengage the lever and rotate the spindle.

Bruce
my original try was engaging on the 1 on thread dial then disengage back off reengage on the 1; I got the thread cut by leaving the half nut engaged and reversing
 
My Grizzly is a step down from yours. I have experienced the threading dial loosening off blues. Really cannot fathom how your threads could possibly shift on you when not disengaging on the return. I turned these threads on mine without a hiccup.

20170614_191356245.jpg
 
Hi Guys,

I cut this today. 30 mm by 1.25 thread. Cut using my Myford lathe at 200 ish rpm.
Cutting away from the chuck and winding back by hand. There is only about 7 mm of thread.
The material 40 mm round mild steel bar. The hole is drilled 12 mm and then bored out to 1/2" inch.
26-09-2018-011.JPG
 
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