you can release the half nuts, but you need to stop the lathe quickly after, then reverse the lathe, and re-engage the half nuts on the same number on the threading dial. if you are not using a threading dial, you can't do what I am saying.Ok, I was successful using a combination of all of you suggestions.
Ya, I tried it with the thread dial like doing standard threads and it wouldn’t work. It wasn’t until someone told me to leave the half nut engaged for metric threads. It worked after I left it engaged.you can release the half nuts, but you need to stop the lathe quickly after, then reverse the lathe, and re-engage the half nuts on the same number on the threading dial. if you are not using a threading dial, you can't do what I am saying.
by keeping the same number during reverse, you are just picking up where you left it.
It works engaging and disengaging on the same number for standard threads fine, but not on metric.
I need to watch all the videos you guys have posted. I have seen bits and pieces of all of them, but I have a bad habit of skimming.
I’m at work, so my last post about skimming made it sound like I don’t pay attention to any of your posts. I meant I skim through YouTube videos. I have done all of the things you guys have told me here. The cutting metric threads with imperial lead screw is the key there, but I couldn’t recall how to explain that. I do have the fishtail gauge as well.Practice @ your lathe's slowest speed. Use the KISS principle. HSS works fine, keep it sharp. Do you have a fishtail? Make a groove to your final depth next to the shoulder of the work (or @ the other end if threading toward the chuck.) Make a few air passes A DRO is nice but not required, touch off, then a scratch pass. It is easiest to see if you magic marker or Dychem it. Check with your thread gage. Was the setup for a right hand thread? What DOC? First pass can be .010+-Successive passes? .004"? or what feels right on your lathe. If you are cutting a metric thread on an imperial leadscrew lathe, you must always keep the half nuts engaged at the same location on the lead screw. You can disengage the halfnuts but don't let the indicator go around past your starting mark on the tread dial or you will loose track! (It is possible to find your start point on the leadscrew again but a PIA.) If you have disengaged halfnuts when you stopped, reverse the lathe and reengage the halfnuts as the mark passes. Rinse & repeat until the tool reaches the depth of the original groove. Chamfer the terminal end and lightly file the top of the threads to get rid of any fuzz and the extreme sharp if it is there. I suggest making yourself a numbered list of the steps (large print) and putting it where you can refer to it as you work.
About KISS.... Turning away from the shoulder is less stressful since it doesn't require a highspeed stop of the lathe and makes it possible to use the groove as the last-cut, set-point. Treat your lathe nicely, don't slam the halfnut lever in. As the mark comes up put a little pressure on the lever and you can feel when it will drop right in.
Note that cutting away from the chuck requires the tool to be used "upside down." Cutting straight in with just the cross slide eliminates having to turn two dials each pass and getting confused. If you go the two dial route, put a mag base indicator on the cross slide so you know you've returned to zero each time. Easier to see and confirm than the lathe dials. If you have a DRO it can also tell you the zero point & successive DOCs. If your lathe has a brake it allows higher speed threading ONCE YOU'VE MASTERED THE ART! Watch the pro's videos. Joe Pie has excellent ones including one on the use of thread wires that makes them a lot easier to use.
I was going to list all the things I've done wrong in learning to thread but there isn't enough room on this site!
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