[Newbie] Correct Insert for LH External Threads

The insert cutting tip will cut equally on either side. Your existing RH insert and tool holder will cut up closer to a shoulder at the chuck than a LH insert and tool holder, by the width of the holder. If you can live with that clearance, both at the chuck and tailstock, then you are good to go.
 
llamatrails said:
The insert cutting tip will cut equally on either side. Your existing RH insert and tool holder will cut up closer to a shoulder at the chuck than a LH insert and tool holder, by the width of the holder. If you can live with that clearance, both at the chuck and tailstock, then you are good to go.
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I think I'd rather have the clearance at the tail stock. For what I am doing, I will probably put a live center in the end of the piece. It'll be 2-5/16" of thread of a 3" piece.
 
Laydown inserts, 16 AG60 will thread from 8-48 TPI. It is also a function of the work diameter vs. TPI. Larger diameter work you can go to a lower TPI, but limited by the depth of the cutting grove.

Laydown Threading inserts 16 AG60 .jpg
There were all cut using a 16 ER AG60, all identical thread start and finish points 5/8-11 threads for aluminum feet. The lay down insert is symmetrical cutting in both direction, at low TPI the anvil nneds to be changed which sets the inclination of the cutter. I would suggest you do a trial run on some softer material and if it works then proceed with further threading. I had no issues doing the left hand threads in hardened 12.9 bolts using a the same Carmex lay down insert. If needed for flexible/small rod or longer turning I use an extended point live center so no issues with clearance of the cutter unless it has a very small diameter.
Vinyasa Triangle 3.jpg
 
MyLilMule said:
I should have provided some additional detail, not that it necessarily changes anything.

I have a threaded chuck, so I won't be running the lathe spindle clockwise, it'll always be counter clockwise facing the chuck. Which necessitates running the carriage away from the chuck for me. And I have my tool in front of the chuck. So it would seem this would be my setup.

View attachment 400342

I currently have a right hand tool holder and some 16ER AG60 inserts which is similar to what is pictured. would have thought that I would want a LH tool holder and possibly would use the 16IR AG60 insert that came with my internal threading tool, but I have no idea if the geometry of the insert would be correct in that situation. I also would have thought that the tool pressures would be vastly different using a RH tool cutting away from the chuck and I could break an insert a lot easier. Plus I think the shim would be in the way. Is that what "Change to Negative Anvil" means? Replace the shim?

Here is my threading tool I have now.

View attachment 400343

I'll also note, I am not making parts for Space-X. Just some missing parts on the South Bend steady rest I have.
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Right handed tools will only cut properly on the leading edge as there is no clearance on the trailing edge. Cutting away from the chuck on the trailing edge may not have sufficient clearance. Right handed boring bars will cut left handed external threads. Unfortunately threaded spindles do not like reverse but a slow speed and a shallow cut should pose no problems if it is fully tightened and not reliant on cutting pressure to tighten the chuck.
 
My concern was this: A 10 pitch thread on a 7/16" diameter will give a pretty large lead angle (helix angle). The lead angle should be calculated based on the minor diameter of the thread. Does the clearance angle of the insert exceed the lead angle? I know Carmex and other high end threading systems use shims to adjust for differing lead angles but I suspect most hobby machinists have tool holders with a fixed seat angle.
 
Illinoyance said:
My concern was this: A 10 pitch thread on a 7/16" diameter will give a pretty large lead angle (helix angle). The lead angle should be calculated based on the minor diameter of the thread. Does the clearance angle of the insert exceed the lead angle? I know Carmex and other high end threading systems use shims to adjust for differing lead angles but I suspect most hobby machinists have tool holders with a fixed seat angle.
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I wish I understood most of what you are trying to convey. Believe me, I do appreciate the information. I am trying to soak up as much as I can. I'll learn this eventually the more I get into this arena.

I did a test with some 7/16" stock and used a 60 degree HSS tool. I was able to cut the threads and it fit into the piece it's intended to mate with. I've decided to just get a LH external thread tool holder and try it again. I suspect it won't be exactly a 7/16-10 NS thread, but it'll be close enough to work for me. (I'm making parts for my steady rest that are missing when I acquired it).
 
You just proved the insert had adequate clearance to cut 7/16-10. You did it by trying it. I would have used math. Same result.
 
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