Internal Threading HS to TS: Laydown Insert Toolholder question

[Splat]

Hey guys. I'm making a piece from 12L14 with both 3/4"-16 and 1"-14 right-handed internal and external threads. I intend to use the tool holder correct-side up but cut the internal threads with the tool at the back so I can see what's happening, not front normal position, and the spindle in reverse (D1-5 mount). Here's the part that gets me....:

I'm looking at laydown type left-hand internal thread bars, such as this bar. Keeping in mind I want to thread internally from the chuck to the tailstock with the tool at the farther-away position what partial profile insert do I need (internal left-handed, external right-handed, internal right-handed)? I think I would need an external left-handed insert. Geez, I just remembered there's anvils to worry about, too. I think I opened the proverbial can o'worms now. What's correct?

 

[benmychree]

I use form relieved boring bars in HSS made by Bokum Tool Co., they will thread in either direction and are sharpened by (only) grinding the top of the tool, they are very long lived.

 

[Splat]

Thanks Benmychree. I'll check into them.

 

[mksj]

You would use an internal LH, but may require an anvil change. The one major drawback with lay down inserts is you need a different insert for internal/external/LH/RH plus anvils in some cases. Carmex is made by Iscar, see attached "Carmex Thread Turning Inserts Technical Section". On smaller internal threads I am looking at getting some Micro100 solid carbide threading bars.

 

[Splat]

Mike, if you look at that picture they give the chuck is turning CC, as in regular turning. In my scenario shouldn't the spindle be turning reverse/clockwise? The material would be coming onto the chip, as in a "regular" turning op. Or, am I missing something?

 

[Splat]

BTW, I'm waiting on c/b from Carmex tech support. If they don't know....

 

[benmychree]

Thanks Benmychree. I'll check into them.

I really like their tools, have been using them since about 1970, they make boring tools as well; occasionally, you can find them on EB.

 

[Splat]

Thanks guys. I just got off phone with Alfie from Carmex. Nice, patient guy. I explained the whole enchilada and he confirmed I would need an internal left-handed insert, or IL16 for that particular left-handed internal bar. You were right, MKSJ! That bar, btw, does not use an anvil. Probably gonna go with a P25C or BMA grade insert. Thanks guys.

 

[mksj]

OK, lets try this figure, the arrows for turning direction can be a bit ambiguous. IN-RH thread cutting away from the chuck use an IN-LH insert.
Mark

 

[Splat]

That's a great diagram, Mark. I'm saving that for reference. Thank you very much for the help.