Internal thread cutting - single point

[miro]

I needed to cut an internal thread 12 TPI pitch and the ID is just over 1 in - 1.115 to be exact. It mates to a stub that has the male thread ( and I cannot alter or change that). The thread is 0.480 in long.
After some searching , I made an upside down threading tool boring bar.
Using my carriage stop I located the start point inside the bore..
The running in reverse I started cutting the thread.
Yes, I know lots of guys question the reverse running , but I'm cutting an aluminum alloy so no big forces involved here.

I got the part done OK, but after reflecting on my lack of visibility ( i.e. can't see what's going on) and the upward force on the cutting tool
it occurred to me that I should have put the tool right side up and machine the far side of the bore , not the near side.
So as an experiment, I made a second piece, using the far side and it was much better going I felt more confident too, about the progress
of the thread cutting.

I've had the SB 9 in lathe for several years and have read lots of notes, books, watch videos etc etc, but I've never seen anyone cutting on the far side using reverse rotation.

The work on the second piece went more quickly too
I thought I'd share this in case some one out there might find it useful.

 

[darkzero]

I've never seen anyone cutting on the far side using reverse rotation.

There are plenty of people who thread an inside bore with a LH threading bar mounted right side up (cutting face) on the far side with the spindle rotating reverse. This is so you can thread from left to right as is safer for a blind hole.

There's a YT'r Joe Pieczynski who has a video where he preaches that this is the only way you should thread, away from the chuck. Well that's his opinion. I do thread internal bores on the far side but my threading bar is a normal RH mounted upside down & I thread from right to left with the spindle rotating normally (counter clockwise).

 

[SLK001]

It's a great way to thread, if you do NOT have a threaded chuck. If you HAVE a threaded chuck, DO NOT THREAD THIS WAY!. The threading forces could unthread your chuck and it will go bouncing across the floor.

IIRC, the 9" SB only had a threaded chuck. Thread like this at your own risk.

 

[petertha]

I just posted this on another topic.

This link/document shows the permutations of left/right, external/internal, upright/inverted cutter combinations. (And other useful information even though its kind of orientated to inserts.)
https://www.sandvik.coromant.com/si.../global/technical guides/en-gb/c-2920-031.pdf

Depending on whether your lathe can directionally feed independent of motor spin direction may dictate which options are available to you. Also as mentioned, if you have screw-on vs camlock (pinned) chuck mounting, that usually precludes running the chuck in reverse because of the risk of unscrewing itself.

'Conventional' upright tool infeeding to chuck seems to be burned into peoples DNA, but its probably because of the smaller and/or more limited lathes we grew up on. Many of the Asian import lathes are not limited in this way so we may have more options available to us that mitigate the knuckle chewing excitement of releasing thread engagement within a groove or before a shoulder.

 

[GK1918]

True but I do it all the time trick is wind the tail stock center in the work , chuck can not go anywhere you should be taking only 10 to 5 thousands at a time anyways.........because the deeper you go back off cause the deeper you go the tool is loaded more. We all know if to dial in .005 which equals .010, if that unscrews your
chuck there is a problem ! with a clean chuck and main treads clean, you should spin the chuck on till it goes
clunk and then you need a 2x2 wood stick to get chuck off with a good bap of your hand and that "ouch"
on your hand is no where near a .010 cut

 

[gerritv]

Those Sandvik manuals are superb, I review them often.

Grizzly G0602/G0752, King KC1022ML et al have threaded chucks with locking grippers to allow reverse rotation. I use it that way often on my KC1022. I think the newer models are bolted chucks.

 

[SLK001]

True but I do it all the time trick is wind the tail stock center in the work , chuck can not go anywhere you should be taking only 10 to 5 thousands at a time anyways...

That's quite a trick. Can you explain how you are threading internal threads with a center in the work? I'm having a tough time visualizing that technique.