Single point threading setups

[mklotz]

Threading to a shoulder, external or internal, on a lathe can be a tricky operation. Many times, threading away from the shoulder makes things easier. Puzzling out the correct setup can be tricky. I did it once, covering all the possibilities, and put together this chart so I would never have to think about it again.

Perhaps some of you might find it useful...

A - Threading tool upright, point toward lathe back
B - Threading tool inverted, point toward lathe back
C - Threading tool upright, point toward lathe front
D - Threading tool inverted, point toward lathe front

L - Direction of feed = Left
R - Direction of feed = Right
f - Forward Spindle Rotation
r - Reverse Spindle Rotation

To Cut Right Hand External Threads: Lf(A/D) Rr(B/C)
To Cut Left Hand External Threads: Lr(B/C) Rf(A/D)
To Cut Right Hand Internal Threads: Lf(B/C) Rr(A/D)
To Cut Left Hand Internal Threads: Lr(A/D) Rf(B/C)

[Mook]

My threading "tip" refers to full profile threading inserts.
Only purchase a threading boring bar that takes carbide inserts. Then use it either at the rear of the part, or inverted at the front of the part to also cut external threads.
The spindle will need to run in reverse, which isn't a problem. The drawback is long threads, where it may not be suitable.
By using the same tip to cut internal and external threads you can save a lot of cash. As a bonus, there is naturally more clearance whixh helps with larger lead angles. If you have the facility for thread milling you can use it for that too.

Or: my preference for a short male thread on the end of a bar, is to tap it and force a grub screw in the end. It enables the mating part to screw up to the shoulder without weakening the bar with an undercut. Plus you can have a high tensile thread in a more ductile material! and it takes far less time.