Help with choosing thread cutting inserts

Hi all,

Quick question, can anyone tell me what I should be searching for please. I am looking for a metric thread cutting insert for a13mm tool, but I need to be able to cut the thread up to a shoulder to the left if that makes sense. My current inserts I have won't allow me to do that as the tip points at the wrong angle. Is there like a LH and RH version?

Thanks Stu

I think I may have just answered my own question, it is an external thread insert I am looking for, I only have internal thread inserts! Doh!!

You need a code with ER in it = external RIGHT

If your lathe will run OK in reverse then the internal tool can be used at the rear of the work, I tend to do that as it is easier to work away from a shoulder than  stop just before it

Edited By JasonB on 29/08/2021 16:32:10

Thanks Jason, I did actually try cutting the thread at the rear of the work using the internal tool but I ended up with a LH thread, but I realise now I should be cutting away from the shoulder as you mentioned not towards the shoulder, sometimes it needs someone to point out the obvious!

Thanks again, Stu

An "on edge" insert will let you thread very close to a shoulder. If you grind your own HSS tools you can grind a tool that lets you thread right up to the shouder.

I'm self-taught, which means book learning supplemented by experiment corrected by much help from forum. Great fun, but self learning leaves a multitude of gaps!

Is there a good reason for threading up to a shoulder?

My reading suggests, and what I've always done, is to start by turning down the blank (hex or round stock), to thread diameter and then cutting a slot as deep as the thread at the shoulder with a parting tool. This creates start or finish space for the threading tool and much reduces the chance of a collision.

I don't believe the slot makes any difference to bolt strength, so why not always make one?

On the subject of collisions, I always thread away from the chuck in reverse like Jason. Possibly I learned the trick from him! However, reverse threading isn't a good idea if you're unfortunate enough to own a lathe with a screw-on chuck...

Dave

Dave aka SoD making an undercut at the shoulder is industry standard but doing it with a parting tool will potentially reduce the strength due to sharp corners creating stress points. Undercut tools as a general rule would be 1-1/2 x pitch wide with a radius on the corner adjacent to the shoulder and the "thread side" having an angle equal to half the thread angle or 45 deg.

John