Left Hand internal Threads

[va4ngo]

Hello All and hope you are all looking forward to the festive season.

I have two questions which I will address separately on different threads.

I need to cut a left hand internal thread for a nut in brass, size 12 x 1.75 mm pitch. just 4 threads needed. This will be cut on a Hercus ATM 260 lathe which has a threaded spindle i e not lockable. (similar to southbend)
The easier method is to run the lathe in reverse and start the thread from the right hand end and cut towards the chuck. (Threading tool facing away fron the operator)

How do I prevent the chuck from unwinding if the cut I am taking is too deep? Or do I go to the more awkward method of starting from the left hand end where the tool tip is not visible and run the lathe forwards (threading tool facing towards the operator) Your help appreciated.
Cheers Phil

 

[aonemarine]

Turn threading tool upside-down....had to stop and think.... Cut on Back side from chuck out... Think that's right....

 

[Shopguy]

Hi Phil,
I hear you, with a threaded spindle the choices are limited. My first ever internal thread was left handed. Maybe because I didn't know any better I always made sure I started at exactly the same number on the thread - chasing gauge. With the compound rest set over to the left 29 degrees the work came out okay.
Ernie Johnson

 

[va4ngo]

Turn threading tool upside-down....had to stop and think.... Cut on Back side from chuck out... Think that's right....

Hello Aone, I am trying to avoid starting to cut from where theh tool is not visible

 

[aonemarine]

I've found it easier to thread from the inside out on blind holes, when threading into the hole I've hit bottom too many times to count. Same thing when threading to a shoulder. A couple of weeks ago i had to rethread a carberator jet 10-32 and there was only 4 threads on it and I had to pick up the threads, found it easier to just rotate the chuck by hand and cut away from the shoulder. It was a real pita.

 

[Ken I]

Like Aonemarine I always screw cut outwards from blind holes or shoulders that way I never have to disconnect the screw and I can run at much higher speeds than you would dare running towards the work.

Ken

 

[va4ngo]

thanks aone; ernie and Ken your responses appreciated.

 

[kvom]

If you have the nut mounted in the chuck, then there's no worry about a relief groove or hitting "bottom". So as said above, cut right to left, normal rotation.

 

[va4ngo]

Thanks KVOM that is the method which will allow me to not grind up another internal tool even though more awkward to cut. Cheers Phil