Left hand threads

I am in the process of restoring a 1928 Austin 12/4 Heavy car, to bring the brakes up to near modern standards I need make 4No nuts approx 2" long but half of the 5/16" BSF internal thread is Right hand and the other half is Left hand.

In all the 60+ years that I have been using a lathe I have never had to make an internal L/H thread, so how do I go about it ?.

Thanks, Ken.

When I screw cut left hand, I start at the bottom of the hole and cut out, as it were. Spindle running the usual way and lead screw "reversed"

Jim

At 5/16" BSF it is a job for a tap not screw cutting. The cheaper option is-- if your conscience allows use M8 only because the taps will be cheaper. I assume you are making a turn buckle for rod adjustment.

+1 on using the method Jimmy B describes. But 5/16" is pretty small diameter to screwcut internally. Can be done of course but it might be worth looking at Tracy Tools or Tap-die.com for a LH tap.

There are a few 5/16 BSF LH taps on the Bay for around a fiver - more or less.

Tracy Tools may be able to help with a LH tap, they don't list them but say call to enquire. I would not fancy internal screwcutting at 5/16 though I am sure it could be done. I am imagining this is part of a rod type braking system and so the material selection and ensuring the thread is correctly formed could be important. I think that as it is so difficult to see what you have done inside a 5/16 thread I would go with the tap option if possible even though is will probably not be cheap.

Mike

Ken,

It may be worth seeing if these folks could help: **LINK**

https://www.lasaero.com/products/article/G000GUJ1P

... Their left hand threaded 'jam nuts' seem reasonably priced.

MichaelG.

I have made odd taps in the past from silver steel. To avoid having to relieve the threads I kept the cutting edges very short. Worked O K for one offs on mild steel. Colin

Chris Evans is right. The the threading tool would be too slender to be practical. Left hand taps are readily available and will make the job a lot easier.

Many moons ago at an auto jumble I bought a box of three 5/16 BSF taps. Wasn't till I got home that I noticed the words "Left Hand' on the box. Never had a need for one, let alone three. If you have a problem getting one let me know and I will pop in the post.

Regards Barry

Thank you to all the members who have responded to my plea for help and in particular to Saxalby, I have fortunately been offered the use of taps from another local friend, once again, Thanks, Ken.