Left hand threads

[Kenneth DeightonParticipant @kennethdeighton43272]

[Kenneth DeightonParticipant @kennethdeighton43272]

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.

[jimmy bParticipant @jimmyb]

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

[Chris Evans 6Participant @chrisevans6]

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.

[HopperParticipant @hopper]

+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.

[Mick B1Participant @mickb1]

Posted by Chris Evans 6 on 08/03/2018 09:52:14:

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.

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

[Mike PooleParticipant @mikepoole82104]

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

[Michael GilliganParticipant @michaelgilligan61133]

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.

[colin hawesParticipant @colinhawes85982]

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

[John ReeseParticipant @johnreese12848]

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.

[SaxalbyParticipant @saxalby]

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

[Kenneth DeightonParticipant @kennethdeighton43272]

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.

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