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Right and left handed threads?

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Andrew Tinsley14/11/2017 15:09:35
699 forum posts

I will need to cut right and left handed threads on round bar and also screw cut internal right and left internal threads.

I intend to use the bar to tension an assembly. I can cut normal threads (are these termed left handed threads, ignorance is bliss!), but cutting right handed threads (?) is a bit of a mystery to me. Can anyone help, or at least point me to some information, so that I can learn the technique?



Martin Connelly14/11/2017 15:23:56
623 forum posts
67 photos

Common threads are right hand threads. Left hand threads are less common. If you go to a shop and buy some nuts and bolts they are going to be right handed threads.

When screw cutting in a lathe usually when the spindle and leadscrew turn the same way a right hand thread is cut. If they turn opposite ways then a left hand thread is cut. Does your lathe have a tumbler gear to reverse the leadscrew? If not then you will probably have to add an extra idler gear in the gear train to achieve the same result.

Martin C

Tim Stevens14/11/2017 15:26:31
828 forum posts

If you are used to cutting 'ordinary threads' (which are right handed) with a die, then the process is the same but with a special, more expensive, left-hand die. Just in case - the die is a block of hard metal, almost always a short cylinder shape, with a threaded central hole and cut-aways around the hole so that the edges can cut into the bar. These will give you the male threads. For female (inside) threads you can use a couple of taps - and again the lefthand version is less common and dearer.

If you are cutting the threads in a lathe, the set-up is almost identical for internal and external threads, as the movement of the tool is geared to the mandrel to give the same pitch for each component. With the lathe rotating towards you at the top, the tool must move left for a right-hand thread, and right for a left-hand thread. Male and female threads use tools held in different ways, that is the main distinction.

But unless this is an exhibition of your skill, have you thought of looking in a boat chandler's window / catalogue? This sort of threaded adjuster goes by several names, but usually has a pair of male threads of opposite hands, drawn together by a central tube with matching internal threads, turned for adjustment by a bar through a hole or a spanner on a hexagon.

Too far from the coast / river / etc? Try an aero supplier, a bit more expensive and lighter, but that might be important depending on the job in hand.

Cheers, Tim

Edited By Tim Stevens on 14/11/2017 15:27:18

Journeyman14/11/2017 15:33:34
493 forum posts
68 photos

Turnbuckles are available from ***Screwfix*** in smaller sizes, a ships chandler will probably stock larger and in stainless steel.


Andrew Tinsley14/11/2017 15:52:18
699 forum posts

Thanks gentlemen!

I should have realised that the tumbler gear would reverse the leadscrew.! Not thinking straight I am afraid. Turnbuckles would be an obvious solution, and less work!


Juddy14/11/2017 16:26:22
34 forum posts

I've used this company before for turnbuckles, fast postage and reasonable quality for the price:


Mike14/11/2017 17:13:51
713 forum posts
6 photos

You have beaten me to it, Juddy. I was about to point out that there's a turnbuckle for tracking adjustment on my tadpole tricycle, and I believe the component is the same as used on a kart. I've followed your link, and can't believe the components are such value for money.

Mick Henshall14/11/2017 17:29:18
392 forum posts
21 photos

Known in the RN as " bottlescrews"


Neil Wyatt15/11/2017 16:41:47
13410 forum posts
576 photos
68 articles
Posted by Mike on 14/11/2017 17:13:51:

You have beaten me to it, Juddy. I was about to point out that there's a turnbuckle for tracking adjustment on my tadpole tricycle, and I believe the component is the same as used on a kart. I've followed your link, and can't believe the components are such value for money.

How does a tadpole work the pedals? Surely it needs to metamorphose a few legs first


Mike15/11/2017 19:58:33
713 forum posts
6 photos

Thanks, Neil. I'm just like Kermit! And I really do fancy Miss Piggy!

ega16/11/2017 10:33:14
784 forum posts
72 photos

Better a Muppet frog at the controls of this fearsome steed than a Toad of Toad Hall!

Andrew Tinsley16/11/2017 13:06:38
699 forum posts

I think I need another cognisance test! I am highly embarrassed at forgetting the tumbler gear reversed the leadscrew!

Just how one can forget this is beyond me!


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