Need adaptor making

[kirso]

I don't have a metal lathe and someone was going to make this for me. But has not got back to me.
So If anyone has access to a metal lathe and can make me an adaptor boss for my wood lathe and chuck, I would be very thank full.
I am willing to pay for the part and postage as long as not too dear.
I have a headstock that is 3/4 x 16 tpi and a chuck that is 20mm x 1.5. So need a male 20mm and female 3/4 ends.
I have 2 other chucks that I use, but it seems a waste having a third just sat there.
Let me know if anyone able to help.
Thanks

 

[dickm]

Gonna be an awful lot of overhang and possibilities for non-concentricity with that design. Completely off-the-wall suggestion:- the two threads are not THAT different. If the register faces of the chuck will allow it, get someone to recut those to match the register on the lathe nose. Then cut a 16 by 3/4 thread in the chuck. It will be rough, but remember that it's the register that matters and the thead is only there to hold the registers together.
(Ducks for cover before the real engineers read this!).

 

[kirso]

Thanks for reply.
It maybe that I am wasting time trying to get this done. But I hate to see a chuck sat there unused.
I suspect I will just use the other 2 chucks and maybe see if its of any use to anyone else.
I suspect the rest of it is compatible with the same make chuck for a different lathe thread. So someone may make use of it
Thanks

 

[dickm]

Just had a thought - given that an internal adaptor would be a very small piece of material, might it be something that a 3D printer would make with sufficient accuracy? See the thread I started in General Woodworking. Have a feeling that CHJ may already be doing something like this.

 

[J-G]

That option would depend upon the ¾ x 16 being no longer than 6 pitches long - ie 3/8" which I suspect would be too short for a safe chuck engagement.

From my diagram you will see that at 7 pitches there is interference (the Yellow section).

 

[chaoticbob]

I spent some time a while ago trying to make a very similar adaptor for a friend's lathe - I couldn't make it work pretty much for the reasons dickm gives. It's doable if both the 3/4x 16tpi on the lathe nose and the 20x1.5 on the chuck have registers which you can measure accurately. Screw fittings without a register just don't work in my experience - you think you've got the blighter right, then next time you screw it on it's all over the place.

Rob

 

[J-G]

...It's doable if both the 3/4x 16tpi on the lathe nose and the 20x1.5 on the chuck have registers which you can measure accurately. ...

I would agree that the simple adaptor sketch posted by kirso would be prone to 'repeatable' error but both the chuck and the spindle are likely to have registers so the proper way to make an adaptor would be as in my attached sketch.

The difficulties for anyone trying to make such - without direct access to both the lathe and the chuck - are immense.