Newbie mistake.

[kirso]

Having been to my local engineering shop, I am told the TH38 thread is M20 x 1.5.
So I need to see if there is a 3/4 x 16 female to M 20 x 1.5 male adaptor out there.
I only paid £35 for the chuck and screw chuck. So it may be a case of just starting again with the correct sized chuck and see if anyone needs a m20 threaded chuck.

 

[minilathe22]

Amazing that they are close enough for it to thread on! I would suggest getting the correct thread, saves the cost of the adapter and prevents using up space behind the chuck. 3/4 x 16tpi is a very common one.

 

[J-G]

Having been to my local engineering shop, I am told the TH38 thread is M20 x 1.5.
So I need to see if there is a 3/4 x 16 female to M 20 x 1.5 male adaptor out there.

Can't be done with an 'insert' - - ie. where a 20mm x 1.5 adaptor is screwed into the chuck flush with the back and having a 3/4 x 16 internal thread - but could be done with what some may refer to as an 'Excert' which would be an extension nose for the spindle. This has negative aspects though as it would push the chuck forward by more than the length of the thread on the spindle.

There is no wonder that if 'felt wrong' - - - see the attached comparison between the two threads. Assuming normal engineering practice where the thread in the chuck has 5/8 depth then the 'interference' between the top of the 3/4" spindle and the 18.78mm core diameter of the 20 x 1.5 thread is only 0.1365mm !!! - or just over 5 thou to those of you still using old money - - - - and that is assuming that the 3/4" thread is 'full' size - I doubt that it would have taken long for that to be stripped away had you run the chuck with a bowl-blank in it

 

[kirso]

I bit the bullet and went to Turners retreat and bought a chuck that fits. Ended up with a Charnworth Viper 2.
It is not the best but will do me for now.
I got to admit though to feeling like I was being taken for a bit of a ride when I bought it . But I better post that story in another section.
So if anyone out there has a need of a 20mm x 1.5 threaded chuck. Or even already has the same type and wants spares then let me know.
Thanks for all the help.