Thread form for Atlas 1 1/2" X 8 lathe spindle.

I will be making an Atlas chuck backplate in the near future, and wondered if the threads are 60, or 55 degree. If they are 60 degree, I will have to buy a carbide insert, as the ones I have for Smart & Brown are Whitworth form.

I believe that the thread is 55 deg Whitworth form but if you find that the thread is 60 deg just grind one in HSS as cast iron cuts better with HSS than carbide and you could save yourself the price of new tooling.

David

Being made in USA, I think you will find the thread angle on an Atlas lathe is 60 degrees. It was on the one I used to have. FYI You can buy ready -threaded 1 1/2 - 8 backplates from several suppliers in North America quite cheaply, if it's a bother to make your own thread.

Not having the dimensions of the Atlas or Boxford is not a disaster for me as the lathe itself is available for measuring. The difficulty is gauging the thread angle. I would think the two makes are not compatible.

The prices of backplates from the USA is cheap, until the postage is added, which quadruples the price.

I already have the blank casting which is about 167mm diameter.

1-1/2" 10TPI on an Atlas is bound to be UNS. Can't see any USA lathe manufacturer specifying a Whitworth thread back in the 1930's/40's.

I have a catch plate that fits the atlas ,if that is any good to you

How about referring a suitable tap or taps to the spindle thread? With everything clean and a light behind it should be possible to ascertain the angle.

I don't know what size Atlas lathe you have, but lathes.co.uk give the spindle thread size for the 10" lathe as 1½ x 8 tpi NF, so that's a 60° angle. I would have thought that they will have a standard thread form across the range, wouldn't they?

John

I have now got an ex16 x 8 unified insert which will go in a left hand internal holder to thread away from the chuck when I do the backplate. The chances of the threads being Whitworth are pretty much zero, it being from the USA as mentioned. The standard UNF, formerly NF 1 1/2" has 12 tpi, so it must be a special. I think the lathe is a 12 X --.