South Bend 9 Cross Feed Thread Conversion

[BobS]

Just wondering if anyone knows if it is possible to change the cross feed screw from 7/16” acme to 1/2” acme. At first sight there looks to be enough room to me.

 

[texasgeartrain]

Cross feed screws are usually left hand thread, fyi.

7/16" acme thread is sort of an oddball size, where 1/2" is a whole lot more available in right or left hand. A primary consideration would be the graduations of your cross feed dial. 1/2" at 10 threads per inch, would need 10 dial turns to travel 1 inch. A direct reading dial would have 200 increments/graduations. A radial reading dial would have 100 graduations in one revolution.

How many grads does your dial have now ?

 

[BobS]

The current 7/16” screw is 10 tpi so I would replace with 1/2” 10 tpi so the dial should be unaffected.

 

[tommy1010]

This is done by many all the time. I myself have done this many times. I do not have the 1/2 x10TPI LH tap anymore but they are rather inexpensive.

 

[BobS]

Did you make a new nut from scratch or did you modify an existing 7/16" threaded one? I was wondering if I could drill an existing one out to 1/2" which would presumably still leave some thread there and then run a 1/2" tap down it. Not sure about the accuracy of doing that.

 

[tommy1010]

Made a new one from scratch. Very easy to do. Someone on this forum may have a tap to borrow. Just ask.

 

[tdmidget]

Did you make a new nut from scratch or did you modify an existing 7/16" threaded one? I was wondering if I could drill an existing one out to 1/2" which would presumably still leave some thread there and then run a 1/2" tap down it. Not sure about the accuracy of doing that.

Pretty sure that if you drill it to 1/2" you will have no threads.

 

[Gard]

I just purchased a new nut (on ebay I think) that fit my SB lathe but is made for the newer 1/2 inch screw, made a new leadscrew but have not reassembled everything yet.

 

[steve-l]

The question has to asked, why? This lathe has been around for about 100 yrs and still functions well and for many, many yrs.using the original specs and parts.

 

[BobS]

Two reasons why it might be worth doing. One financial and the other practical.

Here in the UK 7/16-10 acme threaded bar is unobtainable off the shelf but 1/2-10 is readily available. I know I could import some from the US but that is still more expensive than the 1/2-10 stuff here.

Larger thread = larger load bearing area = reduced bearing stress = reduced wear

I haven’t fully decided yet but at the moment I think that the larger size is the way to go.