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South Bend 9 Cross Feed Thread Conversion

BobS

Plastic
Joined
Sep 30, 2006
Location
UK
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

Titanium
Joined
Feb 23, 2016
Location
Houston, TX
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

Plastic
Joined
Sep 30, 2006
Location
UK
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.
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
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

Aluminum
Joined
Mar 18, 2016
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

Titanium
Joined
Mar 2, 2012
Location
Geilenkirchen, Germany
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

Plastic
Joined
Sep 30, 2006
Location
UK
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.
 








 
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