Craftsman 109 4 jaw chuck help needed

[singleken45]

The 4 threaded holes for the jaws set screws of my lathe chuck are cross threaded . I think if I could learn what die to buy , I can rechase those threads in order to use my chuck . Does anyone here know exactly what the threads are ? I've narrowed them down to 5/8" coarse threads , but exactly what pitch ? Standard coarse threads have the sharo edges , but the threads in these holes have flat edges which means a standard 5/8 coarse thread tap will not screw in . My last resort is to buy a different chuck , ??? so if anyone has one , let me know please .Any & all help will be appreciated . God bless, Ken :bow:

 

[video_man]

Mine (3 inch 4 jaw, original to lathe as best I know) appears to be a 9/16-14 square thread (not v-form). Not even an Acme thread, these are square-cut. I do measure 14 tpi for sure. If you can't find a suitable tap --- and that's likely--- you might be able to cut one out of O1 rod and maybe clean your internal threads up with that and some valve grinding compound. Good Luck!

(Later edit) Looked with a magnifier this am, I think these may be what are called "10-degree modified square threads". If so, according to Machinery's Handbook formulas, the measured .558 major diameter on my sample would yield a minor diameter of .487 and a thread depth of 0.0355. You might cut that with a ground-to-width cutoff tool. Square threads don't have much clearance and are deep for their width which makes cutting them real difficult...shallow cuts, clear the chips often... best advice is in Foozer's post, replace it with a newer chuck...I adapted a Machinex5 (long out of print) 3-jaw by machining an adapter to 3/4" thread, turned in-place, which cured some of the runout on that little 1/2" spindle. Hope this helps!

 

[Foozer]

a 109 with the 1/2-20 threaded nose? I went to using Taig chucks for this lathe. Just had to work up an adapter to go from 1/2-20 to the 3/4-16 IIRC required by the Taig. Much nicer, chuck is easy to work with and pricing is reasonable.

Can find a play by play at http://www.deansphotographica.com/machining/projects/109/spindle/adapter.html (a member of this sites projects page)

109 is a well, my change jar is getting fuller for one a tad more robust.

Robert

 

[bronson]

I have one of these four jaw chunks not in the best shape but you are welcome to it if you want it.