Problems with my knob

During the workshop / extension build, the machine tools ended up being moved around a fair bit. That's one downside of building the workshop around the machine tools. The builders got the hang of moving them using the engine crane but somewhere along the way, a couple of handwheel knobs got bashed off - the carriage and tailstock feed handwheels. 

They are pretty delicate. When you look at the area that failed (same on both), it's a fairly obvious weak spot, being shouldered down to the thread root diameter. So - how to mend them?

The thread is 5/16" BSW, so if I wanted to make up new studs I'd need a 5/16" BSW die - which I don't have. Really didn't fancy making up 2 entire new studs either, just to rectify a simple fracture. Same holds true for welding a blank on the end and threading it - that would require using the lathe to cut a couple of threads. But I've got a life to live and am not contriving excuses to spend days buggering about, screwcutting on the Bantam. I only have BSW taps (no dies apart from 3/8" size) and it's not really an option to open up the hole to 10mm. Keep thinking....

Rummaging through The Big Yellow Bucket won me a couple of black steel hex head bolts and a single BZP (zinc plated) hex head bolt. So one option would be to TIG weld a section of bolt to the end of each of the remaining bodies. Zinc doesn't TIG weld and it's almost impossible to remove it completely, so I went with the black steel ones.

Carefully cut off, cleaned up and aligned the parts using a couple of vee blocks. Tacked them up, then welded the joins. 

Tack welded:

Welded up. I've done worse and these are only feed handles after all:

Finally, turned the weld area down to the root diameter. Look OK.

Reassembled:

Tailstock hand wheel without plastic handle:

Job done!