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I Forge Iron

Fixed my broken vise screw


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I've got this big Parker chipping vise from the early 1900's that I'm quite fond of. Last week the screw broke in half, it could have been partially fractured for decades, who knows? It's an old square cut thread, 7/8 inch diameter, 4-1/2 tpi. My lathe doesn't do 4-1/2 tpi, and it would be expensive and some work to convert to Acme threads. I've been pondering how to fix the screw for a few days, this afternoon I set to it. I ground off the broken ends to smooth, and then ground both ends to points, for a full penetration weld. I mounted both pieces in a vee block set, next the issue was getting the two pieces back timed back in with themselves, in a continuous thread kind of way. I used dial calipers to measure across 4 good threads. I clamped one of the pieces to the vee block, and rotated the other piece until the thread leads across both chunks came to my measurement. I clamped it down, and TIG welded up to the minor diameter of the screw. I tried to guess the lay of the missing thread and was able to TIG up a helix that came real close to matching the threads that were missing. I pondered welding a solid lump, but that would have added to the filework. After it cooled, I went to the lathe and took a cut across the weld area to true up the major diameter of the screw. The whole piece had surprisingly little runout, I think clamping solid in the vee block for each weld pass helped to minimize weld warping. After the major diameter was happy, I set to filing out the threads. I found a mill bastard file that fit loose in the threads, and tried to train my arm to hold the lead angle of the thread. 2 hours and a cramped hand later, It looked pretty close, but wouldn't spin into the nut at the repair. McraigL was over, he eyeballed my work, and found a little spot of minor diameter that looked a bit thick. I worked that piece down, and by gosh, the nut spun all the way to the end of the thread like nothing had ever happened. I greased and re-assembled the vise, and clamped onto a piece of 1 inch sq bar. I jumped down on the handle, lots harder than I usually would. The repair held fine. I'm feeling pretty good about the repair, and my guts don't sink when I look at the vise anymore.

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  • 4 weeks later...
Guest shaperhaven

Tig welding is the way to go on stuff like that. I have tig welded up gears were teeth were missing for one of my tractors and, after 4 years of use they still look good. Shaperhaven

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