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gear rebuild


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i have a 1939 SB lathe with one broken/missing tooth in the back gear...what would be the best method of rebuilding this tooth?? I have info on brazing or tig welding or mig welding a new tooth and shaping to fit... anyone have their personal preference and method?? am leaning toward mig welding with solid wire and shaping from that but i would like other opinions. thanks

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I have a 1924 SB that has a missing tooth on the forward/backward carriage feed lever. My lathe may be older style than yours, it has a whole mess of different gears in a separate box and I change them around manually according to the chart on the cover. Anyway, I was getting something done at the local waterjet shop, and mentioned this broken gear to him. He said he has software to waterjet cut straight gears, given all the measurements.. Might be worth seeking your local waterjet shop out. I'm sold on his work, the tolerances the waterjet keeps are pretty amazing.

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this is not my favorite way to fix a gear tooth but it works ! take's time !
you need to hand file to from or use air tools to get you close then hand file
with Tig you have more control on what youre doing this job can't be done half
way you need to ck gear mesh over and OVER ! DO IT RIGHT you DON"T want
to DO it over !!! take youre time :)
with MIG you have less control over heat & build up of metal

KEEP IT CLEAN LOL

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I have repaired alot of gears on old machines that needed dental work. I dont know how big the gear or the tooth is, but, on bigger teeth, I have drilled and popped steel pins into the broken area, then filled up with brazing material.
You have to take your time, both building up then the final fit of the tooth. A trick you can use is once you are pretty much done, cover the new tooth in dykem or machinist blue, install it in the lathe and SLOWLY BY HAND, run it over a bunch of times. Try to "feel" for binding as the new tooth meshes. Take the gear back out and inspect the dyed area. If you have a big high spot somewhere on it, the dykem will wear of quicker there. Then adjust as you see fit.

Good Luck

Phil

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  • 2 weeks later...
  • 1 year later...

keithh999,
Don't weld on you back gear you will be sorry, braze maybe if you are good. otherwise you are much safer to do a mechanical repair. There are several ways of accomplishing this feat. You can cut the remaining tooth out, drill and screw in pins with locktite and cut to shape as sugguested. Or you can go a step further and after the tooth is cleaned out you can cut a dovetail and insert a new tooth, either braze it in place or pin it in place. Or you can proceed after the dovetail is cut and insert a tooth without shape andset it up on a shaper, horizontal miller or verticle mller and cut a new tooth. Of course you need the machine, a dividing head, a gear tooth cutter, (which you could make) and a good book or two, or you can send it out and have it done.
I wish you luck in your adventure and I would say to read everything you can get you hands on.
Jay

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  • 2 weeks later...

Place the gear flat on a steel plate. Select a good section, and create a dam around the area with three firebricks, cut to size if need be. Weight them with steel so they will not move. Melt some lead and cast an impression of the good section. Then, after you fix the broken tooth/teeth, use the lead block to check clearence. Continue to file, grind, sand or whatever till the lead block slides over the repaired teeth just as well and eaisily as the good teeth. By the way, I use MG600 stick welding rods for most gear repair jobs, but for your gear, I would probably TIG braze it with silicon bronze and proper preheat, post heat, and slow cooling in ashes or dry sand. Also, I have found that a thin cutoff wheel is often the best way to clean up gear teeth after welding.

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