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  • gear repair

    I have a Logan 820 with two teeth missing on the 70 tooth back gear. I would like to build up the missing tooth area with a stick weldor then heat treat, then machine off the excess. If this will work, where can I find the information for rehardening the gear?
    Larry Backer

  • #2
    Larry

    The gear will need to be heated (1000*F for steel) and kept there while welded and cooled very slowly (in an oven or hot sand). The teeth can be checked for hardness before the repair and rehardened to that state afterwards. It may be easier to just make a new one from scratch as well as being more reliable. One of the other guys may have a source for parts.

    Good luck

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    • #3
      Larry,

      Try www.lathe.com for new Logan parts. These people are very nice to deal with and have excellent service. I have an 11" Logan and have ordered a manual for it and will probably order some other stuff. Along with the manual, they sent me a coupon for $20.00 off of my next purchase. (Insert usual disclaimers.....................here. ) A new gear will set you back some $$ but it might be worth it not to have to fool with repairing the old one.

      Good luck,

      Greg
      "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

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      • #4
        I don't think the gear is hardened, is it? Try filing on it; you should be able to cut it.

        A friend of mine had broken teeth on his Logan back gear, too. He got another broken back gear, the same kind, cut out a small block with sufficient teeth on it fix the first gear, milled a recess in the first gear to take the block, and brazed it in place. That was several years ago; it's worked fine.

        Even without a 2nd gear you could do a similar fix: mill out a recess, put in a block, then cut new teeth in the block. I bet you could epoxy the block in place, even, and avoid all the heating/warping problems. Do some undercuts so there are pockets for the epoxy to go into to mechanically lock the block in place.


        [This message has been edited by SGW (edited 08-21-2002).]

        [This message has been edited by SGW (edited 08-21-2002).]
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        • #5
          I don't think it is hardened either. I have repaired many (repairing equipment for school district, kids love to pull backgear lever up while running) and never had a return on those teeth. Under cut the broken area and so that you clean up the face of each adjoining tooth. Tin area including the faces of the two teeth you ground(preferably with a flux designed for cast iron) and then start filling using a magnese bronze rod and regular flux. Over fill and let cool slowly or you will have hard spots. Clean up and mill new teeth. The 2 teeth on each side will be half cast iron and half bronze. Manganese bronze rod is important for strength. There is an article coming out soon on this and I have one coming out next year showing this on a Logan bull gear. It works.

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          • #6
            An additional comment on my gear repair above. The undercut area needs to be below the original bottom of the tooth as you need good metal to braze. Many just try to braze an new tooth on and that will not work. A 1/32 to 1/16" deep is plenty.

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            • #7
              Yeah John, that's the way I'd go about it, only I'd put two steel dowels in each tooth area - you can do the holes with a hand drill & get the dowels a nice firm push fit, gives you something to built the brazing material on to.

              At a pinch, I've gotten by with just the dowels in some 'emergency' jobs - keeps you running 'til you can do it properly.


              ------------------
              Tel
              Tel

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              • #8
                Just got the latest issue of HSM. Cover story article on braizing gear teeth.
                Wes
                Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                ~Practitioner of the Electromechanical Arts~

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