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  • Fixing broken teeth on gear

    So if you read my thread about the 5914 purchase you know I have a few gears to fix. Since broken gears can be from any machine I decided to start a new thread regarding the process to fix and my questions.

    My first question is can anyone give me the pros and cons to either rebuilding with braze or tig? The gears I have are not cast and I have the ability to do either or. If you choose one method over the other could you recommend a rod and or flux to use.

    Second does anyone have any ideas as to cutting the teeth without a dividing head. I have made gears before using the original as a pattern and indexing the new blank using the old gears teeth. The gears I made were made out of uhmd so im not sure it will work as well cutting into either braze or tig...

    Ive considered trying to make a jig where I could hold a shaft the same dia as the ID of the gear. Then making a sorta circular pattern at the rear where I could print off an index pattern using a graphic program the same tooth pattern of the gear. I would then need to manually spin the shaft and line up marks using the template printed . Hard to explain but it sorta makes sense in my head. An alternative is buying a dividing head. I really want one but cant hardly justify the cost.

    Lastly is to buy some gear pitch gauges and see if I can get gears from Boston gear.

    Any thoughts ?????

  • #2
    My Logan came with a missing tooth on the bull gear on the back gear. I got lucky on EBay and bought the entire back gear Assy for $70. I brazed up the missing tooth and carefully filed it to shape such that it would mesh well with its mate. Worked well and now I have a spare, that should guarantee that I'll never break another tooth. You can make an excellent approximation of a proper gear profile with diligent filing. Bob.

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    • #3
      A brazed repair can last for a long, long time. Use borax flux. I'd rather puddle teeth with a torch than TIG the thing, but that works too.
      Like Mr. Fisher said, get after it with a file & diligence. Having the gears mounted makes for quick work provided you have access. Bring into mesh and work the shiny 'til you get what you want.

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      • #4
        Keith Fenner recently did a youtube video of replacing broken gears. It is a multi-part series that starts here. You can jump ahead to part 7 where he begins repairing the original gear.


        https://www.youtube.com/watch?v=qEGAs8OMuJc

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        • #5
          Originally posted by dp View Post
          Keith Fenner recently did a youtube video of replacing broken gears. It is a multi-part series that starts here. You can jump ahead to part 7 where he begins repairing the original gear.


          https://www.youtube.com/watch?v=qEGAs8OMuJc
          Yep... ive watched that video several times. He brazed but I think the gear is Cast so not sure if that makes a difference.

          Also FYI one of the gears I need to fix is missing several teeth in a row. So I dont think hand filing is an option. If someone has a way to file in multiple teeth in a row please let me know

          Thanks

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          • #6
            "Also FYI one of the gears I need to fix is missing several teeth in a row."

            Think stone age. Make a replication by cast, cut a template etc. Do your braze build up, cut the OD w/lathe if it isn't out of action. Rough w/hacksaw and start at the first repaired tooth with the template. Get close and stair step each tooth. If you can mesh with a mating gear, use blue or just cut the shiny.
            If you have the money, buy the gears. But the above will be quicker than getting a D/H and setting up w/cutters etc.

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            • #7
              Found this youtube vid... its kinda what I had in my head for a DIY dividing head using a printout for index degree markings.

              I think I would personally make a more ridged / robust unit... You get the idea

              https://www.youtube.com/watch?v=-we6ORrJgUI

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              • #8
                Originally posted by Axkiker View Post
                Found this youtube vid... its kinda what I had in my head for a DIY dividing head using a printout for index degree markings.

                I think I would personally make a more ridged / robust unit... You get the idea

                https://www.youtube.com/watch?v=-we6ORrJgUI
                Also, after thinking about this a bit more I wonder if instead of using the print out as an angle finder I could use one of those little digital angle finders.

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                • #9
                  Index right off the gear you are repairing. Mount the gear on an arbor, mandrel, or what have you. Turn a taper on the end of a bolt so it will bear on both sides of a tooth space without bottoming out. Drill and tap a hole for the bolt in a piece of bar and find a way to clamp it to a fixed part of the machine you are using for the job.

                  Set up whatever cutter you are going to use and feed it into a good tooth space until it touches both tooth flanks. Then fit the bolt into another tooth space and clamp it to the machine so it will stay put. Back the bolt and the cutter out of the tooth spaces and turn the gear so the first space to be cut lines up with the cutter, run the bolt in till it it fills the tooth space in front of it. The gear is now located for the first cut, it's probably a good idea to clamp the gear to something so it cant turn while cutting.
                  Jim

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                  • #10
                    I've repaired the horizontal+vertical, partial-circle, 16DP feed gears (with integral ratchets as part of the casting) of a shaper, by welding up with nickel rod and re-cutting the teeth. Ended up machining off all the teeth, building the whole lot up, turning the result down and re-cutting all the teeth.

                    For the Beaver milling machine that I'm rebuilding, I just bought replacement gears, from HPC in the UK, and machined them to suit.

                    If it's a spur gear with a relatively simple geometry, it will almost always be simpler to buy or make a new gear rather than trying to repair a few teeth on the existing one. (exceptions are full side traction engine or similar sized gears).

                    The 98% Nickel rod I used has given good service and is probably more resilient than the original cast iron teeth were.
                    Location- Rugby, Warwickshire. UK

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                    • #11
                      I've repaired a cast gear or 2, using braze. In addition to the braze, I D&T'd across the broken section, ran in SHSSs, then brazed over/around them. Seems stronger to me.

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                      • #12
                        Originally posted by Axkiker View Post
                        Yep... ive watched that video several times. He brazed but I think the gear is Cast so not sure if that makes a difference.

                        Also FYI one of the gears I need to fix is missing several teeth in a row. So I dont think hand filing is an option. If someone has a way to file in multiple teeth in a row please let me know

                        Thanks
                        You can try using mill board as a dam on the sides of the gear, or mix up some refractory.

                        Brazing should work as a filler for steel. Steel has a higher melting point than brass by about 1000؛F. You can buy a single involute gear cutter rather cheaply and pick up the teeth for the cutter using the gear itself and a mechanical stopping wedge.

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                        • #13
                          Originally posted by J Harp View Post
                          Index right off the gear you are repairing. Mount the gear on an arbor, mandrel, or what have you. Turn a taper on the end of a bolt so it will bear on both sides of a tooth space without bottoming out. Drill and tap a hole for the bolt in a piece of bar and find a way to clamp it to a fixed part of the machine you are using for the job.

                          Set up whatever cutter you are going to use and feed it into a good tooth space until it touches both tooth flanks. Then fit the bolt into another tooth space and clamp it to the machine so it will stay put. Back the bolt and the cutter out of the tooth spaces and turn the gear so the first space to be cut lines up with the cutter, run the bolt in till it it fills the tooth space in front of it. The gear is now located for the first cut, it's probably a good idea to clamp the gear to something so it cant turn while cutting.

                          Yup thats exactly how I made the gears for the lathe I have which works. Since I have 3 gears of different sizes to fix for this lathe I thought about possibly making something which would make all 3. Plus It could be used for other tasks..

                          Just thinking aloud

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                          • #14
                            My brother bought a lathe that had a number of gear teeth "repaired" by simply drilling and threading a hole into which a screw is inserted (presumably with Loctite or epoxy) and which is then filed to shape - not pretty but it seemed to work.
                            "Patriotism is the last refuge of a scoundrel"

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                            • #15
                              So I was thinking about something. A dividing head uses plates with holes drilled in them to index the gear for cutting. Why could one not use one of the little digital gauges that are out there?

                              Basically if you were making a gear from scratch you would make your first cut then zero the digital protractor. Then spin the blank to the appropriate angle. Make your cut and zero the gauge again. Repeat Repeat Repeat until the gear is complete.

                              My first thoughts are that the little digital protractors just arent accurate enough. After some research I have found some affordable units that claim +- .05 degree of accuracy. Anyone have an idea if this would be accurate enough? I am having a hard time corelating the .05 to real world tooth difference. I would kinda think that there could possibly be more slop in the indexing head etc. When you consider all the moving parts, plates, pins etc the gauge idea really sorta simplifies things.

                              Anyways just an idea.

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