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New tooth on cast gear with weld

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  • New tooth on cast gear with weld

    I'm restoring a 100yr old lathe and one of the back gears (the smaller one) is missing a tooth. The gear is cast.

    I decided to try to make a new tooth from weld using my flux core welder.

    Any advise welcome, please (I'm a poor welder, but getting better)

  • #2
    Find someone who can arc weld it with 55% or 98% nickel rods and pre-heat. Even with pre-heat, a normal steel flux core wire is very likely to end up with a brittle or impossible to machine zone in the transition between the cast iron and the weld metal. If you can find Inconel 82 wire that will do the job, but it's as common as an honest politician.

    I've used all three alloys for weld repairs on cast iron and The nickel (arc) and Inconel (TIG) were machinable. The steel (MIG) needed a surface grinder.
    Location- Rugby, Warwickshire. UK


    • #3
      Hi Mark.

      Are you saying that the problem is not getting the weld to 'take', but grinding/filing to a finish is the tough bit? I don't know what type wire I have but I know it's tough to machine. However, I have filed it down with a nice sharp file. Hard work but it was do-able.
      Last edited by Jonesy; 09-27-2021, 07:09 PM.


      • #4
        No, the problem is that with a mild steel wire, the molten weld pool will pick up carbon from the cast iron and there is an area that becomes, basically, tool steel. Add this to the rapid quenching that the weld undergoes and you end up with a layer of very hard, very brittle material which is almost impossible to machine and is likely to crack because of the shrinkage when the weld solidifies.

        The high nickel fillers get around this problem by not absorbing carbon from the cast iron and by being more ductile, so they dont form the hard brittle layer and don't encourage the cast iron to crack by stressing it. It's normal to peen the weld area as soon as it's solidified to encourage compressive stresses rather than tension as well.
        Location- Rugby, Warwickshire. UK


        • #5
          Thank you Mark. I knew none of that.

          Just watched a few YT vids welding cast with a mig. They seem to suggest heating up first, then small welds to avoid too much heat in one small area, and build up the weld this way.

          I'm going to give this a try after work today. I'll use my plumbing torch to get the gear as hot as I can and small welds on setting 4 (of 6). It's a 130AMP and I know 5 or 6 will be far too high. Fingers crossed.

          Will update!!


          • #6
            Well that went better than expected! The weld was definitely harder in places but it did file down. I need to add some more weld to build up fully and create the shape of the tooth but I am well pleased with the initial result.


            • #7
              I have fixed gears missing 1or 2 teeth but milling a shot in the gear and silver soldering a piece of steel in the shot than filing to fit ken


              • #8
                Originally posted by ken View Post
                I have fixed gears missing 1or 2 teeth but milling a shot in the gear and silver soldering a piece of steel in the shot than filing to fit ken
                Something like that crossed my mind but I was worried that taking out some of the cast below the tooth would weaken the body of the gear as it's not that wide a diameter. I was actually thinking of using superglue or araldite as I don't have a burner that'll get it hot enough to silver solder. Unfortunately I have no access to a mill, but hopefully that will change before I turn up my toes.

                That possibility is on the back burner for the moment.

                I've got to add more weld when I get down the shop tomorrow after work, but before that I want to make a template of the unbroken gears to try to get my final tooth more accurate. Also will bring my mini grinder (really cheap and underpowered dremel wannabe) home from work as that'll help with final finishing.
                Last edited by Jonesy; 09-30-2021, 04:37 PM.


                • #9
                  Replacing a tooth is a good place for brazing. Also - the brass tooth will be a bit softer so it will not wear the other gears if it is a little off. And a brazed in tooth will last a long time, it was a common way to repair when castings were more common. Better yet, Cast Iron weld the tooth, but the cast iron rod for doing that is not very common.

                  grind, preheat the whole gear, and braze it. A much easier to machine repair that will hold up to use very well.


                  • #10
                    Thank you. I fully accept that there are better ways of doing this, and indeed of doing most of the jobs I take on. As a DIYer I'm bound by the materials and equipment that I have to hand. I have a gasless mig with ?? wire and a plumbing blowtorch.

                    I'd love to have the necessary gear to do a better job, and hopefully one day I will. Impending house move and retirement saving mean some things will have to wait. Life is just not fair.

                    But, so far this little project is going better than expected!


                    • #11
                      Considering what you have to work with, you did OK. Mark is exactly right about the nickel and carbon, etc. That is why I prefer the 99% rod or Inconel/TIG but I'll be the first to tell you it's expensive. (I weld for a living)

                      I would use your torch to get the whole gear as hot as possible -- several hundred degrees at least. Not glowing, but just under that. Then keep on welding. Then let the heat down real slow by burying it in cat litter (no kidding, it insulates it.) Then you won't have any hard spots.
                      25 miles north of Buffalo NY, USA


                      • #12
                        The end result was a tooth that meshed better than no tooth! Hardly perfect but running the back gears by hand (the head stock is off the lathe as it's the 1st part to be spruced up) I could feel no interuption as the welded tooth went by. Only once it's under load will I get a better idea, but I'm hopeful!

                        I'm not trying to kid myself that this is a 'restoration'. Far from it. The idea is to get it usable, and enjoy getting it to that stage.

                        I've fallen back to my previous project though.... getting my existing tooling and machines ready for my retirement move to the country. I really shouldn't have even started playing with the lathe. I'm also trying to finish building a twin vertical 48" x 6" belt sander. I've had to rethink and improve the design so many times since I started as what I though would work.... didn't!

                        As stated earlier, I have to work with what's laying around and what I can find in my junk box as much as possible (my promise to myself) so my options are limited, but that makes the projects more fun.