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Cutting gear rumors

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  • #31
    While on the subject of "hobs", heres a link to my post on making up a worm and gear for my Sheldon lathe a while back. (please overlook the fact that I failed to put "hob" with the quotation marks, I am aware that it is not a 'real' hob) As mc_n_g noted this method is not for long term use, my "hob" cutter was pretty shot by the time we were through. Sure saved the Sheldon though, the apron was non-functioning otherwise.

    Since that was done, I have had the lathe under operation for some time now and feeds and threading modes on the apron is working great.
    If everything seems to be going well, you have obviously overlooked something........


    • #32
      For what you are doing you can easily cut 24 DP in one pass. As for as all said . They are right . But in machine work their is no have to do it this way method. What ever works for you. its your machines and your project .So I say get er Done what ever it takes right are wrong. One thing I have learned over the many years of doing this is what works for you may not work for some one else and vice adverser. To each his own way.
      Every Mans Work Is A Portrait of Him Self


      • #33
        Originally posted by mc_n_g View Post
        depending upon the diametric pitch and the number of teeth I can see nothing wrong with this method for simple home use.
        absolutely, i hope my post wasn't taken as casting aspersions, just explaining the difference. I've used it and it works well.
        in Toronto Ontario - where are you?


        • #34
          Absolutely no harm Mcgyver. I did not take it that way. My wife is more angry at me than anyone on these boards.
          If I was doing something long term I would recommend anyone buy a correct involute cutter (if available) and use better materials than I used.
          I was happily surprised by the delrin. It cut cleaner than I thought it would.
          I never used this method before and I think it is very handy for the homeshop.
          I was worried about trying the Dean Williams method of making the cutter( he was not the first but has a fantastic website on the method) .

          I was worried the cutter was going to end up too thick and take out too much leaving the tooth too thin.
          I think the excentric cutting to get relief is fantastic. The pictures are great and really shows how to do it.


          • #35
            Originally posted by Stepside View Post
            Some say that you must cut them in a single pass, giving no reason besides "thats how I was taught".
            No one's mentioned it yet, but lets be honest here, if you're using a manual rotab, everyone screws up X percent of the time, doesn't matter if X is disturbingly large or impressively small, if you make 2 cuts you'll by definition make twice as much scrap as a one cut machinist, or if you make 3 cuts you'll make 3 times as much scrap... Also when you really screw up and destroy a cutter (sometimes arbor!) making 3 cuts per gear means you only make 1/3 as many gears, per destroyed cutter. Finally the labor cost of gear cutting is going to be directly proportional to the number of cuts.

            Its a financial thing from a job shop, not an inherent technical issue. If you're mr super-machinist and never mess up, then technically one cut will cause less wear and less strange shaped profile wear, very much in theory, but the "destruction" and labor time effects swamp the wear argument unless your cutters are like 4 digits each and your labor is one digit/hr etc.


            • #36
              Here are the results: Basicly it depends upon the size of the project, the machines available, if it is for profit or enjoyment as well as the quality required.

              So I used my "home built" dividing head/indexer, my ProLight CNC vertical mill and a new made in China" involute wheel cutter. I hand wrote the code to cut the teeth. The first time I conventional milled the gear in one cut. The results were usable but nothing special. The second time I climb milled the gear and used 3 cutter passes. he results were much better.
              My next step was to use thread wires to check the gear for size. The gears were within .0005 of computed diameter.
              Then I drilled and reamed two dowel pin holes in a plate the correct center distance for the two different gears. I pressed the pins in the plate and installed the gears and they ran great.
              The gears had a reamed bore that fit the pins.
              So my conclusion would be that the numbers work out and how you get there depends upon what you have in your shop and what the gears need to do.
              Thanks for all the input.