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Gear Cutter Question

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  • Gear Cutter Question

    I need to make a cutter to cut a 104T, 32DP, 20*PA Gear.

    Does anybody know the calculations to make the buttons to make to make a cutter for this gear?

    I have the Ivan Law book, and the chart included appears wrong as the button size is larger than the center distance. I also have a copy of instructions by John Stevenson, but these appear to be for 14-1/2*PA.

    This is an small tooth, and hard to grind the profile by eye.
    Jim H.

  • #2
    No guarantee, as this is a work in progress.

    Button Diameter (D)=1.1116
    Lateral Traverse (C)=1.0878
    Radial DOC (E)=.3938

    where (Law's Symbol)

    The basic assumption is that the button radius equals the instant radius of curvature of the involute curve as it crosses the pitch circle. This gives an approximate involute tooth profile which results in a smaller tooth at its tip than the ideal tooth form, the result will be increased backlash.

    I have yet to confirm my results against Law, either original or corrected and J. Stevenson's results. That is the WIP part. Historically "involute" cutters have been based on the basic radius of curvature at the pitch circle and others have modified this curve with a cycloidal component. Brown's original patent shows a single diameter forming cutter.

    Neil Peters
    Neil Peters

    When on the hunt, a broken part is better than no part at all.


    • #3
      Why don't you try a method out of Dudley's gear hand book? It uses the base circle method of developing an involute curve.

      Base circle x TanA = radius of the involute

      A = pressure angle

      If this doesn't work use the one in the good book. (machiniery's Handbook)
      NRA member

      Gun control is using both hands


      • #4
        Thanks to Steve Welcome and John Stevenson, I think I have things sorted out. I'll find out tomorrow, need material for a cutter.
        Jim H.


        • #5
          Another method, cutter .500" dia shank, .125" wide disc 1.000" dia.
          Three points on the involute curve each side of verticle C/L,relative to center of the 104T gear being X0.000000,Y0.000000 at the OD,PD & RD.
          P1= X +/-.037396" Y 1.655828"
          P2= X +/-.024543" Y 1.624815"
          P3= X +/-.012309" Y 1.588796"
          arcs passing through these points equal Rad 0.5471" (a little different than the other approximations).
          Setting a new zero to C/L of .125" disc & the OD of the disc, the C/L's of the two radii forming the tooth form are X +/- 0.5361" Y -0.1579" polish .006"/.009" radii at the tips
          mill out a notch on radial C/L, Harden tool.
          Mount in boring head with about .050"/.060" throw, cut teeth.
          Les H.
          Les H.
          The Impossible Takes Just A Little Bit Longer!