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Fellows Gear Cutter

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  • Fellows Gear Cutter

    Saw this description on an ebay listing:

    No. EX12P43CU Lot 1383-23
    14 H.S.S.
    48 TEETH 12 PITCH P.A. 14-1/2 deg. EX
    BASE CIR. 3.870 D+F= .188

    1) I assume 12 pitch is the same as D.P., is that right?

    2) What's the D+F? Is that describing the clearance at the root and top of the teeth?

    3) What's the more common P.A. nowadays, the 14.5 or 20?

    4) I've thought the Fellows cutters were made for use on a Hor. mill, do they work pretty well on a vertical too? That one shows no keyway, which makes me wonder.

    (the listing is at:

  • #2
    In order of question:-

    [1] 12 pitch is the same as 12 DP

    [2] D+f is the depth to cut to with the cutter.
    D= the depth of the tooth, f= the clearance needed.

    [3] Most common, modern gears are 20 PA, a lot of the older ones like lathe changewheels are 14 1/2 PA.

    [4] Now for the bad news. This cutter doesn't work on a milling machine but a specialised gear shaper.
    Image a vertical slotting machine with the gear blank mounted to a rotary table. The cutter, which looks just like a gear is on the ram.
    You set this off and as it travels by the blank it shapes the tooth form into the work.
    feed is applied to the D+f figure on the cutter.
    When this is reached you will have one tooth formed and two partly formed ones, one either side. You then start the bank AND the gear rotating in mesh and after one revolution you have a finished gear.

    This is the simplified description as you often take one cut near to depth and a finish cut after.
    If your cutter as in this case is 48 teeth and you gear the table and cutter 1:1 you will cut 48 teeth on the blank.
    Gear the table 2:1 increase and you will cut 24 teeth. Setting the gearing is like setting screwcutting gears but you normally have a chart.
    Unfortunatly they don't have a lot of use in the home shop.

    John S.

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


    • #3
      Ahh so... I guess I'd never really paid much attention to that word 'shaper' appended to those.
      So as I'm understanding this, the Fellows gear cutter shaper is being forced thru the blank in broadside fashion.

      Thanks John.