I am trying to machine a spur gear, 20 deg, module 2...
Gear 1 with 35 teeth
Gear 2 with 85 teeth.
The sales person for the inserts says that the gears will have different tooth profiles because of the 2 different Diameters and number of teeth. .
As far as I know, there is no difference in tooth profile for the same module... Can anyone please confirm this?
Involute gear cutters need slightly different cutters as the number of teeth changes. The tooth profile might be similar, but you are cutting the space between the teeth, instead of actually cutting the teeth.
Typical involute gear cutter sets could have different cutters for gears with the following tooth counts
#1: 12-13
#2: 14-16
#3: 17-20
#4: 21-25
#5: 26-34
#6: 35-54
#7: 55-134
#8: 135 or more
Note: some companies label the cutters 1 through 8, others label them 8 through 1. The effect is the same. Each cutter is designed for a small range of tooth counts. The 35 tooth gear should be cut using a #6 cutter and the 85 tooth gear should be cut using a #7 cutter.
You will have less than optimum results if you cut both gears with a single cutter. It may still be functional. Friction may be slightly higher or backlash may be slightly different than expected.
I make my own gear cutters (fly cutters) for some years now. I started making them on the milling machine using the button method. In stead of using the "button", I use an end mill to machine the cutter. Nowadays, I turn the gear cutter on the CNC lathe. This only takes a few minutes. Because it is so fast and easy to do, i turn a cutter for the gear (tooth count) to make. I use silver steel that can be hardened by heating it up (cherry red) and then quench it in water or oil.
Spur gear tooth profile
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