File:Gear 620 contact.svg

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This image shows two gears with involute shaped teeth. Their rotational position is such that a pair of teeth are just engaging in the lower left quadrant. Direction of movement is assumed to be towards the left.

The gears are drawn correctly (almost) according to the AGMA 14-1/2 degree involute tooth coarse pitch system. Both gears are the same. The major parameters of each are:

Number of teeth: 64

Nominal pitch diameter: 1280 pixels, or, assuming a scale of 80 pixels/inch, 16 inches.

Diametrical pitch (follows from the two above parameters): 1/20 teeth/pixel, or 4 teeth/inch.

Minor parameters follow from the AGMA standard, given the above major parameters.

Centre distance is standard: equal to the sum of the nominal pitch radii: in this case 1280 pixels.

The involute portions of the teeth are involutes of base circles. The base circles are shown dashed; they are the smaller circles; the larger are the pitch circles. Base radius is given by

Rb = Rp cos(pressure angle) = 640pixels * cos(14-1/2 degrees).

Rb is base radius; Rp is pitch radius.

The correct Rb, from the above formula, is about 619 pixels. I believe I made a mistake and used approximately 620 pixels as the base radius in the drawing. The error is not huge and I decided to leave it. To change it would mean redrawing the involutes and changing alot of other things.

This is an '.svg' image file, and the source is therefore human-legible. If one wishes to see the gears at different rotational positions, or different centre spacings, it is not difficult to edit the overall layer tags '<g transform="rotate(da, da, da)" . . . >' to achieve this. Please don't overwrite the present file with what you did though! It might be good to upload afew alternate views under different names though.