Worm Gear/Wheel Spacing

I cannot use my CAD (AutoCAD 2005 Mechanical) to draw worms and worm wheels, merely spur gears and that was an add-on that I purchased from a talented user.

There is a virtually identical relationship of the pitch line of the worm and worm wheel with the major and minor diameters, just as in spur, helical, and bevel gears. So you are correct in that regard.

In the end, I think your worm gear tool is leading you astray. The add-on that I purchased draws quite correct tooth profiles, however it has a weirdness as well. It always draws a gear that is "rotated" a slight amount-generally less than 0.5 degrees and if I want it to be perfect I have to strike two (2) lines, measure the variation in displacement, and rotate the entire gear by one-half of that amount.

Evenso, it sure beats trying to draw an involute form, especially with a small number of teeth because I am a stickler for wanting them to at least look correct. Perhaps no system is perfect?

Ing. Robert Forbus