[RICHARD ZASTROW]

watchman, You might snoop around and find a diagram of how a gear tooth is generated by hobbing or shaping. The involute form is generated by a number of cuts by a straight rack form. Its actually a series of flats. The more passes, the more flats the closer the final tooth form to a true involute. If the gears in question are spur gears, you should be able to position the spindle axis and rotary axis then cut the teeth along the axis parallel to the gear centerline. The more cuts per tooth, the better the tooth form. Stack multiples of any gear and place extra stock on ends to prevent excessive burrs or damage at start and finish breakout. If they are flat, personally I,d have them cut on a wire EDM. Mitsubishi has a great gear program as an option.

[watchman]

Thanks guys, all good information but I think you may have missed the info on the type of gears I'm looking at cutting. these are gear wheels and pinions for watches - something like 60 teeth on the wheel of 3/8inch diameter! The tooth form has to match the existing wheels which are always cycloidal in form not involute. Cycloidal teeth have straight parallel sides up to the pitch circle and then a semicircular curve from each side meeting at a point forming the addendum. I have drawn out the path of a tooth and the path a cutter would have to follow in the Z and Y axes whilst the work turns about the X axis but it isn't a constant amount. that is, I couldn't just tell the machine to rotate the work D degrees while moving the Z to E and the Y to F. Is it possible to use mathematical expressions in G-code for the Y and Z values or could I perhaps ..... its just occurred to me - I guess that if I just draw a curve plotting Z against Y in a CAD program and generate the G-code from this I could just edit in a rotation of the A-axis to generate the curve of one side of the tooth, repeat it mirrored for the other side of the tooth and then use this as a subroutine to cut the right number of teeth - would this work?? Thanks..

[Karl_T]

Cycloidal teeth have straight parallel sides up to the pitch circle and then a semicircular curve from each side meeting at a point forming the addendum.

..... its just occurred to me - I guess that if I just draw a curve plotting Z against Y in a CAD program and generate the G-code from this I could just

Thanks..

You just described the problem. Each side of the tooth is a linear move in Z and Y, followed by a circular move. Use Cad to solve for your values and make a subroutine to cut each tooth. Rotate A and repeat.

Karl