Reply To: Spacing of buttons for making involute cutters

[Neil WyattModerator @neilwyatt]

If you study figure 89 on page 113 of Ivan Law's book, it becomes apparent (after sufficient brain-wrangling) that the centre distance and infeed can be calculated by a certain amount of extra trignometry or by a graphical method (on paper or computer screen).

Darn it, it's easier to do than describe -does this help?

WARNING – INFEED DISTANCE IS WRONG – I SHOULD HAVE DRAWN AN INNER CIRCLE OF RADIUS 1/2pcd-DEDENDUM AND MEASURED FROM THAT!

Otherwise this is correct for 14.5 degree 56 tooth gears at 1DP.

The basic distance between buttons is calculated from knowing the length of the arc between two opposing pitch points either side of a gap. The infeed is calculated along a line that bisects the arc between the pitch points. Much easier to draw than do the trig… just draw a pitch circle and base circle with four radii with angles between them of pitch angle, 180/number of teeth, pitch angle. Using fig89 as a guide draw the circles and measure off the diameter, spacing and infeed.

I know this can be done, as against the odds, I made a 20-degree cutter for 13-tooth 20 DP gears. They needed very slight easing at the base of the tooth spaces, but other than that worked fine with other home made 20DP gears.

For the record my figures were

Cutter No 7.5

Teeth 13

D 4.50"

C 5.65"

E 2.25"

Neil