I made this transposing gear for Daryl to cut 19 threads per inch. It is 57/60. The material is delrin. Much easier to deal with than steel for this application where it might be used 10 times in Daryl's entire machining career. For those who might think delrin isn't strong enough, a module 1 (25.4 Dp) gear can take upwards of 8 horsepower in a model helicopter, so the 16 Dp teeth here are plenty, plenty strong.
The gear ratio for a 20 tpi setting is:
24/60 times 60/(everything to the leadscrew) and that equals a carriage movement of 1/20 inches per thread. The 60 in the numerator
and denominator is the 60 tooth idler.
To increase the 1/20 inches to 1/19 inches multiply by 20/19. To keep both sides of the equation equal multiply the left side by 20/19
24/60 * 60/(everything else) * 20/19 = 24/60 * 60/(everything else) * 60/57
which reduces to 24/57 * 60/(everything else)
So using a 57/60 idler will cut 19 TPI on a 20 TPI setting.
It goes without saying that one needs to be very careful and concentrate with no distractions when playing around in the gearbox. If a nut is dropped into the bottom of the gearbox it will be a very unhappy day.
The gear ratio for a 20 tpi setting is:
24/60 times 60/(everything to the leadscrew) and that equals a carriage movement of 1/20 inches per thread. The 60 in the numerator
and denominator is the 60 tooth idler.
To increase the 1/20 inches to 1/19 inches multiply by 20/19. To keep both sides of the equation equal multiply the left side by 20/19
24/60 * 60/(everything else) * 20/19 = 24/60 * 60/(everything else) * 60/57
which reduces to 24/57 * 60/(everything else)
So using a 57/60 idler will cut 19 TPI on a 20 TPI setting.
It goes without saying that one needs to be very careful and concentrate with no distractions when playing around in the gearbox. If a nut is dropped into the bottom of the gearbox it will be a very unhappy day.
had to use my ...gasp. 25yr old Enco.
