19 tpi
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# Thread: 19 tpi

1. Cast Iron
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## 19 tpi

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.

2. Aluminum
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Nice job, looks great!

3. Titanium
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Fantastic!! Many Thanks! Great info.

4. Could this be done in a 100/127 ratio for a 12CK?

5. Any time I need a change gear for my Logan, it gets made out of Delrin. They work great, last near to forever and are much nicer to the gear cutter.

6. And they are smooth and quiet running.

Tom

7. Cast Iron
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Conrad is being modest. I use a program he wrote to calculate 4 gear ratios for my hobber. His program calculates to 6 significant digits. It is a lifesaver for helical gears.

John

8. Cast Iron
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Cole, I am sure I could come up with a solution for just about any lathe for a metric gear. Send me pictures of your gear train and threading chart.

John

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