All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Change gears for a 27 TPI thread

**jackssmirkingrevenge**:

Ah I think I understand better, I was making a spurious correlation between the lead screw thread and the cut thread.

The lead screw advances 3mm per turn, so for a 1mm thread we need it to advance 1mm, so 1/3 of a turn for every turn of the spindle.

--- Quote ---for example if you have a 10 tooth gear driving a 20 tooth gear through an idler, the output shaft will turn in the same direction as the input shaft, but at half the speed.... It does not matter if the idler is 10 teeth or 100 teeth, and even number or an odd number....

--- End quote ---

This is what the setup would look like:

"A" is on a shaft that turns at the same speed as the spindle while D drives the lead screw.

If to cut a 3mm pitch thread the ratio is 1:1 between A and D, then I would expect a 2:1 ratio for a 1.5mm pitch. The listed gear combination for 1.5mm is 70, 80 and 35 which gives us exactly 2:1 which makes sense.

By the same logic, I would expect a 3:1 ratio for 1mm and 6:1 ratio for 0.5mm, however in practice:

1mm: 60 - 110 - 45 gears for a ratio of 1.333:1

0.5mm: 50 - 110 - 75 gears for a ratio of 0.667:1

This is what doesn't seem to make sense.

**rsterne**:

You have 4 gears, but only give 3 tooth sizes, which I find confusing.... Gear B & C turn at the same speed, correct?...

Bob

**jackssmirkingrevenge**:

B and C are on the same shaft, for some combinations it's a single gear.

**sb327**:

In your example we are discussing you gave a combination of 60, 110 and 45.

Something is missing.

Dave

**jackssmirkingrevenge**:

In that case It would be 60, 110, 110, 45

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