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

Change gears for a 27 TPI thread

<< < (3/7) > >>

I'm using this type of tool with a replaceable insert:

The steel is 12L14 which has been a bit of a revelation for me, I used to work mostly with brass and aluminum but these days I barely use them.

The part worked well so far, progress here

While my calculations worked I'm still trying to wrap my head around why the online calculators gave nonsensical results.  I calculated the required ratio relative to the existing combinations listed because trying to work from scratch it didn't seem to be congruent.

The lead screw pitch is 3mm, so to cut a thread with a 3mm thread one would assume that the gear ratio from spindle to lead screw needs to be 1:1, and that is indeed the case.

The gear combination listed for a 3mm pitch is 70, 35, 120 and 60 with the middle pair on the same shaft, so that's a 2:1 and 1:2 ratio which cancels out and gives us 1:1 between spindle and lead screw.

To cut a 1mm pitch thread, the listed gear combination is 60, 110 and 45.  That gives us a ratio of 6:11 and 22:9 which works out to 132/99 or 1.333 turns of the lead screw per one turn of the spindle.

In my head, to cut a pitch that is one third that of the lead screw, then the lead screw should be turning three times as fast, but that's not the case in practice, what am I missing?

A 3mm lead screw should turn .333x per spindle turn for a 1mm pitch thread.

I thinků.



--- Quote from: sb327 on June 14, 2023, 12:17:18 PM ---A 3mm lead screw should turn .333x per spindle turn for a 1mm pitch thread.
--- End quote ---

Wouldn't that give a 9mm pitch thread?  If the lead screw is turning slower then the cutting tool is traveling less per spindle revolution.


--- Quote ---A 3mm lead screw should turn .333x per spindle turn for a 1mm pitch thread.
--- End quote ---

Correct.... Each time the spindle turns one full turn, the 3mm lead screw advances 0.333 turns....  3mm x 0.333 = 1mm....

Is it possible your confusion comes from the fact that idler gears only reverse direction, and have nothing to do with the ratio?.... I have never used a lathe with change gears, so I am not familiar with the setup.... but 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....



[0] Message Index

[#] Next page

[*] Previous page

Go to full version
Powered by SMFPacks Media Embedder
Powered by SMFPacks Alerts Pro Mod
Powered by SMFPacks Ads Manager Mod