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looooo / freecad.gears

a gear module for freecad
GNU General Public License v3.0
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Enveloping worm gear #131

Open Gypaets opened 1 year ago

Gypaets commented 1 year ago

Feature request: enveloping worm gears. The worm gears currently present in the toolbox are just cylindrical, and it would be cool to have enveloping worm gears as well.

looooo commented 9 months ago

ref: https://forum.freecad.org/viewtopic.php?t=83797

azalanono commented 8 months ago

Hello.
I kindly want to ask if (and when, if not) gears matching a worm gear (the "screw-gear") will be implemented.

Because angle of teeth depends on diameter and module of "screw-gear", and also straight teeth do not match a "screw-gear" well, this is a very important but missing thing. almost half-round teeth are not so easy to generate.

I also refer to https://forum.freecad.org/viewtopic.php?t=83797 as looooo does.

slorquet commented 7 months ago

Hi,

I would also like this feature.

looooo commented 7 months ago

I tried to solve this, but failed. The problem were some numeric difficulties with finding the matching "involute" for the different cross sections. Also it's not easy to create the final gear from the computed cross sections. There occt is to blame. At the moment I do not have an idea how to implement the envelop worm gear.

azalanono commented 7 months ago

Looooo, Calculating and constructing wheel's teeth indeed appears to be a very complex task. But is this really nbecessary? I can tell you how I would do it in mechanical workshop (though it exceeds my programming knowledge, so I can't code that)...

Matching gear sets (the small worm gear and the matching big gear - let's name it wheel) are usually produced by using the principle of thread cutters. A "worm gear" shaped milling tool is used to cut the teeth out from the wheel. This is done in a milling machine: While the cutter is rotating, also the "wheel" is rotated, so the right shape of teeth is the final result.

Shouldn't this method be possible in FreeCAD, too?

First, I would generate a short worm gear of 1-2 turns. It should have a little bit oversized teeth to give the right free play.

Now we have to find the right diameter for the matching wheel. The circumference has to be a an even multiple of worm gear's pitch. This (pitch multiplied by number of wheel-teeth) gives the circumference and so it gives the radius (or better said the distance between centers parts).

Now all you have to do is rotate both (wheel and worm) in synchronous way in small steps and remove hereby repeatedly all excess material from wheel. So the worm gear acts like a cutting tool.

This is possibly not the fastest method, but can't most of that be already done by FreeCAD? I mean cutting away parts from one part in shape of another part?