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Originally Posted by D.Fahringer
With this web utility you will be able to generate accurate DXF drawings of ANY gear you will need. The laser should be able to directly import the DXF file you create and go to town on your new gears.
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It's convienient, but watch out if you want to cut those on a laser (or a waterjet or an EDM). The .dxf generated by this utility is only approximate--it doesn't contain a proper involute curve, instead relying on straight lines of just about the right proportion. For a large-pitch gear (over 20 or so), this might work, albeit with a lot of wearing-in necessary. For anything finer, I'd avoid it outright, except in an emergency (i.e. you need the 0.7 module gears yesterday, and PIC is out of the question because they take too long!).
Watch out for the potential for roundoff error when using this to create metric gears (by inverting the module and multiplying by 25.4)--it reports that my 84 tooth 0.7 module gear has 83.55 teeth (that's measuring at the intersection of the two straight lines on the tooth face--these should be a curve--and taking that to be the pitch diameter, then dividing in the module). Maybe this isn't intended to be the pitch diameter, but since there's nothing else specified....
This is a nice approximation for importing into a CAD system, if you feel the need to jazz up your drawings with actual teeth; bear in mind that I usually just draw cylinders in Pro/E, and mate them at the pitch diameter, or specify a few thousandths open centres (0.005" or so, depending on various factors).
So use it, just be warned that it might not produce "real" gears! (I've been searching for something like this that can put a real involute on the teeth, for exactly this reason--putting it on an EDM would simplify the supply chain for those stupid metric gears infinitely!)
P.S. Now that I look at the 20 pitch gear that it generates, there is more than one segment making up the "involute" surface--and there is no clearly defined pitch diameter--so maybe there is no roundoff error to speak of, and the intersection of those two segments on the gear face just happened to occur near where the pitch diameter was supposed to be. (So don't assume what I just did--that if there are two segments on a tooth face, that their intersection falls on the pitch diameter!) Also, finding several segments on the tooth face reinforces my thought that the accuracy of this tool diminishes with the decreasing pitch of the gear--big gears will have lots of segments, and therefore be better approximations (relative to their size) and small gears will be badly modelled.
P.P.S. So what? Maybe you could design a gear with 7 module, and scale it down by a factor of 10, and get a much improved approximation. Or 700 module, and scale by 1000. In fact, I think that I'll try that! (But careful: I know that CNC plasma and flame cutters don't always like lots of little segments on a toolpath--though they aren't accurate enough for gears anyway--but maybe EDM, laser and waterjet don't want small segments either?)