Gear Teeth thickness problem.

[nikolatesla20]

I just finished making a small CNC hotwire cutter (see thread http://www.cnczone.com/forums/showthread.php?t=12187). I figured I would try it out in cutting gear shapes out of foam just to see how it would do. It doesn't have any trouble cutting circular shapes or drawing them, and seems pretty accurate.

The one thing I noticed though was that when it either drew a gear shape using a marker that I attached to it, or cut it out of the foam with the hotwire attachment, that the gear looked weird - the very top and bottom tooth were a little skinnier, and the very left and right tooth were a little wider (in this case they were taller than normal). (see attachment) Note that the teeth aren't out of round wider or narrower, it's only the tooth width that is affected.

It also didn't seem to be a machinery problem because when I cut a gear blank in which the gear DXF file was rotated to the left a bit, the teeth did the same thing, the ones close to vertical came out skinnier.

It doesn't seem like backlash, since when the bottom or top teeth are made the X axis is moving the same direction the whole time.

I don't know if maybe it's a software setup problem? I'm doing this using Mach2, and just importing a DXF from DesignCAD3d.

Here's some pics showing my machine layout, and then a gear blank image, and what happens when it's drawn or cut by the machine.

Maybe it is mechanical, has anyone ever experienced this before?

-niko

[HuFlungDung]

Check your profiles for improper arc tangency and/or poor trim. Copy one of the good teeth and copy and rotate it into all the required tooth positions.

I don't know if Mach2 refuses to move if the arc center is incorrect and issues an alarm, or whether it attempts to complete the move anyways. Non-tangent arcs could explain why you are getting some weirdness. Garbage in, garbage out.

[ViperTX]

Also, which teeth are as they should be...?

[nikolatesla20]

Thanks for the tip HuFlungDung, I looked at Mach2 again and I think it might be how I imported the DXF, I think the "connection tolerance" setting was not good, it's default is .1 , I tried .0001 and it seems to look more correct in the software now in the drawn toolpath, but I'll have to try drawing it with the machine first to see how it goes.

I'm thinking this is probably just a DXF conversion issue. If so maybe I'll try sheetcam to generate the code instead.

-niko