Recent article on home made gears ?

I seem to recall recently reading an article on making your own gears/timing pulleys. I am remebering something that showed how to print out a template,
use a drill to make the teeth, etc.
I am even thinking it was in Servo. The problem is, I can't find it.
Am I halucinating, or can someone remind me when/where I would have seen this ? :-)
TIA
-Chris
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Christopher X. Candreva wrote:

Nobody makes their own ordinary gears unless they're into machine shop work for its own sake.
However, if you're really good at machine shop work, there are situations when gear teeth as an integral part of another part can be useful. See Rosheim's "Robot Evolution" book.
                John Nagle
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: Nobody makes their own ordinary gears unless they're into machine shop work : for its own sake.
Which was exactly my thought when I read the article, so I didn't bookmark/notate it. :-)
I am looking for an alternate way to make my motorized turntable (robot head). I was looking for a cog-belt type pulley in the range of say 6" OD, something that would fit on the outside of a hardware store lazy susan bearing. I haven't seen anything in that size range.
Then I (thought I) rememberd this article, and thought cutting something out of wood on the scale might work. But I can't find it.
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Christopher X. Candreva wrote:

The proper cross section for a gear tooth is a cycloid curve, not a circular curve. If you made it with a drill, it would be noisy, with high friction and lots of backlash. It would be crap.
To make good gears you need a vertical mill, a rotary table and a gear cutter. The right tools will probably cost you $500 to $700 new from Sherline or Taig. You could get them used for maybe half that. Of course, you could use them for much more than making gears, and if you are serious about robotics, you will probably end up buying a mill, lathe and rotary table eventually anyway.
For small gears, you can buy extruded brass or plastic "pinion wire". When you need a gear, just slice off a piece.

Maybe a bicycle chain and sprocket?
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Christopher X. Candreva wrote:

You can always attach the timing belt sprocket to a central shaft of the turntable (most turntables don't have a shaft, but you can add one easily enough). This approach has the benefit of allowing for quite a bit of misalignments.
Or, a plastic flexible rack -- as in rack-and-pinion -- also works. I use them in various homebrew animatronics I build for the family. You glue or otherwise fashion the rack piece to the side of the turntable. A pinion gear on the motor engages the rack. Alignments are more critical, and you may need to put the motor on a spring load.
-- Gordon
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: You can always attach the timing belt sprocket to a central shaft of the : turntable (most turntables don't have a shaft, but you can add one : easily enough). This approach has the benefit of allowing for quite a : bit of misalignments.
That's what I'm doing now. In fact we beat this part to death a few months ago (use a torsion spring on the motor, I wanted to use the pot for tenstion, you said it was a bad idea . . . . :-) This was the pic I posted
http://www.westnet.com/~chris/Robots/RobotHead-3.jpg
Now I feel bad. I REALLY apprecaite everyone jumping in with suggestions -- It just we all went through this already :-) I haven't had time to try out the list from last time. For some reason this idea came to me this morning, it was just bugging me that I remembered reading this but couldn't find it.
So I'm going to assume I either made up this article, or it was such an abysimally bad idea I was right to toss it in the first place.
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Christopher X. Candreva wrote:

Now I remember!
This approach will work as long as the pot is not connected to the same belt as the drive. Otherwise there is too much overhung load on the shaft of the pot, and it may wear out pretty quickly.
-- Gordon
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On 26 Mar 2006 18:01:54 GMT, "Christopher X. Candreva"

If the head only turns something like 180 deg. (not contineous rotation), then you might could use string secured around the turntable edges and connected to a double spool on the motor, Since the string is firmly attached to the spool and the turntable, you don't have to worry about slipage. The spool both takes in the string in one direction and lets it out in the other.
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    --You might want to see what Bryan's doing with a cnc controlled wood router:
http://www.bmumford.com/xyz/details/gears.jpg
    
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Hacking the Trailing Edge! : carne: all is Zen..
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