On Wed, 25 Jun 2008 22:38:19 -0700 (PDT), wrote:

On Jun 25, 10:37*pm, "Tom Gardner"
wrote:
I want to turn a 4" OD x 3/8" thick gear 80 to 110 degrees in 100 ms. *I'm
thinking of a 4" stroke by 1-1/4" bore air cylinder attached to a rack gear that
would engage the round gear. *No, I won't do it with a servo! *I'm thinking a
1/2" round rack gear in a tube with Thomson linear bearings and a scallop cut in
the middle of the tube to expose teeth to the round gear. *This seems simple and
cheap. *In fact, it's so simple it would seem that it should be an off-the-shelf
item! *I just assume it would be easier to do with round rack than square rack.
Is this available or did I invent a new wheel?

The gear would just spin back and forth and the air cylinder/rack will have an
adjustable stop to get my 80 to 100 degrees rotation. *The round gear will have
a one-way clutch installed because I only want the one direction of shaft
rotation. *The shaft will power a wire feed mechanism to feed 3" to 3-1/4" of
wire.

They make pneumatic rotary actuators to do exactly what you want, turn
a shaft through a partial revolution and back. Kind of like a super-
sized version of the old vacuum windshield wiper motor, uses a vane in
a chamber driven by pressure, not vacuum. Might explain why you don't
see a geared actuator like you describe. Unless you've got a lot of
scrap parts laying around, might be the cheaper way to go!

Stan


I thought I sent one of those to Tom already?

Gunner