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Tom Gardner[_2_]

"Gunner" wrote in message
...
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

I didn't see it, I'd be interested in purchasing one if you still have one!