Pneumatic rack and pinion drive

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.
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Tom Gardner wrote:

(...)
Are you converting from linear to rotary to linear motion? How about just an overrruning clutch and pinch roller mounted on the end of your air cylinder shaft? Less mass. Fewer parts. Cheaper.
--Winston
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You have amazing vision, that's exactly what I want to replace, it's not tolerant of hard/soft/dry/oily wire.
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Tom Gardner wrote: (...)

Ah.
In that case I would press the gear on to the end of a combined clutch/brake. I would run the drive motor continuously and feed the wire by actuating the clutch, then I would throw out the clutch and actuate the brake at the end of 'stroke'. Heck, for your app, you could use opposite poles of a SPDT relay. If the brake isn't on, the clutch is feeding your wire.
Have a look at the combined clutch/brake units on page 27, 28 of: http://www.orttech.com/files/pdfs/em206.pdf , for example
--Winston
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Interesting, a quick calc says I need 0.2 hp motor. Motor and clutch won't fit in the amount of room I have available...easily. But, there are many, many ways to skin a cat.
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wrote:

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
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On Wed, 25 Jun 2008 22:38:19 -0700 (PDT), snipped-for-privacy@prolynx.com wrote:

I thought I sent one of those to Tom already?
Gunner
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I didn't see it, I'd be interested in purchasing one if you still have one!
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On Thu, 26 Jun 2008 11:11:20 -0400, "Tom Gardner"

Geeze....email me your freight info again..Since Ive been on a kick to trash stuff...Im down to the pneumatics section in the stacks O stuff
Tell you what...Ill email you pictures of the stuff..and if you want..Ill ship you the entire lot. Might be several thousand pounds of cylinders, etc etc. All NOS, ablit some has some surface rust in non critcal places
Free..you pay for the shipping
Gunner
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EEEEEEEEEEEHHHHHHHAAAAAAWWWWWWW!
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On Thu, 26 Jun 2008 16:13:43 -0400, "Tom Gardner"

Is that a yes, or a no?
Or did you just grab your chest?
<G>
Say..you dont need v and timing belts do you?
If you dont mind picking out the leaves and the dead bugs, Ive got a 4x4x5 steel container filled with them.' Probably a thousand or so in there, all NOS, Gates, Martin, Browning, long, short, skinny, fat..As and Bs, etc
Same deal
Gunner
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On Thu, 26 Jun 2008 16:13:43 -0400, "Tom Gardner"

Oh..if you take the belts...Ill toss in all the right angle drives, most of the Reeves drives, lovejoy couplers and most of the 3ph electric motors, leaving only a few of the machine tool specific motors. And any and all pneumatic valves, solenoids, manifolds etc..though it might take another pallet. Or 2. Or another one of those 4x4x5 scrab bins....
Frankly..Id rather you had them, than give them to the scrappers.
Oh..and of course, all the Linear ways, ballscrews etc I already have boxed for you...that I keep forgetting to ship.
Need any welding rod or wire?
Gunner
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On Thu, 26 Jun 2008 16:13:43 -0400, "Tom Gardner"

If you are interested, call me. You should have the number
Gunner
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I will call! I can't use a lot of that stuff but pneumatics and linear stuff always comes in handy. I can't believe you aren't listing it all on eBay. For every ass, there's a seat.
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On Thu, 26 Jun 2008 16:13:43 -0400, with neither quill nor qualm, "Tom

I take it that that is an affirmative, Tawm? <guffaw>
I'm still working on the free stuff I got from him eons ago.
-- Deep doubts, deep wisdom; small doubts, little wisdom. --Chinese Proverb ----
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The down side of free stuff is when you have to replace it, just TRY and find that model!
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On Fri, 27 Jun 2008 00:09:12 -0400, with neither quill nor qualm, "Tom

Yeah, I'm still trying to locate worm gears for the old Wilton 4x6 saur I got. I should get tires while I'm at it, and by then, I'll be up to the price of a new HF 4x6. Hmmm...
Neely Bearing wanted $8 and change for the new idler General (Chinese) 62022 bearing for the drill press, with retaining ring. Another local bearing place, Applied Industrial Technologies wanted $20 for an identical SKF bearing and no snap ring. I should probably press that together one of these days. I already had a spare LinkBelt for it. I dare say that even a Chinese bearing will likely outlast me.
OK, time for the Heller syllabus...
-- Deep doubts, deep wisdom; small doubts, little wisdom. --Chinese Proverb ----
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    [ ... ]

    O.K. First question: "saur" -- sort for "dinosaur" to indicate the age, or just a creative spelling of "saw"?
    Second -- does the Wilton 4x6 actually *have* tires? The import one which I have from MSC has a cast iron wheel with a flange and a groove to clear the set of the 1/2" blade teeth -- no tire. I thought that all of the 4x6 saws were like this.
    Enjoy,         DoN.
--
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On 28 Jun 2008 03:27:44 GMT, with neither quill nor qualm, "DoN.

Hey, I got it from Gunner. It's a bit of both. <g>

That's the way this is, but someone recently mentioned tires on a metalworking bandsaw and it got me thinking that maybe I was missing something. This thing's pretty clapped out and the local ACE hardware stores now have ShopFox 4x6ers in stock for $149, so...
-- Deep doubts, deep wisdom; small doubts, little wisdom. --Chinese Proverb ----
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    [ ... ]

    O.K. Good enough.

    Hmm ... to put tires on it, you will need to totally re-turn the wheels -- get rid of the flange, and put in a groove for the root of the tires. And I don't know whether tires will work well with the design of the 4x6 -- toss in the sharp twist to the blades, and the short distance from the guides to the wheels, and I'm not sure what will happen.
    The benefit of tires is the ability to use a wide range of blade widths, and to make them self centering on large wheels which can't be easily tilted. There are tires on my Emco three-wheeled saw (with fiberglass-reinforced plastic wheels), but the blade is not twisted like the 4x6 does, and the guides are less aggressive.
    I would suggest keeping the flanged wheels for the 4x6 and just using it as a cutoff saw (it is pretty useless as a vertical saw -- not enough throat to allow much work guiding) and get something better with wheels for freehand sawing to shapes. That's what I do with the Emco three-wheeled one, which has three belt positions including one which gives a high enough speed to make sawing aluminum a lot better. But that is one tiny little belt -- some of these days it is bound to pop. I just don't have room for a proper floor-standing vertical. The 3-wheeler came from an eBay auction. Emco seems to have discontinued it.
    Enjoy,         DoN.
--
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