Pneumatic rack and pinion drive

(...)

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

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

For only about 90 degrees of motion you don't need the rack. just use the crank shaft - connecting rod rod type idea. That is, an air cylinder connected to a shaft with a lever arm. A short lever arm makes for very fast motion, less torque.

Karl

Just search "rotary actuator" on mcmaster.com.

I've seen a mechanism like that; my friend Jim invented it to swing the head on a die cutting machine in order to nest the cuts and save material. The guy who invented the rack-type rotary actuator invented it before him. Jim had cam followers supporting the rack where it meshed with the gear.

Presumably there's enough friction in the wire feed to prevent excessive overrun when the gear slams to a stop.

You have amazing vision, that's exactly what I want to replace, it's not tolerant of hard/soft/dry/oily wire.

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

We currently use a rather large urethane bumpers and they get the crap beat out of them even though the striker is 1" in diameter.

Have you seen the Ace Tubus bumpers? I've used a few and they seem to work better than plain urethane bumpers, though I haven't tried them in an app where they get really beat on. McMaster carries a limited selection.

Sounds like a need for a valve that will give a burst to get the mechanism moving, let it coast most of the way (or continue feeding air somewhat more slowly than full on), then once it hits the stop give full pressure to hold it against the stop.

Maybe use a couple of valves actuated off the moving parts.

Dave

=========== Sounds like another fun project.

Only problem I see is that most off the shelf rack stock is square, and a round rack will have less tooth contact area which may not be a concern if the loading is light, unless the rack is cut on a flat of the shaft.

Can you turn the ends of a square rack round and put some round extensions on the ends to run in the linear bearings?

Cutting a flat rack on a round shaft should be no problem, but as the teeth on a rack are straight, it would appear that full teeth all the way around the shaft could be easily cut on a lathe with something like an Acme thread bit [14-1/2 PA] possibly with rounded corners for fatigue resistance. Depth of a 1 mm module /

Assuming a 4 inch PD, 3 inches is 85 degrees and 4 inches is 115 degrees.

Another thought is to use a worm gear setup but stroke the worm back and forth rather than rotating it. IIRC most worms are acme threads with a DP thread spacing, and this would give you an single envelopment setup for better contact and longer life.

A 1/2 dia round rack gear indicates a fine DP gear, possible like a 1MM module [20 degree PA] / 24 DP gear. For examples see

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

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

F. George McDuffee fired this volley in news: snipped-for-privacy@4ax.com:

Tom, we have an almost identical device feeding time fuse for cutting. The assembly consists of a one-way drum clutch inside the feed tire, moved through a portion of a revolution by a crank rod on the clutch whose outer end is moved an air cylinder. It moves the fuse from 1/2" to

I think that setup is simpler yet than what you described, and does exactly the same function -- precisely and repeatedly for years without any maintenance.

LLoyd

EEEEEEEEEEEHHHHHHHAAAAAAWWWWWWW!

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:

--Winston

It's similar to the way we feed staple wire but that uses a mechanical linkage and a ratchet and pawl rather than a one-way clutch. This is still in the running because it IS so simple,

Is that a yes, or a no?

Or did you just grab your chest?

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

Same deal

Gunner

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