Stomp shear converted to pneumatic

[forhire]

At the beginning of summer the I was given a fairly abused and broken stomp shear. It appears to be a Grizzly G5772 - 52" Sheet Metal Shear. Someone stomped in the middle and broke the treadle and egged out all the pin holes. All said, everything else looked OK so I toyed with fixing or upgrading. Of course I opted for the latter. I didn't take a lot of photos but I thought I'd post what I had in case anyone else wanted to try something similar.

The original treadle consisted of three quarter 2.5"x0.25" flatbar arms. They were bent beyond reusable so I simply torched them off and cleaned up the pipe on the lathe. This will come back to bite me later. Next I ordered some cheap 4"x8" pneumatic cylinders and hardware off amazon. I figured this will give me enough grunt. I likely could have used shorter cylinders but my my quick math put me in the ball park. Maybe I should have made my arms an inch or two longer.

I then drilled and tapped the table for the cylinder mount. I thought about a bunch of other mountings but this was quick and dirty. I was surprised how thin the table was, maybe 3/8"... maybe less. In my mind I was thinking a half inch or better. This may bite me but so far the cylinders haven't popped up though the casting.

I drew up some arms in cad and machined the hinge end and bent them on the press. I then cut them to length on the band saw and machined the cylinder end. The fit was perfectly. I then stitched them together with some 7018 and test fit them on the shear. Everything was going great until I tried to shear some 100 thou aluminum, the maximum for aluminum according to the specs. This twisted the factory pipe, leaving the arms about 10 degrees apart. Argh, I was afraid of that. So this morning I pulled everything back apart, clamped on arm to the welding table and straightened it with a long length of bar. I then found a length of square tube in the scrap pile and burned it in. No bending or flexing now.

My foot pedal is only single acting (3 way 2 position), and I was hoping the return springs would be enough but not really fast enough for my taste. I even tried plugging the cylinders to cause them to spring. I guess I'll need to get a 5 way foot pedal for double acting.

Overall I'm happy with the results. Much easier than stomping. Even with air it's no Pexto.

[Boostinjdm]

Do the cylinders stall or load up when cutting near full capacity? Or did you turn the pressure up enough to easily cycle through?

[forhire]

Do the cylinders stall or load up when cutting near full capacity? Or did you turn the pressure up enough to easily cycle through?

I haven't done full capacity yet but 2' wide was no issue. I still need to fix the the beam tension bolt that was stripped out before I can do a full width test. I'm at about 100 psi and it cycles very well aside from the return being slow.

[Virgil5]

I'm seeing 2 issues. First is the air lines to the cylinders from the valve need to be equal length so both cylinders act together.

Return might be slow because you need to open the ports on the end where the brass plugs are.

Depending on how long the supply hose is there might be advantage to pigging the machine ahead of the valve as well.

[Boostinjdm]

Reread it Virgil. He added the plugs to the dead side in an attempt to make an air spring for the return. Equal length air lines won't do wat you think. Air (and other fluids) will follow the path of least resistance. In this case it means the cylinders will apply equal pressure, but may not travel an equal distance. Also, the rake of the blade comes into play. The left side will hit first. This is what makes the torque tube important. The torque tube mechanically syncs the cylinders, but it needs to be stout as Randy found out.

[forhire]

I'm seeing 2 issues. First is the air lines to the cylinders from the valve need to be equal length so both cylinders act together.

Return might be slow because you need to open the ports on the end where the brass plugs are.

Depending on how long the supply hose is there might be advantage to pigging the machine ahead of the valve as well.

Good point on the hose length. The brass plugs were installed to create an air spring. It worked but I wasn't happy with the solution so I tore it back apart this morning and I re-adjusted everything. I was able to take up the 2" of lost travel. It's now returning fully on it's own and I'm now using the full 8" of stroke. I milled a bolt for the strong back tension. Stoned the knives and adjusted my 0.002" gap. It's can cut paper full width so I must have it correct. I also omitted the brass plugs as it is returning fine with everything cleaned up and adjusted. I also discovered a bolt that was dragging on the lower knife that I suspect was the real culprit.

I ordered a new foot pedal last night.

[Virgil5]

There is a specific valve made for unrestricted flow in one direction and adjustable flow in the other direction. Someplace I have a box full of them, but I can't immediately recall the nomenclature or location of that box.

Honestly, more I think on it, the more I'd want to pig it for maximized available air in the cut.

[forhire]

I replaced the foot valve with a 5 way valve. Now the cylinder is double acting. Speed is a lot better because this valve as it bigger. Today I sheared full width 16 gauge (0.05) 5052 aluminum like it was nothing. I also did 3' width of 10 gauge (0.1) 6061 fairly easily, although I may need to adjust the gap if I'm doing a lot of 10 gauge. I also did some 18 gauge steel very easily. The power and speed are great. I couldn't be happier. I'm simply too old and skinny to handy a jump shear anymore. Now that I've used it I can't imagine going back.

[farmersamm]

Reread it Virgil. He added the plugs to the dead side in an attempt to make an air spring for the return. Equal length air lines won't do wat you think. Air (and other fluids) will follow the path of least resistance. In this case it means the cylinders will apply equal pressure, but may not travel an equal distance. Also, the rake of the blade comes into play. The left side will hit first. This is what makes the torque tube important. The torque tube mechanically syncs the cylinders, but it needs to be stout as Randy found out.

Don't you mean the cylinders won't travel at the same speed, rather than not being able to travel an equal distance?

I'm thinking that ultimately, when charged with air, both cylinders will move to full extension, but may not do it in a synchronized manner.

I noticed this effect when I was researching the design for my new grapple. Dual grapple (two arms) designs won't close simultaneously, one cylinder always lags behind the other (this is probably because of non equal hose lengths like said earlier in the thread). I didn't go with 2 grapples because I felt it was not necessary, not because of the lag effect. Although I may regret not having 2 when it comes to handling non symmetrical stuff in the jaw.

[Boostinjdm]

You're too focused on hose length. If one was a couple hundred feet and the other only a few inches, I might agree to some extent. A T fitting will not split anything equally in a changing system. The reason grapple jaws don't move together is that one jaw always requires less force to move. That's where the fluid goes first. When it meets enough resistance, the next cylinder will start moving. Laying on the lever/button after everything has quit moving will eventually get you equal fluid pressure in all cylinders.

[farmersamm]

You're too focused on hose length. If one was a couple hundred feet and the other only a few inches, I might agree to some extent. A T fitting will not split anything equally in a changing system. The reason grapple jaws don't move together is that one jaw always requires less force to move. That's where the fluid goes first. When it meets enough resistance, the next cylinder will start moving. Laying on the lever/button after everything has quit moving will eventually get you equal fluid pressure in all cylinders.

I didn't accept that it was hose length, was just curious if it did indeed matter.

Interesting read I came across, not that I comprehend the full implications other than the need for monitoring, and compensating flow. Again the principle....flow is speed (or rate of extension for two different cylinders in the same circuit) http://www.sawyersystemsllc.com/site...0Cylinders.pdf

This leads to questions concerning front end loaders operated by twin cylinders. Are the cylinders ever actually synchronized until both cylinders are under full load? Seems there's some inherent instability goin' on I've never come across an ag loader with flow dividers.

[forhire]

For good measure I made the hoses the same length but in reality once I welded in the square cross tube they have been tracking well together. The reason it bent originally was due to be having it maladjusted. Once I equalled everything out it has been fine. It's getting a good slathering of safety yellow paint as we speak.

[farmersamm]

AHAAAAAA!!!!!!!!!!!!!!!!!

https://www.sunhydraulics.com/sites/...ivider-New.pdf

This addresses my question. When tied together by a beam, the lagging cylinder will cavitate, even with a flow divider.

I wish I'd never had to compensate the flow to my measly little cylinder...…….it's opened up another world of ignorance

[farmersamm]

To clarify...….reason I questioned the goin's on in a FEL, is the fact that the cylinders are tied together by a rigid assembly.

[Virgil5]

I always enjoy reading people's impressions of what is happening inside of pneumatic and hydraulic systems.
Sometimes I find myself wishing cylinders had windows in the side so we could watch what's really going on behind the wall.

Another thing I really enjoy is reading people's compressed air theory. Seems like those threads all eventually burn out after 16 guys post pics of their stack of pipe they are sure cools compressed air running up and down the wall in a room that is of the same temperature as the air receiver and the given by God himself Motorguard filter.

Me. I'm just a dumb old weldor who started with a gas torch and learned some Physics along the line. Never much needed a professor in a lab coat to tell me how to pipe air or water, I just know what works and what makes sense. I do enjoy reading some of the rocket scientist posts though.

[Boostinjdm]

Sam,
As far as I know, there is no way to guarantee two cylinders will perfectly match each other by controlling the fluid. The closest would be a metered divider. Which is more or less two gear pumps with the shafts coupled and even that is a mechanical means. Also, any internal leakage throws things out of whack. And there will be internal leakage as components age.

[forhire]

Today I made the foot pedal housing/handle. I've seen similar arrangements on commercial shears. Folded aluminum shroud with plate for the base to mount the pedal. I originally planned to using steel so it would have some gravity but the aluminum was in the scrap bin (note the random holes). Turns out it has plenty of mass as is. Handle is hot bent rod welded to a length of water pipe. The handle attaches with screws and uses PEM inserts for the nuts. The handle adds a fair amount of weight to the assembly. I still need to paint it.

[Virgil5]

Wondered how you were going to accommodate that little finger removing problem. Looks like it will work out well and give you some ergonomic quality to the machine.

[Lis2323]

Nice job on the extended handle. I have three foot switches I’ve been meaning to improve. Your project MAY motivate me.


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[Lis2323]

for hire... thank you for motivating me.












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[forhire]

Figured I'd post an update. It has been almost 2 years since I converted the shear over to pneumatic and I couldn't be happier. It has been trouble free. It's used almost daily for aluminum but we've done 16 gauge steel sheet full width without issue. Not bad for a hand-me-down. It's a lot easier and safer than it was as a jump shear.

This week I was asked to cut down a couple pallets of cardboard boxes for the FFA plant sale. Yes, it even cuts cardboard... I figured share a video. Not sure how many cycles it went through but it didn't miss a beat. Enjoy.

[55REDONE]

I followed your steps for the stomp shear conversion and it works great.

[farmersammm]

You always do nice stuff.