Thread: Help converting guillotine to pneumatic operation

I’m considering converting my English made Edwards treadle guillotine to pneumatic operation. Problem being Is that I know just enough about pneumatics (and most other things in life) to understand I know nothing about it. Looking around on the inter webs it seems the most common way of doing this is to put a cylinder under the machine that actuates the treadle bar. The mechanism seems simple enough, the forces of actuation and control of those forces, ie the control of the air going in and out I don’t really know much about. I have 8bar (120psi) with around 130litre storage available and the line from the compressor to the guillotine will be less than 2m so loss shouldn’t be a problem.

At this point, if your response is likely this is dangerous don’t attempt it because you know nothing, please find another thread.. If I don’t do, I don’t learn....

In my head I figure I need a two way cylinder so I can control both up and down, I found the cylinder below, seems to have about the right stroke and a stack of mounting hardware attached that will save some fabricobbling but beyond that I have no idea of its suitability for this venture.
https://www.ebay.com.au/itm/Festo-Pn...e/123516764657

Id like a lever valve to operate it (I figure that keeps my hands away from any moving parts) but have no idea how to read the pictographs of operation on the side of them. I’m assuming I’ll need something that can shuttle ports so it can exhaust the side that has pressure when I wish to reverse the direction of travel, ie bring the blade up having just bought it down to cut. As I live in a residential area, I think an exhaust silencer would be a good idea too, assuming I need one.

Im also not sure how to size lines and the like, in my head my rattle gun needs big hose for correct operation but that cylinder appears to have smallish lines, so I’m not sure.

I’ll get a picture of the guillotine and the treadle mechanism later today.

Any help with my quest for understanding would be greatly appreciated.

Forgot to mention, the guillotine will cut 1030mm of 1.6mm mild steel, so I’d like to retain that.

Should not be too hard to come up with some sort of setup to make it pneumatic.
That ram you listed will give about 780 lbs force at 100 psi.
Depending where and how its mounted it should be more than enough to do the job.
What ever size hose you have at the moment will be good enough. We are not talking high flow here.
A 2 direction flow control valve on each end of the ram with lever or button hand control (or foot or bum control) and your done.

Tony

Thank you, tells me I’m on the right track.
How did you work out the force applied in relation to air pressure?

I'll start by saying I have no idea how they work and that its been so long since I saw one working its of no help at all, but I'm not so sure its that simple.
I think you need control of the exhaust flow.
Lets say you are cutting 1.6mm 3/4 of your machines max width.
The pressure side of your cylinder is up around 100psi as it cuts the sheet.
About 3/4 the way through the stroke the cutting force required is going to fall of rapidly*, but your cylinder is still at 100psi, things are going to move quickly from there until a short while later they stop with a bang.

Maybe I'm over thinking things?
Perhaps they just have a big rubber stopper somewhere?

*even hydraulic guillo's go off with a bang when the cut finishes, but as their pressure drops pretty much straight away they don't "fly" to the end of the stroke.

I might be barking up the wrong tree, but treadle guillotines generally have hefty return springs to raise the blade and treadle mechanism, so if you were to go pneumatic, I believe that you would only need a single acting ram to push the blade down, and the return springs should be able to raise it once you release the pressure on the ram, i.e it should not need to be driven back up.

Do you have any idea of the force required to push the treadle down to make a maximum width and thickness cut manually? You need to be able to supply that sort of force via the ram and flow the air to generate it fairly quickly into the cylinder. The ram you suggested at 80mm bore equates to about 7.8 sq inches by my rough calcs so at 120psi should be able to generate a force of around 930 pound, way more than you could achieve stomping on the treadle, and use about 1.25L of air per cycle (assuming single acting).

Valving could be as simple as a single two way valve with the common port connected to the cylinder, and the other two connected to supply and exhaust. I would suggest some sort of flow restriction/muffler on the exhaust port to slow the release of pressure, instantaneous release would be approaching the sound of a shotgun firing. If you purchased the double acting you linked, it would also pay to spend a few dollars and filter the air entering/leaving the second chamber to avoid having dust etc drawn in and scoring the cylinder wall (The active side doing the cutting would be using most of the cylinder length, and scoring would create leaks for that as well as the unused side).

Calculation method

convert 80mm bore to imperial and divide by 2 to give bore radius in inches = 1.57in
piston crown area is pi x radius squared = 3.14 x 1.57 x1.57 =7.8 sq in.
force =PSI x crown area = 120 x 7.8 =930 pound at 120PSI or 780 Pound at 100PSI

Air volume = piston crown area x stroke - I calculated using metric for this 8cm bore and 25cm stroke, no conversions to imperial required, pi x r squared x stroke will give an answer in cc's, 1000cc's is a litre.

Hope this helps

Originally Posted by racingtadpole

How did you work out the force applied in relation to air pressure?

Basically
Piston area x pressure.
22/7 X r squared X psi.
Sorry I don`t know how to type it out properly on a key board.

Tony

I just realised malb has it all laid out for you.

A small hydraulic damper could be fitted if it had a tendency to bang straight to the stops after the cut.
Should be a suitable donor on the rear suspension of the nearest mountain bike you can get your hands on

Force to actuate it can be tested by rigging up something to mount a weighing scale of some sort on.
Bathroom scales sat on a piece of board balanced on the treadle is probably about as quick and dirty as it gets.
Or a spring balance (fish weighing scale) hung on a bracket that's mounted to the treadle, with a loop of rope to stomp in.

Steve

Originally Posted by OxxAndBert

A small hydraulic damper could be fitted if it had a tendency to bang straight to the stops after the cut.
Should be a suitable donor on the rear suspension of the nearest mountain bike you can get your hands on

Force to actuate it can be tested by rigging up something to mount a weighing scale of some sort on.
Bathroom scales sat on a piece of board balanced on the treadle is probably about as quick and dirty as it gets.
Or a spring balance (fish weighing scale) hung on a bracket that's mounted to the treadle, with a loop of rope to stomp in.

Steve

Would not be the first time bathroom scales have been used to give a rough idea of the force required.

Not sure if the ram mentioned had air cushion ends but if not rubber cushion blocks can be mounted on the rod inside the ram.


Tony

Also, its been quite a few years since I last used guillotines, but we had 3 different types - hydraulic, flywheel, and manual treadle.
All had essentially a 2 stage operation - clamp, then a second actuation to cut.

Assuming yours has a clamp bar, I'd probably look at attaching the ram to the treadle bar on some sort of a sliding collar/rod arrangement. If you stomp on the treadle then it doesn't have to drag the ram with it, and means you can still do the clamping as an initial part of the travel with your foot, then hit the air and the ram will push the treadle down.
Also means you retain the completely manual operation if you just want to a quick cut or don't want to use the air (ie cutting at midnight).

Steve

Somewhat less scientific, takes another body to cut 16G somewhat more easily, which in my house means a total weight on the bar of around 140kg and is hilarious to onlookers...
My understanding is that the pressure required across the length of the cut will be relatively uniform as the blade is shearing at an angle, like a pair of tin snips, not cleaving the entire length in one go. The cutting edge is only ever shearing a cut that equates to the long side of the triangle formed by the thickness of the material and the angle of the cutting edge at any point through its motion. Please feel free to correct me if my thinking is flawed in that regard.
In the case of my guillotine there’s approx 300mm between the top lever stop and the bottom lever stop and the leaver itself is about 60mm. There is around 600mm of mechanical advantage between the pick up for the blade linkage and and the stomping bar. Picture of one side attached shows the mechanics. There’s a spring on each side to return it.

Having had a closer look at it while taking the picture, I’m wondering if I can remove the manual lever arms in their entirety and fit the cylinder up closer back to the linkage and streamline the footprint of the machine. Hmmm.. scope creep before we’ve even started... bahahaha!!! Those that have seen my workshop will see the reasoning in the insanity on that one.. Seems possible that using the Festo cylinder I linked at 100psi I have sufficient force available to accommodate a reduction in the length of the lever arm. The other thing I noticed that bodes well is there is a heap of space under the table and also quite a few solidly sized (1/2” or larger) bolts protruding in places that should make mounting the cylinder relatively easy.

Thanks you to those that explained the calculation of force, I had for some reason assumed that the volume of air required to fill the cylinder played some part in the calculations.

Thank you all for the input so far, very much appreciated

Originally Posted by racingtadpole

My understanding is that the pressure required across the length of the cut will be relatively uniform as the blade is shearing at an angle, like a pair of tin snips, not cleaving the entire length in one go. The cutting edge is only ever shearing a cut that equates to the long side of the triangle formed by the thickness of the material and the angle of the cutting edge at any point through its motion. Please feel free to correct me if my thinking is flawed in that regard.

Well if we wanted to be pedantic I think it would be material thickness minus fracture depth(which varies with clearance etc). But in general your understanding is correct.

If the above is related to my previous post read on.
If my maths is correct and we assume the "pick up for the blade linkage" is 100mm from the pivot. I make the stroke 36mm. if thats all used for cutting(which it won't be) that would mean you were sheering 28mm per mm of thickness per 1mm of stroke(if that makes sense). Cutting 1.6mm unless you are running your blade clearance tight you won't be cutting more than 1mm. So in less than 1mm of stroke you will go from needing "what ever pressure is to need to cut" to needing nothing. Now you have a cylinder with that pressure in it and nothing to do with it except accelerate to the end of the stroke.

Originally Posted by OxxAndBert

Also, its been quite a few years since I last used guillotines, but we had 3 different types - hydraulic, flywheel, and manual treadle.
All had essentially a 2 stage operation - clamp, then a second actuation to cut.

Assuming yours has a clamp bar, I'd probably look at attaching the ram to the treadle bar on some sort of a sliding collar/rod arrangement. If you stomp on the treadle then it doesn't have to drag the ram with it, and means you can still do the clamping as an initial part of the travel with your foot, then hit the air and the ram will push the treadle down.
Also means you retain the completely manual operation if you just want to a quick cut or don't want to use the air (ie cutting at midnight).

Steve

That idea has some merit, I shall ponder it further. The Edwards does have a clamping bar, around the first 50mm of movement on the treadle engages and bottoms the clamp bar.

Originally Posted by Stustoys

Well if we wanted to be pedantic I think it would be material thickness minus fracture depth(which varies with clearance etc). But in general your understanding is correct.

If the above is related to my previous post read on.
If my maths is correct and we assume the "pick up for the blade linkage" is 100mm from the pivot. I make the stroke 36mm. if thats all used for cutting(which it won't be) that would mean you were sheering 28mm per mm of thickness per 1mm of stroke(if that makes sense). Cutting 1.6mm unless you are running your blade clearance tight you won't be cutting more than 1mm. So in less than 1mm of stroke you will go from needing "what ever pressure is to need to cut" to needing nothing. Now you have a cylinder with that pressure in it and nothing to do with it except accelerate to the end of the stroke.

Could that not be overcome by putting a mechanically operated valve at the end of travel, so as it bottoms it opens and exhausts?

There is a mistake in my maths above, I used a lever arm of 600mm, connection at 100mm from pivot and 240mm as the stroke. But the stops are at more like 300mm from the pivot not 600mm so the stroke becomes about 480mm making the stroke of the blade more like 80mm

Originally Posted by racingtadpole

Having had a closer look at it while taking the picture, I’m wondering if I can remove the manual lever arms in their entirety and fit the cylinder up closer back to the linkage and streamline the footprint of the machine. Hmmm.. scope creep before we’ve even started... bahahaha!!! Those that have seen my workshop will see the reasoning in the insanity on that one.. Seems possible that using the Festo cylinder I linked at 100psi I have sufficient force available to accommodate a reduction in the length of the lever arm.

If my maths is right, to fit the cylinder about where the lever stops are you you'll be at about 80psi
140kgs*2.2=308lbs
308/7.8sq inch= 39.5psi
39.5*2 because the lever is about 1/2 as long=79psi

The cylinder cant go much further out as you'd run out of stroke

Originally Posted by racingtadpole

Could that not be overcome by putting a mechanically operated valve at the end of travel, so as it bottoms it opens and exhausts?

I don't think so, even if you could it would be loud.
It might only be an issue on wider cuts of thick material. Maybe build it assuming I'm wrong but have some rubber blocks handy.

To say what I am talking about another way. When you have 140kg on the pedal and the sheet shears, you and your assistant are limited to accelerating at the speed of gravity give or take. The cylinder isn't. Maybe the masses involved are enough to make what I am saying insignificant?

Just 10 days ago I put a cylinder on a little old 24” Pex, Stow and Wilcox guillotine (old, as in 1895 cast into the blade). I started as Tony suggested in post 9, a test cut using bathroom scales to size the cylinder. As it is just cutting laminated cardboard/plastic it only needed 80 pounds on the treadle, 1.5inch cyl was plenty..
I used a 5 port 2 position valve, single solenoid operated. The blade is driven in both directions. Needed a 24Vdc power supply and a microswitch. Also guarding so no can get their fingernails clipped.
The cyl in the shown original post has cushioning at each end of its stroke, adjusted with a screw in the threaded holes near the connection fittings. In addition it is fitted with two adjustable flow controllers. These allow free flow into the cyl, but restrict the exhaust flow out, giving really good speed control, right down to the point of not moving. The airlines look about 10mm, should be fine. If it has enough thrust all should be good.
Test with the scales. If you need to leap up and down on the treadle to cut 1.6mm steel might need a rethink!