Converting guillotine from manual to air power.

[sparky mikeParticipant @sparkymike]

I have a treadle operated guillotine which I want to convert to air ram cylinder working. I have compressed air on tap and intend using two air rams, one each end of the machine, to work on the treadle arms.

I have located a ram 20mm bore and 500mm stroke , but not sure if two of these would be ok.

Not sure how to calculate the poundage each ram would develop at say 80psi.

The force needed is just over the weigh of a normal human being. Say 12 stone. I would be interested to hear from anyone else who has done similar conversion.

Mike.

[sparky mikeParticipant @sparkymike]

[noel shelleyParticipant @noelshelley55608]

35Lb per cylinder. 32mm would give you 100Lb per cyl at 80psi. 2 would work on your guidelines. Noel.

Thats the maths !!! But an air cylinder will be like a spring – once the load has gone if there is nothing to stop it it will go full stroke. Hydraulics would be more controllable.

Edited By noel shelley on 11/01/2020 18:30:52

Edited By noel shelley on 11/01/2020 18:31:55

[sparky mikeParticipant @sparkymike]

How about if a small bleed hole was drilled in the cylinder wall, just past the point where you want it to stop ?

Some kind of lever operated valve would also be required to turn on on off the air supply. I don't need return air supply as the beam springs will do that job, but I would think that yo would need to vacate the air from the cylinder after the stroke or it would then become a vacuum ?

Mike.

[David George 1Participant @davidgeorge1]

Have you thought of using an Air oil converter to make hydraulic pressure which is more controllable. You just need a double cylinder with air pressure to compress the hydraulic oil which in turn operates the cutting cylinder.

David

[Martin CargillParticipant @martincargill50290]

Noel, you may want to check if your calculator is working correctly. A 20mm bore cylinder operating at 80 psi will generate 49 pounds of force, a 32 mm one will generate 127 pounds of force. This assumes you are using the side of the cylinder that does not have the rod in it, the side with the rod will be less powerful.

Using air cylinders for this type of operation is difficult, they never operate as a pair, one always tends to lead the other no matter how hard you try to regulate air flows etc and in air systems you need to regulate the air exiting from the other side of the cylinder, not the air going into the cylinder.

David's suggestion of using an air over oil system is a better idea but it tends to be messy to set up and modern air components don't like to be in contact with oil – it tends to destroy the seals. I used to look after an air/oil system on a machine that cut the sides for coffins, we had to replace all of the valves every two or three years because they would begin to leak, in addition we found that push-in type air fittings would weep a tiny bit of oil every time the air (oil) pressure reduced to atmospheric, We has to pipe the system with copper pipe and compression fittings to stop the oil leaks.

Martin

Edited By Martin Cargill on 12/01/2020 15:11:14

[sparky mikeParticipant @sparkymike]

I suppose you could say if compressor was at 80psi, if the piston was the same area as one square inch, taking into account the piston rod, then you would get a force of 80 lbs on end of the ram, or would pressure split between foot of ram and head ? I was getting a rough idea of what is needed and then probably try one of the Chinese rams on that auction site. One with 500mm stroke is only £20.00, so in the event of failure then not too much to waste. Those with the four external tie rods look to be a stronger proposition, than those where the ends are just screwed into the alloy sleeve.

Mike.

[Martin CargillParticipant @martincargill50290]

If the piston area is 1 square inch then it will generate 80 pounds of force when 80 psi is applied to the cylinder. The rod end will generate the same force minus the cross sectional area of the piston rod.

The type of construction of the cylinder does not make much difference, the type with a round body are normally steel with alloy ends crimped into the cylinder, they tend to have an end that has a mounting flag with a single hole. The ones with tie rods tend to have a flat end and the mounting bracket is a separate part (purchased separately).

If it is going to be a problem that the cylinder will slam out to the end of the stroke after the cut, then try to get cylinders with damping built into them – they have a small(adjustable) section at the end of the ram that slows the motion at the end of the stroke.

Regarding the size of the rams you need I would be tempted to go oversize on the diameter – Its easy to reduce the pressure and therefore the force, but not so easy to go the other way…

For control you need an air valve that will allow the operating air to escape during the return stroke otherwise the springs will not be able to pull the cylinders back to the start position i.e. not just a simple on/off valve.

Martin

[OldironParticipant @oldiron]

Posted by sparky mike on 12/01/2020 15:50:10:

I suppose you could say if compressor was at 80psi, if the piston was the same area as one square inch, taking into account the piston rod, then you would get a force of 80 lbs on end of the ram, or would pressure split between foot of ram and head ? I was getting a rough idea of what is needed and then probably try one of the Chinese rams on that auction site. One with 500mm stroke is only £20.00, so in the event of failure then not too much to waste. Those with the four external tie rods look to be a stronger proposition, than those where the ends are just screwed into the alloy sleeve.

Mike.

What auction site would that be then ?????

regards

[vintage engineerParticipant @vintageengineer]

The formula is simple. Area of piston times pressure gives you force.

[John ReeseParticipant @johnreese12848]

Posted by David George 1 on 12/01/2020 09:08:38:

Have you thought of using an Air oil converter to make hydraulic pressure which is more controllable. You just need a double cylinder with air pressure to compress the hydraulic oil which in turn operates the cutting cylinder.

David

Definitely air over oil. Throttle the oil going into the cylinder.

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