[adbuch]

Hi,

I purchased a new Pexto 16 ga. x 52" foot shear a about 5 years ago. Although this shear is rated at 16 ga. capacity, I have been told by a local machine tool dealer that it would require approximately 800 lbs of force on the foot lever to shear a piece of 16 ga. steel that is a full 48" wide. I am considering adding some sort of power assist to reduce the required operator effort. One possibility would be to use air cylinders for power assist. By this I mean the type of air cylinders that operate in the same manner as a porto-power ram. Another approach would be to convert the shear to full hydraulic operation.

Do any of you have any ideas or experience with this type of conversion, or have you seen a power upgrade kit that is commercially available?

Thanks,
David

[apache405]

if it only takes 800lbs of force on the foot lever, get 800lbs-(your body weight) in free weights from the sporting goods store. just lash the free weights on to the foot lever and then step on it your self.
a pulley system might be the cheapest way to go though.
going to air or hydraulic cylinders would require a redesign of the tool and a lot of work.

[sqatch]

I put a 4 in air ram on my tennsmith it works well at 120 psi. I also chopped the foot board off and closed in the front. This makes the machine a pleasure to use.

[malbeen]

I had a similar problem, I used the pump off a cheap pressure washer to power 2 small hydraulic rams the shear was 16 g rated I put an extra support in the middle of the shear and was cutting 6 mm plate 1ft long. the shears were made of steel not cast iron.
MBB

[rmarz]

David - I have the same Pexto shear (many years old), but when I bought it it had two air cylinders on it with spring returns that were actuated by a foot operated valve. I'm sure this was an addition that someone 'cobbled' together, but it works fine. If you want I could send you some photos later in the week.

Rick Marz

[rjohnson]

I think the two 2 inch air cylinders with a foot switch would be the way to go. double cylinders with a 3 way valve.

If you have employees this wouldn't be OSHA approved, with out some safety devices interfaced.

[rjohnson]

woops don't forget the flow control valves!

[sqatch]

Yes I had to put on a limiter on the exust, after cut through the ram takes off at mach 8.

[Geof]

[I]woops don't forget the flow control valves!

Yes I had to put on a limiter on the exust, after cut through the ram takes off at mach 8. [I]

Flow control valves do not help much with air.

Use an air over hydraulic system.

You want 800 lbs force so if you use two cylinders, one at each end of the foot plate, and your air supply works at 100psi you need cylinders with a bore of 2.5". Each cylinder will give you about 490lbs force so you have more than enough.

But you do not supply air directly to the cylinders, you have a reservoir filled with oil and this is connected to the cylinders through a needle valve to control the flow. The air supply goes to the reservoir through the valve you control.

You only need single acting cylinders because you can rig up a spring return.

The reason for using the air over hydraulic is that when you turn the air on it takes the reservoir up to full pressure very quickly. The pressure is applied to the cylinders through the oil but because there is a flow control valve the rate of movement of the shear can be controlled. And, most importantly, when the cut is almost complete and the required force is getting less, the flow control stops everything banging through with a great rush.

[rjohnson]

corcerning the flow controls I would put them on the cylinders so the flow is being controlled on the outlet side, free flowing one direction, as it flows in. and restricting on the port thats exhausting.
with single cylinders you loose that effect. hydraulic would be wonderful and smooth but would sure drive the price up unless you find some great deals, like on Ebay for the required equipment

[rjohnson]

I agree air over hydraulic would be a good way to go. If you can figure out the plumbing / valve setup. I have a globe underground lift that has. air over hydraulic. it works smooth. it has two control valves. one to charge it with air and the other is hydraulic flow control.

[MicroMill]

We just send the shop "fat kid" over there to stomp it down. )

[rjohnson]

in the reply that stated, the "flow control valves don't work very well with pneumantics"

I just want to mention the better equipment I have worked on that use air devices cylinders etc. the flow control valves are set up to free flow into a cylinder and restrict on the way out. (adjustable flow control) with a single cylinder you would loose that effect. maybe air isn't the best way to go, but it sure has the ability.

[Geof]

Two alternate ways are;

Get a long stroke jack and just put it between the foot pad and the bottom edge of the table. Slow but you get plenty of controllable force.

Just make an extension to the foot pad so you have a longer lever arm. It looks like you have the room to go twice the length.

[TheEquineFencer]

I realize this is an old thread, but I have a G-52a that has air operation on it. It has a big 4 inch looking cylinder to operate it but the lines are missing in places. That's how I found this thread, trying to figure out how it works. The foot pedal is cut off.