DIY 20 Ton Forging Press: Part 2 - Pneumatic Controls


This is the air compressor, the jack motor, cylinder and all the hoses, valves and fittings to make the jack go up and down. The trick here is to have the ram stop and stay stopped when you are idle. I tried using the air switch with that came with the jack and whenever the ram wasn't going up, it was going down; that is being pulled by the springs. That's a huge waste of time and air as each new press you have to start the ram moving from it's lowest (retracted) point.

I needed a way for the ram to stay put. I came up with a two switch idea that uses a pneumatic cylinder to operated the release valve on the base of the jack. This way, one switch presses (raises the ram) and the other switch let's the springs do their thing and lower the ram.


Pneumatic cylinder, 50mm stroke. (Amazon has this one that will work just fine up to 145 psi.)
Three-way pneumatic foot switch. (I used this one VF200-08) This makes the jack go down.
1/4" NPT Milton Male
1/4" NPT Elbow
1/4" NPT Tee
1/4" NPT x 8" Nipple
1/4" NPT (Close) Nipple
1/8" NPT male, straight fittings
1/8" NPT male, 90° fittings
1/4" pneumatic hose (300 psi rating good)
1/2" flat washer
Screws to mount foot switches


Auxiliary springs, 2
1/4" x 3/4" bolt
1/4" x 2" all thread bolt
1/4" external tooth washer
1/4" hex nut
1/4" nylon lock nut
1/4" flat washers
10-32 x 1/2" machine screw
Schedule 40 1/8" x 8" nipple or similar black pipe
1/8" x 1" x 3-1/4" flat steel
1/2" x 3/4" x 1" steel
Teflon tape or pipe dope

This is the basic layout of the control system.

The mechanical coupler to the jack's release valve involves a little bit of fabricating. The parts need to be adjustable so as to provide enough travel for the valve to close and open with the movement of the pneumatic cylinder's ram. The ram moves 50 mm or about 2 inches.

The jack I bought came with a hand operated valve and a short piece of air hose. I needed some way to mount the valve to make it foot operated so I (over) engineered this switch frame thing.  It's made of some 1/8" steel about 3" x 4", two pieces of 1" angle and short piece of schedule 40 3/4" pipe.

I slightly enlarged the hole in a 1/2" washer to slip over the Milton male NPT threads. This threads into the air valve and holds the switch on the switch frame.

Once the switch is in and the Milton male is tightened it stays put in the frame. Now to drill a hole in the actuator to bolt a decent sized pedal on it.

For plumbing I used some nipples and elbows and a tee, all 1/4" NPT and some pipe dope to seal the threads. 

I positioned the two switches so that they are about in the same position on the pedal board. I used a couple of 5/4 deck boards. Use whatever you like. Heavy is good.

I used another 3" x 4" piece of 1/8" steel and a short 1/4" carriage bolt and nut to attach the pedal to the air switch. The airlines get connected and you should be off and running.

You'll need some 1/8" and 1/4" pneumatic control line connectors. The tee on the pedal board and the three-way switch need a 1/4" straight connectors.
The pneumatic cylinder needs two 1/8" elbow connectors. Make sure to seal the threads with Teflon tape or pipe dope.

For additional protection, I am putting the air hoses inside some protective tubing. I don't want hot scale burning a hole in the sensitive air hose.

Coupling the Jack's Release Valve to the Cylinder Ram

In normal use, the jack handle is fitted on to the release valve screw and turned clockwise to close the valve and counter clockwise to release. We need to couple this valve screw to an air actuated cylinder.

I started with a piece of 1/2" steel cut to 3/4" x 1" rectangle (C). I drilled it about center to slip over the jack's valve screw. I welded a 1/4" x 3/4" NC bolt (A) right over the hole.

It will go on a little ways, but the valve screw has a pin in it to hold the jack handle. I cut a couple of slots with a hacksaw and filed them out. I then drilled and tapped for 10-32 machine screw to act like a set screw on the jack's valve screw (B).

For the adjustable arm, I took some 1/8" steel and drilled a hole and a series of holes to make a slot about 1-1/4" long.  (D)

Finally a way was needed to attach the pneumatic cylinder ram to the arm.  Using the hex nut that came with the cylinder (E) I welded a short section of schedule 40 1/8"pipe (F) and cleaned it out with a round file.

Fabricating the couplers

The fabricated pieces are show here to help better make sense of them. This piece attaches to the jack's release valve screw and holds the arm.

This is a closeup of the pipe and nut that threads on to the end of the pneumatic cylinder ram. My nut was a metric 10 mm which came with the cylinder.

Here the adjustable arm is shown with the ram coupler attached to the arm. Note this is meant to be loose enough to rotate freely. I used one hex nut to lock the bolt on the arm and a nylon locknut to secure the coupler, yet still allow some play in it.

Here the arm is attached with a star washer and nut. The machine screw acts as a set screw. You can see the pin that's in the release valve screw and how it fits into the slots I made in the 1/2" steel.

The rear end of the cylinder needs to be fastened to the upper anvil holder so I used some 1" angle back to back.

Here's how it comes together. In the "going up" mode the pneumatic cylinder's ram is extended and it pushes the adjustable arm clockwise and closes the jack's release valve screw.

When in the "going down" mode, the ram pulls the arm to the left and opens the release valve screw, the springs pull the hydraulic jack's ram down in this mode.

Next will be making the dies...


mauricio said...

se podra usar de 30 toneladas? o con 20 toneladas es suficiente?gracia

Unknown said...

Thanks for this, it really helped me out. One question though that I'm having issues with. The release valve adapter with the 10-32 set screw keeps wanting to slip off after 2-3 cycles. I've made the adapter twice, one like yours and one that I made by cutting off the slotted end of the original valve handle then welding on a plate. It seems that no matter how hard I tighten the set screw, the adapter eventually slips off. Have you had this issue or know of an option to fix it?

D. Comeau said...


I haven't had issues with the adapter slipping off. I wonder if the set screw is gripping the the T properly. A quick fix might be to wrap some nylon cable ties around the block to ensure the valve handle doens't come off. If you could send me a picture of the pieces together I may be able to suggests something better. Email is knives at