Poor Man's 20 Ton Air-Over Hydraulic Press

Last Date Revised: October 1, 2007




Here is an overview of my modified Chinese 20 Ton press with a Harbor Freight Air-over-Hydraulic 20 Ton jack and some special controls.

You can probably see that I have added a release valve cylinder and I plumbed the system so I can operate the jack in both directions from the (now) floor-located valves.
The release valve is a 1" Bimba spring return air cylinder that I had laying around for years, but I bought some more of them recently, so they are still available. They cost me about $16 each, direct from Bimba.

The very best feature of this design is that it leaves both hands available to manipulate the work. The second best feature is that the air motor raises the jack at least 5 times faster than you could do it by hand.
I mentioned this modification to a knife-maker friend (Jim Moenck) and he asked if we could try to weld and draw out Damascus billets with it.
If you look closely at the top picture (the one that shows the complete machine), you can see a successfully press-welded Damascus billet that he and I welded with it. For this process, I use mild steel dies that are 2" X 2". The foot-operated controls allow one to do a "squeeze" and quickly raise the dies just enough (1/4" to 3/8") to advance the work, then squeeze again. I can get 3 or 4 squeezes per heat on the initial weld heat.

Details of the Modifications

-The release valve that comes with the jack is just a 1/4" diameter needle valve that you have to twist with the jack handle. I made the knob (which is held onto the needle valve by a set screw) and the arm that attaches to the air cylinder. The arm gives an effective radius of about 1". I also made the bracket that the cylinder is connected to and the angled bracket upon which the air cylinder pivots. That bracket is held to the base of the jack by a 1/4-20 screw into a hole I drilled and tapped into the base.

-The bottom picture shows the foot operated valves. The little valve that is closest to the bottom of that picture is the valve that comes with the jack. It has a little thumb-operated lever. It simply lets air into the jack's air motor to make the jack work (putt-putt-putt). The upper valve in the picture runs the release lever. (I found that valve in a box of stuff I got at an auction years ago. I think it is called a 3-way valve. When pushed down, it sends air to the Bimba air cylinder to pull it IN and open the release valve about 1/4 turn, allowing the jack to relax back to its shortest position. When you release the foot pedal, the valve opens the air line from the cylinder to the atmosphere to let the pressure out of the cylinder. The return spring inside the cylinder pushes the release valve shut.

This press is a very useful tool.

We use this press for lots of things. For instance, I have made a couple of sizes of sheet metal bending brakes for it. I have used the home-made Press Brake in the lower picture to bend 12" of 3/16" thick mild steel to 90 degrees. And, of course the machine comes in handy often for pressing bearings, straightening and flattening.
An example of flattening: A friend chiseled and chased 6 very fancy 4" by 12" facets for a dining room chandelier. By the time he was done, the mild steel panels were warped a lot from all that cold working. We simply pressed them between them between 2 pieces of 1/2" plate and they came out remarkably flat. Flattening by hand hammer would surely have stretched the metal more and obliterated some of the fine details.

I recently put the press on casters. (These pictures don't show the caster setup) That way I can move it into the work area when needed, then back into a corner when not in use.
Another refinement will be to add a pressure gage so I can get an idea of the force I am using. A fellow Guild of Metalsmiths member told me how a friend of his modified this jack for a gage port, but I haven't done it yet.
For those who don't want to go to all the trouble of adding the release cylinder and valve, I will someday try to replace that mechanism with a autombile cluctch cable or bicycle brake cable.

Feel free to email me if you have any questions.







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