20 ton air-over hydraulic press

7/29/2019 20 Ton Air-Over Hydraulic Press

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Last Date Revised: October 20, 2012

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Here's how the press works as you buy it:The 20 ton hydraulic jack does all the work. When you buy one, you use muscle power to pump ahandle on the jack which, acting on a small piston, forces oil from the jack's reservior into the main(much larger) cylinder, pushing the main piston up a tiny bit with each stroke. Since the piston ispushing against the top of the press frame, that effort simply pushes the base of the jack, and thereforethe spring loaded jack stage, downward. There is a small valve in the base of the jack that releases theoil to allow the jack piston to retract. You have to twist this valve 1/4 turn ccw or so (using the end ofthe jack handle) to let the piston return. That's the standard 20 ton press that you buy for about $250

n Air-over Hydraulic Press http://spaco.org/

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these days.Note that on this style of "Bottle Jack" press, the jack stage is well guided.

The basic press comes with a regular 20 ton hand operated hydraulic "bottle" jack. I replaced it withHarbor Freight's 20 ton air-over-hydraulic jack; the model that is exactly the same size as the one that

came with the press. I added a release valve cylinder to the air-over-hydraulic jack, then added footcontrols to extend and release the jack.The release cylinder is a Bimba Model 091-R spring-return air cylinder that I had laying around foryears, but I bought some more of them recently, so they are still available. They cost me about $25 each(fall of 2012), direct from www.bimba.com.If you don't want to shop around or make some of the parts, you can get the D-166-A Clevis and the D-95/8-18 nut from them, too.Although my system works well, you might consider the Model 091-HR cylinder. It has about twice asmuch spring return pressure.

1. The foot controls leave both hands available to manipulate the work.2. The air motor raises the jack at least 5 times faster than you could do it by hand.3. (This one that wasn't in the original plan) You can forge weld in this press!I mentioned this modification to a knife-maker friend (Jim Moenck) and he asked if we could try toweld and draw out Damascus billets with it. And we did.If you look closely at the top picture (the one that shows the complete machine), you can see asuccessfully press-welded Damascus billet that he and I welded with it. For this process, I use mild steeldies 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. At 130 psi, and no load, the press moves 1/8" per second.With this speed, I can get 3 or 4 "squeezes" per heat on the initial weld heat.

Jack Release Cylinder:

Here is the release mechanism. The white plastic hose goes directly to the output of the 3 way valve onthe floor.


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-The release valve that comes with the jack is just a 1/4" diameter needle valve that you have to twistwith the jack handle. I made the knob (which is held onto the needle valve by a set screw) and the armthat attaches to the air cylinder clevis. The arm gives an effective radius of about 1". I also made thebracket 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 thebase.

Even if you don't add the air-over-hydraulic jack or add this release cylinder, I recommend that youDO add a knob onto the jack's release valve. Once the knob is there, you don't have to grab for the jackhandle to get the jack to return.

Here's a picture of a release knob that I made before I started this "automation" project. It is currentlyfitted to the non-air powered jack that I took off the press.


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If you want to make a knob like this, Click Here for a fully dimensioned drawingThe release valve shafts for both of my jacks have a small hole cross-drilled in them and a pin inserted.That pin is what you turn with the jack handle to rotate the release shaft. In some cases, I have seenjacks where the mfr. has simply sqaushed the end of the release shaft instead of using the cross pin. Ifthis is the case with your jack, you'll have to modify my design accordingly.

Foot operated Valves

120 psi air comes in from the compressor through the black hose (with a quick disconnect)to a tee, thento both valves.

The white plastic hose leaving the larger valve on the right (that's the "3-way" valve) goes directly tothe Bimba release cylinder.The red hose goes from the smaller valve on the left, directly to the air motor on the back of theair-over-hydraulic jack.


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The little valve that is closest to the bottom of that picture is the valve that comes with the air-over-hydraulic jack, on the end of a 3 foot long air hose. Obviously, I had to replace that short hose with a

longer one. It has a little thumb-operated lever (which I now operate with my foot). It simply lets airinto the jack's air motor to make the jack work (putt-putt-putt).

I found this 3-way foot valve in a box of stuff I got at an auction years ago. When pushed down, this3-way valve sends air to the Bimba air cylinder to pull it IN which rotates the release valve about 1/4turn ccw, 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 letthe pressure out of the Bimba air cylinder. The return spring inside the cylinder pushes the jack'srelease valve clockwise to close it.

Rear View Showing Air Motor on Jack


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Casters

I recently put the press on casters. That way I can move it into the currently active work area whenneeded, then back into a corner when not in use.


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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. Click this link to see what he told me: Adding a Gage to your 20 Ton JackI haven't tried it yet, so you are one your own

Simplify the release mechanism: For those who don't want to go to all the trouble of adding the releasecylinder and valve, I may someday try to replace the "Bimba cylinder" mechanism with a autombileclutch cable or bicycle brake cable. That would also make it cheaper to build.

Here, you can see a small amount of the tooling we use at the press.


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I have made a couple of different 10" long press brakes for it and they work quite well for sheet metalup to 1/8" thick and maybe 16" wide. The press throat is about 20" wide. I have even bent 1/8" mildsteel 16" wide to 90 degrees by making partial bends and moving along. So far, I have used mild steelfor most of the dies. I have simply used mild steel square bars on the diamond for the upper die andmachined a 45 in the lower die. In the future, I intend to make (or maybe even buy) a moreconventional press brake accessory.

The home-made Press Brake in the lower part of the picture can bend 12" of 3/16" thick mild steel to90 degrees. And, of course the machine comes in handy most often for pressing bearings, straighteningand flattening.An example of flattening: A friend chiseled and chased 6 very fancy 4" by 12" facets for a dining roomchandelier.By the time he was done, the mild steel panels were warped a lot from all that cold working. We simplypressed 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 thefine details.

You can even use it as a clamp to hold work pieces together for drilling or for welding.

My air-over-hydraulic jacks (I have made 2 of these machines, one for me and one for a son) came fromH-F at least 4 or 5 years ago and neither one has leaked yet.

In Closing:

I'm not saying that this is the only way to accomplish foot controlled operation. I just hope that you canuse some of these ideas here to produce your own hydraulic press solution.


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20 ton air-over hydraulic press

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