Homemade press brake

I have enough iron now, to make what I always wanted to make, which is a homemade press brake. It would be shaped along these lines:
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_21896_21896
With a couple of exceptions. One, is that it would accept removable press dies. This way I could make my own dies to do whatever I want or use the dies I have.
The hope was to use it in the 12 ton arbor press.
Second, and here lies the crux of my question, I thought to replace vertical posts with an ACME screw and nuts. This way, first, I can limit travel of the vertical die a little better, and second, my thinking went, I could use the nuts to to provide greater pressure compared to my arbor press. I have an ACME screw approx. 4cm in diameter.
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Sorry, I was inerrupted. I meant to say that I calculated clamping force for the screw ofthat diameter and 250 N*m torque, and came up only with 14 ton force for both nuts combined.
Does this sound in the ballpark, if so, the nuts would not improve anything.
i
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wrote:

What is the size of the ram in your 12 ton press? Remember to divide the size of the ram, in square inches, into the 12 ton to get the PSI for your press. If twere me, I would use the arbor press as is to see what you can do with the press brake. Then machine up an adapter for your ACME screw test.
I have a set of the Harbor Freight dies for use in a large vice. I machined up adapters to put them in my 20 ton hydraulic press. They work, but I can tell you it doesn't take much metal being bent to discover the limit of the 20 ton jack.
The real problem I found is not the pressing, but holding the material in alignment during the pressing operation.
Be sure to give us the results of your project.
Paul
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I will give an update on this. I have another idea, that may increase the force of the arbor press fourfold or so, of course at the cost of correspondingly smaller travel. I need to do some calculations first.
i
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Ignoramus5865 wrote:

Instead of trying to overload and potentially damage a good arbor press, why don't you build a dedicated mini hydraulic H or A press for just the short stroke of the press brake?
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Here is a professionally designed 12 ton hydraulic press brake: http://www.sterlingmachinery.com/6466/Di-+Acro+16-+36
Notice how heavy the dies are, to keep them from deflecting, and the open-ended C frame with a 6.5" throat that lets it make bends incrementally in longer pieces.
jsw
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wrote:
...

I just went downstairs and checked, my bench vise applies 2000 lbs to a force gauge, the milling vise 3000. That's using normal pressure on their handles as I don't want to damage them.
I think the rule of thumb is that a nut is 25% efficient. The torque to break one loose is only a little less than the torque used to tighten it.
These work reasonably well for pieces up to 4" wide, like hinges and angle brackets: http://www.toolplanet.com/product/TD-Industrial-Sheet-Metal-Form-Bender-and-Bending-Brake/brakes-benders The male die is a simple part that would be easy to copy if you wanted a sharper bend radius.
It requires a substantial mount. I clamp it to a piece of wide-flange beam lying across the tailgate.
If I need a bent piece that exceeds its capacity for a home project I saw off some heavy angle iron or weld two plates. Sometimes (like now) I work at places with industrial shears and brakes but I design home projects to not need them.
jsw
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Ignoramus5865 wrote:

In other words, you'd tighten the nuts to provide the braking pressure? And just not use the arbor press? Or used together in some way that I'm not seeing?
If you're thinking of just using the nuts, you will be very quickly disillusioned by all the wrenching that you have to do. Unless you power the tightening. In which case you'd be better off turning the screws with the nuts fixed.
Bob
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