Thoughts on making a sheet metal brake?

[FlyFishn]

The kits from swag off road look good and might provide diy ideas

SWAG 20 TON Finger Brake Heavy Duty DIY Builder Kit

Heavy Duty 20 TON Finger Brake Press DIY Builder Kit Press Brake kit comes un-assembled, you do the final assembly and welding. Designed to fit the Harbor Freight 20 ton hydraulic press Item # 32879, 60603 & 70603. Press brake kit includes an adjustable back stop for accurate and repeatable...

www.swagoffroad.com

Stu

That is an excellent starting point. Aside from the dies, I could fabricate that pretty easy.

Now my wheels are spinning because I need to bend 60" material for my current project so my gut tells me go bigger - like 72". The 20 ton HF press is the one I have. I could use that as a base and make a new table + top frame + jack stabilizer, then use the same sides, feet, and hardware (I replaced the bolts with grade 5's from Fastenal last year).

Edit:
The stabilizer bar would be a moot point on the wide brake. The top of the brake that holds the dies is on a track so there is no need to stabilize the jack separately, provided the pin or bottom of the jack is attached to the top of the brake where it won't lift out/away = dual function, as opposed to separate parts with separate functions.

 

[FlyFishn]

The force needed is a combination of material being bent, length of the bend, material thickness, and V die opening.

Here is a calculator that will give you the required tonnage for the bend.

Load Calculator

The CINCINNATI Press Brake Load Calculator will calculate the tonnage to form a part with the variables of material type, vee die opening, bend length, and material thickness inputted.

www.e-ci.com

According to that chart, .125" thick 6061-T6 aluminum 60" wide takes 18.57 tons to bend with a 1.5" V opening. The .125" is overkill for my current project. I got a recommendation of .090", but that was with the caveat of the bent sheet metal serving as a sort of unibody frame. I am not going that route - I am putting the bent sheet metal portion on top of a rigid C channel frame which means I can go much lighter on the sheet metal. So if I go down to, say, .050" or .063" then that would be that much less force required to bend it. .050" x 60" would be closer to 4 tons.

 

[Flyinfool]

You also need to watch your bend radii, 6061-T6 is a bit on the brittle side, you will want a radii of about 3 material thicknesses to avoid cracking.

 

[stupoty]

Aside from the dies, I could fabricate that pretty easy.

I was really suppressed as I had initially been looking at replacement die / knife sets from folders to maybe use in a diy folder and saw that a lot of manufacturers list them as mild steel.

I had presumed they were hardened but maybe they could be made from gauge plate and be quite good.

Stu

 

[finsruskw]

Good grief man, hold that camera still will Ya!!
Makes me nauseous just to watch that.

 

[FlyFishn]

Thinking....... That is a dangerous proposition, you know?

What are the physics behind how crisp a bend is?

Reason I question it is, from what I see and what I have experienced with my cheap HF brake, is that the crisp'ness of "bend" depends on how much pressure can be generated close to the exterior radius of the bend.

That is, in the reverse, the further away the pressure is from the exterior radius of the bend the less crisp the bend is.

To verbally illustrate this - with the HF brake I have the part of the brake that pivots with the handles that bends the metal is only rigid enough for very light gauge metal. The thicker the metal the more the levered part of the brake flexes during the bend. That flexing takes the force further and further away from the exterior radius of the bend with the stiffer metal (thicker or different grades requiring more force to bend). The result is the metal next to the bend exterior radius ends up getting bowed.

How do you control where the pressure is on a press style brake so as to maintain crisp bends - and adjust that for different grade/thicknesses of metal? Is it simply the opening width of the V - provided the same dies are used (same tip/radius on the tip)? Or is there more to the process?

I am mostly wanting 90deg bends for the time being, but I want the flexibility in the brake idea here to be able to make any angle in "light gauge" sheet metal - with a crisp bend. I realize greater than 90deg bends (under 90deg interior angle) are going to be more difficult.

While I am at it I think I'll make a narrow brake for the normal width of the HF 20 ton press for thicker bracket type metal of only a few inches in width at the bend. I don't want to limit myself to using the wide set up for heavy bends. My intent with the wide set up is to be a specialty set up specifically for sheet metal work - were my HF press falls short. Though, I imagine 95% of my pressing needs (automotive/mechanical, metal fab/bending) would be handled with the original 20 ton press frame as it sits - a very good bang for the buck from HF, by the way - so long as yours comes with the plate steel press plates, not the cast iron press plates. The cast iron ones have larger radius edges and look like sandpaper, plate steel has sharper radius edges and are smooth. Cast iron plates can shatter under high loading and shock loading.

 

[Flyinfool]

I guess the fist question is just what are you referring to as "crispness of the bend"?
There are many variables to play with to get various results.

 

[JimDawson]

How do you control where the pressure is on a press style brake so as to maintain crisp bends - and adjust that for different grade/thicknesses of metal? Is it simply the opening width of the V - provided the same dies are used (same tip/radius on the tip)? Or is there more to the process?

All of the above. The V width requirement is mostly a function of the material thickness. The thicker the material, the wider the V must be. But having said that, you can make perfect bends with slot rather than a V as long as you can control the height. My press brake has a micrometer adjustment for the shut height. We just stuff the material in and adjust the height until we get the bend we want.

Here are couple of pictures of my ''wood splitter'' press brake. I used this until I bought a real one. I threw this one together for a couple of specific jobs.




This is what we have now. 48'', 28 ton hydraulic. Shown with a special crimping die we built for a project. Micrometer adjustment is on the lower left.

 

[aliva]

I tried the calculator for 5/8 plate with a opening of 3.125' . 130 tons. So a 20 ton bender shown in the link won't do it. False advertising.

 

[FlyFishn]

I guess the fist question is just what are you referring to as "crispness of the bend"?
There are many variables to play with to get various results.

By "crispness" I mean a sharp, small radius bend where the sheet on either side of the radius is flat - not bowed requiring extra tooling to make "flat".

Though, I would throw in there that in some cases larger radius bends might be desired down the road. In that case I would say the same thing regarding "crispness" where the sheet on either side of the radius is flat, not bowed.

Perhaps a better term might be "accurate" as opposed to "crispness"?

In the project I have in mind at the moment the smaller the interior radius the better. I know I can't get a sharp crease akin to an extruded piece, but I don't want an interior radius of as large as .125" either.