SBA: Sheet Metal Folding Machine A

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1. Introduction

This is a very small (3-inch capacity) sheet metal folding machine intended for use with thin soft metals such as cut-up aluminum cans. It is designed for fabrication in plastic (plus some hardware) on a 3-D printer.

Beyond the limitations imposed by its size, it is limited in two other ways by its design. First, its Clamp is a single solid piece without movable/removable fingers. It is thus more like a "cornice brake" than the now more common "box and pan" brake, and it cannot be used for fabricating boxes. Second, its Bending Leaf is in the form of a paddle projecting in-line with the bed of the machine. This is unlike the construction of traditional brakes, and is more like that of the simpler "folding machine." In practice, this wide Bending Leaf means that this brake cannot perform all of the operations necessary to produce a Pittsburgh seam. But (confusingly, if you're trying to categorize machines) it allows the passage of a (nearly) full-width workpiece through the machine. Traditional "sheet iron folders" did not. So it's a sort of an unintentionally strange hybrid, halfway between a folding machine and a real brake.

However, as this present design works well for its limited purposes, I've left it as-is and plan to address its deficiencies in a future project ( SBB - Sheet metal Brake B).

For an explanation of the part symboling scheme used for this and other CircuitousRoot projects, see: Part Symbols section of the CircuitousRoot Project Organization Notebook. This project is "SBA", for "Sheetmetal Brake, type A" (even though it's really a Folding Machine).

This sheet metal brake is Open Source Hardware. See the Notebook on Open Source Hardware on CircuitousRoot for further details.

2. Explanation

We have a regular commercially made "box and pan" sheet metal brake in our metalshop. It's a rather ordinary, low-end Grizzly model G-0557:

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As you can see, it doesn't get much use. The fact that my hand sheet metal tools are in front of it in a plastic tray is deeply embarassing.

In any case, Rollande wanted something much smaller and more portable than our G-0557 brake that she could both use on her jewelry work and take with her on trips to shows. It wouldn't have to handle very thick sheet metal at all - thin brass and aluminum can metal at most. Since we had just revived our 3-D printer, we thought that, surely, there must be a design "out there" already that we could just print up. Surprisingly, there was not. There are a number of sheet metal brakes for 3-D printing online, but they are generally "press brakes" which operate by pushing a V-shaped top piece into a V-shaped bottom, bending the metal in between. I wanted something much more like a regular box brake. So I tried to build it. Through my ignorance of the actual operation of a sheet metal brake, I ended up with something much more like a sheet metal folder.

Here's one style of sheet metal folder:

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(From Broemel, L. and J. S. Daugherty, Sheet Metal Workers' Manual. (Wilmette, IL: Frederick J. Drake & Co., 1942. Scanned from my own copy.)

For a good look at the use of a folding machine, see the article "Bending Brakes for Your Sheet-Metal Jobs" by Sam Brown ( the greatest technical writer the world has ever known) in the August, 1947 issue of Popular Mechanics (online but not downloadable via Google Books at:

For comparison, here is a "press brake" at a scale similar to that of the present project. It's the "mini sheet metal brake" designed by "lonsnail" and published on the Thingiverse at As shown here we built it without (yet) adding the two springs specified in the original dsign. It's a good little device, but not in the style we wanted (it's harder to use up close to an edge).

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(In the photo above left, the left bend in the sample piece was made on our SBA metal folder and the right bend was made on lonsnail's "mini sheet metal brake.")

3. Design

So here is Sheet Metal Folding Machine "SBA," first in all of its digital CAD perfection:

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And as a mundane physical (that's redundant) object which has just bent a tiny piece of aluminum soda can metal:

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For a sense of scale, the maximum workpiece width for this brake is three inches.

As you can see, it works in principle just like the larger sheet metal brake out in the shop, with three differences:

First, where its big brother pulled its Clamp down using an eccentric and a set of linkages, this tiny version has a Clamp which you force down with a lever/handle. (The Clamp is the part colored gold-ish on the CAD view and pink on the physical object.)

Second, this is closer to being a "cornice brake" rather than a "box and pan" brake. The difference is that a box and pan brake has a Clamp which is divided into adjustable (or removable) "fingers." This gives you the flexibility of configuration that you need for making metal boxes and pans. A "cornice brake" has an undivided Clamp. It would have been used for bending metal into fancy cornices back when buildings were more elegant than they are today.

Third, as noted earlier, the Bending Leaf is a wide paddle sticking straight out. This means that it cannot perform the second fold necessary to produce a Pittsburgh Seam. This is really just a "folding machine" rather than a proper brake.

4. Parts and Files

Parts List:

The Base, Bending Leaf, and Clamp are all intended to be 3-D printed (I'm using ABS plastic in an ordinary Fused-Filament Fabrication machine). I modeled these using the "Onshape"® CAD service: The Onshape model(s) for this project are in a public "document" (Onshape's name for a set of related models).

To access their source, establish at least a free-level account with Onshape. Then log in and search the Onshape model space for "SBA - Sheet Metal Brake A". (Searching from the Onshape front page, without logging in to the CAD facility, won't work - that'll just search their website, not the CAD models.) You can then copy the source to your own Onshape workspace and modify it and do with it as you wish (within the terms of the Creative Commons Attribution-ShareAlike 4.0 International license).

If you do not wish to use the source within Onshape, I've exported it in the following ways:

Parts 2SBA2 Bending Leaf Pivot Rod (2 required) are just 1/4 inch rods of about 5/8 or 3/4 inch length. I've made them in an odd, but effective manner: I simply took two 2-inch long 1/4-inch hex bolts and cut them off to approximately 3/4 inch length. I used bolt cutters. You could use a hacksaw, but bolt cutters are easier. If you don't have a pair, think of it as an opportunity to justify the purchase of that pair of bolt cutters you've always wanted. Since 3-D printed holes in ABS seem to come out undersize (ABS shrinks on cooling), these cut bolts end up being a light drive fit into the Base (tap them in with a small hammer).

Part 3SBA2 Clamp Pivot Rod could be any 1/4 inch diameter rod. I've used an ordinary 3 1/2 inch long 1/4-20 hex bolt. This allows me to use 1/4 inch plain washers for 3SBA3 Clamp Pivot Rod Washers and a 1/4-20 hex nut for 3SBA4 Clamp Pivot Rod Nut. If you wish, you could use a nylon-insert locking nut for 3SBA4 instead.

Here's the hardware for these (showing also a 1/4 inch nylon-insert nut and an extra un-cut 2 inch bolt):

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Part 1SBA2 Base Mounting Screw (4 required) is optional; it is needed only if the machine is to be mounted to a base. This part could be any appropriate wood screw (if you're mounting to a wood base). The holes are 1/4 inch, so a US No. 14 (0.242 thread diameter) or No. 12 (0.212 dia) should work. Or use whatever is handy.

5. Details

I didn't finish the drawings for this project. In part this was because Onshape's drawing capabilities were in flux (they went from alpha to "public beta" as I was writing this up). But in part it is because this is a very simple model and you don't really have much control over things such as tolerances in 3-D printing anyway. So here are incomplete drawings of the Base and the Bending Leaf. The only features worth taking note of are the allowances for hole diameters (the actual value relative to a nominal 0.25 inch diameter) and for the width of the two circular "bearings" (the actual value relative tothe 0.25 inch slot they'll run in). Don't take the expression of these values to three decimal places seriously.

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Here are some additional views of the CAD model.

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6. Fabrication Notes

I built this in ABS plastic on a Makerbot® Replicator 2X (a badly engineered machine which cannot be recommended) using Simplify3D® as the slicer (a well-written piece of software which I can recommend). I used the stock slicing profile provided by Simplify3D for this printer, with a raft and supports (extruder temp 230 C., bed heat 110 C.) The printer's bed is covered in (a) kapton tape, plus (b) a slurry of "ABS juice" (approx. 4 grams ABS in 6 fl. oz acetone), plus (c) a secondary coating of cheap hairspray.

I printed the Base on its "back" side. This was because as nice as the Simplify3D software is, it still has trouble generating rafts which detatch (at all) from the piece. It also tends to generate a pretty coarse first layer. Printing this piece on its back puts all of this ugliness someplace where it doesn't matter.

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In the photo above you can see the bit of dangling cable that we had to patch in to the stepper motor wiring for the Makerbot. This wiring failed after 80 hours due to a really dumb design flaw by Makerbot.

7. Use

CAUTION: Sheet metal has sharp edges, and you can get a nasty cut. If you do any kind of sheet metal work, including tiny aluminum can material work such as this, follow all standard sheet metal working safety practices. If you don't know them, LEARN THEM FIRST.

To use, lift the Clamp (the pink part in the pictures below) and slip a piece of thin sheet metal under it. Clamp down on the metal by pivoting the Clamp and then raise up the Bending Leaf (the green part in the pictures below) to make the bend. Release the Bending Leaf and then the Clamp and remove the bent part.

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And a closeup of the results (with a different workpiece, but basically the same):

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8. Improvements?

This was a very quick "first draft" of a design. Clearly it could be subject to much improvement. Here are some possibilities:

(A) The angle of the Clamp at its clamping edge is probably too nearly vertical. A shallower angle (allowing a fuller bend) would facilitate making hems (turned-over edges).

(B) The vertical supports for the Clamp pivot are set in from the side of the Base. They therefore obstruct the passage of a full-width sheet through the Base. Moving them out would fix this.

(C) It lacks any kind of limiting gauge to allow quick repeated work to a given depth.

(D) Redesigning the Bending Leaf to make this a true brake (as noted earlier) would be nice. I'll try this in project SBB - Sheet metal Brake B.

(E) Some way of adding fingers to the Clamp (thus making it capable of box and pan work) would (obviously) make it more useful. (But for a clever alternative, see the Sam Brown article cited earlier. To turn a sheet metal folder into a (limited) box and pan brake, he cuts into the Clamp on his machine. (In 3-D printing, which is usually hollow, you'd have to mold slots into the Clamp instead.)

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