Folding Metal

This article was first published in 2005.

The requirement was to fit two electronic modules up under the dash. Easy enough said, but they also had to be mounted securely – and the only bolts that could be used were positioned at one end of where the boxes needed to sit. No off-the-shelf brackets would do it, so something custom was needed. Another job for my home-built metal folder... perhaps one of a hundred that I’ve used it for over the last 10 years. An hour or so later, two aluminium shelves were in place under the dashboard, neatly and securely holding the modules in place.

Until you have a small sheet metal folder available, you don’t really realise how useful it is in car modification. (And, come to think of it, it’s not only good for metal. A folder can also be used to bend plastic, such as the bends put into both sides of the 3mm ABS undertray shown here.)  But back to metal, a folder can be used to make battery trays, brackets, dashboard panels and boxes. It can be used to stiffen new panels that would otherwise flap around, and to put lips on pieces of sheet that would normally need screws passed through the front face.

In short, a metal folder is an extraordinary useful tool.

But it can also be a very confusing tool to select. For starters, most references to folders call them sheet metal ‘brakes’, rather than folders. And then there are ‘pan brakes’ as well! Not to mention the fact that a small sheet metal folder can cost thousands of dollars – or, alternatively, less than $80...

So let’s take a look at what metal folders consist of, then start with a very simple one that you can build yourself.

The Designs

Metal folders fall into two basic designs.

A folding brake clamps the sheet between two strong flat bars of steel while a third piece of steel, pivoted at each end, pushes up against the sheet and folds it around the upper bar that’s holding the material in place. This upper bar is usually heavily chamfered on its front face so that an angle of more than 90 degrees can be achieved in the fold.

The other design - a press brake - pushes the sheet into a die. If the die is in the shape of a V, the further that the sheet is pushed down into it, the sharper the bend will become, to a maximum dictated by the internal angle of the V.

The first design is most often used in small hand folders and home-built folders. The latter approach is usual in large machines, although it is also featured in some small multi-purpose machines, such as the one shown at left that can also roll and cut sheet.

A ‘brake’ is a folder than can make only parallel folds in sheet. So for example, a brake can fold-up the two opposite edges of a sheet, making a U-shaped tray with a flat bottom. However, it can’t then fold-up the two other ends of the tray to make an open box or pan. It can’t do this because the folds already made will hit the machine.

A ‘pan brake’ allows the folding-up of boxes or pans. It does this by having removable fingers of different widths in the upper bar of the folder. When the remaining ends of a box need to be folded, the fingers are selected that just match the inner width of the box. Other fingers are removed to provide clearance so when the final two folds are made, the previously folded edges don’t foul the machine.

Pan brakes are usually much more expensive than brakes, but being able to fold all the edges of a sheet is a very useful capability.

Another major impact on cost is the maximum width of material the machine can fold. Cost goes up quickly as you go wider – and goes up even more quickly if you also want the ability to fold heavy gauge sheet. In fact, it’s astonishing how fast you can get into the AUD$3-5,000 territory... while still looking at only small hand-operated pan brakes!

However, at the most basic end of the folding spectrum, a bit of work and about AUD$50 can get you a simple metal bending brake.

Forces The forces involved in bending sheet metal can be very great. In a normal bending brake, the movable lower bar wants to bow outwards as the bend is being made, while the upper clamping bar is also subjected to large loads. Good brakes are therefore made from very heavy gauge materials, often with tension rods used in the design to give even greater stiffness. The corollary of this is that sheet metal bending brakes are very heavy – something to keep in mind when shopping. Another important point is to never force a bender to do its work – it should always work without a huge amount of pressure.

Do It Yourself Light Gauge Brake

This is the metal folder that I made myself. It’s done about a decade of hobbyist work, mostly on light gauge aluminium. Over time, the hinges have stretched and distorted, so the folder is now incapable of doing really tight, short radius bends. (However, in aluminium this is an advantage, as aluminium can crack along sharp bends.) It’s good for bends in aluminium sheet up to a few millimetres in thickness, and up to perhaps 1mm in sheet steel.

In short, it’s a non-precision design that gives good results in light gauge materials. And it can be built at home using just an electric drill and a hacksaw. Depending on how you source the steel angle and bolts, it might cost you anything from AUD$30-50.

Light Gauge Commercial Brake

If you don’t want to build the DIY model described above, similar designs are available commercially. Typically they use a pair of G-clamps to hold the material in place, can handle material up to 18 inches (sometimes 30 inches) width, and may have screw adjustment for the radius of the bend. Note that again they are not pan brakes (they cannot fold up the ends of a box or pan) and some are of very lightweight (ie non rigid!) construction.

These folders are available from about AUD$100 – check eBay.

Light Gauge Commercial Pan Brake

As we said above, commercial pan brakes tend to be expensive – however, there is a cheat’s way of achieving the ability to fold-up boxes.

If the upper bar that holds the material in place has deep slots cut within it, it’s possible to fold all four edges of a sheet – as long as these folds are fairly shallow. So for example, in the folder shown here, the slots are 25mm long – which means the two ends of the box which are last to be folded cannot be more than 25mm high. Also, unlike a proper pan brake, you can’t mix and match the fingers to achieve a very wide variety of internal box dimensions – here you’re limited to the distance between slots. (See the opening pic for a close-up of this folder in action.)

This unit was bought on eBay and cost AUD$75.

Medium Gauge Commercial Pan Brake

A hand-operated pan brake capable of taking up to 4-foot wide sheet and 2mm sheet steel costs about AUD$3000. This is an ideal folder for general purpose work, with the width and pan capabilities allowing you also to make shelves and trays as well as all the other shapes previously mentioned. But its cost means it probably won’t be bought by the do-it-yourselfer!

When you get to this size of pan brake, the clamping bar should be able to be locked-down on the sheet by a lever working an eccentric cam action, the folding leaf should be heavily counterweighted (making it much easier to do the bend), and the beams should be in thick, reinforced steel.

New vs Secondhand A good quality brake or pan brake will have a life of at least 100 years. If it’s looked after, perhaps even longer than that. So it’s no real surprise that the price of secondhand sheet metal folders is very close to the new prices. If it’s an old, heavily constructed unit, the price of the used machine can even be higher than the price of a new - but not so well constructed – bender. So the prices mentioned in this article apply to both new and used machines.

Conclusion

Even a simple bender made from angle steel and bolts will give much better results than trying to fold material in a vice or with bits of wood clamped in place.