How to work out the tonnage on a sheet metal press brake FAQ

Image of person working out calculations

Let’s take you out of that busy workshop for a while, it’s time for a sit down perhaps, maybe even enjoy a well-earned cup of tea. If you ever fancied reliving your school days a little, then now is your chance.

No doubt you know how to work a Press Brake, but can you honestly say that you understand how it works? Working out tonnage for example? If you can then fantastic, if not then at Selmach we feel it is something you should know, and we are going to invite you into the classroom for a basic rundown (Tea and biscuits are on the way).

Step 1 Working out the Vee size

We need to know what size Vee is needed for what material and up to 3mm the basic formula is as follows:

6 to 8 x material = Vee size (up to 3mm)

So…We can see that, for folding a 3mm work piece we can multiply the 8 x 3 which gives us 24mm

Therefore if you’re folding 3mm, then a 24mm Vee is strongly recommended.

For Vee sizes beyond 3mm the formula is slightly different:

10 to 12 x material = Vee size (above 3mm)

So here, let’s imagine we are folding a 10mm plate, so 10 x 10 =100mm

Therefore if you’re folding 10mm, then a 100mm Vee is the one to choose.

Step 2 Working out the correct radius of the top tool

So with the Vee size worked out based on the thickness of material, we now need to work out the correct radius on the top tool.

Let’s say we are folding 1mm, we use the following radiuses:

1mm = .2 to .8mm radius would be plenty.

For 3mm a 3mm radius would be recommended.

For 10mm plate a 6mm radius would be needed.

For aluminium of around 8-10mm a much greater radius is needed of at least 24mm

That’s about it for the maths but don’t worry, there is a bending chart on every machine we sell, to allow everyone to familiarise themselves with this essential information and to act as a vital reference. The width of material is in the left hand column, follow the row across to your Vee and the radiuses will be displayed at the top of the chart. It is important to remember the chart is based on mild steel, for aluminium you must use a bigger inside radius, if in any doubt, we are here to help, so please feel free to Get in touch.

There are of course a range of different Vees, and sizes such as the ‘T’ shaped single Vee which comes in sizes up to 25mm, along with different angles and heights. Beyond 25mm we offer large single Vees, again with a range of angles and others available in our catalogue and online, we can also make bespoke Vees for your individual needs.

As for top tools, there are standard Goose neck punches of different heights, different angled noses and differing radiuses, depending on the type of material you are folding. We also offer Swan neck variations for tighter bending and thinner materials as well as heavy-duty punches for thicker materials such as heavy plate.

So…That’s it class dismissed, we hope you found it useful, our in-house Press Brake Professor Nigel has made a useful visual guide on everything above over on our YouTube channel feel free to subscribe!

Published 21st October 2016