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Thinking my way toward the ideal sheet metal brake.

a generic pan.

a generic pan.

There is a term called “paralysis by analysis”. It is the trap a person can fall into trying to create perfect and never getting anything done. However, there is also a term for going out and purchasing something that sounds great, and then finding it will not do the job. It is called dumb. Somewhere between those two is probably not “just right”, but the best that can be done.

I have been all over the map trying to figure out what I want to do to bend sheet metal for enclosures.  Although I have not been getting anywhere very fast, I think I am coming close to a solution.   The first step in trying to solve a problem of any type is to first understand the problem.   What I hope to be able to accomplish is to be able to make my own small metal enclosures for electronics projects.   When I really think about that I have to ask myself the question:  “Why?”  My answer is “Heck if I know except that it is a skill I would like to learn.

The tool used to bend metal is called a brake.  There are two basic types.   One type is called a press brake and uses a lot of force to press the metal between two dies.  This a heavy-duty operation and useful for thick metal bars or rods.  The kind of brake I am thinking about is a relatively simple device and consists of a couple of flat pieces hinged together and a clamp to hold the metal to be bent against the non-moving piece.

Metal Brake shown schematically

Metal Brake shown schematically

I show this schematically in my second picture.  The hinge is shown in blue. The two plates connected to the hinge are shown in black.  The metal being bent is shown in red and the clamp is shown in green and the dashed lines show it in the semi-raised position.   Simple and straight-forward isn’t it?  So what is the problem?

The first problem is due to the way metal acts like a spring.   At the point where the metal is being bent the metal is being stretched on the outside of the bend and compressed on the inside.   It is actually being permanently deformed due to the stress at that point, but metal before getting to the point of actual permanent deformation, called plastic deformation, has some elastic deformation.  Once the stress is removed the metal will spring back toward its original shape.   Note the word “toward”; it will not spring back completely, but only partially.  This means the metal will have to be bent more than 90 degrees to obtain a permanent 90 degree bend.  How much more depends upon many things including the thickness of the sheet, the alloy and temperature. That is the reason I show the clamp at a 45 deg angle.  That allows plenty of room to “over bend” the metal.

Another simple problem to determine is where to locate the hinge.   On the horizontal axis the center of the hinge pin needs to be located even with the edge of the table.  That way when the hinged surface is brought upward it will not be slipping against the sheet.   The placement of the clamp to the joint in the table probably needs to be adjustable.  It needs to be at least the thickness of the sheet away from the edge, and probably a little more.  When the sheet deforms the outer surface of the corner will probably be a little thinner due to the stretching of the metal, but the inner surface will be thicker due to the shrinking, compression, of the metal.   Will this be important?  I don’t know, but I do want to find out and I better have an adjustment available to cope with it.   Obviously, the hinges will have to be on either side of the clamp and sheet metal because the hinge will be above the surface of the table.

The next problem is due to what exactly do I want to create.   The first picture shows a simplified pan..  It is simplified because I do not show a method to close the corners but it is useful to use to start thinking out the problems.   Lets say I first bend the two sides and form a channel.   Already I have a problem. If the side that is already bent is placed behind the clamp, the width of the pan must be wider than the clamp.  If the clamp is a 45 deg plate like I have shown this probably will not be a problem unless the height of the pan is large.   Should I decide to clamp the side and use the hinged side against the bottom of the pan, I have to think about it clearing the top, front of the clamp.   All of the dimensions will depend upon what I want to create.

The plans for the enclosure  in an earlier post.

The plans for the enclosure in an earlier post.

It gets even worse once the two sides of the pan are bent.  Once those two sides are bent the clamp has to fit between the two sides.   This is handled by a common type of brake called a box and pan brake.   The clamp consists of “fingers” that can be removed to clear the sides.  However, again we have to worry about the problems described in the previous paragraph.  Things get even more complicated once extra folds are created to make tabs to join the sides together like I did on doing the first enclosure.

So far I have described lots and lots about the problems.  It was necessary to figure out where to go and what I will do.  The next steps are: First, figure out what is the largest and smallest enclosure I will think I ever will want to build;  Second, build a hinge plate and base to handle the biggest.  Third, come up with a very very flexible clamping method.

I am close to determining all of those, but details will be in a future post.   This one was mostly to define the problems.

I am going to link several videos I have viewed to show how others have solved the problem and how “off-the-shelf” may not be the answer.

The first video shows how a guy built a very large brake for a special one time job.
How to make a cheap 72 inch wide sheet metal brake for bending sheet metal

This second video shows a guy that worked through several problems.
DIY Sheet Metal Brake

The final video shows a guy that bought a Box and Pan Brake and was surprised to find things did not work out.
Sheet Metal Box & Pan Brake Tutorial – Grizzly Brake in my home shop

The next one shows a homemade press brake.
Making Of a DIY Mini Press Brake (Metal Bender)

And finally of course, my previous post about building an enclosure.  (The hard way of doing it.)

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Thinking my way toward the ideal sheet metal brake.” by Create-and-Make.com is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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Gary


 

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2 comments to Thinking my way toward the ideal sheet metal brake.

  • wim rhebergen

    Dear Gary,
    That was my trade,I had a sheetmetal factory in South-Africa with the name ,,Kaaskop Engineering CC ,, We did all the bending on a bending brake.That works perfect.But to have a bending brake at home,is a street to far.What also is possible,to use a flypress with a two column guiding.For people who have plenty of money there are nice machines on the market, http://www.northerntool.com/shop/tools/product_21800_21800
    But let me stick to my clocks for the timebeing.
    Good Luck Wim

    • Gary

      Thanks a bunch Wim… I doubt very much I will go very far with the brake and if I do it will be a small one. Actually all of this stuff is in a lot of ways “stupid” to have at home. But then it is all a lot more fun than sitting in front of the TV all the time.

      I saw a joke/test on facebook… what is the difference between a nerd and a geek? I am definitely in the nerd camp. I like knowing why things work and how they work than I care to have the latest and greatest high-tech gadget.

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