Friday, 2 December 2011

DIY: How to bend aluminium the easy way with a home made brake and a few tricks


If you have ever been into electronics, a problem often arises at the end of a project...  “What the hell am i going to put all this in !“

Some people’s standards are different to others,  some are quite happy putting their projects in any type of box and believe me I've seen some things online, from a pc in a cardboard box to amplifiers in cigar boxes.

Now, don't get me wrong this can be well implemented at times, you only have to look at the Cmoy "Mint Amps" housed in an Altoids Tin.

There are quite a few nice off the shelf commercial chassis available, such as Hammond
Mfg extruded aluminium series but, they are very height limited, you aren't going to fit any type of large transformer in there!

 Some of the Chinese chassis are great but, factor in shipping and tax, and your soon racking up £100 + only to have to modify it and this is where my journey begins.......

For many years i have wanted to make a my own PC case  but, this would involved bending metal

Cygnus X1  a bending work of art!

Earlier this year I decided to start a new D.I.Y Audio project. I wanted a small yet powerful amplifier for the PC, powering a pair of  Q Acoustics 1010i bookshelf speakers. I decided a Gainclone was the way to go, I decided on a LM3875 Classic kit from Audiosector. Peter is a great force in the DIY Audio community, he is a master at making simple yet beautiful chassis, as well as the bits inside :)

Some of Peters art...  a 2x68watt amplifier!

So, the kit was built and the prototype chassis was made to house and tweak the layout. After a week or so I had the layout down. I now knew the dimensions of the chassis that was required .I had already decided that I would need to make my own chassis and the prospect of bending aluminium had reared its ugly head yet again!

The test bed  ready to be re-housed!

The one thing I was certain about! I wanted perfect bends, and bending 3mm aluminium wasn't going to be easy. Not only that! but actually getting precise bends and keeping everything square would also be a challenge. You have to factor in how much material the bend will use, and where it will end up. I thought about this for a few days... I even looked around for a brake press but they were either too expensive or feeble, even some of the larger ones could only bend thin gauge metals .

I have a bit of a motto “if you can’t buy it or borrow it then make it! “ , This is when I came to the conclusion I would make my own bender!

I rang my friend Mick, as I remembered he had some angle iron floating around. As it turned out he had used it!!

I couldn't wait any longer, I looked around for any materials I had lying around. This is when I noticed quite a lot of 38mm  bamboo worktop off cuts.  I decided this might just fit the bill,  I wouldn't be bending steel! and the impact on the edge of the backstop would be a lot less

    Here is the result of an afternoons work...

 I'm not going to get into the construction of the bender as its pretty self explanatory, the lengths will differ depending on what the size of sheet you need to bend.

One of the most important parts are the hinges, these will take a lot of force during the bend. It is  pretty critical that there is as little play as possible, as this will influence the quality and tightness of the bend. I used some 4 inch heavy duty stainless hinges, because they were the best I had. One of the bonuses of the 38mm plywood was the fact that the hinges could be screwed in place, I didn't need to bolt them through the base and swing arm.

The other bit of advice is to run the face edge of the backstop through a table saw. I used a angle of 5 degrees, this is because when you bend the metal you usually want 90 degrees and when you hit 90 the metal will want to spring back a little. The idea of adding an angle 5 degrees past 90 is so that you can bend past 90 to allow for the spring back. When you release the handle the bent material will spring back to 90 not 85.

The two M10 bolts in the top are to clamp the sheet between the backstop and the base. The backstops bolt holes have a slot cut in them to allow the backstop to be slid back, to allow for the thickness of the material to be bend .

    See how the face of the backstop slopes backward, slightly...

Time to bend or nearly.

So we have the bender but we aren't finished, as there is another trick to getting the perfect bend. This involves making a score or cut  line on the sheet, where you want the bend to start. For this you will need a table saw, with a blade that has as many Carbide teeth as possible and preferably sharp!

Aluminium cuts surprisingly easy with a decent table saw, especially when you use a blade designed for cutting non-ferrous metals. Remember if it grabs it won’t be as forgiving as wood, or the saw.

Make sure you take precautions with guards and safety glasses e.t.c I take no responsibility if it goes all horribly wrong. It is up to you to gauge your ability, and the risks involved when following these methods.The guards were removed from the photos for clarity!!

Here we can see that the blade it set at about 1/3rd of the thickness of aluminium, this figure will depend on the thickness of the material to be bent.

    Here's a piece of aluminium 3mm thick, It’s a good idea is to practice on some scrap first...

    So we have the depth set on the table saw, and the lines marked on the material to bend...

Once you’re happy with the depth we can set the saw table fence for the first cut. (A little note here using this method of cutting the line removing a third/half of the material will give perfect 90 degree sharp inside corner) if we just bent using the bender, you would end up with a radius on the inside as well the outside.

    Here you can see the channel made by the Saw blade..........


If you are making a “U” shaped cover or lid for something, you would have cut 2 lines in the sheet so you would have a side/middle or top/side sections. If you want the middle(top) section to keep the same width as the mark, make the cut on the other side of the marks towards the sides. This way when you bend it you will maintain this measurement, any excess can be cut off the side later by placing the bent piece on its side in the table saw.

    Here I rotated the sheet , to duplicate the other side..........


    Time to Bend the sheet into something useful..........

Here, you can see that the backstop has been slid back and the bolts tightened, to allow for the thickness of the material.

The edge of the cut is exactly lined up with the gap between the edge of the backstop base and the swinging side. The opposite cut edge is directly in line with the bottom of the backstop.

As we start to fold, the whole cut line will act as a weak point, the bend will follow this path exactly, till each cut edge meet together, producing a smooth square bend.

   If you didn’t quite get 90 degrees, try pushing the bend slightly past 90, to allow for spring back. Now I just turn the piece around in the backstop re-clamped then bent again..........

   We now have a Chassis lid with perfect bends! including a nice radius, with perfect 90 degree sharp internal corners!

    The Amplifier enclosure lid is ready !..........

   This is a more complicated 4 part bend, for the Amplifier enclosure base..........

The amplifier enclosure parts, ready for assembly
( More pictures of the fully assembled amplifier )

Few Extra Tips 

 Get a good long stainless steel ruler, preferably with 0.5mm increments, for precise measurements.

Get a Sliding Engineers square or Combination Square, you will use it constantly! Everything from checking the squareness of lines, transferring marks, checking depths and marking centres for drill holes

   Get a pair of Digital Calipers, you will never look back !

The finest permanent marker, such as, the Pentel NMF50 (my favourite) or the Sharpie Ultra Fine these will draw a 0.5mm lines on anything. You can also use a craft knife, to mark soft metals such as aluminium.

The Finer the marks, the more accurate your bends and cuts will be. With a  2mm line  you could be out of square by 2mm  or the hole you just drilled is off 2mm. This doesn’t sound like a lot but, when you are drilling four holes to mate up to another piece, its important!

Aluminium Grades

5251 H22:
(Medium strength alloy, work hardens rapidly. Resistant to marine atmosphere

(Malleable. Good corrosion resistance.)

(Readily welded, suitable for use in cryogenic applications  e.g. storage & transportation of liquid gases & in shipbuilding. Used in general engineering for tooling, jigs & fixtures.)

(The recommended alloy for structural purposes with good strength & general
Corrosion resistance. Used for vehicles, bridges & cranes, general engineering & tooling plates.
Not recommended for folding/forming)

Have Fun...