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 in any particular way the problem often arises at the end of a project the enclosure  “What the hell am i going to put all this in !“

Some people’s standards are different to others and some are quite happy putting their projects in any type of box and believe me I've seen some things online verging 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 to see a good implementation.

There are quite a few nice off the shelf commercial chassis's 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 .There are many others some from EBay, 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 involved bending metal and i have to say i won’t bother starting a project if the end result doesn't look professional .
You have only to look at Cygnus X1 ,a work of bending 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 to run a pair of  Q Acoustics 1010i bookshelf speakers. I decided a Gainclone was the way to go and decided on a LM3875 Classic kit from Audiosector .Peter is a great force in the DIY Audio community and is a master at making simple yet beautiful chassis’s as well as the bits inside :)

Some of Peters genius artwork ..... what your looking at is 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 and i knew the dimensions of the chassis that i required .I already had decided that i would need to make my own chassis and the prospect of bending aluminium arose yet again.

The testbed prototype ready to be re'housed..........

One thing i knew was that 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! “  and this is when i thought i would make my own bender .I rang my friend Mick as i remembered he had some angle iron floating around but as it turned out he had used it .As i couldn't wait and had a look around for  materials i had lying around when i noticed  quite a bit of 38mm  bamboo worktop off cuts ,so i decided this might just fit the bill as i wasn't bending steel the impact on the edge of the backstop would be a lot less

    Here’s the result of an afternoons work..........

 I'm not going to get into the construction of the bender as its pretty self explanatory and 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 allot of force during the bend and its 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 around .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 so the idea by adding an angle 5 degrees past 90  is so that you can bend past 90 to allow for the spring back so when you release the handle the bent angle will spring back to 90 not 85. (This isn’t set in stone you can have less of an angle or more)

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 and 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 with as many Carbide teeth as you 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 ,but remember if it grabs it won’t be as forgiving as wood to you or the saw.

Make sure you take precautions with guards and safety glasses e.t.c and of cause 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 now we set the saw table fence to 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..........

(A tip here is if you are making a “U” shaped cover/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 marks make the cut on the other side of the marks towards the sides that way when you bend it you will maintain this measurement and any excess can be cut off the side later by placing the bent piece on its side in the table

    Here i rotated the sheet over 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 other cut edge is directly in line with the bottom of the backstop.

       When we start to fold the whole cut line will act as a weak point and 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 push the piece slightly passed 90 to allow for spring back .Now i just turned the piece round in the backstop re-clamped and bent again..........

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

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

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

 Here are all the bent enclosure parts ready for assembly of  the Amplifier
( More pictures of the fully assembled amplifier )

Few Extra Tips and Bits

 Get a  good long stainless steel ruler preferably with 0.5mm increments for precise measurements and straight marking

Get a Sliding Engineers square or Combination Square you will use this constantly from everything from checking for square lines, transferring lines also 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 Pentel NMF50 (my favourite) or the Sharpie Ultra Fine will draw 0.5mm lines on anything ,or use a craft knife to mark soft metals such as aluminium.

The Finer the marks the more accurate your bends and cuts will be .A 2mm line with mean you could be out by 2mm off square or that hole you drilled just wandered off 2mm doesn’t sound like a lot but when your drilling four holes to mate up to another piece it wont !

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...  

I hope  a few readers found the article useful.