Saturday, January 24, 2009

Bending Plexiglas

As shown in the initial design, the outside casing for this PC will have rounded edges...
This means that I will need to have to create the case by bending the plexiglass.

Looking through the web, seems that the best way to do this is using a hot air gun.
Managed to pick up a relatively cheap one in the hardware store east of People square



(I use the mask for all of the plastic work - the sweet smell when working the plastic is probably not that healthy.

To form the plastic, I plan to use a 'last' - or whatever it is called. The 'last' is basically a mould for the shape of the plastic case. You heat the sheet of plastic and bend it to fit the 'last'.
I chose to make the 'last' out of spare soft wood lying around the house.

The basic shape of the 'last' is as follows. I used a cutout piece of plastic milk bottle as a stencil.



Then used the wood plane to round the edge.



The finished shape is as follows:



This 'last' has an angle slightly less that 90 degress, as with the bending, it apparently will spring back slightly on cooling. I will do a test bend with some plastic to find out the best angle - current is around 2 degrees less than 90.

The test bend started as follows



with the result




The plastic had actually bent well past the angle defined by the 'last'... I dont need to be so enthusiastic at ensuring the bend is less than 90 :-)

So enough of the testing - to the real thing.
I cut the case plastic sheet to size, and attached to the 'last'. It is worth noting that the 'last' had one end properly squared up in all directions. When clamping the plastic on I just needed to ensure that the edge was flush with this squared-up end.

I peeled the protective cover off, and started the heating. Progressively moving down around the bend as things progressed. The result was OK for a first bend...



Very close to 90 degrees, and the bottom remaining square.

For bending the other front corner of the case, I did some sizing up with the 'last' and the already bent piece against the metal case pieces.



I drew some alignment guides, then clamped things in place on the 'last' ready for another bend. Had to be done on a stool this time due to the existing bend.




All seemed square - which was confirmed when fitted over the main metal casing. Very good fit - surprisingly.



Here are a few more images of the front bends.





The next lot of bending will be for the back corners - however I will hold off on that until I have solved all the unknowns relating to how I will attach the casing piece, how I will fit the power button, etc...

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