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Lasercut Acrylic
Case Tutorial
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Lasercut Acrylic Case Tutorial - Body Fabrication
Design
I do my case designs in Autocad. I use a seperate layer for each different layer in the case and also a seperate layer if I am going to use multiple laser power settings on the same piece of acrylic. This screenshot shows the juicebox case up in Autocad:


You can pull the CAD files for this case from the juicebox sourceforge site. Download the cases package. In this picture, the black lines are the 0 layer, which I am using for the top, bottom, side plate, and buttons, since I want to make all of those pieces out of the same stock thickness. The pink lines are for the GFX layer (graphics), which will be etched at low power into the pieces on the 0 layer. The pieces are mirrored so that the laser will cut the graphics features into the back side of the 0 layer. The blue layer is for the core piece, which happens to be called something like 4.8mm even though in this case it is more like 9mm

Most of the design is done in Autocad, while sitting with the electronics package and a pair of calipers. It seems to take a couple of iterations to get all the dimensions just right. Don't forget to take the laser kerf size into account.

The graphics are partly done in Autocad and partly done in Illustrator. In this design, only the text was done in Illustrator. I wrote the text using the text function, then stroked it with a one pixel outline. I had to play with some options in the DFX export from illustrator to make the import right to Autocad. I also had to delete the hatching that came filling up the text interiors. One really annoying feature of the cutter I use, which utilizes I-Cut CAM software, is that it refuses to import splines from the CAD file. Some shops may have the same problem. To avoid sending splines into the CAM software, don't use them when designing your part in CAD (duh!). But sometimes you might end up with splines, like when importing stuff from Illustrator. One solution is to:

  • Export from autocad to .wmf. Include a little line of known length if you want the scale to be right when you bring it back in.
  • Insert the .wmf, reassign your features to the correct layer, rescale and reposition
This makes splines into 2D polylines.

One other feature that is required for I-cut CAM software is a little reference mark for each layer, all in the same place. This makes sure your different layers line up on the cutter, which is important if you are cutting two layers on the same piece of stock (like for the graphics).

Save the file as DXF and move on to pick the materials for your different layers.

Selecting Stock
You will want to select a thickness for the center layer which is as thick or thicker than your electronics package. Keep in mind that nominal thicknesses of acrylic are not at all accurate, so you will probably want some stock on hand in order to make your choice. A particular brand and product seem to be pretty consistant in thickness, but across brands and products thickness varies by quite a bit. For instance, one abrasion resistant brand 1/4in nominal cast acrylic I got from McMaster Carr measures 4.9mm, while a sheet of standard cast acrylic (also 1/4in nominal) measures 5.5mm. Kind of annoying, but it is actually sometimes useful since the nominal sizes only come in 1/8in incrememnts and sometimes you want a somewhat thinner or thicker size than the nominal. All the acutal measurements I have made indicate that the sheets are pretty much always undersize, but by differing amounts.

For this case, I chose 1/16 nominal 1.4mm actual cast sheet for the top and bottom plates, and 3/8 nominal 9mm actual cast sheet for the core. I usually attach the front sheet to the core with either epoxy or sheet adhesiv. For this case I was going to use sheet adhesive so I peeled one side of the protective sheet off the core stock and roll laminated some 3M 300LSE to the plastic before getting the cutter fired up.

On the cutter
I have been using a Eurolaser cutter for these project. The cutter belongs to E Ink, and I am fortunate enough to be able to use it for prototyping and some side projects as long as no one can tell that I have been using it (i.e. not changing settings, leaving trash on the table, etc.). Kind of the LNT shop philosophy.

The Eurolaser is a medium power laser coupled to a stainless belt drive Zund motion platform. It is a pretty nice machine. Can't cut metal, but it has a nice big bed.

The only annoying part of the Euro is that it uses i-Cut for CAM, and I think this program kind of stinks. Better than some CAM tools though! Anyway, the first step is to import the DXF file into i-Cut.

Next, we must choose a ``Tool`` for each layer in the file. For the graphics layer, we want to choose a laser setting which will etch through the protective film that comes laminated to the acrylic, but not cut too much into the plastic itself. For my laser, this is about 8% power, speed at 150mm/s max. On this exact case I was a little strong on the laser power and it ended up cutting into the plastic a little too much, but I was in a hurry to finish with the cutter so I didn't go back and recut.

In general, it is a good idea to do some test cuts on scrap stock before you cut into your juicy new sheets of material. This is particularly true of the graphics layer since that is the only one where we are trying to cut part way through instead of a full through cut.

For all the through cut layers (top, back, core) I set power to 100% and speed to 50mm/s. For the thicker stock we will even still have to run the same cut program several times to make it all the way through the bulk of the material.

Now turn off all the layers except graphics and put the top/back/side stock on the machine. Run the graphics cut once. Then without moving the material in the machine, turn off the graphics layer and run the top/back/side program. Then lift the pieces off the cutter and remove the rest of the stock.

Next comes the core cutting, so throw the core stock on the machine. If adhesive is pre-laminated to the stock, make sure whether you should put the sheet with the adhesive facing up or down so that it will end up on the right side to stick the top plate on.


On to graphics

Design partially original and partially ripped off from other websites
by Holly Gates