Solar Power 4: Not So Easy After All...

Today I started laser cutting the enclosure. Acrylic is probably the best material to laser cut, as it leaves straight, smooth edges. As with any material, however, the laser removes material in excess of what you specify, called "kerf". Kerf is often as small as .007" (on both sides of any closed shape), which doesn't seem like much, until you want a screw hole .098"  and the hole is suddenly 15% larger than you wanted it to be.

The laser's other problem is that it's only two-dimensional; in other words, you can only cut straight down into the material. For many applications, that's all you need, but for the two end pieces that hold the captured nuts in this design, I had to manually drill holes through the sides of the pieces where the screws will go. It's a good thing I cut lots of extra pieces, because I needed a lot of practice before I could drill holes reasonably close to being on-center. Here's just a sample of all parts I mangled before getting it right:

If you look closely in these, you can see the places where the bit drifted off to the side or the acrylic cracked and split completely.

The key, I learned, is to first drill a pilot hole using a counter-sinking bit. Instead of trying to resist the machine's natural tendency to vibrate the piece to be drilled out of alignment, you have to use that force to gently guide the part under the drill.

Of course, while that's great in theory, six holes have to be drilled for each end-piece. And one screw up (haha!) means re-cutting and drilling the whole thing.