Monday, October 26, 2009

plexiglass sucks

Spent the weekend cutting up a sheet of plexiglass for the table top. I hate cutting the stuff, but it seems to have worked out ok (aside from my complete inability to cut a straight line).

Ended up snagging a sheet of 36"x30" sheet of 0.203" acrylic from Home Depot for about $43 (total cost of project so far is around $120). Since 0.203" is about 5mm and the diameter of the laz0rs is 12mm, I decided to just cut 4 grooves at 45 degrees in each of the corners, then glue on a 1"x1" base plate on the bottom to support the lasers. I then cut about 8 3/4"x1/2" blocks to glue on the top side of the plexiglass on each side of the groove in order to something close to the top of the laser that I can bolt a cap on to.

The extra bits (baseplates and blocks) came from the scrap I had after cutting 3" off the sides and 5" off the top so that I ended up with a 33"x25" piece (32"x24" for projection area, 1" margin for mounting lasers and the frame later on). I also use a piece of scrap to do some test cuts and to check out the laser to make sure it was sitting about right down in the groove.

My previous experience was with much thinner plexiglass, and the only viable way to cut that was with a scoring tool. With this thicker stuff, so I was able to put masking tape on both sides of the sheet, draw the cut line, and move a jigsaw through it at about 1/2 speed without any melting or the sheet cracking. I did a test cut on some of the scrap I had left over without the tape and the blade made it about 2" into the cut before the melted plastic jammed the jigsaw blade.

And speaking of the blade... I went with a carbon blade designed for cutting metal.

For the 45 degree grooves, I cut in with the jigsaw, tried to round out a corner cut, and then just cleaned out any left over with a dremel.

Testing out with the laser showed revealed something I hadn't accounted for in my earlier designs -- the fact that lasers are very precise little bitches, and that while the grooves I made for them gets them pointing in generally the right direction there still needs to be some way to do fine grained calibration. Namely, elevate the rear end of the lasers and make sure that they're throwing the beam parallel to the glass.

Next tasks: rigging up power for all 4 lasers, doing tests to find out how far away to mount the camera, and figuring out how to mount the lasers so that they can be adjusted.

For the support frame, I'm kicking around just getting an old vanity cabinet or something to hold everything. Still ignoring the project problem for the time being.

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