Fab Academy 2012 at AS220

Week 4: Computer-Controlled Cutting - Cam & Gear Box

As a side project, I've been working to miniaturize and create in acrylic a cam and gear box I ran across in a book on automata and mechanical movements.
Cam Box in wood

Tabs in the original plans accounted for the actual thickness of the acrylic (.220"); tab-depth was adjusted accordingly to ensure none of the tabs extended past the edge of the joining sides.  The first prototype was cut from paper-backed display board.  Not an ideal material for prototyping:  the laser cut cleanly through the top layer of paper but not the bottom.  Additional attempts were made using slower speed, higher power, and/or multiple passes -- however, the foam core tended to melt anywhere from 1/16" to 1/8" into the pieces, raising concerns that they would not give me a true sense of fit, due to compromised structural integrity.

Foam board prototype

for the press-fit exercise, I modified plans for the bottom support beams to make them fully inter-lockable.
Mod sketch

Comparison of original and press-fit SVGs
Three attempts were made to cut press-fit box: two in plywood, and one in masonite.  Plywood attempts failed to cut completely through the wood.
plywood try

The Masonite trial was my first experience with Flaming Things In The Laser Cutter.
Ooo, crap!

Root cause -- a previous student had used a plywood with high sap or glue content. Thorough cleaning of lens and mirror eliminated the charring, but no luck with full-depth cutting (1/8" masonite, so well within tolerances of the Epilog).  Inspection of the machine suggests that a full maintenance cleaning and calibration is due.

While I do not have a box to show, I did learn this week that the word "kerf" comes from the Old English cyrf, a cutting, and has been used to designate the amount of material lost during cutting since pre-industrial times.  Early sawmills used large cutting blades with kerfs exceeding 6 inches.  Spontaneous explosions due to a saturation of airborne sawdust was common.