• Raster paint: Use acrylic paint, let it dry, then scratch off with another piece of acrylic
  

     If you're trying to add a second color to a raster image on a piece of acrylic, getting the color to stay can be difficult. Shane suggests using a squeegee and avoiding acrylic/other tools for scraping off paint as this scratches the surface. At least for clear acrylic plastic, I found that letting the acrylic paint dry and scraping it off with another piece of acrylic worked very well. The flatness of the scraper means you don't remove any of the paint in the raster indentations. The acrylic surface will no longer look pristine, but if your main goal is for the raster to stand out (as it was for me with a ruler on the top arm of the camera-detected protractor), the scratches really aren't that noticeable.  If they are, Novus Fine Scratch Remover works like a charm (for laser-cutter-induced burn marks, too)! Many thanks to Jessica Ji for suggesting I use it.

• Acrylic springs: BRITTLE! Try a smaller diameter and an intermediate number of turns.
  

    An acrylic spring is easy to make in CorelDRAW: use Polygon tool (icon is a hexagon) => Spiral. You can specify the number of turns in the spiral, even or logarithmic revolution spacing, and the expansion factor. When printed, the spiral becomes springy--namely, it recoils when you pull it back. First warning: the spiral needs to be narrow in order to work as a spring, which makes it VERY BRITTLE and easy to snap, particularly when stretched to >=70% of the max. Don't pull it back too far. Fortunately, when you have the CorelDRAW file saved, it's fairly easy to print a new spring.

     In search of the best spring for an object launcher, I made several prototypes testing these properties. I found that an outer diameter that is close to the size of the object works best. Yes, the elasticity of the spring increases with diameter (you can pull the object back further and presumably launch it further with more force). However, with a bigger diameter, the object is much more likely to fall out of the spring or bounce off the opening, altering the launch trajectory. A spring that is only slightly bigger (+0.5-1 inch in diameter) than the object still allows a considerable stretch and launches more predictably in a straight line.

     I used a spring of even width with an expansion factor of 1 (as opposed to logarithmic revolution spacing/a higher expansion factor). This is because I wanted a linear relationship between spring stretch and launch force. A spring whose thickness varied along its length wouldn't have uniform elasticity, making the correlation between launch force (i.e. how far back you stretched the spring) and object trajectory less clear. I also found that a good TTD (turns to diameter) ratio is around 5-7, with my optimal value being 6 turns per inch of spiral diameter. Too many turns per inch result in a more brittle spring that is more likely to fall out of alignment with the opening (i.e. launch an object too low) due to its many separate coils. Too few turns per inch result in a more rigid/less elastic spring, though in my experience it's better to err on this side of the optimum (gives more consistent launches).

• Magnetic feet: Know the strength of your magnets!

     My magnetic foot idea for the obejct launcher/protractor is very simple: glue a washer-shaped acrylic foot to the component of interest, then glue a small magnet into the inner hollow of the foot. This helps keep the component of interest flat relative to the support surface, looks more polished than a single magnet, etc. I was very surprised by the strength of the magnets I was using. As I was hot gluing them into the washer-shaped acrylic feet, they would jump out of the hollows to attach to nearby magnet friends. Also, they very easily rip out of the hot glue and stay stuck to the whiteboard instead of the surrounding/backing acrylic. If you're using magnetic feet of this persuasion, I would suggest 1) using weaker magnets so the hot glue can overcome the attraction of the whiteboard/other magnetic surface or 2) placing a piece of acrylic between the magnet and the backing--a full circle glued to the bottom of the washer-shaped foot that keeps the magnet from direct contact with the backing. The second solution's isolating layer of acrylic also prevents your magnets from leaving gray streaks on the backing when the object is moved.