How to build a Multi-Touch surface

Step 5 Prepare the acrylic

 The most important acrylic layer is the EndLighten acrylic.  This layer is the one responsible for redirecting the IR light from its sides out the top and bottom surfaces of the acrylic.  Therefore it is necessary to polish the edges of this layer in order to maximize the amount of IR light that can be injected into it.

If it is possible, I recommend laser cutting the EndLighten layer since that will automatically polish the edge to perfection.  If a laser cutter is not an option, then automotive sandpaper will do the trick.  Start with 600 grit (lower if the saw cut is rough) and sand each edge until they are perfectly smooth.  Finish each of the sides with 1000 grit.  Finally, polish the edges with a plastic polish (Brasso will work too).  Notice, the edges will still appear milky at this point, this is normal for EndLighten acrylic.

You do not need to polish the other two layers, and I actually recommend that they remain rough that way no IR light can shine into them.  The rear projection layer should be placed directly on top of the EndLighten layer.  This layer will act as a diffuser for the projector, that way the projector does not simply shine directly though the surface at the user.  The abrasion resistant layer should be placed on top of the rear projection layer.  This layer is important since it protects the other more expensive layers and is the layer that the actual user will be touching.