Clear Plastics and Plastic Guards

I am now making plastic guards and clear plastic sets for some machines - mostly those that I own, or those of friends. For the guards, I am using .060 PETG. PETG is a very tough plastic, but has a soft surface that marks easily. the material will also yellow over time.

For clear plastics, I am working in .090 acrylic, in four grades. All three grades have superb transparency and optical characteristics. They are also brittle to a certain degree, the tradeoff for a hard surface. The ball doesn't pose much of a threat, but the user of the machine can break them by bending them too far, or by overtightening screws (which will cause crazing).

So - don't overtighten, and don't try to pull the acrylics around, and all will be fine.


Cell cast acrylic has the hardest surface of just about any uncoated transparent plastic, and is notably clearer than PETG or polycarbonate. It is also the strongest, stiffest acrylic. It has a medium edge quality.  The AFM sample to the right is cell cast acrylic, the clear support is extruded acrylic.

Extruded acrylic is close to cell cast in physical properties;  it also takes a superb edge finish when cut with the laser, as you can see on the edge of the support.

Impact modified acrylic has the softest surface (but still much harder than PETG or polycarbonate). This appears to be what people describe as "acrylic polycarbonate". It is more flexible than the standard grades, and about twice as resistant to impact. The edge finish is less attractive than that of extruded acrylic. The washer on the right is cut from impact modified acrylic, the support from extruded acrylic.
The fourth grade is an abrasion resistant acrylic in 1/8" thickness. This material is extruded, and takes a fine polish on the edges. It has a silicon-based surface coating that resists marring - and should reduce ball trails.

here you see a triangle I made for my MM ramps (top). The bottom triangle is made from PETG. You can see the scruffy surface and cloudy edges. These marks don't polish out, they have to be flamed.

One piece of trivia is that you cannot buy ramps in the U.S. with these plastic triangles. This is because of U.S. patent 5,899,454. This patent describes a ramp very similar to the ones used in Medieval Madness (the actual game uses the triangles the other way around from the patent, which is very odd). Therefore, it is illegal to make complete ramps or ramp kits unless you have a license from the patent holder, Illinois Pinball. I'll be making these available as part of a shop-out clears kit for MM.

Finally, here's a piece of PETG cut into a "shadow" for the hunter-killer ship in T2.