They are actually both polycarbonates, in fact a lot of plastics are polycarbonates it has to do mostly with stuff like crosslinking and such. But the two are sold usually by the same people like our friendly local Home Despot, and they differentiate the two by calling one by the trade name plexiglass and the other polycarbonate, Polycarb is distinctly more expensive and stronger, and harder to polish.

 

Excuse me please, it seems I spoke in haste (too many years out of the field). You are right, in that Plexiglas and polycarbonate are different materials. The trade name I was thinking of was Lexan, which is GEPlastic's name for polycarbonate. Plexiglas is the trade name that Rohm and Haas Co uses for their Acrylic, which is definitely a different material.

Each of these materials has different blends, resulting in different properties, but each is an amorphous material. The cross-linking you refer to is a process typically used to improve structural properties of polyethylene, which is a crystalline material. It is not a distinguishing factor among polycarbonates.

 

I have used a jitterbug sander to smooth edges that will show. Works well.

 

That Lexan is strange stuff. We use it all the time for machine guards at work. Did you know you can actually put Lexan in a metal brake and bend it 90 degrees? We do it all the time, no heat or anything.

 

Lexan bends once, just don't try it again.

When drilling in plastics I sometimes grind a special drill for the job. Use a very very small rake angle and a 15 degree clearance/relief angle. The drill bit looks like it would scrape the material out rather than cut it. The point should have a ~60 degree angle for thin material and 90 for thick material.

For odd shape holes use a teflon coated scroll saw blade.

Band saws work better than circular saws (cooler). Tooth offset should be such that the cut is twice the thickness of the blade

You can use soapy water for coolant and lubricating the tool. Air can also be used to cool the tool and blow chips away.

 

Lexan is the stuff used for bullet-proof windows at banks (and quickie-marts). Thinking that if a little is good, then more must be better, it was soon discovered that after a certain point, Lexan starts to become brittle again. While a 1" thick window could stop a .357, a 4" thick window would shatter like tempered glass.

Don't know how they discovered this. Maybe they studied the mortality rates of bank tellers and 7-11 clerks. Maybe they went to the local gun club and said "Here, see if you can break this."

When machining polycarbonate, slow and steady is the rule, and heat is the enemy. Tool marks can be polished out - heat crazing and chips cost extra.

 

I work for a Plastic distributor. I run a saw cutting plastic all day long. It depends on how thick and type of plastic you are cutting as to which type of blade to use. But generally speaking, any thing less the ½ inch thick a 10 inch carbide tip blade, very sharp, with about 80 to 100 teeth should do a good job. To Fast and it will chip, to slow and it can melt. Practice on some scrap pieces until you find the right speed if you are using hand tools. All my blades are a Triple Chip Design. Where the cutting edge of every other tooth is beveled. The beveled tooth, or crown tooth, removes the material in the center of the cut while the flat-top raker tooth follows behind, removing material from the edges of the cut. This results in the production of three separate “chips” – center, left side and right side – and hence, the term triple-chip design. On some designs, the flat-top raker tooth also has very slight bevels along the top side-edges of the tooth. This helps to reduce chipping by reducing the notching affect caused by a square cutting edge.
The masking on the Acrylic sheets do help protect the material from scratching while you move it around and also help in the cutting . It doesn’t cause the plastic to melt. But an improper blade and feed speed will.
Plexiglas is used as a general term to describe a clear see through plastics. At least where I work it is. Acrylic comes in clear and all most any color you can think of. Lexan or polycarbonate is about 300 times stronger then acrylic. Acrylic is about 15 times strong then glass of the same thickness.
Lexan has a higher moisture content. It’s takes a little more finesse to heat and bend. Acrylic is easy to heat and bend.
If you want the edge to look good, run it through a jointer. Remove about a 32 or less. Then use a torch to polish the edge.
The heat melts it smooth.( Practice, Practice) . Keep the torch moving, don’t stop. Start at one end and keep a steady pace to the other end.
Drilling , Clear the out the hole very often. If your not using bits designed for plastic. Us a air or a Coolant to keep the blade cool to help stop melting.