What kinda plastic do I have?!

Question

The current American Woodworker has an article on making clear router baseplates. And... I found a large sheet of 1/4" clear plastic at a garage sale yesterday. So I decided to make a base.

The plastic cut, drilled, and routed very easily, with none of the brittleness I associate with acrylic; so I figured it must be polycarbonate (which I have not used before).

The article says to use either acrylic or polycarbonate, and to "flame finish" it. As soon as I touched it with the flame, it caught on fire! (actually I tested it on a piece of scrap first, so nothing was lost...)

So what kinda plastic do I have? If acrylic and polycarb can be flame finished, then I must have something different?

Ba r r y · Accepted Answer

You didn't tape that?  I would have loved to see it!Barry

Dhakala · Answer

Without knowing more, I can't tell if it's flammable or inflammable plastic. :-)

Seriously, it's probably acrylic. Flame polishing is a tricky business. Touching the flame to the plastic will very likely ruin it.Here are some other ideas for smoothing edges:

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Frank K. · Answer

One way of identifying the two is to look at the edge. If it is clear, it's acrylic. If it has a blue tint, it's polycarbonate.Frank

CW · Answer

You probably do have polycarbonate. Try taking a strip of the scrap andbending it. If it snaps, its acrylic. If it bends, its poly. The stuff burnswell, as you found out. Flame polishing is tricky. Don't actually touch theflame to the plastic. Just get close.polycarbonate

Michael Daly · Answer

Don't bother - just sand it with ever finer grits until you get a finish you like. If you want it really clear, use a polishing compound. You can use the stuff that is sold for finishing gelcoat on boats or repairs on cars. For really fine finish, you can use the finest polishing compounds for glass or metal. A Dremel with a small buffing wheel can speed things up.

Mike

Robatoy · Answer

Did the 'fire' continue to burn, after you removed the flame? Or did it go out after you removed the flame?

In the countertop business, acrylic material won't burn by themselves. Polyester (which can also be completely clear) will continue to burn after the starting flame has been removed.

The edge colour, as pointed out by another reader, can give you some guidelines.

Acrylic, polyester, and polycarbonate all smell different too. Polyester smells like fibreglass.

Brittleness, is not an indication of acrylic as it is les brittle than polyester...but I do not know about polycarbonate.

Odds are that 1/4" clear plastic at a garage sale won't be polycarbonate as it is ghastly expensive.

My bet is that you have a piece of of basic plexiglass. Plexiglas is the same chemically as Lucite: poly(methyl methACRYLate). Polycarbonate is Lexan. Another hint is that plexiglass is almost always 1/4".

HTH

Toller · Answer

Not blue, but it lit very easily and continued to burn vigorously after I removed the torch.  Polyester?  Didn't know that was a possibility.

Michael Daly · Answer

Polyester is common - Mylar is a brand name and is in sheet form. Vivak is another brand. Clear plastic pop bottles are a type of polyester.

There are lots of other plastics. Polystyrene burns easily - are you sure it's not polystyrene?

Mike

What kinda plastic do I have?!

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