Identifying plastics

[john moorhead]

Folks -

I picked up a sheet of plastic ~1/4 thick for use as part of a fence and for shielding, and I am wondering if I got the right stuff... There are no trademarks or anything on the blue plastic film protecting the plastic, so I don't know if it's plexiglass, acrylic or what. I am pretty sure it's not Lexan as they had other sheets of plastic with the Lexan trademark all over the film.

How can I identify what I have? I don't want something that will shatter with a sharp impact ala a kickback, etc. I understand the Lexan is good, but the stuff they had there didn't look like it was over 1/16" and pretty small sheets.

If there isn't a way to identify what I have, what type of plastic should I look for to use as a guard or for clear parts of jigs, safety tools and the like?

Thanks in advance,

John Moorhead Lakeport, CA

[Andy Dingley]

You got the right stuff.

It'll be either acrylic (Lucite / Perspex / Plexiglass) or polycarbonate (Lexan). In 1/4", either is reasonable as a woodworking guard.

With practice, or some comparison pieces, scratching the surface or bending the sheet will let you "feel" the difference between the two.

1/16" thickness needs to be polycarbonate, as acrylic would be far too brittle. In 1/4" though, either works. Polycarbonate absorbs more energy on breaking. If acrylic cracks, then it'll suffer a brittle failure and crack right the way through. Polycarbonate is also less susceptible to failing around a scratch or crack causing a stress riser.

Polycarbonate is softer though (so watch for scratches) and it has problems with chemical exposure weakening it. It's also flexible, which can be either good or bad, depending on how you design the guard.

I generally use acrylic, or polycarbonate in thin sheets if I want to bend a smooth curve. A good source for thin polycarbonate is replacement visors for face shields; they're cheap, and you don't have to buy a big sheet.

-- Die Gotterspammerung - Junkmail of the Gods

[Doug]

"john moorhead" wrote in news:FSjsb.178558$e01.648621@attbi_s02:

Polycarbonate/lexan will have a darker, usually blue tinted edge as opposed to a white edge on acrylic. If it's not obvious which you have you may want to peal back a little of the protective plastic on both sides and take it out in sunlight to see better.

Either may work for what you need, I don't know.

Doug

[Fletis Humplebacker]

"john moorhead"

It isn't that scientific. Wear protection and fold a piece in half. If it bends it's poly, if it breaks, it's acrylic.

[john moorhead]

Fletis -

Okay, it's 1/4" thick sheet... If I bend/break it in half in "folding" it, I'll be in the category of "it was necessary to destroy the village in order to save it." Maybe I can rip off a strip.... How far do I have to bend it? Wouldn't even poly break if I folded a strip of it in half? Any tips appreciated...

John

[Andy Dingley]

6" length of polycarbonate will usually bend back to touch itself, if you've got the strength to bend it.

-- Die Gotterspammerung - Junkmail of the Gods

[DLGlos]

Others have offered some good advice.

Lexan has a grayish/blue cast when looked at from the edge. Clear acrylic is generally water clear to very, very sligthly warm amber tinged when looked at the same way. If your have a piece of each, the difference is obvious, otherwise, perhaps not.

That said, using a sharp handsaw or hacksaw, cut off a small strip,

1/4" wide by 1" long is plenty. Put it on a hard surface, or mount halfway in a bench vise, and whack firmly with a small hammer. If acrylic, it will shatter or snap like glass. Polycarb will just bend, tear or deflect the blow.

DLG

[Mark]

Unfair analogy, Your destroying a very small sample.

A quality Poly carbonate should be able to be folded back on it's self and hit with a hammer without fracture.