Identifying plastics
 

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

Identifying plastics
 

On Wed, 12 Nov 2003 05:50:30 GMT, "john moorhead"
wrote:

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...

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

Identifying plastics
 

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

...

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.


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

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



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.

Identifying plastics
 

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

Identifying plastics
 

On Wed, 12 Nov 2003 18:17:35 GMT, "john moorhead"
wrote:

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?

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

Identifying plastics
 

On Wed, 12 Nov 2003 18:17:35 GMT, "john moorhead"
wrote:

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


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

Identifying plastics
 

DLGlos writes:


[...]

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.

A blueish tint on the edge can also be seen in polyethylene or
plyvinyltoulouene (which is probably carcinogene), but these are very
rare to start with. Where was the piece in question picked up?

--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23

Identifying plastics
 

john moorhead wrote:

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."


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.



--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart. (S. Clemens,
A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure ends the
suspense. (Gaz, r.moto)