LaserUser.com Forum (formerly RDWorksLab)

Full article here - http://www.pmma.dk/Acryl_stobt_kontra_e ... Lang=en-GB

With a CO2 laser both cast and extruded clear acrylic can be laser engraved. The colour of the engraving becomes white on cast acrylic - light grey on extruded acrylic. Note that clear acrylic cannot be laser engraved with a YAG laser.

There exists also a modified Acrylic with different properties. I first ran into this with microplastics [plastic with a thin layer of different colored plastic] from Duets and Rowmark intended for engraving small signs. They are not as brittle as acrylic and are sometimes called sign acrylic and are commonly used for formed pan faces [ where the face of the sign pops out like a cake pan, it strengthens the face and gets it farther away from the light source, to prevent 'hot' spots showing on the sign]. Most plastic companies sell it on rolls that are 10-12' wide, sometimes on sheets larger than 4x8. It is expensive but very useful. The modified acrylic is sold by Duets as tactile plastic in one color to be used on ADA signage, which has to be raised letters.

Is there any way to see the difference between cast and extruded, because when I ask my local suppliers, they look at me as if I was an alien speaking a language based on farting and tap dancing. They don't even know what I'm asking about.

there is a supposedly working burn test

from https://sawmillcreek.org/showthread.php ... post343935 :

Its easy to identify , burn a little piece/strip. Extruded burns silently and drips molten flaming balls , cast burns with a crackly flame and wont drip burning pieces.

never tested myself, so can't confirm if this works.

I can't speak for areas out side the USA - but typically here the paper or plastic wrapping on the sheet plastic I purchase states "cast" or "extruded"

In my experience cheaper acrylic[extruded] is not marked at all and usually has a plastic mask, and cast will have brand name info and is labeled cast. That being said, I buy a lot of acrylics but mostly from the same supplier [E&T plastics] so usually get the same brands, and like everything in China, I am sure there is a wide variation in practices. Unless the product is made on contract for a US company, then there would be standardization.

>>Is there any way to see the difference between cast and extruded<<

While at the store during pickup, other than looking at a label or printing on the protective paper like Gene said, no, I can't visually tell the difference. Here are a couple of generalities in my experience that are not guaranteed to be correct:
* Extruded is usually cheaper when comparing the same thickness and size
* The .060"/1.5 mm and thinner is usually extruded just because it gets difficult to cast accurately
* If it is a P95 acrylic, which means it has a matte surface on one side, it most likely will be cast

The following won't help determining things when picking up, but when you get home and start cutting, you will be able to tell the difference by the cutting fume smell. Extruded has a really acrid, nasty smell. Cast almost smells sweet in comparison.

I buy my acrylic from Tap Plastics. I am in the US. The cast is paper coated and the extruded is plastic coated. It says cast on the paper.

Cast is about 50% cheaper but its properties for the edge lit signs that I make are much better and so I can use a thinner material which brings the cost back down to being on par with the extruded. The results on the thinner cast sheets are better than the thicker extruded sheet for the same price.

As an example, for extruded I may use a quarter inch sheet but for cast I can use 3/16".

I drive 60 miles to go to a Tap Plastics store but it is worthwhile as sell me offcuts (often 12 x 8) for as little as 50 cents each. These are great for all sorts of projects and prototypes.

Steve C

In my experience it is extruded that is cheaper?

Thank you for this info, I always wanted to know more about why some some of my engravings comes out diffirently...Cast vs Extruded....there we go