Cast vs. Extruded Acrylic

[Joe Peacock]

As some of you know I am making templates for the craft industry with my laser. I was wondering which type of acrylic would be best for my application, cast or acrylic. Most of the work done by the laser is cutting out the shapes in the middle and the outline of the 3 x 5 templates, there is minimal amount of lettering that I cut on the back using a single line font, vector cutting it with very low power and high speed on the reverse on the "back" of the piece so that it will show through. I get pretty good results with the extruded I am using but I was wondering if there is enough difference in cast vs. acrylic to warrant looking at it. What uses do they both best lend themselves to?
In my area the cost on 1/16" 48x60 cast is $37 per sheet and extruded 48x96 is $37 per sheet so there is better yield from the extruded.
Joe

[Tom Bull]

For your project I would go with the less cost.

[Joe Pelonio]

And the less cost is extruded. It also does cut with a nicer smoother edge.
Cast is a must for detailed engravaving but with your single-line vector font, extruded will be fine.

[Joe Peacock]

Thanks once again!
Joe

[Frank Corker]

Joe if you are making templates, extruded would be your better bet, it's much more robust and will take quite a lot of flexing. Cast acrylic although the laser engravers dream material can be brittle and can shatter.

[Mike Null]

Frank

I find the opposite to be true. Though I would still use extruded for this project as it seems suitable.

[Joe Pelonio]

Frank

I find the opposite to be true. Though I would still use extruded for this project as it seems suitable.
I suppose it can vary by manufacturer, I have really not noticed a difference in flexibility, but really haven't tested it.

For any that are not familiar, the difference between the way cast, cell cast and extruded are made may be interesting, and also shows why the price difference.

Cast is made by melting acrylic beads and catalyst and running between two sheets of stainless steel. The thickness can vary some, and the equipment is expensive. I once bough a sheet 8' x 12' and it actually showed the tapered, rounded edges from the pour which I had to trim off.

More expensive yet is cell cast, where the liquid is poured into a glass mold for each sheet. That makes the labor cost go up but results in the best clarity. It does also have the most variance in thickness.

The Extruded is cheapest because it is totally automated, resulting in cost savings for mass production. The combination of acrylic beads and catalyst are run through rollers in a semi-molten form, and squeezed to the flat sheet, much like a pasta dough machine. This actually results in a more consistent thickness but shrinkage than cast. of course that shrinkage is still minimal and not an issue for most appli8cations.

The difference in sign lettering vinyl shows the shrinkage difference in exaggeration. Cast will last 7-8 years on a vehicle, before the edges of the letters begin to start curling up. Extruded (which is called "calendered" in vinyl) will almost immediately try to return to it's original shape, and is not recommended for vehicle lettering.

Within a few months, the shrinkage results in dirt/dust sticking to the adhesive left on the paint, so the letters are outlined in an ugly gray.
I have seen 1/4" of shrinkage on 6" extruded vinyl letters after just one summer.

[Mike Null]

Normally when I use extruded I use 1/16" stock and it tends to be brittle and is very sensitive to any chemicals. Cast doesn't seem to be sensitive to chemicals--I always clean with alcohol, and it doesn't seem to be fragile. But I use 1/8" and thicker material.

[Frank Corker]

Yep I agree, it is down to the manufacturer. The extruded that I have lots of is what they make registration plates for vehicles in Europe. It's usually sprayed from the back with reflective stuff and black writing. However they take quite a battering.

[Mike Null]

Frank

What is the thickness of that material? I'm buying low end stuff from HD and it may even be .050".

[Frank Corker]

It's about 2mm or.07". I actually got given the off cuts. I use them for putting over my work piece and engrave as a visual practice to make certain its all aligned. Because it's clear it's easy to confirm that the engraving is going in the right place and it's certainly saved me from making huge mistakes on expensive stuff.

[Rodne Gold]

The "real" difference between the 2 is the polymer length , cast has a longer chain and the extruded is short chains which makes it less than ideal for structural stuff ...it's also a lot more susceptible to stress cracking (extruded) and expands in the direction of the extrusion whereas cast expands equally over its surface.
However Perspex or acrylic is an expensive option for templates , PETG or ABS or even Styrene is much cheaper and will work for this application.