Machining acrylic, cast versus extruded

We machine some covers for assemblies we make out of 3/16 thick acrylic. The last batch we made machined like a dream. I'm trying to figure out if the YG-1 cutter (hi polish made for aluminium) made the difference, or the type (cast vs extruded) acrylic made such a big difference. Cast is more expensive, but if that is the reason it machines nicer, it would be worth it to me. I have never paid attention to what was ordered in the past, but I know the last batch we ordered was cast. Will it machine that much better, or is my cutter selection the reason?

Cast is definitely far nicer to machine, nice big fluffy chips. I have, perversely, found a duller HSS tools gives a nicer finish than a sharp carbide cutter, but the carbide cutter's geometry might've been wrong - I can't remember.

Yep- extruded acrylic machines like 5052 or 3000 series aluminum- gummy and gooey. Always use cast if possible. Trick is not assume its "plastic" and I can go like hell- if your chips are melting, you're tool speed is too high- you want those nice fluffy chips. Usually carbide will last longer as acrylic is somewhat abrasive. If the chips start getting hard and crumbly, the tool is too dull and you are melting the chips.

As noted already, cast material is the way to go for anything you care about. Better machining properties, more resistant to thermal and mechanical stress. Cutter geometry can have a big effect on results. I typically use razor-sharp neutral rake HSS with 7-15 degrees of relief behind the cutting edge, for lathe work and finish flycutting in the mills. The previous comment about duller HSS tools = better finish may be accurate in that context, but typically what can happen is that if the tool has less relief, or a slightly dulled edge, it may be burnishing the surface somewhat during cutting, like a carbide insert with wiper edge geometry. It will produce a more "polished" appearance, but may also be imparting higher temps into the finished part. Four months later, the parts are crazing due to stress relief. Extruded material is infinitely worse with respect to these issues.

cast for sure. we often build prototypes out of clear acrylic and polycarbonate. these are functional test models for air flow, etc, appearance is not important. I have a source of 1/4 inch cast drops which work really well. occasionally when I have used extruded it has been nothing but problems, difficult to saw and drill and cracks at the worse times. if I have to do any bending I just use polycarbonate, I can roll it, bend it on a brake, etc. again, appearance doesn't matter, we just break these up when we are done with them.

Does the same apply for polycarbonate? Is it made in cast and extruded?