For a very clean cut I like using a
20-teeth-per-inch hollow ground blade.
There is no set to the teeth like on most blades, and the teeth don't hook upwards like a wood blade. On plywood the cut rivals a bandsaw cut, looking almost sanded, and it leaves the best-finished edge I have ever seen on acrylic. I have even used it on aluminum as thick as 1/4-inch, slowly, with plenty of lubricant.
I have used it on aluminum composites, and it seemed to work great. Because the teeth have no set, the blade gets hot. I go slow and change blades fairly often. I don't mind running through extra blades if the result is near perfect.
The down side of the blade is that when cutting heavier material, or multiple layers at the same time, it gets hot enough to break without warning. When making channel letters, I used to cut 2, 3, or even 4 acrylic letters at the same time this way in the "before router tables" era, and when the blade broke it often marred the face of the letter on top of the stack. So I started cutting all letters from the back side, which solved the problem unless an acrylic letter actually cracked when the blade broke.
Also, the heat generated by the blade will melt cheaper grade acrylics so that the cut will virtually close back up behind the blade. But it was not a problem on high grade cast acrylic, like Plexiglas GP.
I bought these blades, of all places, at Sears. The package was labeled "fine tooth scrolling blade, hollow ground." Of course, they didn't fit my Bosch's proprietary mounting system. But any commercial quality jigsaw/sabre saw with a 3-1/2 to 4-1/5 AMP motor will have similar power.
Brad in Kansas City
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I found this in a search. It looks like the blade I'm referring to. The description doesn't say "hollow ground," but it looks like it in the picture. And it has the T-mount shank. Also note that the blade is not as wide as a regular wood or metal blade, allowing for tighter turns.
Bosch Jigsaw Blade, T-Shank, 3 In. L, PK5 T101AO | Zoro.com
Brad