HDPE/Acrylic/Nylon/RG1000

[Ocracoke]

Angle grinders will spin too fast and melt the plastic I would have thought, I can melt it with my Dremel and a cutting disc attachment at full power. I too am going to borrow a jigsaw and a workbench to cut the side panels for my featherweight. Like wood, I would think using a junior hacksaw to make a guide for the jigsaw would help ensure a straight cut (least that is my plan anyway).

[Roboteernat]

I would plan your parts on the big sheet, then see what managable size you can cut it to to neatly trim the parts from that.

jigsaw - if budget is problem then the cheapo jigsaw from argos shall be fine - £17.99 http://www.argos.co.uk/product/7110948 but if budget is better then i would get a better one with variable speed control and bigger wattage. i bought a battery one from Lidl for £39.99
People have used fine cut hand saws to cut it too, i guess this will also lead to straighter edges! also clamping some wood to run against will give you a nice edge https://www.youtube.com/watch?v=EFCGYVH1frc

[Liftoff]

You need wood working tools for HDPE, so no angle grinders and such tools. A jigsaw, crosscut, mitersaw or manual saw will work, then finish off with a hand planer to get a good finish or take small amounts of material at a time and get a good fit.

[RogueTwoRobots]

Don't use an angle grinder for main cuts on plastics, use a jigsaw as advised. But for getting nice smooth surfaces and small chamfered edges, I use a angle grinder for that stuff. Either a standard grinding disc or a flap disc. It will melt easily but the discs just power through. Best to make light passes, and prepare to be covered in plastic dust