This goes for any prototype or one of a kind piece; Go online and study and find the best ideas of everything that is out there. Step 2, you "borrow" them.
I take cardboard, a sharpie and a box cutter and I mock up what I want to build. Then I get comfortable and stare at it for a long time(wine or corona helps), making improvements as they come to me. It's difficult to build something as well as something in production, but when you get finished it is your's! (except for the good ideas you stole, I mean borrowed)
The plastic I bought is something the plastic company said was their most UV resistant material. I imagine it is similar to starboard. IIRC it cost like $180-$200 for a 4'X8'X1/2" thick sheet at a wholesale plastic supply company. It is soft compared to pvc. I bought a sheet of 3/4" pvc and I tear up bits with it left and right. It is too hard.
I use a table saw, router with a router table and a circle jig that I bought. You can make your own though. I used an 1/8" round over bit with a bearing on top, and a straight bit.
One side of the plastic should be covered in a thin transparent cover. Draw your plans on that side. Drill your center holes for the circle jig. Cut the circles, largest first. Then cut the straight edges on a table saw. For the small radii on the corners, I eyeball them and do them with a disc sander. The kind that has a rest in front of it to keep the piece square. Then run the piece over the roundover bit. Scrape off the fuzzies that are on all the edges and voila.
The plastic clamps I made are done by drilling a 1" hole and then cut a notch in it with the table saw. ( done with a drill press to make them go through perpindicular, very important) Drill the hole through it and drive in a 1/4" SS bolt. Drill the threaded part 3/16". Don't thread it just drive the bolt in with an impact. Stopping before you get to the end. Then tighten it by hand. They grip that tube suprisingly well.
You can also drill through and through and put a nut on the end if the design allows.
The more pieces you make the better they get. Plastic is pretty cheap so jsut keep making them and messing them up until you get something you can live with.
It's not for everyone. If I had the money I would just buy what I want. but with some tools, patients and the ability to fail until you get it right, anyone can do it.
