DISCLAIMER: Please note that I will not be held liable for the use of the following chemicals or making of objects such as lightboxes. Always be very careful when handling chemicals, and have a poisons information number nearby at all times. A mask and gloves should be compulsory for this type of hobby. Crude lightboxes like the one shown on this page can be considered a fire hazard. Never leave one unattended.
Most Rubik type puzzles are created with a process called injection molding. It starts with a steel mold and hot plastic is injected into the mold. This is an expensive method for building your own puzzles, but there are alternatives.
Building the simplest pieces takes a lot of effort, but the rewards are definately worth it. The materials that you will need to start building plastic are:
You need the most hardcore mask. This will be a chemical mask with a twin filter system. My friends Bell and Mango (Bell is into polyester plastics) insisted I start using a proper mask and gloves. You need a mask if you intend to use polyester resin. It is not so urgent with polyurethane resins.
So like me, get the mask, and thin rubber gloves.
A fine clay is the best to use, like Das Pronto. Learn to use it well and make your pieces perfect. The way you create your piece, is the way it will look in plastic. Make it smooth and clean. Spend time on it. The smallest faults can affect the turning ability of your puzzle.
This stuff is great. It works much like clay. When you wet it, you can use the slick to smooth over areas. Unlike clay, it's not easy to chip away sections and file. But it is good to sand. Once it dries, it goes rock hard. Basically it's epoxy plastic. Every decent craft shop will have it in most countries (if Australia can get it, anyone can), but check their site at www.milliput.co.uk if you're looking for an outlet.
Latex Rubber (not recommended)
Using rubber latex, you can paint layers on your piece to mold until you build up your mold. This is painful and time comsuming. I don't offer much info on latex anymore as it's not worth the bother. Silicone rubber is the only way to go.
This stuff is incredibly superior to latex. Latex must be painted on a piece layer by layer. Silicone can be poured and allowed to set in a few hours to a couple of days. Its detailing and flexibility is so much better. If you can afford it, you want to save time and you're fairly serious about your results, get silicone instead of latex.
Polyurethane Plastic Resin
For puzzle casting, this is the only stuff to use. It is superior in it's application, look and feel. Polyurethane uses a part A and B setup. This means that you have a can of A and a can of B. Usually mixed 1:1 or 1:2, depending on brand or type. It feels like injected molded plastic. For the casting process, Polyurethane is the one to choose.
Polyester Plastics Resin
Polyester resin, however, is still useful as a cheap filler for making solid parts if you wish to grind them down into different shapes. I wasted many months trying to cast this stuff and for that purpose, it is absolute rubbish. Even with casting resin. Some people say good things about it, but at the end of the day, it is not worth your time and money trying to get it right. For making solid cubies for later grinding, it is ideal.
Oh, and if you ever spill polyester resin, prepare for a major sticky clean up or even permanent damage to carpets or clothing. Acetone is the only thinner that works to try and clean up polyester messes. Keep it nearby. Although it tends to just thin the stickiness as opposed to working like mineral terpentine would.
Yes, lego bricks. This stuff is brillant for the modelling process. Build a wall, place your piece, and pour silicone rubber in. Cures overnight.