I wanted to make solid plastic parts for some of my amateur science experiments. There are a number of ways to make things out of plastic, each with its advantages and disadvantages. Often just cutting raw material to the desired shape works best. Some plastics can be cast by pouring a liquid resin with hardener into a mold (see “DIY Rotocaster,” Make: Volume 41). Vacuum forming works well for making things out of thin sheets of plastic (see “Kitchen Floor Vacuum Former,” Make: Volume 11). I considered making a 3D printer, but for the few plastic parts I envisioned needing, it wasn’t worth the time
and money.
Plastic injection molding has been around since thermoplastics were invented. It’s a great way to make many copies of a part quickly, and what I like best is that it’s easy to reuse old plastic objects to make new ones.

So I built an injection molder based on the plans in Vincent R. Gingery’s book Secrets of Building a Plastic Injection Molding Machine. David Gingery could be considered a forerunner of the Maker Movement — he and his son Vincent have written a whole series of books on building tools for the machine shop.

This project should cost between $100 and $200. It depends a lot on where the metal is purchased. I had a lot of the metal already, left over from other projects. Try to find a friendly local iron dealer, rather than getting the metal online or from a hardware store. They’ll often let you pick through their cut-off pile and sell it for almost scrap prices.