Casting resin parts in a room temperature vulcanization (RTV) mold is a process familiar to cottage-industry aftermarket part producers and a growing number of hobbyists.

In this process, a master part is prepared, usually by scratch-building. It is then used to produce a flexible mold using silicone RTV, a synthetic rubber. Replicas of the master can then be produced by pouring various types of liquid resins, which harden through a chemical process, into the mold.

RTV molds have a limited lifetime, so if they are being used for production, new molds have to be made as the old ones wear out.

Unfortunately, in many cases, making the RTV mold damages or destroys the master part. With scratch-built master parts, either the master needs to be repaired or recreated to make new molds, or some number of initial pristine first-generation resin parts must be preserved to serve as masters to make second-generation molds as needed.

Making masters from a 3-D model and printapart.com has several advantages:

1. Once you've learned to use the 3-D modeling program, making the masters is easier. You will be able to "make" the part on the computer, visualize it, and edit it until it's right. Compared to the scratch-build method of master creation, it's like using a word processor instead of a typewriter (remember those?!)
2. A digital model can be reused as a basis for making variants of the original. Consider how many the objects we model that are slight variations on each other. Making cockpits for, say, F-16As, F-16Bs, F-16Cs, etc., can be done with much less work since you don't have to "start over" for each variant. Instead, you simply copy files and edit them to reflect the differences.
3. Another advantage of having your masters in the form of digital 3-D models is that new casting masters, identical to the originals, can be produced simply by ordering them from printapart.com when a mold has reached or is reaching the end of its life. This makes it practical to use first-generation molds, even for parts with a long production run.