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KitMaker Network

Mold Making and Resin Casting

Mixing Resin and Making Cast Parts
We now have our two molds ready for some resin. But before we start, let's discuss resin, the pre-cautions you should take when working with it, and the materials you need before you start.

First of all, there are many resins that you can use, but the most common for making the plastic like parts that we use in modeling is a 1/1 ratio polyurethane. There are a few variables when dealing with this type, such as working time, de-mold time, shore hardness and so on. For our purposes, we want a resin with a shore hardness of 70-75D as that sets very hard but not brittle. Most basic casting resins have this rating. There are a few variables within this range also. The brand that I work with, has a 1 1/2 minute working time (mixing), a 3 minute pot-life and gels in 5 minutes with a de-mold time of 20 minutes. You can produce multiple parts very quickly with this type of resin. Believe me, 1 1/2 minutes doesn't sound like very much time but once you start mixing, you will find that it is more than enough. I usually let my parts sit in the mold for a half an hour as 20 minutes, depending on the temperature and humidity in the pouring location, can sometimes leave the parts a bit soft, thus deforming them while removing. Resin generates heat, so you will know if the part is ready to remove or not. If your mold is very warm to the touch, let it sit a bit longer. A general rule of thumb is, the larger the part, the more heat generated, thus the quicker the part will set.

Another point about resin; Moisture is it's enemy. Always keep your resin stored in the airtight containers that it comes in and always try to use up your stock within 30 days of opening.

Figure 27 is a picture of the resin that I use and stock

The materials you need to mix the resin are pretty basic. Some clear plastic mixing cups (the same ones we used for the RTV are fine) stir sticks, some disposable latex gloves and some wiping rags to address spills.
  • fig27
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