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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

About the Author

About Steve Sherman (bowjunkie35)

Steve is a freelance propmaker (the movie kind) and machinist. A former construction worker, he has been working with tools since childhood. He learned the construction/ metal fabrication business from his Father, so to follow in Dads footsteps was natural. Since leaving the construction industry, h...


Good informative article, very interesting. I've often considered making my own castings but have been deterred by the cost and lack of advice- at least one of those hurdles has now been addressed!
JAN 03, 2005 - 07:24 AM
Informative article, thanks, now maybe I can get rid of those lousy rubber/vinyl tires...... :-) :-) :-) :-)
JAN 03, 2005 - 08:23 AM
Yep, that is what I do also. It's in the article! Thanks Again guys for the compliments. LogansDad, I also use the 10:1 ratio RTV as it is more economical but much harder to use especially for someone just starting out. I used the 1:1 ratio RTV for the artivle for simplicities sake.
JAN 03, 2005 - 08:24 AM
Great article, Steve. I recently made my first attempts at molds and casting, and it seems like fun. Your info will help a lot. Thanks for all your hard work!
JAN 03, 2005 - 01:21 PM
I was trying to use the micro - mark info but it wasn't as awsome as yours. Now I might be able to do some stuff without ruining it., or waste money to just buy one part from a figure set. Thanks for the info. Happy Modeling
JAN 03, 2005 - 04:34 PM
Well thanks a million for sharing all these nice info with us . U really capture the whole procedure in a very good way amd very simpe to follow. Now i just have to come over there and get all the materials , rubber silicone and resin ...... Super nice article Costas
JAN 03, 2005 - 08:04 PM
hi Steve, thanks so much for the great article and very good photos. I felt reading a chapter of a modelling book more than a feature.it was very very helpful. congrats
JAN 03, 2005 - 11:40 PM
Just in time. I'm actually casting a couple of alice packs and German ww2 bergens.
JAN 05, 2005 - 01:25 AM
Wow!! You all are far too kind! It was really my pleasure, but the positive feedback is great. I am getting misty eyed! *tear* :-) :-) Again, Thanks for the comments, they do not go un-noticed!
JAN 05, 2005 - 03:43 AM
it's been said,but still...great info, very well presented, nice tone, am excoted about casting! Thank You!
APR 03, 2008 - 11:28 PM