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135
Mold Making and Resin Casting

The Basic Single over the top mold

This is the easiest mold to make. We use this type of mold for simple parts that have a front and sides, but no exposed detail on the back or bottom, such as turret hatches for instance; or cylindrical parts with no undercuts such as a figure torso that can stand upright in a mold box. An undercut is detail on a part that would prevent it from being removed easily from a single part mold. For example, a torso with arms attached could never be done with a single part mold because the arms would prevent the piece from being removed. You would literally have to cut the mold open to remove the piece being molded, thus, in most cases, ruining your mold.

For this tutorial, we will make molds for multiple small parts at once. (Fig 1) This allows flexibility in that when you are ready to cast parts, you can cast all of them in one pour, or just the ones you need. Here we have an ammo box and wood crate.

For this mold, we can make a mold box (see 2 part mold section) but because of the small size of these parts, we will use a piece of acrylic for the base, and hot glue a small cut-off section of PVC tubing for our walls (Fig 2). With this method, you have a mold box created in about 10 seconds. Small food storage containers also work well for makeshift mold boxes.
You want to make sure that your subject sits relatively flat in relation to the bottom of the container or base you are using. . You want about a half an inch of clear space on each side of the part for stability (Fig 3).

Now, depending on the material your subject is made from, it might have a tendency to float when you pour the silicone into the mold box. . If you think it may, you can secure it to the bottom of the container with a drop of super glue.

Now that our subject(s) is in the mold box, we are ready to mix and pour some silicone.
  • fig11
  • fig21
  • fig3

About the Author

About Steve Sherman (bowjunkie35)
FROM: IOWA, UNITED STATES

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...


Comments

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