Casting Guide

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[http://gremlins.com/denis_bohm/mold_cast.html Another casting guide]
 
[http://gremlins.com/denis_bohm/mold_cast.html Another casting guide]
  
[http://www.alumilite.com/howto.cfm?ID=2 Almilite Corporation's guides]
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[http://www.alumilite.com/howto.cfm?ID=2 Alumilite Corporation's guides]
  
 
[http://www.danperezstudios.com/workshoppages/molding_casting.htm Detailed guide to two-part molding and casting]
 
[http://www.danperezstudios.com/workshoppages/molding_casting.htm Detailed guide to two-part molding and casting]

Revision as of 03:31, 23 February 2006

This tutorial was written by Glassman and posted on the Iron-Cow forums. It is reproduced here with his permission. Links to additional guides are listed at the bottom of this page.


Contents

Preface

A handfull of folks have asked me in the past how I make molds/cast for the custom figures I make. So i thought I'd share.

I'm gonna give you my step by step process of making the mold and casting the part. There are a few methods of doing this, so this is just how I do it, not the only way to do it.

Lets start with Subject matter.

I am finally making a custom of my wife. She's been buggin me for years, but I have never made one of her. Its good to think in advance about parts you need, and who you are gonna take them from as most of you do when choosing parts.

I thought about making her from a Hawkgirl figure, but I want it to be her, not a superhero. So I went with the animated whitchblade action figure. She's got jeans, and tanktop and jacket. The only thing I cant use is her right arm. I'll show you how I got around that later.


Materials

I use a few different brands of silicone rubber and few different plastics. I was refered to some and chose to try some others. This is not an endorsment, this is just what I use. The different manufacturers that I reffer to all make a comparable product so you can get all your stuff from one place if you want. I chose different product for speed of curing and viscosity.


One-Piece Molds

For molds I use Silicone Rubber and for casts I use liquid plastic.

For 1 piece molds I use silicone rubber. Its very durable, cures fast and stretches. (Strength in stretching is important for de-molding) One piece molds are great casue you dont get the seam lines on the piece. This is done by attaching the piece being cast to a sprew. The sprew creates a opening to be used as a pour hole when the mold is finished.


Glassman01.jpg


This is Smooth Sil- 920 from Smooth-On ( smoothon.com) As with all the products I use, you mix equal parts of two compounds. Labled A & B. I mix this stuff in plastic cups-( i use litttle plastic bathroom cups), This stuff is thick so I dont pour it, I scoop it out with a plastic spoon. It is important not to use the same spoon in both parts A & B. It will contaminate one of the parts, and your Silicone wont work right after a while or worse, react and solidify in the bottle. It has a 30 minute pot-life and 4 hour cure time. Which means you have 30 minutes to work with it after its mixed and it dries completely in 4 hours.

Here is what a prepared head looks like for a 1-piece mold:


Glassman02.jpg


In this case the neck peg is acting as a sprue. The sprue is glued to a piece of cardboard (in this case foam core) and the Head is glued to the sprue. Depending on where the pointy parts are will deterine the orientation. Since Hawkman's ears are pointy, when the mold is upside down and I am pouring my plastic into the mold, the ears fill first. This limits most airbubbles.

When I'm doing heads (I know it sounds bad) with long hair or hollow heads that snap onto a ball joint or peg, I put the sprew on the top of the head and put the head upside down. This is so the mold material fills the hole in the neck and creates the hollow head when cast. Also when doing figures with long hair, the hair fills first.

Like I did here with whichblade's head:


Glassman03.jpg


Then when my mold is dry(3 to 4 hours) I force it through the little hole. This is where the strength is important. Here is the head being squezed through the sprew hole and the finished mold with the origial piece.


Glassman04.jpg


Here is the top of the mold, where you pour in your plastic.


Glassman05.jpg


  • This is where I didnt take pictures. Since I am sculpting my wife's head, I just used the mold of the whichblade head for scale. I filled the mold with melted wax, and had a perfect wax cast to sculpt and re-tool when it hardend. I forced it out through the pourhole.

Since this isnt a wax sculpting turtorial, I skipped taking pics of this part. *


Two-Part Molds

A 2 part mold is as it's named, you make 2 halves of a mold and fill each with your casting material and press them together to make your piece.

For 2-part molds I use a different Silicone Rubber from a company called MicroMark. (micromark.com) It has a 10 minute pot-life and 4 hour cure time. Its not as strong as Smoth-Sil (IMO)


Glassman06.jpg


This is poured into 2 separate plastic cups so you can get a close even mesurement (it doesnt have to be precise). Then they are poured into a 3rd cup and mixed. I sometimes use plastic spoons to dip out what I need if the mold isn't big.

You first need to make a housing for the mold. Usually a box. I am using a cassete case and mini baking pan. Vary the size by how many pieces you are making.

Here is the first half of the mold being prepared with hawkgirls arms in one and witchblade's body parts in the other. On the first part of the 2 part mold, I fill it half way and wait 5 minutes or so. This lets the rubber start to thicken so the arms dont sink to the bottom. Then I carefully place the piece being molded into. I press it till its half way in.


Glassman07.jpg


Notice that the back of the mold has been padded with clay. This keeps the silicone from seeping out before it solidifies.

When you make the frist half of the mold, you want to place the pieces in the mold so that they sit half way into the silicone.


Glassman08.jpg


Then you place something to create a locking device. ( in this picture the litte white balls) Notice they are only half way in.


Glassman09.jpg


When this half is dry, you then remove the balls(or whatever you use for a locking device) Then you add a releaser. This is so the two silicone halves dont stick together. I use Vaseline. I take a tooth q-tip and rub the first half of the mold getting it into the corners and crevases.

Then its ready for the second half.


Glassman10.jpg


Then repeat the mixing and pouring process to fill the rest of the mold. It looks like this:


Glassman11.jpg


Now, since the balls were removed they will fill the half holes left and the two molds will lock in place. This ensures that the 2 halves line up properly. When the mold is dry 8 hours later, you can pull the parts aprt with ease.


Glassman12.jpg

Glassman13.jpg


Casting

Now that your molds are made, its time to cast your spare parts. As long as you are careful with your molds, can get more pulls (pulling the cast from the mold) from it.

The liquid plastic I use mainly is from Plolytek (polytek.com)

Here is what it looks like.


Glassman14.jpg


This stuff has a potlife of 3-5 minutes (so you gotta work fast) and a cure time of 30 minutes. Thats why I like this stuff casue its cures fast. It is hard plastic when it cures. I also use Smooth-on smooth cast 45D and 60D.( Not Pictured) These are more flexable after they cure. My rule of thumb is if it bends alot I use 45D (clothing). If it just bends a little i use 60D (arms/legs)

Again mix parts A & B. I pour it in separate plastic cups for measuring and then mix the two.


Glassman15.jpg


Then I carefully pour it into each half of the mold.


Glassman16.jpg


I use a tooth pick to force the airbubbles out of the small crevases, like thumbs and fingers, corners... etc.

Then I press the 2 sides together, lining up the lock holes.


Glassman17.jpg


After cure time has passed, pull the halves of the mold apart. The excess plastic is now paper thin and can be peeled off or shaved with an exacto.


Glassman18.jpg

Glassman19.jpg


I only made casts of the arms the first time and the rest of the parts after. Since the potlife of the plastic is fast, its best to make a few parts at a time so it doesnt start curing befroe you have the mold filled. I do let it sit for a minute and then flip one half onto the other. This keeps the plastic from running out before I get the mold halves together.

Now, back the the arm problem I had. I first made casts of the left arm and right arm. Then I used the shoulder of the right arm of whichblade, the forearm of the left arm of whichblade and the right hand of hawkgirl's. I pieced these together and made a matching right arm.


Glassman20.jpg


Now if you want you can glue these parts together and use that, if you think you can use it again, repeat the mold process and make a mold of the new part (thats what I did).

Then after all the parts are cast and cleaned you can assemble them I also made the sculpt, mold and cast of my wife's head.

So here is the complete plastic figure next to the origial:


Glassman21.jpg


I hope this helps someone and answers some questions.


Other Tutorials

Another casting guide

Alumilite Corporation's guides

Detailed guide to two-part molding and casting

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