Friday, November 25, 2011

How to make a mold

I hope you all enjoyed a wonderful Thanksgiving! This year I gave thanks for Super Dungeon Explore! Of course I also gave thanks for my family, friends, and health etc., etc. :). But I was thankful for the extra vacation time that allowed me to dig into my miniatures hobby again. Since I've posted my how-to on making bases, I felt like I should complete the tutorial and post a how-to on making a mold of the bases I sculpted. The perfect opportunity came up with the full release of the Super Dungeon Explore game from Soda Pop Miniatures. The game uses 50mm bases for some of the bigger miniatures and it required me to sculpt a 50mm base to carry on the theme of the stone bases to all my SDE miniatures.

So I took to my sculpting tools and sculpted a 50mm base using the one provided with the game as a base for my base (yes you read that correctly). Nothing different or special. Used the same pattern as my current theme

Next I made a mold box from Legos. This is the best thing to use for mold boxes since you can make molds any size you need. Want to fit more pieces in the mold, just add more Legos!

The only problem I found with using Legos is that the silicone rubber would get into the cracks of the Lego blocks and would be rather cumbersome to clean after. so  to remedy the problem I started lining the inside of the boxes with blue painting tape and since then clean-up has been easier.

So next I take a piece Styrofoam(or plexiglass) and first glue my sculpting master to the Styrofoam using wood glue like Titebond II. The wood glue is strong enough to hold the master down in place and still makes it easy to remove the master afterwards without damaging it. Make sure the Syrofoam lays flat on a surface and has no indents in it. The master needs to lay as flat as possible so no RTV can get underneath it and can mold properly. Be sure to glue only the edges of the master so it can seal it as well. Next take your mold box and also glue it down to the Styrofoam. Be sure to glue the edges only since your aim is to seal it from allowing any silicone rubber to leak(as well as holding it down).  

Since my sculpted base is made from dental plaster, I then took some Future shine and brushed it on the master to seal it so it can release easier and not tear the silicone rubber in the process.

Looks nice and shiny huh? :). So I let the Future shine dry for about an hour before I do anything else. I am sure it does not take that long for Future floor shine to dry but I am a bit over-cautious. Next I take some Smooth-on Ease Release 200 and spray it on the mold box and wait 5 minutes for it to dry. Be sure to spray this in a well ventilated area or maybe even outdoors. The odor from this pretty strong and I am sure it's not safe to breathe the vapors from it.

Alright so here is a bit of info that I know on silicone rubber products. You have typically 2 types of rubber that are made from silicone. Tin-cure and Platinum-cure. Tin-cure is very versatile, cheaper, but as a side effect can tear easier and usually needs some type of release agent with casting resins since the heat from the chemical reaction can slowly damage the mold over time. Platinum-Cure is more fickle and will not cure if the master you are molding is made from latex or has sulfur in it which typically is most things made out of clay.  But it's strong point is that it can not tear easily, can even withstand being cast with low melt metals, and you can cast resin with it and not even use any release agent if you choose. Molds that are made from this rubber have a shelf life of at least 3 years. Platinum-Cure rubber is a lot more expensive but well worth the price you pay. I have made over 100 casts with resin and no release agent with  a platinum-cure mold I made and it still looks brand new.
For most of my hobby molding needs I use Oomoo 30 also from Smooth-on. It is a simple to use 1 to 1 ratio Tin-cure silicone rubber. Not my first choice but I will get the occasional 40% off coupon from Blick Art in the mail which makes it the perfect choice for making hobby molds for the price. The product I recommend for a long shelf life and over 100 casts is Mold Star 30 from Smooth-on. For the extra money you get a high quality platinum cure product that is easy to use.

So you have to do a little experimenting with how much silicone rubber you're going to need for your mold. The best thing to use for estimating the amount is rice. I tried using water before but some water droplets get left behind in the mold box and then reacts with the silicone rubber while it cures and can ruin your mold. Rice is dry and can get cleaned up easier and it gives you an almost exact measurement of what you'll need. So then I poured out the 2 rubbers into 2 separate cups making sure they line up pretty evenly. if you go a bit over it's OK, Tin-cure rubber is more forgiving than platinum cure. I then pour the blue rubber into the cup with the pink one. The blue rubber is less stiff and flows easier out of the cup. Be sure to wear gloves when using silicone rubbers. Rubber is hard to clean off your hands and will require the use of paint thinner to remove it completely(or a good 30 minute shower works too).

Next take an acrylic rod and mix the rubber together for 2 minutes. The rod helps by minimizing bubbles in your rubber and that is definitely what you want to avoid when making molds. Bubbles in your silicone rubber can prevent your master from molding properly and capturing every detail of the surface. Oomoo 30 has a light purple color when it is mixed together so take care to make sure it is well mixed or else you'll pour unmixed rubber into your mold and it won't cure. Let me tell you there has been many times when I ended up with uncured rubber in my molds and it always happens to be right on the master so basically the mold becomes unusable.  Sometimes I pour it into the other cup I used just to be sure it mixed all the way through.

Next take an old but clean brush and brush some mixed rubber onto the top of the master. This insures that the little details on the top surface will mold properly after you pour the rest of the rubber into the box.

To minimize the bubbles that can form while you pour the rubber into the mold box, I usually hold the cup about 18 inches from the mold box and slowly start to pour a small stream of rubber into one of the edges of the mold box. Try not to pour any on the master and just let the rubber flow over it till it's covered up completely. It will get messy, very messy, but once the rubber cures you can just peel the cured rubber from any surface it fell on. Now just let it stand untouched and uncovered for a minimum of 6 hours.

So this is what you it should look like in after 6 hours if you mixed and poured the rubber properly. You might need to trim some of the edges of the mold if some rubber got underneath your master during molding, but otherwise it is ready to use. Casting it in resin is a similar process. You also pour equal amounts of resin and then mix together and pour it into the mold.

Here is a comparison of the sculpted piece and it's duplicate cast in Smooth-cast 300 from Smooth-on. I was impressed since the rubber actually molded the surface detail properly without any visible defects. This ended up being one of the better molds I have made as far as quality in the detail that got molded.

Already getting mass produced for all the miniatures in the game.

And as you can see the SDE Angry Bear is excited about his new base he gets to stand on. His hands are up in excitement over it :P. The new base is more sturdy then the stock base and will survive all the handling from gaming with it. So now you should have all the tips you need to start sculpting and molding your own bases. If you have any questions always feel free to ask and as always... Keep on gaming! 

P.S. as promised here is the templates for the bases. It should print to a 8-1/2 x 11 sheet of paper if you save the full image size by right clicking the picture and opening it in a new tab.