Tuesday, August 18, 2009

Tutorial: Mold Making 101

So I posted late last night on the pitfalls of making molds for small bitz for a 40K army. Today I am going to try to explain the process I went through from beginning to end and help anyone else with the learning curve. Let me first say by no means am I a expert in this, but after getting my feet wet I will give what I think are some key mistakes I made the first time around. Just as a side note, I do have a few friends who I will be getting with the first week of October who used to work at the old Ral Partha plant here in Cincinnati before Wizards got a hold of them, so be prepared for Class 102 later in October.

To make this tutorial easier to follow I will post a picture first followed by the explanation of what I did to get to that point and some things to look out for during that step.

It was late when I got around to mounting the shoulder pads and I forgot to take a picture of the "master" so this pic was actually taken after I poured the first part of the silicone. I put this here so you could get a idea of what the first part looked like. Use this pic and the one below to get a idea of what it looked like before I tore it apart with out thinking.
  • I used a plasticard base and synthetic clay to attach the shoulder pads to the card. The key here is to fill the inner part of the shoulder pad so it gets a good tight seal between the two. You do not want any silicone to leak under when you are pouring the first part of your mold.
  • Also if you look at the picture below I had a pour hole going down the center of the shoulder pads. In the picture below this is the blue clay you see. Attached to the underside of that is the tube you see left over in the first picture.
  • Of course when I bought the Lego's it came with the apparently useless single pieces which in my tired state I used as guide posts so when I pour the second part of the mold these will allow me to match up both halves exactly every time. (the lego's are worth it in the long run let me tell you)
  • After getting everything together I placed the "master" in the mold box. A couple things to remember before doing this...the clay can be messy so make sure you have all the little bits cleaned up on your master pieces. If you don't these will leave textures on your mold and pieces you wont want in your final product. The second thing is to seal the inside of the mold box with the Rubber Latex. It takes a thin coat so no need to go over board.
  • Mix your silicone according to the manufacture specifications. When you are pouring your mold, pour from one location letting the silicone run over every part so it gets in all the little creases and undercuts.
The key before pouring is to be patient and make sure you have EVERYTHING in place before you mix you silicone. Once it is mixed you have a limited time to pour it before it starts to cure. Any mistakes at this point and you may lose the mix unless it is something minor you missed.

After the first half is cured (approx. 4 hours for the stuff I used), carefully pull everything apart and clean up any flash form the mold. **Important** Do not pull the originals from the mold as you are separating the pieces. These have made a very important seal with the first half that you need intact so when pouring the second half you don't get silicone leaking into your first mold. Again, be patient and be careful.
  • During this process you need to clean all the clay or any other debris from your part. For my shoulder pads I cleaned out the insides making sure I got all the little tiny particles off the original.
  • After your mold is cleaned set it off to the side. At this point you need to clean all the excess latex and silicone from your Lego's and the area in general. Once clean make your mold box as the original, but now it needs to be higher with more depth. This will allow you to pour the second half of your mold with out spillage.
  • Before you start mixing the second half of your mold you need to treat the first half with "Rubber to Rubber" release. If you fail to do this your mold halves will bind together and you will have to cut your original out most likely damaging it and making more waste. Be liberal with the stuff. Put on at least 3 coats making sure you get the edges of your mold even going down the outsides where the two halves will meet. It will not damage your part so don't worry if you get a little excess on your original pieces.
  • In between applying your mold release you should be re-coating the inside of your mold box with latex again making sure you get the cracks. Depending on the viscosity of the silicone you may not need any latex, but that is your call.
I decided to get rid of the air chamber I formed in the first mold so I removed the tube from part of my pour chamber (i later added this back in, all I had to do was shave off the silicone in that section after it cured). Again the pour for the second is just like the first pour slow and steady and allow the silicone to reach all the areas and undercuts.

Above is the finished mold after carefully removing and separating everything I cleaned it with a soft bristle toothbrush, warm water, and some Dawn dish soap. Be careful during this part as to not damage any of your details of the mold.
  • Before you start pouring resin into your mold I will note a few things. Look at or look up the viscosity the resin you are using. The viscosity of the Alumilite I used was 190 it had the consistency of motor oil, give or take. The reason I mention this is that your pour chamber and air releases need to be big enough so the weight of your resin can get into all the crevices and undercuts and allow air to push out before it cures.
  • Also you need to warm up your mold to around 120-140 degrees I did this in the microwave for about 1 min. 20 sec. until it was warm to the touch. The resin uses pressure to get a chemical reaction going, and with the tiny amounts of fluid for parts you have to pre-warm your mold to help get this action to occur.
When I poured my first batch I made a pretty big mess as all my resin backed up because I didn't leave enough room for the air to push itself out. The weight of the resin was just to much. This is why I not only opened the air shaft but also cut the pour chamber deeper and wider. The silicone is real easy to work with and a Xacto knife goes a long way. As a side note all this stuff makes a real mess if you screw something up or are not careful, but just let it all cure and none of it actually sticks to anything so clean it up at a later time not while it is still soft.
  • Just like with the silicone mold mixes before you get all giggity-giggity make sure you mold is dry. Having even the slightest water bead will ruin that part of the mold pour and the surrounding area.
  • Mix your resin according to the manufacture specifications. Remember you have a very short time to get the mold poured and get the air to release. Burb the mold by squeezing it and try to get the bubbles to the surface. Let it cure for the required amount of time and then separate it and see what you got.
  • I noted each part of my mold and what each shoulder pad looked like to see if I could fix any mistakes from previous batches..

The picture above is my very first batch as you can see the first one has a large hole in it. This came from not getting enough resin in that particular chamber. At first I threw it away then pulled it back out thinking of the positive and realizing now I didn't have to sculpt some acid spray damage. The first mold I would say was about 40% successful, but with the quick cure times of resin you can make a ton. Just try to learn form the previous batch until you get it the way you want it.

Some things I will change in the future will be to find a lower viscosity resin (around 90) with a longer pot life. It was tough managing everything and getting everything just right to make it work out.

Thanks in advance for reading this please leave any comments to help me adjust or make it better. Hope you enjoyed reading this and it has helped you out or at least made you aware of the possibilities of molding. Any adjustment I make at a later date will be posted in blue to help you better find anything that may have changed.

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