Some people from the Modern GB asked I would put some information on casting. So without further adoo…
Items you will need before we can start
Ok…time to make a shopping trip. Don’t use your wife’s (or girlfriend’s) kitchen stuff as once she sees what you are doing you might be in pain![#dots]
These are the common items needed, you may have some that you can use but ask the kitchen boss first:
- A digital kitchen scale or a decent analog spring scale, preferably measuring also in grams. ~$20 - $50 (Bed Bath & Beyond or similar)
- Small graduated measuring cups, For starters nothing more than 400 ml. ~$2 (Bed Bath & Beyond or similar)
- Small set of Lego blocks with a Lego board. A nice size for the board should be about 6 to 8 inches square. ~$10 (E-bay) or for small five sided items an old Altoids box or similar shallow box.
- Bag of Popsicle sticks. $2 (Michael’s or similar)
- Clear bathroom cups or small drinking cups. ($3 Sam’s Club or similar)
- Scrap card board, paper towels, and a table to work on.
The “stuff” consists of two parts. One is the material to make a mold the other is the casting resin to make the parts.
- Smooth-On Mold Max 30 molding rubber, one quart kit for $30
- Smooth-On Smooth Cast 300 series casting resin, starter kit $30
You can find these products at:
By time you are done you will invest ~$95 - $125 to set up your casting. This will allow you to cast simple small parts like bedrolls, ammo boxes, tires, etc. Complex shapes and large size items won’t work well and become very difficult (unless you become very good at this at which point you may be doing more of this and less modeling).
Be advised these casting products, based on the manufacturer, have a limited shelf life ~2 months once opened. They also go a long way so if you are going to try this you should line up a number of things you want to make. Make molds of all the items and then cast your items. Think ahead and cast spares rather than throw away spoiled resin. Look at what you want to cast and what you think the value may be to justify the expense of doing your own casting. This may not work for everyone.
Making the mold
There are two types of molds. A five sided mold, where one part is intended to be glued to the model and will not show. These are the easier of the two. An example is a backpack or bedroll or what I am showing here a doors
Layout what you are going to mold and leave space between them, I like 2 Lego stick ups all around each item.
Begin building Lego wall around all the items with the same spacing of 2 Lego stick ups.
Make the wall a minimum of 1 block taller than the tallest item
For these types of molds I like a flat bottom finish so cut a piece of cardboard the size of the floor and insert it. Use double stick tape and hold down the item you want to cast.
Now we are ready. First figure out how much compound you will need to mix. Measure the length, width and height in inches of the inside of the mold. Then take out the old calculator, convert the fractions to decimals and
Length x Width x Height x 16.387 = XX ml of compound
Weigh out in a measuring cup the Part A rubber (white material in big jar). Measure to the volume you calculated above. Now look at the scale and weight you have of part A (hopefully you zero the scale with the empty measuring cup first). Take that weight (I find it easier if the scale is set to grams) and divide by 10. Add that amount of the cure agent (red stuff in glass bottle. It is important that you get the correct ratio of 10 to 1 part A & B “BY WEIGHT” of the Mold Max 30. Stir with a popsicle stick until the mixture is uniformly “Pepto Pink”.
Now we are ready to pour. This material is thick and holds air. Since we don’t have a vacuum unit, we get the air out by pouring very slowly from about 2 feet above the mold. As the material stretches out over the pour the air is released. Once the mold is full, put it off to the side as it will need a good 24 hours to cure. Any minor spills or the measuring cup will be easier to clean when the material cures.
After the mold has cured, peel back the Lego blocks down to the board and take out the mold.
Remove the master items and you now have a mold.
Casting a Part in the mold
OK…You are half way there. Now we are ready to cast a part. First, let’s figure out how much compound we will need for the part. Put a measured amount of water in your measuring cup, about half full to a whole measurement (I prefer ml as opposed to oz). Drop the part into the water and see how much the level increases. That’s how much compound (with maybe 10% extra) you will need. Since the casting compound is mixed 1 to 1 “BY VOLUME”
Using your throw away plastic cups and water, measure ½ the amount you will need using the water and put it into your measuring cup. Pour it into the throw away cup and make a pen or tape mark on the cup. Now add another ½ amount of water and make another pen or tape mark. Pour out the water and dry you cup (make sure it is completly dry)
Fill the cup to the first mark with part A. Fill to the second mark with B and mix with a Popsicle stick. As soon as it is mixed pour slowly into the mold. Remember, your time is limited as this material begins to cure anywhere from 3 to 10 minutes after you mix them (depending on which one of the 300 series compounds you buy. Longer is better)
Mixed material cleans up better after cured. Separate A or B needs to be wiped up. Now wait until material cures, ~10 - 30 minutes. You will see it turn completely white from clear.
Once cured, pop the part from the mold
TA DA!!! You did it.
Tires or all sided items are molded in a split mold. Everything is done the same as above except you have to cut ~2/3 the way around the tire or part to get it out. Then you just refill the mold and once cured open it and remove the new part.
Once the split mold is closed you pour the resin in through the top.
I am by no means an expert at this and I have to thank an instruction seminar at AMPSEAST on casting and hints. After this, it is trial and experiment and find what works for you. Hopefully the bit I have shown here is enough to either get you started or based on your circumstance, convince you not to try it. (I’m no “Doog”) (Trust me, I’m better with slide presentations)[banghead]
This is not worth the investment unless you cast up a whole bunch of stuff you know you are either currently or going to use in the future or making one of a kind item over and over again. As I said in the Modern GB, I needed about 120 105mm ammunition crates for the build I was working on and since I have other builds of 105mm, I will probably cast close to 200 crates!! That alone will take care of my investment.
Next let me say, this is time consuming. Between making molds, casting items, trimming (if required) finished items and cleanup. You need to plan to either have a separate spot or table for casting. When your casting, your casting…its not like working on kits where you can switch from one task or kit to another. You don’t want to mix the two.
Lastly, let me say again, DO NOT COPY items and sell them. It is against the law. Make items for your own modeling use only. Otherwise have fun!!
Hope you enjoyed this and maybe get something from it!! (I tried)[:-^]
Any questions feel free to ask.
Rounds Complete!!