What is a SMUSH mold?
A SMUSH mold is a name I use for this type of mold. To be honest, I have no idea what the actual name of he mold is. But basically, you fill both halves of the mold with resin and literally 'smush' the mold together as quick as possible so as not to let any resin fall out. There are no sprues or vent holes.
If you aren't familiar with Homeworld...we make 3 3/4" action figures here. While 6"-7" Magnos are coming, so far and for the future, Homeworlds base figure size is 3 3/4".
Smush molds are quite easy to make. They are useful for high detail awkward parts that would be difficult orientating for a Sprue Mold. Also, they are less work. But because of the fact the resin has an opportunity to spill out when "smushing" the mold halves together there is a greater risk of a failed cast. My experiences have led me to about a 50/50 waste rate. But we are dealing with small parts so it isn't as bad as it sounds. But every cast wears down the mold and if you are throwing out half of your casts you are really only getting a half life out of your mold. OK...lets make a mold.
I have put up these pictures in order of how I make a mold. Im sure you will adapt anything you take from here to suit your own purposes and needs. I am picky so there is a lot I might do that maybe you don't feel needs to be done under your circumstances.
First we figure out where we want the mold to split and determine how to orient it on the bed. the bed is what we call the clay (I use clay other mediums can be used) base we sit the master on. I like to have it so the mold split line is made through areas where sanding is easy to get at and wont affect any detail. I like to hide it along the corners of the master is possible. Its easier to sand without maring the detail and the cast looks super clean.
Here I am making 2 Smush molds. One of Deimos and one of Marauder. One will be easy...one wont be. Cant you spot it and the problems it will provide?
|Above view of masters prepped for mold|
|Improper bedding technique|
ALSO important is to have alignment holes for your mold. This keeps the mold from moving and ensures your mold halves are aligned properly. Its a REAL bitch if you forget this. This can be done easily with the tip of the handle of a paint brush or the unusable end of a drill bit.
MAKING THE SILICONE
Generally, there are really only 3 mistakes that can happen. I managed to find a WHOLE LOT MORE...but we wont talk about me...lol.
If something goes wrong its because of 1)Improper Mixing 2) Improper Mixing Ratio or 3) Temperature. For both storing or curing.
I use Smooth On Products. They work well for me, are close by, have good MSDS and use products that results in safe casts. There are other products out there. Always follow directions.
Smooth on Products are generally a 50/50 or 1:1 ratio which makes it almost idiot proof. Of course I managed to get it wrong at least once. lol. But its very simple. You don't need exact scale weights. there is some room for manual error.
FIRST...the one thing I cant stand to stress enough and you are probably tired of hearing this by now...MIX WELL...if a spray bomb says shake for 2-3 minutes...your arm should be drop dead tired . Mix all your products in their own containers for at least 2 minutes first. Careful you don't accidentally use the same stir stick for both containers unless you have properly cleaned it. I came close a couple of times. Also...make sure you have a good seal when tightening the lids. The better the seal, the longer shelf life you will get. AIR IS THE ENEMY HERE!
In the picture above the blue molds in the back ground are not silicone. Your silicone will not turn that color when cured.
Now there are various kinds of silicones that will give you different lengths of curing times. For small molds I like the OOMOO 30. it has about a 7 minute Pot Life which works well for me. Spend at least 2 FULL minutes mixing or until you have mixed the silicone together completely so that the mixture is a nice purple and there are no pink streaks running through the mixture. Get into the corners of your mixing container if there are some.
Always be well organized because you have to allow time to put the mold together and into the pressure pot. If you have multiple molds poured at once, your silicone could already be at the end of its pot life for the last few molds and may have already started curing. So don't rush yourself or try to do more than you feel comfortable doing.
When you feel confident you have mixed your silicone properly, pour it into the mold from a reasonable height so as to produce a thin stream. This will break down any bubbles in the silicone. IF you are using s pressure pot ( I wouldn't cast without one) you can cheat a little here. You are still on POT LIFE time and need to get these into the pot before they start curing and have to calculate for the time needed. If you aren't using a pressure pot then this is an IMPORTANT step because you have nothing to stop air bubbles except this step and maybe dragging a exact knife through the wet silicone while it is in the mold to break up air bubbles. Also...where you live will impact your cast. I live 3300 feet above sea level, so we have thinner air here. if you live at sea level...your results may vary.
OK...so you have filled your mold frame...
Now lets get it into the pressure pot. If you aren't using one then set the frame aside and follow curing directions. I like to leave everything in the pressure pot for full cure, but really once the silicone has set, it can be removed from the pressure pot and left to cure on a shelf. I feel comfortable taking it out after 2 hours, you might feel that is still too long. Your call.
Everything I do is done at 55 PSI. This way if it doesn't seal right, a piece of flash gets in the lid seal and the pressure slowly drops, I don't have to worry. You generally only need about 35 PSI for casting.
The beauty of using LEGO is that you can destroy and rebuild the frame with considerable ease. I like to build up my frames high enough so that when I take them apart I can then build up the bottom of the mold. This helps keep the frame strong while I work on removing the bed from the cured silicone and master. I would NOT recommend MEGA Bocks. They deteriorate and break down. They become gummy and greasy.
This next step is quite important. You want to remove the clay bed WITHOUT disturbing the master. If the master becomes separated from the silicone mold you might have problems reseating it fully and this will create an air pocket and will distort your cast by creating a bigger pocket. You then need to clean the Master. You need all and any clay removed or it will transmitted to the mold. or whatever other media you used. And you need to do this without disturbing the master. So always make sure you pour the silicone to get good coverage of the master with the first half of the mold. This helps keep it secure. The less you have imbedded into the clay, the easier it is to clean.
Removed LEGO builds up frame temporarily on the flipside to keep frame strength then are removed and the frame built back up when clay bed is removed and master is clean. Be careful removing the clay. If the clay is stuck in any way to the master it may want to pull the master when you remove the clay if you aren't careful. If your frame breaks or becomes disassembled at this or any point, you can easily re create the exact frame with no harm done.
See how nice and clean Deimos on the left is. See how much trouble I will have later removing Marauders cast??? This is where we use the mold release. For the second half of the mold. 2 or 3 light coatings on the first half of the mold. Which is now your new bed. Let each coat dry.
Repeat the silicone procedure. Fill the second half of the mold. Put back into the pot and pressurize to 55 psi.
The pressure pot builds up pressure inside the pot. This increase in internal air pressure breaks down air bubbles into smaller air bubbles that cannot be detected by normal viewing and helps to push the silicone into hard to get places around the master. It also does the same thing with the resin when you cast.
When fully cured remove the LEGO frame.
Remove masters, follow resin instructions, fill both halves of the mold, smush em together and put into pressure pot. If your resin is TOO RUNNY you might want to let it sit for a minute to thicken up a hair before smushing the mold halves together. This is where the err kicks in. You need to smush the halves together without having any resin run out. You cant have an air pocket, and the very design of this mold works toward that. So some practice might be required.
Check Casts. Even though Marauders head mold was done improperly by my standards, it will still work, but it will have more stresses applied to the mold when removing the cast than the Deimos head cast will, so it will break down much quicker. I suspect maybe only 4 or 5 casts before its useless. Deimos...I should get 25 casts out of it easy...unless I go to urethane...but that's another post.
I hope this helps everyone some. I been meaning to do this for a while. Video takes too long to upload. If you have any questions regarding this process please email me directly at email@example.com
The next time I do a Sprue mold I'll make the same type of post.