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Made in us
Dakka Veteran

Hello! I want to share some tips, Ill be updating this as i find out new things.
I am assuming you have some basic knowledge of rubber mold making and casting! If you have any questions post them or PM me!
Kind of rambly, but the information here is good!

I use OOMOO 30, smooth-cast 300, and ease-release 205. Ive made about 34 molds so far, 6 of them being for other people, who have been exceedingly happy and shocked with my ability to 100% accurately reproduce their item in casting resin.

Starting with why i use OOMOO 30. I tried Smooth-on's OOMOO type that cured in 75 minutes because i thought i would really be popping them out and just working and working and knocking out pieces that Ive molded. I found with that type of rubber, every mold i made had all sorts of air bubbles, and i basically wasted the time and energy and money i put into it.
Using OOMOO 30 gives you PLENTY of time to make and correct mistakes, and it doesnt cure so fast that air bubbles get stuck where they are.

Ease-release 205 is a MIRACLE worker. As a matter of fact I am almost out right now and i need to get my hands on some more.
Ease-release 205 does several things. Firstly, when you spray it on your project it allows the project and the liquid mold rubber not to bond together, making something you have to exacto knife apart.
Secondly, something i recently found out about it...prepare yourselves...It breaks the surface tension of the liquid rubber, making air bubbles pop!
So, what i do when i have put the 2 parts of OOMOO together in the container, i spray some ease-release into the container! Crazy right? But wait, theres more! This helps remove bubbles when you mix the two halves together. I am waay too impatient to NOT mix the two parts together like a cyclone, so i just stir it up like a glass of tea with sugar, nice and heartily, which naturally creates air bubbles.
Have no fear! The easerelease gets rid of some, and, following the directions i have already sprayed the project i am about to pour into and let dry. The real trick is, just BEFORE while the rubber is basically about to fall into the project, you spray the project nice and thick, leaving a sheen of "wet" ease release on the project. The rubber pushes excess away from the project and at the same time any airbubbles coming in contact with the excess ease release are popped! Doing this, ive had no air bubbles in my projects since i started doing it. I barely bother to tap the project to bring the air bubbles to the top. Did i mention i spray ease release on top of the poured rubber too, just to help the bubbles pop on top? Not necessary but it helps.

For the mold box i use legos. Pretty straight forward. But heres the kicker, if your mold rubber is as thick, or thicker than 2 legos high (no math here sirrah!) then the project, you dont need hardbacks to stop the mold from being distorted when its being closed with rubber bands or any of that nonsense. Unless you use a vice. Then you are silly.
I use rubber bands to close the mold. Oh, and I have only been successful with two-part molds.
As for the rubber bands, i use just what is necessary to comfortably close the mold. If you dont use the "keys" that help you "align" the mold halves when you put it back together, youll need more. If you use tiny "keys" youll need the same amount of rubber bands. If you use pencil head sized "keys" and you use about three or more of them, youll need less rubber bands. Ive found "keys" help lock together mold halves fairly well, even when ive slacked on the rubber bands.

Do not try and mold an entire model that is completely put together! Itll just end in heartbreak. I found that out the hard way. TWICE.

Now, heres another trick that circumvents the use of one-piece molds for (so far) small parts. I call it 3d molding (which, ah, all molding is 3d, but it just sounds cool. 3d molding.)
I have a couple of examples to share that i have NOT done, they are just examples that are easily recognizable so you can get a mental image of what im talking about. I do not suggest you go out and start cloning GW products or anything like that nor am i saying that i am (/enddisclaimer). Take a look at the necron immortal gauss blaster, the deathmark synaptic disintigrator, the ork burna, etc. They all have loops that protude outwards and give you hell when you are trying to place it in the clay. While making something for an rpg board game i came across the solution! Take the loop, put it down in the clay, and put it halfway in the clay like any normal other piece. This leaves the rest of the item sticking up, by itself with no support, but have no fear! Take another piece of clay, and press it around the vertical (or slanted) piece. It makes an "L'ish shape. Wa la! Problem solved! When you are ready to flip the mold and you remove the clay, youll find the piece is now upside down and resting comfortably, waiting for more liquid to be poured on it. This way, you dont have to rip the piece out of the rubber, ruining the mold, you dont have to cut it out, and you dont have to cut the piece into pieces just to get it molded!

If you are new or starting to mold you may be inclined to make massive molds with multiple pieces to "save" time and effort. INCORRECT SIRRAH! Dont do it, dont do it, dont do it!
Why you ask? Ive found several reasons. If you dont mix the right amount of casting materials and you inject (more on that later) that into the mold, now you have a bunch of incomplete pieces, or a couple partial with a bunch of sprues. If you mess up once piece in the mold, whether its when you are molding it, or trimming it, you will most likely ruin the whole thing. Nothing like your mold of 3 legs, three bodies thats 12 inches wide and 6 inches tall, 4 inches thick, producing 1 and a half bodies, and one leg. Yay.

Always do single, small molds. NEVER mold a sprue in. Just as an example (i always measure by eye, but we'll use a little bit of numbers, stick with me) lets say your piece is 2 inches across, three inches tall. So make a lego box that is what, 2 1/2 inches across, by 6 inches tall. Also, orient the piece so you can get the easiest, least noticeable piece facing the "long" end. For example, lets say you have a single leg, with a foot at the bottom, and a ball joint thats supposed to be glued into a pelvis socket. You dont want to make the foot part the sprue part because youll be cutting and damage the look of the foot. If the ball joint isnt going to be seen, who cares if it looks a little out of shape? Use that end as the "up" that has the spare inches above it.

When the mold is done, both halves are done and youve removed the piece you mold out of the mold, take an exacto knife and cut a small incision into the edge of the piece you are using for the ugly end. It should be the side that has plenty of space above it. Then, cut out a big pyramid cone chunk out of both sides. Go on. No, bigger! If youve ever cast a mold and youve filled it alllll the way up and the resin is pouring out of the top and you are like crap im wasting it panic panic blah blah but you leave and come back when its complete and you notice that there is a big hole there where there once was overflow and you take the halves apart and see that your piece is part of the way hollow and you go crap man! What a waste! This is because the air inside of the mold has escaped, leaving a void that the resin moves to fill. If there isnt enough resin, then the piece becomes hollow. If there is too much resin, then the piece becomes perfect. Thats what the cut out section does for you. Oh, you use the end of a syringe to do the same thing? Well buddy, thats called molding a sprue and you are WRONG.

Talking about syringes...I use a couple. Bought em from walmart for what, 2 dollars apiece? Dont use those eyedropper things. Use syringes. Also, when you are preparing to cast, make sure your syringe is clean, and clear. Like the shampoo? Part A of the smooth-cast 300 has a low (high?) viscosity and it causes it to run down the side when i try and pour it. Ive figured that for every 15 cc's i pour of part A, i lose 15 cc's. Thats a lot! So to fix it, i bought and specially (read heavily) marked a separate syringe to move the fluid from the part A container to the little medicine cup i use to measure volume.

Pressure casting. Do it! Do it! Without pressure casting, i was getting 1 in 4 casting "perfect". With pressure casting, i get 10 out of 10 castings perfect. 100% detail, NO bubbles, holes, all noses ears, flat spaces filled up. If you have access to a harbor freight, a paint pot is 70-80 bucks. Get a 50 dollar large size air compressor (dont bother with an airbrush compressor, too slow) and play around with it till you get about 40-50 psi. Plenty of info out there to make a pressure pot. I do not, have not, and will not use a vacuum chamber. OOMOO 30 has virtually zero bubbles naturally and its tested and true for me, but, ive seen the paint pot be used as a vacuum and a pressure chamber in one so it can be done. GET A PRESSURE SYSTEM!

Ive also found spraying the mold with a release agent prior to casting in it SUCKS. I was wondering why when i was pressure casting, some of my molds would be perfect, and some would be really bad full of air bubbles. I forgot to spray all my molds one time and they all came out perfect, so i did a few more castings without and realized some things. Those air bubbles, wernt air bubbles. They were actually the places the resin pushed the liquid/residue from the spray into leaving the resin unable to fill the spaces because they were already filled with another liquid. Also, ive found that the OOMOO doesnt need a release when you are casting I feel kinda dumb for taking a long time to figure that out.

When you are casting...preparation prevents piss poor molds!
What I do, in this exact order, every single time.
1) blow out all the crap in the molds ive chosen to cast.
2) I put the molds together, rubber banding them snugly. Not tightly, not herculean.
3) I place the sealed molds in order from most wanted, to least, with the fill cones facing up, in order out of the way but in easy reach, ensuring that I have plenty of spares incase i mix too much resin.
4) I check and clean the resin syringe, making sure it is still able to hold liquid without spilling. I place that aside within easy reach.
5) I ready 4 premarked medicine cups. I reuse them everytime. Sure, i bought 500 for 4 dollars, but i only need 4. Two are marked A, and two are marked B. Exalt +1 if you can figure out what goes in them. I make sure they are placed infront of a cut in half (horizontally) plastic clear cup, A's on the left, B's on the right.
6) I check my stir stick and mixing cup. If the stick is too sticky, lumpy, i try to fix it. If it i cant, i discard and get a new one.
7) I take my specially marked part A syringe and measure 15 cc of liquid into the A cup. Then i take the part b container and pour 15 cc of liquid into the b cup. (If i wanted to do a large number of molds at once, 15-25, id do this twice, filling all four cups appropriately)
8) I empty the part A cup into the plastic half mixing cup, adding color if wanted (for some reason, if you add color to part B it doesnt work)
9) This is when time starts ticking. I add part b to the mixing cup, letting it dribble out, then i set the cup down, immediately grab the stir stick and starting stirring. I use a largish cup because no matter what some ALWAYS shoots out and spills on me.
10) Immediately after im convinced the two parts are mixed together, i grab the resin syringe, fill it to the max.
11) I inject each mold starting in order from the ones i most want. I inject the mold, give it a squeeze to get some of the air bubbles out (not really needed, just a habit. Remember the cone and pressure casting!) and then turn and place the filled mold into the pressure chamber.
12) After the last mold has been filled (At 30 cc of material, its usually about 10ish molds done at once) i pump the syringe out into the mixing cup and ensure that the syringe isnt left "open" this lengthens the life of the syringe. (30-50 casting sets done on this one syringe so far no problems)
13) I turn around, put the lid on the pressure pot, seal it, make sure the air vent valve is shut (i added it) and turn on the air compressor. The compressor is preset so it gets the pressure pot to 40-50ish psi in about 6-8 minutes and shuts off, only turning on to increase the pressure as needed.

Steps 9-13 take me about 30 seconds to complete.
I tried recently to do 60 cc of material all at once. That ended up with about half of the material being wasted because i couldnt get it into the syringe and into the molds i had set up fast enough before it cured too much. Needless to say i was furious at myself.

Thats about it for now...Ill add more as i come to it. Hope this helps! Ask or present away!
Made in us
Dakka Veteran

Ok! Thanks for the response! Ill take a picture and explain what I have! Itll probably be around midday friday or so that i can get it out! Thanks again!
Made in us
Dakka Veteran

AG. wrote:

It would be great if you could expand on your pressure casting routine/setup - that would be great.

Uh, actually, what do you mean exactly?

Automatically Appended Next Post:
davethepak wrote:Good post, thanks for taking the time.

As a person who also casts a lot, I would add a few other thoughts;

1 - If you are getting bubbles in pooling with the release, you are spraying too much in the mold - some resins need it more than others, just spray it lightly.

2 - Be aware of the temperature in your casting area - if it is cold this could slow the process significantly, if it is very hot it could give you less working time.

3 - I pressure cast my silicon as well, this also helps reduce air bubbles - not 100% necessary, but does help.

4 - Be patient and do it right the first time - I can say a lot of good advice in this long post - if you try to rush any step or take shortcuts, you may be have wasted your time and materials.

thanks again for the post.

Thanks for the feedback and for adding your own tips!

Automatically Appended Next Post:
chromedog wrote:I just use lego to make the formwork for the mould, and then use the same stuff to hold the mould together when I cast.

No rubber bands, no muss, no fuss. No blowouts, and resin and rubber just peel off it if it gets any splash.

I'm using stuff from Barnes (my local specialist in mould and casting supplies. All the professionals use them here - as shipping oomoo or smooth-on from across the pond is crippling.

Yeah its ridiculous where im at too, and im at the very furthest 600 miles over land away from the nearest shipping place. Maybe you can try and get it from a retail store in your area? I have a retail store near me that will order it and not only not charge me shipping, but give me a 10% discount.

But, if youre happy with the results you get, thats what ultimately matters!

This message was edited 2 times. Last update was at 2012/04/08 09:29:22

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