Hello Geekhackers,
This is an update as well of a summary of my trek into keycap prototyping and casting.
First I’d like to thank every one of my backers which made my start up possible. It all started with this post
Uhhhh I'm gonna do it!
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and these people,
-Bunnylake
-Dgsbllx
-Halverson
-Badwrench
-SpAmRaY
-Glissant
-Lu_e
-lanlav123
-YMSNoms
-HoffmanMyster
-ApocalypseMaow
-do_Og@on
-esoomenona
Without the support of these individuals I would be several steps behind in my workflow.
When I started out with this project my mind was set on making a cast plastic figure of a modified keycap. Brobots, Clickclack, Nubbinator, and others were really inspirational to me, and the unknowns of their craft had me drawing mold making concepts, keycap concepts, and planning out my next few months’ income to facilitate tinkering. The resulting experience could be a great read, inspirational, or just plain boring enough that I’ve felt it important to detail. Trolololol to all ya bored folks. :p
Part 1 – Sculpting a Concept
Before I could make molds it was really important that a prototype/master figure was made. A surplus of gamer profile keys from Signature Plastics keycapsdirect.com were just what I needed to get going. These caps would provide me with a wide base on which to sculpt. From this base I developed the following shopping list by which to minimize cost and achieve maximum versatility with this project.
**Disclaimer: Please exercise caution when using any materials listed in this write-up. Some of them are highly toxic and a little bit of reading and use of protective clothing are conducive to a healthy lifestyle**-Super Sculpey, Polymer Clay
-Apoxy Sculpt, Epoxy Clay
-Wax Sculpting Tools (dentists sculpting tools)
-Nitrocellulose lacquers
Super Sculpey – Polymer Clay is neat. This is a thermoset which is semi-solid and bakes hard. The gamer profile keys I use as bases are PBT and PBT will not change state in the temperatures used to set this material. Temperatures for Super Sculpey, 275 °F (130 °C). 15 min/ 1/4 in (6 mm) thickness. (Not toxic, not food safe)
Apoxy Sculpt – Epoxy meets a filler material and cures rock hard. This stuff is awesome and requires no baking. The material is two-part and sets hard in 3 hours without exposure to oxygen, and no heat is generated during this process. I’ve gotten it to stick to metal, wood, POM, ABS, and PBT. High retention of detail and the end result responds well to sanding/painting. (Highly Toxic)
Wax Sculpting Tools – Every kind of poke, pull, scoop, or slice you could think to apply to your medium a standard set of Wax Sculpting utensils will do the trick.
Nitrocellulose Lacquers – Great for most applications on plastic. The lacquers will slightly harm the surface of your plastics and bond with them. The benefit is the hardness and the drawback is the permanence. Without a lot of care or brush control the only solution for screwing up is to let it dry and use MOAR PAINT! (Highly Toxic)
Between starting and following through my perception of this task changed. With it I developed an understanding that to do this one needs a little bit of coordination, patience, and time, lots of time, to dedicate to the figure. In the past few months I’ve made over 20 sculpts. Each sculpting takes from start to finish, including paint, about 5 hours. Without paint about half of that time is taken from the project bringing a complete sculpture to 2.5 hours give or take 30 minutes. I’m sure with more practice this time could be taken down to an hour, but that is a stretch.
From concept to finished product has been a bit more of an adventure than just playing with clay. These materials, in one way or another, produce a challenge to overcome by exercising great care. With Super Sculpey temperature is a problem for working with most standard keycaps, Apoxy Sculpt uses toxic chemicals to harden, and nitrocellulose paint produces fumes which make most people feel pretty terrible. Like I mentioned earlier the more knowledge one has about their medium the less it will harm person or project with just a bit of care.
Part 2 – Mold Making
Interesting sculptures are just the beginning and all of the mold-making ideas I had considered were ready to be tested. There are two kinds of molds as far as I’m concerned for this application which are known as single, and two part molds. A single mold takes the least time to make, and it is technically the least complicated to implement. The single mold is also easy to destroy for a number of reasons.
The reasons to avoid single molds for keycaps are only ones I can conceptualize. I have spent no man moments, minutes, or hours practicing key-craft with this technique.
I am primarily concerned with demolding. Demolding is the act of removing your finished subject from the mold. Most single molds are open backed or single sprue* and used to make candles, soap, pendants, or set props. I just don’t see this technique as being practical for making keycaps.
Being a two-part mold man I can say a lot about them… a whole lot. I used to think about two part molds during my breaks at work, while spending time with my fiancé, meals, and sometimes in my dreams. There was always room for improvement or a new method to ensure success until I accidentally made the best 2 part mold for my application after acquiring a pressure system.
When you make a 2 part mold it is cast in two stages and one or both parts may contain a sprue*. The first stage captures a part of the subject, and once it cures the mold is flipped over with the subject still inside the mold. After the mold is turned over a release agent is applied and another layer of molding material is poured to cast the 2nd part of the subject. When I cast two part molds I capture the top of the key and then the bottom. Capturing the bottom last ensures that the connecting joint is at the bottom of the key. The joint at which the molds connect can allow some liquid thermoset to escape and if that buildup occurs at the bottom of the key there is very little work in cleaning up the cast figure.
I will detail the methodology behind my current molding system once it proves effective for long enough. So far, at the time of writing, out of about 7 casts 4 have come out without any visible defect. There are a number of variables that cause blemishes in cast plastic, and once I narrow down the cause I can determine if the molding needs to change.
*Sprue: The path by which liquid fill enters and air escapes a mold.
Part 3: Casting
With a proper two part mold made from a proper subject I have been able to produce great casts. The process of refining these casts involved a lot of theory. At first I started with a two piece mold, measuring cups, and a pourable thermoset. The resulting cast greatly varied based on the mold design. There’s a lot of experience which developed this understanding, and to help communicate my findings I will make sure to list them as simple theories.
Theory #1: The materials and tools available with which to cast thermosets will determine the shape, dimensions, and sprue locations of the mold.
Before making my master molds with pressure equipment it took me 5-6 molds before I had a working system for successful hand-poured casts. It is also far easier to capture simple shapes and cast them with a hand-poured mold than it is something complex like my hand-e-caps.
If one were to work with a mold and hand pouring system I would recommend a low viscosity opaque urethane plastic such as Smooth-on 320/Task 3. Because making a mold is also a form of casting I would recommend the same. Smooth-on makes OOMOO RTV silicone which is great for hand pouring, and platinum cure silicone known as Mold Star. There are other manufacturers of plastic resins, and molding rubbers but Smooth-on is based out of Easton Pennsylvania which is local and makes shipping a
smooth process.
To help with understanding of viscosity here is a chart of terms/measurements for viscosity.
Approximate Viscosities of Common Materials
(At Room Temperature-70°F) *
Material Viscosity in Centipoise
Water 1 cps
Milk 3 cps
SAE 10 Motor Oil 85-140 cps
SAE 20 Motor Oil 140-420 cps
SAE 30 Motor Oil 420-650 cps
SAE 40 Motor Oil 650-900 cps
Castrol Oil 1,000 cps
Karo Syrup 5,000 cps
Honey 10,000 cps
Chocolate 25,000 cps
Ketchup 50,000 cps
Mustard 70,000 cps
Sour Cream 100,000 cps
Peanut Butter 250,000 cps
http://www.vp-scientific.com/Viscosity_Tables.htmWith my experience and a little bit of research I’ve learned a bit about my thermoset of choice, urethane plastics. To better help people understand what I’ve learned below is a point summary of useful information.
- Liquid urethane plastics are A/B mixture thermosets which generate their own heat using a chemical reaction resulting in a cured solid.
- Curing urethane thermosets are affected by atmospheric conditions including but not limited to temperature, humidity, and pressure.
- The quality of a urethane thermoset cure can be enhanced by a post-cure process. This process is usually a heat treatment @ 150 deg F. Time and temperature for post-cures are detailed in material technical sheets. Please read your technical sheets. Do not under any circumstance post cure in an oven used for food. You will poison yourself.
- Clear urethane plastics and opaque urethane plastics may react with the addition of chemically suspended plastic/dye based pigments. Reactions include but are not limited to the production of additional gasses.
- Opaque urethanes are significantly less toxic and have lower surface tensions than clear urethanes. With hand pouring techniques an opaque urethane will produce better results.
- Chemical sensitivity to parts A/B of urethanes and silicones are common and can be prevented with proper safety wear. E.g. liquid proof gloves, filtration breather, safety goggles, and long leg/long sleeve clothes.
- Thermosets vary in cure-time and pot life. The trend of thermosets is that the longer the cure-time/pot life the lower the shrinkage. I find it very hard to work with quick set urethanes as the slightest mistake will waste time and material.
Theory #2: When creating a finished product the viscosity, surface tension, and additives of/to liquid thermosets will ultimately determine the need for additional tools.
When starting out I purchased Smooth-Cast 325 which is low viscosity, but the surface tension of the liquid would impede off-gassing. The air mixed into the A/B solution would suspend and any of that air would expand once poured into the mold once the urethane began to cure as a result of its thermoset reaction. Due to the high surface tension of this material any oxygen which was in the mold and became trapped would have to be “fished” out. I used a thin metal tube or straw prodded into mold crevasses to extract trapped air. This additional step in a hand pouring process will not work with a mixed thermoset pot life under under 5 minutes. Smooth-Cast 325 has a 3 minute pot life, and every cast I made with hand-pouring failed. I could also not have used a vacuum degassing chamber as it would have taken too much time to degass. The material was most likely best for open back single-piece molds or very thick molds. If a thicker mold were rolled/turned during its curing process bubbles would have travelled into the center only to be captured. If it is not yet obvious there’s just too much to be considered when choosing materials/methods, and hand pouring will create a challenge for anyone making keycaps without additional tools.
Tools used in casting and their function,
Filling syringe: This tool is the best means by which to fill parts of a mold with great control.
Vacuum chamber: A vacuum treating of silicone/urethane before pouring will result in less cast defects. This solution requires a vacuum pump to function.
Pressure Pot: Pressurized casting is a process which pulverizes trapped air, and forces liquid into places air pockets would normally create a void in the finished product. This solution requires a pressurized air pump to achieve pressure.
Gram Scale: 90% of casting resins are mixed in ratio by weight. Scales measure weight. Zip zop boom.
Measuring cups: Buy this stuff from a resin supply place. They make these cups out of materials which will not contaminate liquid plastics and rubbers.
After acquiring a pressure pot and playing with a bunch of Smooth-on’s available stock of plastics and rubbers I have been able to work out a mold and shopping list to go forward in making 99-100% defect free casts. I’d be happy to discuss my process in great detail with anyone who is hitting a brick wall, but there are just some things I will not detail with everyone. I have a limited understanding, and I believe that anyone reading this and asking the right questions will determine what works best for them and their project. To summarize any novice caster will benefit from my two theories, and should be able to grow considerably with information contained in this post.
Theory #1: The materials and tools available with which to cast thermosets will determine the shape, dimensions, and sprue locations of the mold.
Theory #2: When creating a finished product the viscosity, surface tension, and additives of/to liquid thermosets will ultimately determine the need for additional tools.
