Introduction: Assistance Dog Light Switches
Hello, this Instructable will teach you how to create a small series production of customized light switches.
It will demonstrate how to customise the switch, two different molding techniques and one casting method.
This is a project assigned to us by Hachiko, an assistance dog training center. It was a project of cocreation to provide a solution for a specific end user and a specific problem. We are three students industrial design at the university of ghent, Belgium. You can find a detail of the design process on our blog. http://dominolichtschakelaar2014.blogspot.be/
Julie has motor control problems due to a degenerative disease. Julie goes through life with the help of her companion the assistance dog Eclips. Her house is adapted, the doors for instance are replaced with sliding doors attached to a tug cord. Julie can ask Eclips to open the door and because the door is adapted Eclips can comply.
Julie wants Eclips to turn of the living room lights. The living room lights are accesed from the bottom switch of a stacked switch. Because of the height 1m20 (47 inches) at which the switch is positioned Eclips touches all of the three switches instead of just the bottom one.
We found a solution, a simple triangle. Key design rules: The triangle should start above the center and should be between 20 and 35 degrees in angle.
(This is a short wrewrite, Instructables lost my elaboration and I'm not going to write that all back up)
Step 1: Customisation
In our case the design has the aim to be unobtrusive. Only the assistance dog Eclips should notice the difference. Care was taken to match the fillets and the texture of the original switch so the end result would blend.
Think about how you want your switch to look and make a shape out of any material. We had a simple design and used a soft wood.
Now pry of the housing. To do this you insert a screwdriver at the bottom of the housing and twist. Work your way up, alternately left and right, inserting the screwdriver underneath the housing and twisting. Once you're over halfway it should pop of.
To pry of the switch push the switch to the right, insert your screwdriver underneath the right edge and twist. Caution: make sure you have an insulated screwdriver/glove or temporarily turn of the power. You shouldn’t be able to electrocute yourself but better safe than sorry.
When you’ve got the switch, glue your design onto it and start finishing the piece. We used modeling clay (Fig. 2) and fine filler (Fig. 3) to finish the edges. Apply the filler in thin layers with a plastic pallet, wait for it to dry and sand the filler. Keep repeating this process until you receive the result you want.
To get a glossy smooth finish you should sand with a 600+ sanding paper and finish the piece with varnish/lacquer.
Our aim is to copy this piece, not to actually use it. Casting your own switch has advantages.
The triangle and the switch will be one solid component making it a wear resistent solution.
When you only need one switch changed you can stop here. However the switch may soon start to show wear and tear (adhesive coming loose, filler breaking of, fading color on the place you frequently touch,…) so even for one switch we advise to continue the instructable.
Step 2: Mold Design
- finished master
- correct silicone mold
- correct resin injection
Thinking about how you will design your mold in advance will help you with the last two items on that list. There is one key concept to keep in mind: air rises and gets trapped in high negative shapes. This applies for pouring the silicone mold and injection of the resin into the mold.
Silicone mold air traps
When you pour the silicone it will rise slowly upwards, any negative shapes will trap air and result in a failed mold. In our switch both pins and the triangle will catch air, resulting in three air cavities inside the silicone. (Fig. 1 & 2)
The correct placement of the master is with all negative cavities pointing up. (Fig. 3) Now the silicone will flow into these cavities filling them.
Now you created a useless two part mold. (Fig. 4) This mold is missing the injection point and the air escape holes.
Resin air traps
The resin will trap air in exactly the same way. All highest negative points of the cavity will trap air. (Fig. 5)
These highest points need to be provided of air escape holes. (Fig. 6) Off course you should supply all these holes in advance, drilling through silicone is difficult. We provide one bigger injection point so a 20cc syringe can fit in. Air escape holes are provided on multiple places to ensure the air can get away. (Fig. 7) The mold is then suspended at the correct orientation ready to be poured.
Result (Fig. 8)
The result of both steps is a silicone mold you still need to cut apart but that will create a great copy.
Step 3: Preparation
Before we start making a silicone mold and casting resin copies of our design you need the materials.
- Mixing cups
- Scale (preferably 0.1gram accuracy but kitchen scale will do fine)
- Protective throwaway gloves (latex, nitril,..)
- hot glue gun
- kebab sticks
- (moddeling clay)
Condensation curing silicone
- Condensation curing silicone
- MEKP hardner for your silicone
- (Vacuum chamber)
If you cannot get the silicone you could use acetic curing silicone to make the mold. (Step. 7)
- 2 part resin casting system (isocyanate & polyol)
- 20CC syringe
- (Pigment coloring)
- (Pressure chamber)
- Sanding paper
Step 4: Build the Mold
Use sticks and hot glue to provide the master with a pouring hole and air release holes.
Cut the kebab sticks (Fig. 1) into smaller sticks and attach them, according to Step 2, to the piece using hot glue. You can provide a clearly bigger pouring hole using bamboo. (Fig. 2)
It is best to place the pouring hole in a low part of the piece and the air release holes on the highest parts.This way air will be pushed out when the resin is poured in.
We need a closed encasement to pour the silicone in. The mold box you can make using cardboard glue and tape. We used perfectly cut wood, sargeants and moddeling clay (Fig. 4 & 5). It doesn't really matter how you build it, most important is to make watertight. Make shure the encasement is at least 1cm bigger on each side (left, right, up, down, above, below) of the master. Calculate the surface area of your box in square centimeters. Now multiply with the height you'd like.We chose 3,5cm high for a total volume of 8cmx8cmx3,5cm = 224cm3. Your volume should also be in cubic centimeters.
Suspend the master in the encasement using the rules in Step 2.
Step 5: Condensation Curing Silicone Mold
Gather your materials, put on your gloves and provide a protected working surface.
Check the specifications of your silicone.
It should note a density. Ours is 1,15g/cm3. Wich means our 224cm3 translates to 256gram of silicone.
Our ratio is 100:4. We divide 256/104 and multiply by 100 to get 246g of component A.Since component A is in the big bucket and is hard to pour accuratly we will pour it first.(Fig. 1) Then we will take the actual amount of A to calculate our amount of B. (Fig. 2)
When both components are measured correctly to ratio it's time to add them together and mix them.Make shure to mix it up very well. (Fig. 3)
To provide the best results you should put the pot of mixed silicone into a vacuum chamber and release all air bubbles inside. This will aid in a good curing of the silicone and a smooth surface.
Pour into a corner and keep pouring in the same corner until the mixing pot is empty. (Fig. 4)
Additional Vacuum, this step is not entirely necessary. Placing the freshly poured mold into a vacuum chamber will make shure you didn't create any new air bubbles when pouring.
Let it cure; in the specifications of the silicone you will find the curing time. Ours cures in 5 hours but it's safer to let it cure a full day before cutting it open. (Fig. 5)
Cut only 3 of the 4 edges and use curved and unique cutting lines. This will aid the mold in closing correctly. (Fig. 6)
Step 6: Resin Injection Cast
Strap down your mold using cardboard and rubber bands.
Put on your gloves and provide a protected working surface.
Provide a cup of water.
Every cup/syringe you use with the resin system has to be perfectly dry or the resin will foam.
PU casting systems are usually 50/50 weight but check your specifications before you measure.
Also check how much handling time you have (this can vary from 1 to 30 minutes).
Measure out parts of A and B. If you want to add pigment add 2-4% of the total weight of A and B.
The pigment needs to be a concentrated solution specifically for casting or pigment powder (very fine oxidised metals FeO, MgO, Al,.... or synthetic pigments)
Adding the pigment to A before adding B extend the curing time.
Add B to A and mix before adding the pigment to keep the original curing time.
Suck up the mixed resin in the 20CC syringe. Release the air from the syringe.
Place the syringe in the pouring hole and inject the contents. Keep injecting till all air holes have flooded and inject some more for good measure.
Suck the syringe full of water and leave it in the cup.
Wait for the curing time to pass. Open the mold to retrieve your copy. Clean out the syringe an dry it before its next use.
Cut off all the tubes and finish the product with sanding paper. (Fig. 4 & 5)
Click it over the switch and you are done. (Fig. 6 & 7)
Step 7: Acetic Curing Silicone Mold
Warning: This will reek of vinegar!
You can make the mold for cheap using the clear caulking silicone you can find in every hardware store. (Fig. 1) This is cheaper (€6/kg instead of €17/kg for condensation curing silicones) and you can massage it around the master eliminating the need for a mold encasement.
The caulking silicone cures by releasing acetic acid (vinegar) when in contact with moist air. If you simply apply the caulking silicone on the master the silicone will form a hard outer layer and seal up the silicone inside, preventing it from curing. You need to prepare the silicone so it cures from the inside out.
Curing can be accelerated using glycerine (found in dishwashing soap or beauty products), ethanol and acrylates (acrylates are sometimes found in soap, but acrylic crafts paint is a sure bet). These accelerants will be used to start the curing process from the inside out and accelerate the curing time to 2 hours.(Fig. 1)
- Clear Caulking Silicone
- Green soap
- Acrylic paint
Provide a protected working space and put on your gloves.
Prepare a bath with a big amount of dishwashing soap. This breaks the surface tension of the water and will provide a better contact surface between the silicone and the water filled with accelerant. Smaller amounts of acrylic paint and ethanol are also mixed in the bath.(Fig. 2)
Next a cup of 2 parts soap 1 part ethanol is prepared. This cup will be the release agent. (Fig. 3) The soap prevents the silicone from sticking to the master and the accelerants will let it form a skin quickly ensuring a hardened inside.
After the silicone is deftly kneaded underwater into a uniformly colored mass (Fig. 4, 5 & 6) it can be applied to the master. (Fig. 7)
To further accelerate curing it is placed in a humid oven (oven with a cup of water at 50°C).
Attention: Speeding up the hardening process like this has a severe impact on the lifecycle of the silicone. The accelerated and inner mass curing causes the silicone to dry up. The acceleration also causes all of the vinegar to be released at once, resulting in a very smelly mold.
Step 8: Result
You now have the means to produce your own light switches, in a variety of colors.
The condensation curing silicone technique is a very cheap way to accomplish a small series production. The mold cost us €4,32 and each copy costs €0,30 in material. This means making one switch costs €4,62! Cheaper than buying a new one. Making ten only costs €7,32. (not counting other consumables like gloves, mixing cups, filler,..)
Various unique switches
- Handcrafting as shown in Step 1
- 3D printing
Small series of one type
- Acetic cure silicone mold (1 to 50 pieces)
- Condensation cure silicone mold (1 to 200 pieces)
Because of the resin cure time of 1-3 hours a limited number of switches can be made in one day.
You can make multiple molds to solve this problem.
From the co-design team we wish you lots of succes!
Simon Boury, Niels Kinds, Jonathan Van der Smissen