Category: Upper Extremity Disabilities∨g=

Assistance Dog Light Switches

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Assistance dog light switch is designed for use by individuals with limited motor control and coordination as a result degenerative disease. This project was created to provide a solution for a specific end user and a specific problem. It designed to allow a companion dog turn on the lights in a home for an individual with limited motor coordination.  

Technical Specifications: 

Step 1: Customization

Think about how you want your switch to look and make a shape out of any material. 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 and fine filler 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.

The goal 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 resistant 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).

Step 2: Mold design

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 slowly rise 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.

Step 3: Preparation

General

Mixing cups

Scale (preferably 0.1gram accuracy but kitchen scale will do fine)

Protective throwaway gloves

Stick

Mold

hot glue gun

kebab sticks

wood/cardboard

(modeling 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)

Polyurethane resin

2 part resin casting system (isocyanate & polyol)

20CC syringe

(Pigment coloring)

(Pressure chamber)

Finishing

Knife

Sanding paper

Step 4: Build the mold

Master

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.

Encasement

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.

Positioning

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. The author’s combination is 1,15 grams/centimeters3, which means our 224centimeters3 translates to 256 gram of silicone.

Our ratio is 100:4. We divide 256/104 and multiply by 100 to get 246 gram of component A. Since component A is in the big bucket and is hard to pour accurately we will pour it first. Then we will take the actual amount of A to calculate our amount of B.

When both components are measured correctly to ratio it's time to add them together and mix.  Make sure to mix it up very well.

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.

Additional Vacuum, this step is not entirely necessary. Placing the freshly poured mold into a vacuum chamber will make sure not create any new air bubbles when pouring.

Let it cure; in the specifications of the silicone you will find the curing time. The author cured in 5 hours but it's safer to let it cure a full day before cutting it open.

Cut only 3 of the 4 edges and use curved and unique cutting lines. This will aid the mold in closing correctly.

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.

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 and dry it before its next use.

Cut off all the tubes and finish the product with sanding paper. Click it over the switch and you are done.

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. 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.

Requirements

Clear Caulking Silicone

Green soap

Ethanol

Acrylic paint

Tub

Gloves

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.

Next a cup of 2 parts soap 1 part ethanol is prepared. This cup will be the release agent. 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, it can be applied to the master.

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.

Scenarios 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.

Available

Price Check
Price: 
0.00
as of: 
06/17/2015
Additional Pricing Notes: 
Price of materials to complete project.
Seller(s): 
Assistance dog light switches