DIY - A Prototype (week 8-10)

In order to build the Synapse lamp out of resin, the next step is to make a silicone mold for each resin part.

Some of the parts mirror each other, so the lamp requires 3 molds for the body. For the base, the decision whether it will be resin or different material is postponed for later.

There are many different materials in the market for making a silicone mold. And each type of material will vary in application methods, drying time, consistency, and cost.

For this project, I experiment with two products from different suppliers, and I faced completely different cost, experience, and results. To my surprise, the cheaper option (a 1/3 of the cost), despite the fact that it had an unpleasant odor, was easier to use and more successful. But I must take into consideration that my inexperience had something to do with it. So knowledge and experience matters.

Cenusil M385 FLEX, RTV-2 silicone rubber and a set of gloves

Also, for a DIY project, results are limited to the facilities and resources that one has to use. In order to maximize results, professionals, for example, use industrial vacuum canister to suck the air in order to avoid bubbles in the curing silicone. Those are quite pricey off course.

Specs for Cenusil M385 FLEX, RTV-2 silicone rubber

The first, and successful, product is called Cenusil M385 FLEX, a pourable, condensation-curing RTV-2 silicone rubber, made by a German company: Wacker Chemie AG, and purchased through its Thai distributor: Resin Rungart. (google map).

Silicone can come in different colors. This one is blue. 1/2 kg bottle cost 210 Baht and it includes the hardening agent. For the Synapse lamp, one bottle was enough to make the mold for part #4, the smallest one; Part 3, the synapse head, required 2 bottles - 1 kg. (420 baht). It has a curing time of 4 hours, and 20 minutes of workable time (for mixing, stirring, and pouring).

Make sure to be equipped with heavy duty gloves and preferably a mouth mask. I made a mistake the first time not using gloves and I had an unpleasant allergic reaction to the acetone which I used for cleaning my hands. Potentially, acetone poisoning. Not fun!

Making the molds step by step

1. Prepare the parts

When the parts come out of the 3D printer, they have an attached base that needs to be removed. The parts are also not necessarily smooth. They need to be filled with putty and sanded down. This is a delicate process. For the resin to be shiny and smooth, the surface of the mold has to also be smooth. Any imperfections on the part that we use to create the mold, will be filled with silicone and later on transfer to the resin.

Cutting off the attached base from the printed part #6

Part #2 filled with putty

2. Find or build a container to fit the mold

The silicone needs to be poured into a container that houses the part. In order for the part to fit the container and also avoid material waste, either find a suitable container or build one. If the container is too big, it is possible to reduce the silicone volume by adding pieces of rubber in the void spaces.

There are two ways to place the part in the container:

silicone mold release

1. Bottom side up - Glue it to the bottom of the container. In this case, leave enough space at the top to fully cover the part with silicone (at least 1 cm above the part) so the mold has a strong bottom
2. Top side up - hang it on the edges of the container, leaving at least 1 cm space at the bottom to fill up with silicone

***Before placing the part into the container, it is advisable to cover it with Vaseline or spray on it silicone mold release. This way, it will be easy to remove the part from the silicone after the silicone fully dries.

Part #4 was done in a plastic bottle that was cut into half. It was much wider than the piece itself, so I could have reduced the volume of by filling in some of the space.
Part #2 was put into a plastic cup that seemed to fit quite well.

Part #2

Part #6 was placed in a custom built container made out of corrugated plastic board. The most important is to make sure that the container is 100% sealed. Even a tiny hole can create a leakage. To make sure that the joints are sealed, I used hot glue as well as an extra layer of clay, just to be safe. The container will be torn apart after the silicone cures, so it doesn't need to be pretty. The most important is that there is enough between the part and the walls of the container to to make a strong silicone mold. (I used at least 1 cm space).

Making container for part #6

Fitting the pieces, leaving at least 1 cm space for the silicone

Using hot glue to seal the joint

Adding clay to extra seal the joints

3. Mix the silicone

This is a step of mixing the silicone with the hardening agent in a separate container. This required a measuring scale and extra caution. It's important to carefully read the instructions on the silicone bottle as well as on the hardening agent and know the percentage of hardener needed for the mixture. Here are some tips I learned from the trial and errors of mixing the silicone rubber:

Use another empty, preferably plastic and strong container, that is big enough to fill the sufficient amount of silicone that will be poured into the mold container.

Put the empty container on the scale, let it fully register the weight and then zero out the scale. (this way can calculate the exact amount of hardening)

Pour enough silicone into the container estimated to fill the mold while leaving enough space for the hardening agent and enough space to stir. The stirring can be a little tough, so is best to leave sufficient space.

Know what is the "working time" of the silicone. This should be written on the bottle label. otherwise on the product website. In case the container isn't big enough for sufficient supply of silicone, there might be enough time to mix two batches of silicone. For part #6, I had to make two batches since I underestimated my container size, and once I poured into the silicone into the mold, I needed extra silicone. The blue silicone had a working time of 20 minutes. So I could easily mix a second batch which after pouring into the mold, blended into the first one.

Before adding the hardening agent, zero out the scale again and use a calculator to measure the percentage needed to add to the mixture

Since the hardening agent uses a tiny percentage (usually between 2% - 4%), pour very slowly.

It isn't a big deal to slightly over-pour the hardening agent. In fact, I heard that some chose to put in a little extra so the silicone becomes harder. (if the calculator estimates 17.8 grams of hardening agent, is not a big deal if 18.5 grams gets poured)

Use a strong large wooden stick to mix the silicone. If it is too small, it might break while stirring, since the silicone toughens up while stirring.

When stirring, avoid shifting the stick up and down. This can create bubbles.

Use gloves! and no finger licking :)

Pouring silicone rubber into an empty container on a scale

Mixing in the hardening agent

Stirring

4. Pour the silicone into the mold container

Right after stirring the mixture, and without waiting, it needs to be poured into the mold container gently, carefully and evenly

pouring the silicone mixture into the mold container part #6

5. Wait for the mold to cure

Best not to touch the container or move it until it is properly cured. Wait for the silicone to dry at least the recommended amount. The blue silicone was listed at 4 drying hours. I let it dry over night.

letting the silicone sure

6. Remove the part

After the silicone fully cures, the part is removed. I also removed the surrounding container by cutting it out. If all goes well, the mold is ready for the resin.