LEARNING
TO MAKE

Week 12: Molding & Casting

Making a Cyborg Bracelet

For the assignment we have to design and make a 3D mold. I will make a prototype for my final project: a silicon bracelet with a one negative and two positive molds to embed a pcb board and two small copper boards that function as galvanic skin sensor. The dimensions are rather huge: the pcb board is 15 cm long, as I include NEOPixel LED stripes. The design follows an "transparent technology" approach, aiming to leave all parts visible for the user.

Materials & Tools

Software: Rhino
Matter: Foam for Milling, Silicon "FormSil25Pro" and catalyst liquid from FormX (mixing: 100:5 (weight of silicon x 100 : 5 = amount of catalyst)
Machines: Rolland SMR-20; radial saw

Overview - Working Process

* generate Rhino design of molding form
* cut mold in two pieces in Blender
* mill form in SMR-20
* correct form with radial saw
* wax the mold
* glue top/button leyer together to have only two instead of four parts
* prepare casting workspace (scale, mixing stick, gloves, colour pigment): 130g silicon matches 6.5g catalyst liquid
* distribute silicon evenly in form
* stick two forms together, tape
* drying for 14 h
* opening mold, done

Design Casting Form

I drew a rectangle in Rhino in the bracelet meassurements (150mm x 250mm x 5mm) and extruded planar curve. I then added three more rectangles, extruded the planar curves, moved them into the proper positions and ran the boolean difference command. I set an offset for the outer form of the mold to allow for the casting.

Rhino design of bracelet mold, prototype for final project (unfortunatley not created in week 12 but shortly before the presentation deadline...)

Experiment: Mill the Casting Form

Because of the larger measurments and the busyness of the Shopbot milling machine, we split the model in four parts (2 and 2) in Rhino, saving 4 .stl files in order to use the small Rolland mill. Instead of wax - a pricy material of which none is left - we use foam, that I covered with a wood wax (brand: "Alex" Cera Incolora, para todo tipo e madera) to prevent the foam from soaking up all the silicon. We don´t know if this works, it´s an experiment.

Ferdi has tried the wood wax/foam form with plastic as casting material. it´s not easy to get the plastic out of the form, and the foam easily breaks. Now we try with silicon!

milling the mold

waxing

As we couldn´t mill the mold in the Shopbot (too many people wanted to use it), Ferdi helped me to correct the right angle where the two parts join with the radial saw.

nice and even. next I had to glue the two parts together (top and bottom leyer)

in the casting process

after the casting process. I first used the purple colour, but I had trouble opening the lit so time ran out and the casting material already dried up. for my second try I used the red colour - opening the lit before the action.

The Result

the silicon has not been evenly distributed in the mold.

I could not pour the silicon into the two openings at the edge, but had to fill it in eithe rone side and then stick the two mold forms together. In consequence, the two leyers didn´t join nicely. The silicon dried too quickly to have them melted within the colsed mold.

the form for the sensors and as visible here the board came out nicely and I also like my uneven colour distribution experiment. However, I don´t think silicon will be the material of choice for my final project.

Second Thoughts: Silicon Bracelet?

Will not use silicon for the final project bracelet, instead I plan to use leather. I will make a "protection box" that I can easily put on my final board to protect it from clumsy fingers, dust and stuff. Additionally, Anastasia in the Fab Textile experimented with wood patterns on a jeans textile. The patterns are flexible and look fantastic. As I need some thickness of material to allow for the board and sensor pockets, I might combine the leather with the wood cuts.

Inspiration. Done by Eliah (FabAcademy BCN 2016) and Anastasia Pistofidou at FabTextile, FabLab BCN

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