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Image via PTI Prototype

Injection molding is awesome. It’s also freaking expensive, with high tooling costs that keep it out of reach for your average independent designer, craftsperson or hobbyist. For those seeking to create smaller runs of smaller objects, the production method known as spin casting provides similar capability at a fraction of the cost.

To dumb it down a bit for the non-production-method-initiated, injection molding requires the mold—typically made from steel—be precision-machined, which is where the high cost comes in; obviously it depends on the size of what you’re molding, but generally speaking you’ll pay anywhere from high four to low six figures. Manufacturers offset these costs by producing high runs.

In contrast, with spin casting the tooling cost is absurdly low; if some of the spin casters’, well, spin is to be believed, you’d pay in the tens or hundreds of dollars for what would cost the aforementioned four to six figures to tool for injection molding. That’s because spin casting uses cured rubber molds that are cast around your initial object, providing good accuracy at a much lower cost (and an attendant shorter lifespan for the mold, though it’s still capable of cycles in the thousands).

Image via Contenti Spin Casting

The way spin casting works is that your initial object(s), represented by the white circles in the image above, is surrounded in a circular vat by molten rubber, represented in blue. The rubber is then vulcanized, “locking in” what will be the negative space after your piece is removed. The vulcanized mold then has the gates and vents, or channels that the final molten material will flow through, cut into it as seen below. As opposed to a milling machine cutting channels into steel, this is done here by an expert wielding a knife.

Image via Contenti Spin Casting

Your object is removed, and the mold is placed into a spin caster, which is essentially an industrial turntable. Like VCRs of yore, they come in both top- and front-loading models.

Image via PTI Prototype

The turntable is spun up, and molten material is poured into the center of the mold through a hole at the top.

Image via PTI Prototype

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