Cryogenic Machining: Custom Rubber Parts

Cryogenic Machining Custom Rubber Parts

Fashioning a custom, one-off rubber part for your project isn’t usually an option, but [Ben Krasnow] has an alternative to injection molding and casting: machining frozen rubber.

As [Ben] points out, you can’t exactly pop a sheet of rubber on your mill and CNC the needed shape; the bit will push the material around rather than cut it. Freezing the rubber first, however, allows you to carve into the now-hardened material.

His initial setup consisted of a sheet of aluminum with water drizzled on top, a square of neoprene placed on the water, and a steady stream of -60 to -80C alcohol flowing directly onto the rubber. The water underneath freezes, holding the neoprene in place. This proved problematic as the ice-clamp gives way before the milling is complete. [Ben] later adds some bolts to clamp the pieces down, allowing the milling process finish as planned.

A small plastic tray sits underneath this assembly to capture the alcohol as it runs off, feeding it back with some tubing. [Ben] recommends against a submersible aquarium pump—his initial choice—because the pump stopped working after a few minutes immersed in the chilly alcohol. An external, magnetically-driven pump solved the problem although it does require manual priming.

Stick around after the jump for the video and check out some of [Ben's] other projects, like his quest for the perfect cookie, or CT scanning a turkey.

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Building touch sensors from digital barometer chips

A couple of Harvard researchers have developed a method of using digital barometers as a touch sensor. The good news for us is that they’ve open sourced the project, including Eagle board files, firmware, and details about the materials they used.

The digital barometers were chosen for their characteristics, availability, and low-cost. The sensor uses an array of Freescale MPL115A2 chips, a MEMS Barometer designed for use in altimeters. The mass production makes them cheap (Octopart found some in single quantities for $1.71 at the time of writing). The chips are soldered onto a board which is then cast in rubber. This distributes the force while protecting the sensors. The video after the break shows them standing up to rubber hammer blows and supporting a 25 pound weight.

There are a few tricks to reading the array. The first is that the devices are designed to be used one-to-a-project so they have a fixed i2 address. A separate chip must be used to address them individually. But one it’s up and running you should be able to use it as feedback for the fingertips of that robot arm you’ve been building.

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Gently stroke this drum

The silent drum is played with your hands. It acts as a midi device by analyzing the movement of the rubbery black drum head. As you can see in the photo, one side of the body is clear and the other is white. A light shines up into it to boost the contrast and a camera picks up the black head as it moves past the white side of the shell. [Jaime Oliver] has provided an interesting look at the analysis method used with this instrument and there’s also a system of notating a composition for future performance. See and hear it played in the demo after the break.

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Transparent rubber enclosures

This clear rubber puck serves as the enclosure for a diy mp3 player. The wires encapsulated in the rubber are just there for looks but the utility of using this material as a case is fascinating.  Alas, there’s no details on the material other than that it’s clear rubber. Update: [Reboots] picked up on some info that we originally missed. Looks like this is made from some Smooth-On PCM 780 urethane rubber.

We’ve looked into casting our own molds from silicone rubber in the past.  That may be the process used here but we can’t tell what allows the two halves to be pried apart. We’ve embedded video after the break that details casting rubber around a part in one solid block, then cutting the rubber off of that to create a mold. We’re also familiar with the mold making kits from Tap plastics but as far as we know, they’re always colored and never clear.

We keep our eyes peeled for new prototyping products and we want to know more about the materials and the process used to make this cylindrical elastomer. If you’ve got the goods on how this is done, please share them in the comments.

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