Injection Molding Silicone Parts For Under $50

September 5, 2021 by Zoe Skyforest 14 Comments

You’ve likely seen many tutorials on making silicone parts using 3D printed molds online. The vast majority of these methods use a simple pour method to fill the mold. This relies on careful degassing and gentle pouring to reduce the presence of bubbles in the final result. [Jan Mrázek] has been working on an alternative method however, that allows for injection molding at low cost in the home shop.

The process relies on the use of printed resin molds. [Jan] notes that this generally necessitates the use of condensation-cure silicones, as additive types don’t cure well in resin molds. The condensation silicone is mixed up, degassed, and poured into a standard cartridge. From there, it’s installed in a silicone delivery air gun, which uses compressed air to force the silicone out of the nozzle and into the waiting mold.

It’s basically using a bunch of home DIY gear to create a cheap injection molding solution for silicone parts. [Jan] notes that there are a few mods needed to mold design to suit the process, and that 400-800 kPa is a good pressure to inject the silicone at.

Having the silicone injected under pressure is great for complex mold designs, as it forces the material into all the little difficult nooks and crannies. Of course, we’ve seen other methods for making silicone parts before, too. Be sure to sound off in the comments with your own favored techniques for producing quality silicone parts. Video after the break.

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‘Quiet On The Set’ Goes For Objects, Too

September 4, 2021 by Kristina Panos 10 Comments

Unless you’re sonically savvy, trying to sleep, or simply on edge, you probably don’t realize just how noisy common items can be. Pretty much everything makes enough racket to ruin a sound man’s day, or at the very least, their chance of picking up the dialogue between two characters. What you need on a set are noiseless but realistic versions of common noisemakers like paper bags, ice cubes, and to a lesser extent, billiard balls.

If you’ve spent any time at all on Reddit, you’ve probably seen frustratingly short GIFs of [Tim Schultz] quickly explaining how this or that noiseless prop is made. Embedded below is a compendium of prop hacks with more information worked in along the way. Talk about dream job! Problem solving and then hacking together a solution for a living sounds terrifying and delightful all at once.

Speaking of terrifying and delightful hacks, there’s still plenty of time to enter our Halloween Hackfest contest, which runs through Monday, October 11th. Halloween is the best time to go all out, so show us what you can do!

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The BornHack Badge Gets A Bubble

September 3, 2021 by Jenny List 2 Comments

In a year of semiconductor shortages it’s a difficult task to deliver an electronic conference badge, so this year’s BornHack camp in Denmark had an SAO prototyping board as its badge. Some people made blinkies with theirs, but that wasn’t enough for [Inne] who had to go a step further with a light-up pneumatic bubble badge. It’s based upon a previous project producing silicone inflatable bubbles, but in a portable badge form.

On the front of the PCB is a multi-colour LED for illumination, while on the back is a small microcontroller board, a pressure sensor, and a motor driver circuit. A small air pump and battery sits in a pocket connected by a cable and a flexible tube, allowing the bubble to inflate at will. An interesting detail was the use of a cut-down hypodermic needle to carry the air through the silicone wall of the bubble. When seen up close at the camp it was an unnervingly organic effect, if there’s an uncanny valley of badges this is it.

We don’t see much in the way of soft robotics on these pages, so this happy crossover with BadgeLife is a special treat. It’s not entirely alone here though.

Casting Silicone Parts With 3D-Printed Inserts For Stiffness

August 17, 2021 by Donald Papp 8 Comments

Prolific maker [Jan Mrázek] shared his process for casting soft silicone parts that nevertheless have some added stiffness, which he accomplished by embedding porous, 3D-printed “ribs” into the pieces during the casting process. The 3D-printed inserts act as a sort of skeleton, and as a result, the parts have a soft silicone surface but gain structure and rigidity that simply wouldn’t be obtained if the part were cast entirely in silicone. The nice thing is that no new materials or tools were needed; [Jan] 3D printed both the molds for the parts as well as the structural inserts. It’s always nice when one can use the same tool and materials to accomplish different functions.

The parts [Jan] is making are interesting, as well. He observed that the process of swapping resin in his printer’s build tank was an unpleasant experience for a number of reasons, chief among them being that resin is sticky and messy, and the shape of the build tank doesn’t make pouring resin from it a clean job.

His solution was to design a pour spout that could be pressed onto the build tank, and some specially-designed squeegees to allow scraping the tank clean with ease. Silicone is the ideal material for the parts because it turns out that sticky resin beads nicely on silicone’s surface. Anywhere else, resin tends to spread out and form a sticky mess, but on silicone resin it forms tidy drops and is much easier to clean up.

It’s a technique worth keeping in mind, because one never knows when it could come in handy. Fabricating soft robots for example tends to involve silicone casting and clever techniques. See [Jan]’s parts in action in the video, embedded below.

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How To Make A Collapsible Container Without Breaking Down

July 5, 2021 by Kristina Panos 5 Comments

How hard could it be to make a collapsible silicone container? Turns out, it’s really, really hard — collapsible containers have rigid guidelines. Just ask [Eric Strebel], who failed dozens of times before finally getting it right (video, embedded below).

[Eric] started with an SLA-printed two-part mold and a silicone formulation with a Shore durometer of A 40 — this is the measure of hardness for silicone, polymers, and elastomers in the sense that the piece will resist indentation. The first twenty-four attempts all came out looking great, but not a single one of them would collapse and stay collapsed.

Eventually, [Eric] went back to the drawing board and played with the angles of the flex points, the thickness of the living hinges, and the wall thicknesses, which have to be strong enough to stay collapsed.

For attempt #25, [Eric] took the part out of the mold about three hours in and tried curing it in the collapsed state. Persistence paid off, and the part finally collapses and stays that way. Get yourself some popcorn and check out the fail-fest after the break. You know what we always say — fail fast, fail often.

[Eric] has made many molds both from silicone and for silicone. Some of them are really big!

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Modular Box Design Eases Silicone Mold-Making

June 16, 2021 by Donald Papp 13 Comments

Resin casting is a fantastic way to produce highly detailed parts in a wide variety of colors and properties, and while the process isn’t complicated, it does require a certain amount of care and setup. Most molds are made by putting a part into a custom-made disposable box and pouring silicone over it, but [Foaly] was finding the process of making and re-making those boxes a bit less optimized than it could be. That led to this design for a re-usable, modular, adjustable mold box that makes the workflow for small parts considerably more efficient.

The walls of the adjustable box are four identical 3D-printed parts with captive magnets, and the base of the box is a piece of laser-cut steel sheet upon which the magnetic walls attach. The positioning and polarity of the magnets are such that the box can be assembled in a variety of sizes, and multiple walls can be stacked to make a taller mold. To aid cleanup and help prevent contamination that might interfere with curing, the inner surfaces of each piece are coated in Kapton tape.

The result is a modular box that can be used and re-used, and doesn’t slow down the process of creating and iterating on mold designs. The system as designed is intended for small parts, but [Foaly] feels there is (probably) no reason it can’t be scaled up to some degree. Interested? The design files are available from the project’s GitHub repository, and if you need to brush up a bit on how resin casting works, you can read all about it here.

Spy Tech: CIA Masks In Five Minutes Or Less

May 18, 2021 by Al Williams 23 Comments

You know the old trope: James Bond is killed but it turns out to be someone else in an incredibly good-looking Sean Connery mask. Mission: Impossible and Scooby Doo regularly had some variation of the theme. But, apparently, truth is stranger than fiction. The CIA has — or at least had — a chief of disguise. A former holder of that office now works for the International Spy Museum and has some very interesting stories about the real masks CIA operatives would use in the field.

According to the video you can see below, the agency enlisted the help of Hollywood — particularly the mask maker from Planet of the Apes — to help them with this project. Of course, in the movies, you can take hours to apply a mask and control how it is lit, how closely the camera examines it, and if something goes wrong you just redo the scene. If you are buying secret plans and your nose falls off, it would probably be hard to explain.

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