Blowing an acrylic sheet after heating it is an easy way to make a smooth and transparent canopy or bubble for anything from clams to light fixtures. [Michael Barton-Sweeney] does it using plastic blow ovens he made cheaply, mainly from stuff which most of us already have in our workshops.
All you need is a way to heat the plastic, to then clamp it down around the edges, and finally to blow air into it as you would when blowing up a balloon. Of course, there are things to watch out for such as making sure the plastic is heated evenly and letting it cool slowly afterward but he covers all that on his hackaday.io page.
He’s also on his second plastics blow oven. The first one worked very well and is perhaps the easiest to make, building up an enclosure of CMUs (cinder blocks) and brick. He had success heating it with both propane and with electric current run through Kanthal wire. But the CMUs absorbed a lot of heat, slowing down the process. So for his second one he made a cast concrete enclosure with aluminum reflectors inside to focus the heat more to where needed.
We’re not sure of everything he’s blown acrylic bubbles for but we first learned of his ovens from the transparent clams in his underwater distributed sensor network. In fact, he was inspired to do plastics blowing from a childhood memory of the Air Force museum in Dayton, Ohio, where they visited the restoration hanger and watched the restorers blowing bubbles for a B-17 ball turret.
Though if you want to go smaller and simpler for something like a light fixture then you can get away with using a toaster oven, a PVC pipe, and a toilet flange.
Thermoplastics are amazingly versatile materials. Apply some heat, add a little force, and within seconds you’ve got a part. It’s not always quite that simple, but as [maxelrad] discovered, sometimes thermoforming can be as easy as blowing up a balloon.
In need of a cowling for an exterior light fixture on an experimental aircraft, [maxelrad] turned to pressure forming of Plexiglas for the hemispherical shape he needed. His DIY forming rig was a plumbing-aisle special: PVC pipe and caps, some air hose and fittings, and a toilet flange for the pressure chamber. The Plexiglas was softened in a toaster oven, clamped over the business end of the chamber, and a few puffs of air inflated the plastic to form a dome. [maxelrad] points out that a template could be applied over the plastic sheet to create the streamlined teardrop shape he needs, and he notes that the rig would likely work just as well for vacuum forming. Of course, a mold could be substituted for the template to make this a true blow-molding outfit, but that would take away from the simplicity of this solution.
There have been a fair number of thermoforming projects featured on Hackaday before, from this DIY vacuum former to a scratch-built blow molder. And while we really like the simplicity of [maxelrad]’s technique, what we’d really love to see is some details on that airplane build.
3D printers are the tool of choice for all the hackerspaces we’ve been to, and laser cutters take a close second. There’s another class of plastic manipulating machines that doesn’t get enough credit with the hackerspace crowd – the vacuum thermoformer. Surprisingly, there haven’t been many – if any – vacuum formers on Kickstarter. Until now, that is.
[Ben] and [Calvin] are the guys behind the MOFO, and built their machine around ease of use and reliability. After a few prototypes, they settled on their design of aluminum extrusion for the frame, a ceramic heating element for the heater, and an off-the-shelf PID controller for the electronics.
The MOFO has so far been tested with polycarbonate, acrylic, PETG and styrene with good results. The Kickstarter has reward levels of $500 for a 12″x12″ work area, and $1000 for a 24″x24″ work area. That’s not too bad, and building your own similar thermoformer would probably cost just as much. Just the thing if you need to print out a few dozen sets of storm trooper armor.