Stereolithography is the process by which certain materials can be solidified by exposure to light. This effect utilizes a process called photopolymerization, where molecules are induced to join together into long polymer chains. This effect happens almost instantaneously, and can be used to form objects in the material being exposed.
I have loved the concept of 3D printing since I was first exposed to it, but it was always too expensive and the material too weak (your end product is generally plastic after all). I started learning about stereolithography a few weeks ago, and was instantly hooked. Large industrial 3D printing rigs will use a laser to 'draw' layers of an object on flat plate that's slightly submerged in a photopolymer resin, which then causes the resin to harden, and stick to the plate. Then the plate moves down slightly, in order to allow more of the resin to flow over top of the newly created object, and the process repeats, drawing each new layer right on top of the last.
I decided to by-pass the laser all together, by using a DLP projector to 'draw' the entire layer all at the same time. While the light isn't as intense as the laser, the advantage of being able to solidify the entire cross-section simultaneously more than makes up for the difference in speed. Picture the projector as using the image it displays instead of moving on the x- and y-axes. The x- and y- is still almost as precise, since all the pixels of the projector are crammed into a tiny space, which means 1024 pixels in ~3 inches produces a whopping 300 pixels-per-inch (ppi). That means the resolution is about 85 microns in the x-y directions. The main advantage is as follows: suddenly there aren't 3 axis of motion to worry about having mechanical parts fail on-- there's only up and down, which can be controlled by a single stepper motor.
Said stepper motors are expensive (we're talking 17 whole dollars !) so I decided to start small, and use a stepper motor that I scrounged out of an old DVD player from a local thrift shop. DVD drives use a laser track controlled by a stepper motor to finely position a laser to 'read' data that's encoded in small rings around a DVD ... never mind, that's a topic for another day. I figured this would be an easy to get stepper motor to test with.
Que the Arduino: my personal favorite should-be-ubiquitous microcontroller, used here to manage the stepper motor and accept commands coming from a Python-based slicer (shout out to Paul Bomke who wrote the Slicer software, http://robotsinthesun.org/monkeyprint/). Slicers are software that can take any 3D model, and slice it into layers, which if built on top of each other form the object. Then it sends the slices one at a time as pictures out the normal HDMI port on the computer running the software, which is connected to the projector. In between layers, my laptop also sends commands to the Arduino, telling the stepper motor to rotate slightly to move the plate up or down as the case may be. This was also my first exposure to stepper motors, they are cool all by themselves!
The first few test prints have been ... actually pretty good. Still rough, and layers aren't perfect, as I'm still figuring out the settings (and as the stepper motor is from a DVD drive, haha) but they've already exceeded my expectations. First print was Sun Wu Kong's head (the Monkey King) which turned out alright, but I think I had the exposure duration too long, and layer height too large. Naturally, the first good print, had to be a Perry the Platypus in-action figure. "Who would play with that?" you might ask, "It does absolutely nothing. And aren't you a little old to be playing with in-action figures?"
Well... yes, yes I am.
Well... yes, yes I am.
Everything done here is open-source, all the software is free, all the hardware is cheap. Outside of the resin, and the projector (which was $39 on eBay) the parts I've used so far cost less than $15. More than anything, this was a huge learning experience for me, and is more and more fun the more I get into it.
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