I had a birthday recently and my young nephew, who is very into the technologies of making things, and his dad sent me a 3D printer! Very cool. I’ve been well aware of the possibilities of 3D printing for awhile, but just as much its limitations. At the consumer level it’s just not a practical or economical way to make production parts, it’s the only technology I’m aware of that breaks the standing rule of “Price. Speed. Quality: Pick any two,” because it is at once the most expensive, slowest, and lowest quality production technique. That’s just talking about the consumer-level equipment and methods available today, I also feel just as strongly that in time it at the industrial level it will revolutionise manufacturing, and there are already some high-end machines being used in industry (they’ve been around for quite some time, in fact) to make parts that can’t be made any other way. And there are new methods on the horizon that are truly mind-blowing, like the CLIP system (see the TED talk and be amazed: https://www.youtube.com/watch?v=ihR9SX7dgRo ). But since I can already prototype most things with the machines I have, I’ve put off getting a printer for my own shop, my budget being very limited there are more useful things for me to get. But I always thought I’d want to get into this someday, so this thing landed in my lap and I’m pretty glad it did.
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First of all, it was very generous ( especially since my family is not into sending gifts, you’re lucky to get a phone call on your birthday! ) but they didn’t exactly break the bank for it, I haven’t looked up the actual price (that would be a little rude) but in poking around the web for resources I happened to see this exact machine, the Creality Ender3 Pro, touted in some magazine review as “one of the best machines under $200.” Wow. One of the upsides of my waiting to get into 3D printing is that every month there are more and more machines available at lower and lower prices, but that’s a staggeringly small investment for something that is actually pretty amazing and, once I thought about it a bit, useful for me right away.
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So for grins I started by running one of the files that came on the tiny SD card that had the instructions and the “slicer” program that’s needed to convert a solid model file to G-code, the machine language that controls the movements of CNC machines, whether it’s a mill, lathe, or 3D printer. There were a few files for little tchotschkes, I chose a tiny piggy bank. So the machine sat happily on the table and the printer head and print table wiggled to and fro for 5 or 6 hours and produced a cute little hollow pig with perky ears, a slot in its back, but no tail (seems they forgot).
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While that was working I started thinking about what I might do with this thing. My next shop project is to build a vacuum-forming rig and a male mold for the plastic tops for the Redshiftt relay boxes, pictured in my recent blog post. The mold I was going to make out of built-up MDF for the main body and 1/8″ thick aluminum bar for the endcaps that form a hollow ridge along each end that give the cover stiffness and house a rubber strip that will press against the bent-up ends of the metal base to affect a seal. I’ve been rolling around in my head for days how I would go about this, pondering other features the mold might have to enable accurate trimming of the molded piece and thinking they would make it much more complicated to make with my planned methods, when the 3D printer showed up, and watching the piggy grow on the print table it occurred to me that this little machine could do this job for me.
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So I opened a copy of the file I already had for this mold piece, basically a big rectangular block with angled sides, and started hollowing it out to make the print take less time and use less material, while leaving some internal bracing since it does need some strength to stay rigid for the thermoforming. I first tried a grid hollowing pattern, you can see the first few layers laid down behind Mr. Piggy above, but I aborted that print, it still needed to have less material.
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After a bunch of messing around with various methods I came up with a model that had mostly empty space underneath, and had tiny air channels in places to suck the air out from under the softened plastic sheet so it will be drawn into those tight corners. And I added those other features that will make it so the post-forming trimming can be done quickly and accurately on a bandsaw. Then I looked at the maximum Y-axis print size and realised that the added features would make the single part 8mm too long to be printed on this machine. No problem, since it’s symmetrical end-to-end, I just cut the model in half for two identical pieces.
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So, save the file as an .STL, open the slicer program, and let it do its thing. It really couldn’t have been any easier. Put the G-code file on the SD card, punch that into the printer, and let ‘er rip, …for 17 hours…each.
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This particular machine touts itself as being able to resume a print job if the power is interrupted, and of course there’s a command to pause a print voluntarily, but it kinda comes up short there, it never has been able to pull that off. So, oh boy, the first part was about 3/4 printed when I had to shut it off, and naturally it didn’t want to pick up where it left off. A call to my brilliant nephew, who sent me a Youtube video, where the guy shows how to solve this by using the print head to measure the height of the piece on the printer, opening the G-code file, editing out the layers that have already been printed, saving the remainder as a new file, and having the printer print that. As long as you don’t move the partly-finished piece off the table, this works just as pretty as you please.
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So in the end I have these two identical pieces that together make the male mold for my vacuum formed box cover. Pretty cool, I say, as long as you’re not in a hurry!
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Now these may not be able to do multiple forms since it’s PLA plastic and the PETG I think I’ll be using has a softening temp just a little higher than PLA’s, but it should be good for at least a couple tests, and I can use these to make plaster molds so I can pour resin or aluminum for a more durable mold for larger numbers.
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Which leads to the second thing I’ll use the printer for: I decided to use PETG sheet instead of polycarbonate (PC) because PC is pretty hygroscopic, so you need to dry the sheet stock in an oven before thermoforming to cook the water out to assure good results. PETG shouldn’t require that step, so I won’t need to get an oven for the shop. But PETG, as far as I can find so far, isn’t available in red transparent sheets. But it is available in red translucent filament for 3D printers! So I’ll make the covers from clear or smoke thermoformed PETG, and use the printer to print the Redshiftt logo on the inside of the covers, which should be fast since only maybe two or three layers need to be laid down.
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So this little gadget that landed in my lap, that I thought was a neat novelty but probably wouldn’t be that useful, is helping me solve two problems in my production planning. Sweet! Thanks Rob and Spencer!