3D Printing School: Print. It. Big!

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In summer 2014 I made my way out to the Science Museum in London to check out my WALLY – Wallplate Generator on display. It was pretty awesome. While I was there I stopped in Oxford for a day and captured some  “scanvenirs“. One of them turned out particularly well.

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My scan of the Marble portrait of the Greek playwright Menander (342-291 BC) is available for download on Thingiverse and was generated by running 45 images I took on my iPhone 5S through 123D Catch. Considering I only took 2 minutes to take all the photos (according to the photos Exif data) in a crowded museum, I’m very happy with how it turned out. When I got back to the states I processed the scan in Meshmixer and printed a few copies of the model at pretty small scale. I also used the model for the base of a couple other remixes, and because the scan and prints turned out so well I just keep going back to it, trying to figure out new ways to use it.

I’ve been following Cosmo Wenman’s amazing work with 3D scanning for a couple of years now. One of the things that really stood out to me was his life size recreations of sculptures.

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Head of a horse of Selene. Photo courtesy of Cosmo Wenman

 

Between printing at full-size and the finishing work/paint jobs he does they end up looking incredibly close to the real thing. Now don’t get me wrong, I love my miniature prints but there is something really striking about seeing a sculpture at the original scale it was meant to be viewed. Because my scan of Menander turned out so nice I thought this would be a perfect opportunity to try printing something life-sized myself.Screen Shot 2015-08-15 at 7.38.08 PM

The first step was the scale the STL file to the appropriate height in Meshmixer. I did this using the the Units/Dimensions tool under the Analysis menu. I scaled this to 18 inches (457mm) tall which is around life-size.

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The next step was to hollow out the model. I’m not sure if this is necessary (or even a good idea), the only large scale print project I’ve been involved with (WeTheBuilders) used solid blocks through out the model. But I thought using a thinner walled print might help with alignment and filling any gaps that formed form curling or shrinking during printing. I hollowed out the model to 5mm which I thought would be a good mix between strength and print bed adhesion.Screen Shot 2015-08-15 at 7.51.56 PM

Then the cutting process began… My printer, the Makerbot Replicator 2 has a build volume of 285mm x 153mm x 155mm. I used Netfabb Basic to slice my model into “chunks” that fit these dimensions. I made my slices 150mm tall (5mm under my max build volume), I thought I could just cube up my model to fit my printers build volume, but this wasn’t as cut as dry as I had originally thought.

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As it turns out, simply slicing the model into cube-ish peices that fit your printer isn’t really the best option. As you can see from the picture above if I had continued to slice the model into 150mm slices tall I would have cut right through the middle of the face. I feel like having a smooth seamless face is pretty important for this print, and while I know things like that can be hidden during my finishing process I’m not quite good at it to do a very good job hiding the seam.

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I ended up slicing some parts slightly smaller or larger to help hide seams. The animation above shows a pretty good break down of how that worked out. So there are definitely some artistic considerations when slicing up a large model for print.

After slicing all my parts I gave them a quick look over. A couple of the parts had some pretty severe overhangs, but I was able to avoid using support material by rotating the parts so the overhangs would print build-plate side down.

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When everything was said and done this project had 9 huge prints. With the shortest print coming in at 3.5 hours, and the longest at 16 hours I thought it might make sense to find a way to track my prints. I put together a Google Sheets document to track all my prints and printer settings. I’ve since continued to improve upon it to give me better print time estimates and even a real-time print timer/dashboard.

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After 56(!) total hours of printing I had myself a nice pile of parts. Assembly was the next step and involved some processes I wasn’t super familiar with before starting. I started by gluing all my parts together using Loctite “Gel Control” Super Glue. This worked pretty well, but I ended up reinforcing all my internal seams with some heavy duty superglue from McMaster Carr (Part #7518A61). I’ve used this hot glue in the part on my Proton Pack build and it’s held strong for years so far.

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While I had pretty good luck with my print bed adhesion and used PLA to reduce shrinkage during my prints there were still some gaps after gluing. I used Apoxie Sculpt (a two part epoxy putty), to seal all my cracks. The putty is pretty easy to work with, you mix the two clay-like parts (wear gloves!) until it’s a solid color. Then use it like clay to fill the holes in your model. I found that using small clay/sculpting tools helped avoid large globs that would need to be sanded down later. Wetting your fingers also helps smooth the epoxy after applying it. The epoxy has a working time of a couple of hours, but after waiting overnight it cures into a very hard plastic that can be sanded smooth.

After letting the epoxy cure overnight I sanded the seams smooth. I’ll admit looking back I should have spend more time on this step, but I was pretty anxious to get panting. Before moving on to paint I gave the whole print a coat of filler primer. This made the surface of the print look even nice and hid some of the prints imperfections.

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Then came the exciting part, the final coat of paint. I used Rustolium Ultimate White Satin spray paint. I’ve used this in the past for painting prints and it seems to adhere pretty well to plastics, I figured with a primer coat it would work perfectly. I really didn’t have any issue with the paint and I like the slight sheen the satin paint gave to the print.

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While I may not print everything I make at a true to life scale, this was a really fun project. It’s really interesting to see what details hold up to the scale.