21
Oct 12

Battling Gravity

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Lately I’ve been experimenting with how best to print more complicated designs on my Makerbot Replicator. The issues you usually run into are objects with overhangs – areas of plastic that don’t have anything underneath them to support them as they’re being extruded. My typical process has been to design something and then figure out some way to orient the object to minimize overhangs. But lately I’ve discovered some techniques that can easily allow you to print things with minimal support.

As an example, here’s a desk ornament I’m working on for a project. The picture below shows two views of the 3D model as designed. The first rule of thumb I applied here is for continuous surfaces to make sure anything that deviates from vertical creating an overhang does so at an angle of less than 45 degrees. The Android figure is designed at a 30 degree tilt which is sufficient to allow new layers to build upon older ones. Also, the support arms are curved to satisfy this constraint.

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There are two sections of the design that are not well supported. If you didn’t notice them above, the next picture which shows my first attempt at printing shows the problematic areas well.

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As the printer is building up layers, when it gets to the bottom of the body just above the legs it’s literally laying out a string of plastic in the air with nothing to support it. The same thing happens when it reaches the bottom of the arms. What happens is the string usually catches on something in the vicinity and after a few layers can end up providing just enough support for the layers above it. You can see that in the pictures above – there are about 10 layers of string but beyond that things worked fairly well.

This made me think that perhaps adding just a little bit of support structure to hold those first layers (and that could be cut off later) would solve the issue. But looking at the arm, the very first layer is a tiny little little corner and might not be enough to build on. So first I sliced the bottom of the arm parallel to the ground by about 1/10th of an inch to expose some surface. The first picture shows the side view of the sliced arm and the second shows a view looking up at the arm from the ground. The blue selected outline is the first layer of plastic we’ll need to support.

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So I designed some small rods and positioned them at the corners and apex of the blue profile curve so there would be something for them to attach to. Supporting the perimeter is usually enough, as the infill is made by zig-zagging back and forth which ends up sticking to the perimeter.

fail-thin-supportIt turns out it was the correct strategy, but I failed several times in how I connected the support to the build platform. My theory was to make the supports tiny little pins so they would be easily broken off. But my first try the pins were so tiny they got knocked down or apart and didn’t last long enough to support the arm. The picture here shows the tiny pin supports on the right failing to support the arm layers. And the pins I had put on the left got knocked over during the print.

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The second try is shown here. I made the supports small rods of 0.075 inches in diameter. This was enough to support the layers but also small enough to break off by hand. However, the bottom of the support base wasn’t large enough and didn’t stick reliably to the build platform. When printing with ABS anything with much mass needs a decent surface area to stick to the platform.

In my final attempt I made large ovals for the support bases and started the print. Three hours later the result was great. Below is a sequence of photos showing the result in the printer, then some details of the support structure. The final picture is after I snapped them off by hand, which required very little force.

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The final result after some light cleaning with a knife and sanding down some areas is shown below. It’s encouraging enough that I can see doing some more ambitious parts that I previously had thought were not printable with a Makerbot.

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I published the 3D design files at Thingiverse so you can print your own. http://www.thingiverse.com/thing:32836


07
Oct 12

3D Printed Cufflinks

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Every once in a while my family makes me socialize with other people. We recently attended a community benefit that required me to wear a tuxedo. It may come as some shock to you, but the reality is that I don’t normally have a lot of cufflinks on hand. While I could certainly go to the mall to get a pair in 15 minutes, I decided to spend the better part of an afternoon making my own.

I recently purchased a 3D printer, and it’s far exceeded my already lofty expectations in terms of its possibilities. It’s Maslow’s Hammer become real, because everything actually is a nail when your hammer has the ability to command matter into existence. Like most tools, there are constraints you need to work within, but spitting out cufflinks felt well within the envelope.

The first step is creating a 3D model of the object you want to print. I use a CAD package called SolidWorks, which is a bit complex but quite powerful once you get the hang of it. I was able to design something I was happy with in about an hour.

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The printer creates objects using ABS plastic in one of a few solid colors like White, Black, Red, etc. The printer that I have also can print out support material to prop up parts of the model as needed during the build process. The photo below shows 3 of the cufflinks fresh out of the printer. the leftmost one is the orientation as printed. The middle one shows the support material “raft” on the bottom, and the final one shows the black plastic cufflink after I manually broke the raft off.

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You can break away the support material with tools if you are patient and careful, but if you don’t mind waiting a while it’s far easier to dissolve it. I dropped the cufflinks into a heated agitation tank filled with lye and a few hours later the white support material was completely gone.

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I was going to wear a black shirt, so I wanted the cufflinks to look silver. I spray painted two coats of Krylon Chrome spraypaint and it looked reasonably well from a distance. The final touch was to paint the bowtie black using some acrylic paint and a tiny brush.

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The printer uses a process called FDM which creates a somewhat rough surface texture that is apparent in the close-up pictures. It’s possible to smooth out the surface by sanding and applying solvents, but I actually wanted a matte finish so the result was good as-is from the printer. At the party someone saw my cufflinks and asked if they were silver – achievement unlocked.

I’m sure I could make literally dozens of dollars selling these on Etsy, but instead I’ve published the design files so anyone can make a pair themselves. Even if you don’t have a 3D printer, there are sites like Shapeways or Ponoko that will print them for you for a fee. The design files can be found on Thingiverse. You can upload the file to Shapeways and print a pair in plastic for about US$7 or they’ll also gladly print them in silver for about US$100. If someone actually does that, I’d love to see some pictures!


04
Jul 11

When Life Gives You Lemons…

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“When life gives you lemons? Don’t make lemonade. Make life take the lemons back! Get mad!

I don’t want your damn lemons! What am I supposed to do with these?

Demand to see life’s manager! Make life rue the day it thought it could give Cave Johnson lemons! Do you know who I am? I’m the man who’s going to burn your house down! With the lemons! I’m going to get my engineers to invent a combustible lemon that burns your house down!”

– Cave Johnson’s lemon rant after realizing that it turns out ground up moon rocks are pure poison.

Inspired by the speech and the hot temperatures outside we made combustible lemon props. I even hung one on our lemon tree. For science.