I Love 3D – Part 3

Wednesday, June 5th, 2013

Part 3 – Advanced Applications:

It occurs to me that there is so much to discuss that this certainly will not be my last post on the topic. In addition, I’m sure the technology will change rapidly, and there will constantly be new things to share. And if you have anything relevant to share on this topic… you are welcome to share it here. Contact me via email and I’ll set you up!

Now, to continue…

In this post I want to discuss more advanced applications that I have engaged and experimented with, in addition to some new techniques, tips and tricks.

Lets start with some really cool new techniques, tips, tricks… Most of this revolves around what is referred to on various forums as an ABS Slurry or ABS Glue. It’s really simple and amazing. Lets start with a simple fact… Acetone dissolves ABS Plastic. It’s actually quite efficient at doing so. So you take acetone and ABS and combine them in a container (make sure it’s not an ABS container… that would be bad). Wait a bit and stir occasionally… and you get a liquid that is part acetone and part dissolved ABS. Now you can use this for various purposes…



Glue – use it to glue two ABS parts together… You have to give it time to fully dry, but its quite strong!

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Finish – paint it onto a printed part or soak the part and it alters the finish by both dissolving the perimeter layers of the part, and adding some of the ABS from the slurry. The effect is a glossy finish. In this photo the slurry was painted on…

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And in this photo the part on the left was soaked in pure acetone for just a few seconds. 20130604-175023.jpg

Stick – paint the slurry onto the printer bed and parts will stick like glue, which helps immensely in preventing warping.

For more tips, check back later for future posts “Pimp my Printer” and “AKS for 3D Printing.”

Now, onto the fun stuff! I wasn’t sure how broad to get when it came to advanced applications… as there are obviously so many different things you can do with this technology. In fact, recently doctors used a 3D printer to save an infants life (read article here). So anything I have to share clearly pales in comparison to saving a life! But there is something I am particularly psyched about that I want to share, and it certainly falls into the advanced application category. So let me break it down for you.

As I have mentioned previosly, parts are limited in strength due to the material and the characteristics of the way parts are printed… but I didn’t want to accept this fact… I wanted a way to use the printer to make strong parts quickly. There are other 3D printing techniques out there (such as stainless steel), but I clearly don’t have access to that tech… so I had to work within my budget and capabilities. This all began with a part I wanted to make… it was in fact a part I had designed years ago but never made due to its complexity. Here’s the part as seen in Solidworks.



This part was intended to securely hold a gyro at 45 degrees from the surface you were mounting it to, and my rod brackets and other mounting bracketry would allow you to precisely position the gyro bracket in 45 degree intervals, thereby placing the gyro at 45 degrees to two axis (such as pan & tilt, etc.)

Thrilled to have the ability to just print the part, I plugged it into Slic3r and printed it out. I was impressed how well it printed… but it was weak due to the nature of 3D printing. This weakness was inherent in the design, which required two load bearing surfaces to be at 45 degrees to each other. This places stress against the grain of the print, and the parts would break. I knew there was no way they were strong enough to hold a gyro safely. So I started working on a solution. I did spend quite some time trying to figure out if there was a better orientation to print in or mods to the part, but this ended up being futile. So what could I do?

Now my criteria was simple… find a way to make parts stronger without increasing production time or complexity, and thereby undermining the benefits of 3D printing. Obviously this would consume some time, but if successful I’d have a solution for the future.

So my next thought was perhaps there was a simple way to make a mold from the 3D printed part. So, I bought a product called Composimold which is a material that you heat up in the microwave, pour over your part, remove your part and fill the cavity with your cast material. The casting material I chose was polyurethane. It had a good hardness rating, and was machinable. It comes in two parts, which you combine and the cast hardens in about 15minutes. Simple, right!

Now, after playing with the Composimold I started to find it to be a little problematic to use other than for non-critical applications. So I started to rethink my strategy. I took another approach… using the cavity function in Solidworks I desgined the mold and printed it in ABS plastic.

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This worked great … or so it seemed. The mold printed great, and clamped shut well. I used a little silicone to seal the mold. So what was the issue. Well, I would say this approach is viable but removing the parts from the mold was a struggle. In fact, I was able to remove the cast successfully once, but after that I had to rip apart the mold on a subsequent cast and gave up entirely on a third cast.

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In addition, there was a big problem with holes in the cast part. In my first attempt I tried to cast the part with holes. That didn’t work. In my second attempt I tried to spot the placement of the holes, and then drill them out later. This wasn’t very accurate. I then started contemplating putting the part in the mill after casting it, and drilling precision located holes… but this started to sound time consuming and I felt like i was veering away from the spirit of 3D printing. So back to the drawing board!

Third times a charm! So I took another swing at this problem and I think I came up with a winner. This time when I printed the part I set it to print without any infill, which basically means it was hollow. This worked well.

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Then I simply drilled a hole in the bottom of the part and filled the hollow part with the polyurethane (the same two part casting material I used earlier). It worked GREAT! Now I had a quick solution. The part printed in a third of the time it normally took. Infusing it took minutes. And the end result was a really strong part, with precision located holes, and a finish color of my choosing. So, figuring I had a winning solution I moved forward in perfecting the process.

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There were a couple problems to overcome. First, I wanted a better way to fill the part. So I added two holes to the model and reprinted. Why two holes… one is to fill, and the other serves a dual purpose. The first purpose is to allow air to escape as the polyurethane filled the cavity. The second was to see when the part was full. After printing, I then drilled out the holes, progressively making them bigger, until the tip of a syringe could fit. Once that was complete, I did a wet test. This served two purposes as well… the first was to let me identify any leaks (which there were), and the second purpose was to determine how much polyurethane was required.

Leaks are always going to be present… this is because you are printing hollow, and without the infill the top side of the part becomes an overhang. The printer did a pretty good job, but you still get some gapping in the first or second perimeter layers which leads to leaking. I tweaked my design slightly to help with this… but some of it was unavoidable. So to solve this I located the leaks (which were always in the same place every time) and I applied a little silicone to them. This would be easy to remove later, and you really don’t even need to wait until its dry to proceed.

Now with my improvements I tried again, and it worked great. Parts were produced quickly with a lot of strength. There was a little work to do to clean up parts. Using a probe you can easily pick away excess polyurethane.

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Finally, if you so desire, you can gloss the finish of the part with a little ABS slurry.

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Quick Note: Polyurethane is an elastomer in the rubber family; it is not a plastic. Plastic and nylon can be compressed, and it does not return to its original size; polyurethane has memory. Also, plastics and nylons have a shorter life expectancy than any urethane, especially the hardest compound polyurethanes. We also exclude the use of Delrin in our mounts and suspension bushings due to its brittleness. Poly 75D has virtually the same hardness as Delrin, but is not a brittle material.

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