Comura Articulatum

by 4MULE8, published

Comura Articulatum by 4MULE8 Mar 11, 2013
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In the words of AuntDaisy, "Comura looks fun!"

If you built a home made 3D printer you're probably already a nerd, but if not then printing a moveable model trilobite will definitely earn you some nerd points! (Nerds are sexy these days, right?)

I spotted AuntDaisy's excellent "Trilobite Articulatum" design http://www.thingiverse.com/thing:28259 about a week ago, and immediately thought about the other wacky and excellent trilobite fossils. Without having finished reading the description I was already looking at google images of Comura, then came back re-read the description and realised we'd had the same idea!


The chain clips are designed to lock quite strongly so the segments don't come apart easily, however this makes it a bit more difficult to assemble. PLA will probably snap if you try to force the segments together. ABS might be flexible enough but I haven't tested it.

Starting with the largest body segment, heat the wall of the arch enough to soften the plastic slightly (about 60-70 Celsius for PLA, hotter for ABS). You don't want the plastic to melt, just to soften. If you have a heated print bed that's perfect, otherwise a hair dryer should do the trick. Place the head piece on a flat surface and firmly press the heated body segment down over its locking pin. This will slightly deform the tabs on either side of the arch. Quickly turn the model over and, while the piece is still warm, press the tabs back into shape (a small flat-head screwdriver will be helpful). Heat the wall of the second largest body segment and use the same technique to attach it to the other two. Repeat this procedure all the way down to the tail.

I've split the model into two prints, which are sized to fit onto a RepRap Huxley print bed. The pieces can possibly be rearranged to fit into a single Mendel print. The scale given in the STL files will produce an assembled Comura of 19cm long and 9.5cm wide at the head. I would suggest scaling this model to 100% or greater, as the chain clips might be too weak at smaller sizes.

Some of the spines might come out a bit poorly and need some TLC to tidy them up. Printing at a slower speed might help. The spines are the last thing to come out of the printer, so it may help to use use a small fan to cool the plastic more quickly as it exits the nozzle during this last part.

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This model is really awesome. I had a lot of trouble trying to get the pieces to snap together, even the hot water didn't help. However I found that if you heat up the cylinder pieces just a little bit with a heat gun for about 3 seconds they will fall right into the retraining cavity and cool trapped inside! Just be careful not to overheat the part.

I'm running this now to understand just how it's constructed; I made one on Autodesk 123D Creature and want to reduce the print time and supports (yuck). All these comments are a great help for our classroom at Trinity High School, Manchester NH. Will let you know how it all turns out :)

I made the mistake of printing the pieces separately. It turned out looking incredible, but now I am having difficulty getting them together. Any tips? I know i have to heat it, but I am not sure what method would be best.

There's a pretty detailed description in the instructions tab. Did you print with ABS or PLA? I have no trouble with PLA at 60-70C, but I've not tried ABS. I designed it to be printed separately, and was surprised when people had success printing it pre-assembled.

I used PLA. I di managed to get it together by briefly soaking the hinges in boiling water and reshaping them using some pliers. I'll post pictures of my make when I get the chance. Awesome build!

Thanks! I normally sit the pieces on my heated bed with the arch shape of the socket facing down (and the hinge pointing up in the air). That way the hinge pins stay properly rounded and move really well.

Printing went great, and came out great, sadly, I wasn't able to get the parts together as they were too stiff... Sad day.

Printed with silver ABS on a Rep. 2X.

4MULE8 - in reply to

Oh no! What did you use to heat the pieces when you tried to assemble it?

I tried heating them with a heat gun, but it just didn't work. This print might be better suited to PLA.

Great file! I printed this on my Rep2 with orange PLA. A hairdryer helped with the assembly. Love the articulation! Pics on my G+ page: https://plus.google.com/u/0/photos/116780922551677170912/albums/5864142053013038705https://plus.google.com/u/0/ph...

Nice work, and thanks for posting the photos! My reprap had a bit of trouble with the spines too. I think I'll be able to make some tweaks to the skeinforge profile to improve the way they turn out though. Hopefully. :D

You know what would be cool is you could arrange the pieces so that the odd pieces print on one plate and the even on the other. It would make it much easier to print a two color version.

That being said I just finished a black one and a blue one that I plan to mix together.

Actually that's a good idea. I hadn't thought of split colours when I made them. I'll upload two new plates when I return from holiday next week. I'll leave the originals up too, because just printing plate 1 can be used to make a tiny baby.

Also, nice prints!

Tiny baby! I didn't even realize that. That's hilarious.

A beautiful, organic model - much more realistic than mine. It deserves to be called Comura Articulatum Splendens (if my dog Latin is right ;-)

Haha, thanks! :D It's probably a lot less kid-proof than yours, with the fragile/sharp little spines. And with half the number of segments he's actually less flexible too!

I built the model out of polygon meshes with a subdivision algorithm running on it. It's much easier to achieve an organic looking model than trying to do the same thing in a CAD package.

I've been hoping someone would jazz the trilobite up. Nice!

Why thank you, sir! I'd love to see photos if you try printing it.

Thanks! I hope it turns out well if you try printing it.