writes:Thingiverse is a website devoted to Makerbot-brand 3Dprinters, but 3D models in STL format can be printed on any 3Dprinter. So I was browsing there, and I found these Jersey Barriers:
Jersey Barriers are a form of concrete barrier, and since they weigh so much, are made locally in a bazillion different lengths and styles. These 3D models are a good representation of a popular style, and Rob R. AKA rbross has made available both intact and damaged versions.
So I downloaded the models, and printed some out. I did this at my printer's highest resolution (100 microns, horizontally and vertically), 15% infill, no supports or rafts.
Digressing Into Triangles & STL
Some of the printed barriers had a prominent triangle outline on one side. I was curious to see what caused this.
Now, a word about the STL format: The file format currently used to share 3D models is the STL (stereo lithography) format. You might think this is some kind of 'common 3D modeling' datafile, but it's not. It is actually a translation of the model into a mesh consisting entirely of triangles – even flat planes are broken up into triangles.
So if you take an STL file and open it up in a 3D modeling application, you do not see the original model the way the designer made it, but instead you see the original model with a heck of a lot of extra triangles tossed in. (Some software can automatically 'merge' some of these triangles for you.)
(Consequently, the STL format is not an optimal way to share 3D models, and someday it will be replaced with something better.)
It turns out that when this model is translated to STL format, the big flat surface with the two round indentations is turned into triangles (and the round indents are turned into polygonal indents).
Now, there's nothing technically wrong with representing the model this way. The surface is still perfectly flat, despite all of those triangles. However, when my 3Dprinter's software 'slices' the model for printing, a raised triangle outline is created. It's a software fault.
Prepping & Painting
It was the work of a moment to pick off the excess plastic strings, and I used a dull blade to knock off some excess plastic bits.
I didn't try to sand or file away the striations, as I figured maybe what's they look like in the grim dark future.
In a previous article, I tried using a Dremel with a sanding drum on a 3Dprinted object, and it was either so fast it melted the plastic, or so powerful that it gouged the plastic. This time, I thought to try the Dremel with an aluminum oxide grinding stone. It's not as bad as the sanding drum, but the same problems: too powerful, hard to control, but good if you want to put a few dents in something!
For painting, I skipped a primer coat, basecoated in dark gray, drybrushed in two lighter shades of gray, and finished with a diluted black ink wash. That was my approach – you might prefer a lighter 'concrete' look, or maybe the colorful look of plastic-sheathed barriers.
And this is the one I 'damaged' with the Dremel:
Final Notes
Of course, this model can be resized for other miniature scales, or stretched (if your printer software allows) to make longer or shorter barriers.
And if you want to see how this model has turned out for other users, follow this link.