dual_sport_dork 🐧🗡️

Progenitor of the Weird Knife Wednesday feature column. Is “column” the right word? Anyway, apparently I also coined the Very Specific Object nomenclature now sporadically used in the 3D printing community. Yeah, that was me. This must be how Cory Doctorow feels all the time these days.

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Cake day: July 20th, 2023

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  • Some people are apparently incapable of learning anything except by rote. To them, every problem or situation has one solution, and they have no answer for any situation that has not previously been explicitly spelled out to them and the solution memorized, and failing that they not only won’t know what to do but they flat out won’t even try. There is no such thing as figuring out a new solution to anything based on logic or deduction. In any process, they will refuse to understand how the result is actually derived from the actions taken, nor what each step does or why it is done.

    I’ve had to work with several people like this over the years and it’s both exhausting and infuriating.

    In my line of work I have also been forced to interact with people, mostly clients, who cannot understand hypotheticals. Any abstract or non-concrete concept is completely lost on them and worse, usually exposing them to one will make them irrationally angry in response – which they will immediately direct at you, you nerd.

    These people are not only allowed to vote, but also drive cars, own firearms, and have children. It’s shocking.



  • Measuring with the printer is an excellent idea. When in jog mode, mine displays the nozzle coordinates right on the screen.

    I was considering that a truly dedicated nut could figure out which layer the print failed at (possibly approximately) and hand edit the gcode for the print to just replace all the layers up until the failed one with Z axis move up to that height. I think that would be problematic, though, because on my machine at least the model still being on the bed would definitely be in the way of the print head homing at the beginning of the print, and I don’t know if there’s any way to force it to skip that part of the procedure. Failure seems likely, and the penalty for failure is high.

    Just printing the remaining half of the model and supergluing the parts together seems like a better idea.



  • Your slicer should also be able to compensate for this already.

    PLA only shrinks about 0.3% which is negligible unless you are designing with super tight clearances. A 6mm hole, for instance, will be out 0.018mm which is probably scraping against the XY resolution limits of most consumer 3D printers anyhow.

    Other materials can definitely shrink more. ABS is harder to manage than PLA, but for instance Nylon/PA’s shrink rate is comparatively immense – around 2%. The various engineering polymers that are filled with something like carbon or glass fibers actually tend to shrink less than their raw counterparts.



  • If it were me, I probably would not be able to resist the urge to make whatever inserts you develop compatible with a Gridfinity baseplate, because I am that kind of nerd.

    To create perfectly console-shaped two dimensional inserts, or at least close enough, I would start by laying each system flat on a piece of paper and tracing around it with a narrow bodied mechanical pencil. Stick this in your scanner and make an image out of it, and then trace over that image at scale in the CAD software of your choice (FreeCAD is… free). This will automatically come with a built in amount of clearance in the amount of half of the width of the body of your pencil.

    Just make a flat base with a wall sticking up maybe 2-3mm thick or more if you feel like it, to roughly half the height of each object. You can put some gaps in it if you prefer to have places to grab the item directly.


  • And for anyone who winds up struggling with this when trying to gauge their own printer, make sure this option is enabled:

    This is in Prusa/Slic3r and its derivatives. If this is disabled, the final outer wall perimeter can wind up being pushed out by some fraction of the width of the wall behind it, which will have the net effect of shrinking vertical holes in your model (and other critical clearances in the X/Y dimensions) by an unpredictable amount.


  • As long as you stay within its plastic deformation limit, “many cycles” should not matter.

    PLA’s downfall for flexible design elements is permanent deflection. It cannot be used on anything that is expected to stay in its tensioned state for anything more than a few seconds. This is why PLA works for catapults and toothpick guns and latches that have a single position rest state where the flexible element is relaxed. If you leave it under tension, though, even just for a few hours, it will not spring back fully. Eventually, it just won’t spring back at all.

    Through much testing (read: slowly pissing myself off) I determined in the course of developing my Rockhopper that ABS is the best commonly available choice for permanently or semi-permanently loaded printed spring fixtures – at least out of what most normal and sane people can print with their hobby level machines. Even PETG is better than PLA in that respect, but PLA was useless for me.



  • I usually attack it with a terrycloth and some Flitz. A little will go a surprisingly long way.

    There are various methods of oiling, waxing, or otherwise preserving it afterwards. I prefer boiled linseed oil for that, personally.

    In Ye Modern Times, you could also just make your mail out of something that doesn’t rust. I didn’t, though.


  • IIRC the whole thing about the land mines exploding when you step off of them is purely down to the Bouncing Betty or the German S-Mine, which saw widespread use and gained its infamy in WW2. They almost worked in the manner described, actually going off with a time delay rather than waiting until the hapless soldier removed his foot from the plunger. But they used a small lift charge to pop the main explosive up into the air a couple of feet and then went off, with the aim of shrapneling in a circle a whole group of soldiers passing by and not just whoever stepped on it. Obviously this wouldn’t work so well if someone were standing on it at the time.

    The popular conception formed that they went off “after you stepped off of them,” which was true in most cases (who was going to just stand there like a nincompoop after you’d just triggered it?) and then Hollywood writers of the era just assumed that most or all landmines worked that way and wouldn’t let that misconception go. So now here we are.