Irreproducible, Accumulative Hacks

Last weekend, I made an incredibly accurate CNC pen-plotter bot in just 20 minutes, for a total expenditure of $0. How did I pull this off? Hacks accumulate.

In particular, the main ingredients were a CNC router, some 3D-printed mounts that I’d designed and built for it, and a sweet used linear rail that I picked up on eBay as part of a set a few years back because it was just too good of a deal. If you had to replicate this build exactly, it would probably take a month or two of labor and cost maybe $2,000 on top of that. Heck, just tuning up the Chinese 6040 CNC machine alone took me four good weekends and involved replacing the stepper motors.

Pen-plotter CNC router conversion
Oh yeah, dowels as end stops for lifting the pen

On Sunday night, I had all this stuff on hand, so for me it was free, fast, and the path of least resistance. But it’s an objectively horrible idea. The linear rail is holding a pen, although it is designed to hold hundreds of newtons of side-force. Consequently, it weighs a lot. You wouldn’t be able to strap it to your 3D printer chassis, which is normally a fantastic way to make a pen plotter. But I didn’t need to, and the CNC can swing weight like that around all day without even complaining.

The custom mounts? I designed it a couple years ago to hold the vacuum hose for the dust shoe. But because the CNC makes such a convenient platform for all kinds of hacks, I printed out five of them. So far, I’ve put on a laser head, a vinyl cutter, and now a pen plotter.

The entire effort in building the pen plotter consisted of drilling holes in a piece of thin scrap plywood and screwing things together. But while I was doing so, I was laughing because of how tremendously overkill it all was. Too heavy, too rigid, too noisy, and if I didn’t already have it all lying around, too expensive. It made me consider whether documenting some projects is simply worthless, because they’re fundamentally irreproducible.

But here we are, and I’m showing you the project. Why? Because I’m hoping it will inspire you to make a pen plotter with whatever you’ve got on hand. Even just taping a pen to the hot end of a 3D printer would make an easy start, but you’ll quickly run into two issues that the linear rail solved for me: holding the pen stiff in all directions except one, along which it floats freely with a little weight to hold the pen on the paper. I’m sure you can solve them, but I can’t tell you how, because I don’t know what you’ve got lying around. I don’t know what your stockpile of previous hacks looks like. In that sense, we’re all on our own with some hacks.

Of course there are STL files out there for a pen head that will fit your exact 3D printer model, so if that’s the way you want to go, you’re set. And I love reproducible hacks. But I think there’s something to learn from the irreproducible, accumulative, idiosyncratic hacks as well. What do you think?

29 thoughts on “Irreproducible, Accumulative Hacks

  1. I call it “Redneck Engineering” but there’s probably a slightly wider term for doing with what you have.

    Overkill, underkill, duct tape monstrosity that works once with someone holding it together: doesn’t matter as long as it does the job.

    Expedient Engineering? Effective Problem Solving? if we come up with a good enough name there’s all sorts of fundraising potential I’m sure.

        1. This one has always bugged me. It’s supposed to be JERRY rigging, regardless of language. “Jury” rigging is what corrupt judges do in courtroom dramas to give the protagonists something to do.

  2. Been there, done that, with my 3D printer’s corexy mechanism, about 6 years ago, and even used a linear guide for the pen mount:

    https://drmrehorst.blogspot.com/2017/07/ummd-corexy-mechanism.html

    I found that the weight of the linear guide would cause felt tip pens to flatten out, and that most ball point pens couldn’t keep up with the speed of the mechanism and there would be gaps in the lines. Koh-i-noor art pens seemed to work well- they are ball point pens with a large ink reservoir and the ink flow was able to keep up with high drawing speeds.

    1. Hah! That’s hilarious that you did almost exactly the same thing. :)

      Yeah, the linear sled weighs a bit — I wouldn’t put a felt tip under it. But for pencils and rollers, so far, so good. It’s also got a ton of preload, so there’s more resistance to up-down travel than you’d otherwise expect, and I guess it’s not bearing down with its full weight.

  3. I don’t think any such project can ever be too stupid in existing BOM to be worth documenting at least a little bit if its what you do in general – so you might just have an audience who knows all the steps that got you to this point. In this case its rather a basic bodge that can be done on any CNC like object, but shows the versatility of the tool. The greater value here being IMO the sensible thinking you put in to create that custom mount with some modularity in mind for future uses to make more use of the tool. And the techniques sometimes provide the ‘now why didn’t I think of that’ solution to some other problem entirely.

  4. Using the CNC portion as a platform to build other functions is a good idea.
    I don’t think it is overkill, yes, a pen plotter does not need all that strength, but it is a wiser move than turning a pen plotter into a CNC router. B^) as it can easily (?) revert to its original function.

    COUNTERPOINT Last night I was perusing a DR Power catalog, and they have a brush cutter with the brush cutting front end detachable from the engine and control portion. Other “power heads” can be attached instead, as I recall, a snow blower, edge trimmer, lawn mower, and margarita blender (just kidding about the last one). But each of those optional attachments costs as much as a standalone device. So, as I see it, the main advantage of owning a set of interchangeable “heads” is the reduced storage requirements. But if one owned property that required all that functionality, they probably have enough space to store dedicated equipment.

    1. It’s an old idea, too. We had a Toro system like that–an engine/handlebar assembly that would attach to a mower deck, power edger, and snow blower. It was built in the late 60’s.

      1. There have been a few attempts at a 2 stage snowblower that could have the snow blowing front swapped out for garden tiller tines. Seems like a great concept, you’re highly unlikely to be tilling up a garden when there’s snow on the driveway.

        But the problem is that a snow blower’s drive out to the front needs to be closer to the ground. You want a lower center of gravity in a blower. For a blower there’s rotary action in two planes so it makes sense to mount the engine sideways so all the belts and shafts can spin axially aligned with the impeller while a single 90 degree gearset runs the auger.

        In a tiller there’s just one axis of rotation at the ‘business end’ so it makes no sense to mount the engine crosswise to it. It’s easiest to use an enclosed chain case to drive the tines and have a pulley at the top end.

        A tiller engine should be higher up to keep it away from the dirt, and the tines have to dig into the ground.

        The applications are just too different in their requirements.

        But for yard tools several systems of swappable components have been successful. There are some guys who do overgrown yard cleanups for free and post videos of the jobs on YouTube. Many of them use gas or cordless electric string trimmers that can have the trimmer head swapped for an edger, a chainsaw, a variable angle hedge trimmer bar, and other tools. One guy can only use one tool at a time and it only takes a few seconds to switch heads.

  5. Just stop with the $0 nonsense.
    Something costs however much it takes for SOMEONE ELSE to reproduce it.

    A meal of leftovers isn’t free.
    Getting a plane ticket with airline miles/points isn’t free.

    If you made something with the castoffs of another project? Great!
    If you made something from a failed project? Great!
    If you made something with common materials you had on hand? Great!

    But none of those cost $0.

    1. That and it’s a bit disingenuous to say you made a pen plotter in 20 minutes for $0 when to the prerequisite is a working CNC machine and some duct tape. A CNC machine is already a plotter, this is just attaching a different tool. Hooray.

  6. “Conventional” engineering accumulates just the same way hacks do. This is a good case study on why stripped down ultrasimple products aren’t worth it. Sure, you don’t need 488374 layers of frameworks for a basic task. But having them there means everything is all ready to go the moment requirements change.

    I’d rather have extensibility and features than simplicity any day, especially if it’s mass manufactured and doesn’t really cost extra money or time.

      1. Pohl’s story is satire about consumerism as an economic drive. The fundamental reason behind consumerism is that some people want other people to consume stuff in order to “eat off the cart” themselves. This happens commonly when people find themselves unable to think of anything productive to do – such as when robots (slaves, imported cheap workers, outsourcing to poor countries…) do all the real work, yet you too have to work in order to earn a living.

        The premise of the story is that people don’t have to work thanks to the robots, but the robots must produce ever more stuff to be consumed by people. This suggests that people still have to work to earn a living but there’s not enough work to go around because people aren’t consuming enough of the products; people want to work, but work means making the robots produce more stuff.

        The main issue with the story is that once the society goes into such overproduction, the people responsible for it would have nothing to gain from it. In the story the “rich” people actually want to live in simple austerity, which isn’t helped in any sense by forcing other people to consume. If they didn’t want to, they could just… not consume. The only thing doing it was the “ranking” system where consuming enough gets you to a higher rank, which means you get to consume less, which makes it easier to fill your quota, which means you get to consume less… but that’s entirely arbitrary and comes from nowhere. Why would such a system ever exist?

        One can kind-of creep up to the point where people are fighting over increasingly meaningless yet scarce jobs in order to stake a claim on the stuff that the robots are producing, but going past that to a system of quotas where you have to consume needlessly, for people to have jobs, so they could earn money to buy the stuff you’re already forcing them to consume… it’s just a non-sequitur. Maybe that’s the point: maybe they made having a job such a fetish that people wanted to work despite the fact? In any case, it would require the entire world to become clueless idiots – which by some comments I’ve read was exactly Pohl’s intent: to write a critical story about “mindless capitalism”.

        In the end. the Midas Plague wasn’t coherent: it never explained why the robots had to keep producing past the point of post-scarcity. The whole thing is a silly satire that was made as a literary dare: to write a story out of a completely ridiculous premise, that people took seriously because they didn’t understand it, or read something completely different into it.

  7. This is one reason that building something in my lab full of stuff, and teaching someone else to has quite a large gap. Similarly – making anything as a kit. I have so many tools, equipment, including custom 3d printed stuff or bits of code that I can deal with most issues here, somehow, some way.

    But when there’s a page limit plus being able to safely assume the majority of readers won’t have those tools, those methods wont work.

    1. We run into this a lot with 3D printers, for example. For some readers “just send the file over to the printer” is natural, and for others it reads like “go out and buy a 3D printer”. There are a whole bunch of tools like that.

      Still, I’ll admit that I enjoy seeing folks do high-vacuum stuff that I don’t have any of the pumps for.

      Design for kits is even a whole ‘nother can of worms. How much do you assume / require? Tough.

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