[Jacob Stanton]’s design for 3D-printable, stacking and locking boxes is a great example of design for manufacturability (DFM). MicroStacks show how part of good DFM is taking the manufacturing method’s strengths and weaknesses into account. [Jacob]’s boxes are created specifically with 3D printing in mind, which is great design whether somebody is making one, or dozens.
The boxes have sturdy parts that all print without any need for supports, fasteners, or post-processing. In addition, since no two 3D printers are quite alike and some print better than others, the parts are also designed to be quite forgiving of loose tolerances. Even on a printer that is less well-tuned than it could be, the design should still work. The boxes also have a nice stacking feature: a sturdy dovetail combined with a sliding tab means that once boxes are stacked, they’re not coming apart by accident unless something breaks in the process.
The boxes as designed are about big enough to store AA cells. Not the right size for you? One nice thing about a 3D-printable design that doesn’t need supports is that it’s trivial to uniformly scale the size of the models up or down to match one’s needs without introducing any print complications in the process. You can watch [Jacob] assemble and demonstrate his design in the video, embedded below.
[Tommy]’s POLY555 is an analog, 20-note polyphonic synthesizer that makes heavy use of 3D printing and shows off some clever design. The POLY555, as well as [Tommy]’s earlier synth designs, are based around the 555 timer. But one 555 is one oscillator, which means only one note can be played at a time. To make the POLY555 polyphonic, [Tommy] took things to their logical extreme and simply added multiple 555s, expanding the capabilities while keeping the classic 555 synth heritage.
The real gem here is [Tommy]’s writeup. In it, he explains the various design choices and improvements that went into the POLY555, not just as an instrument, but as a kit intended to be produced and easy to assemble. Good DFM (Design For Manufacturability) takes time and effort, but pays off big time even for things made in relatively small quantities. Anything that reduces complexity, eliminates steps, or improves reliability is a change worth investigating.
For example, the volume wheel is not a thumbwheel pot. It is actually a 3D-printed piece attached to the same potentiometer that the 555s use for tuning; meaning one less part to keep track of in the bill of materials. It’s all a gold mine of tips for anyone looking at making more than just a handful of something, and a peek into the hard work that goes into designing something to be produced. [Tommy] even has a short section dedicated to abandoned or rejected ideas that didn’t make the cut, which is educational in itself. Want more? Good news! This isn’t the first time we’ve been delighted with [Tommy]’s prototyping and design discussions.
POLY555’s design files (OpenSCAD for enclosure and parts, and KiCad for schematic and PCB) as well as assembly guide are all available on GitHub, and STL files can be found on Thingiverse. [Tommy] sells partial and complete kits as well, so there’s something for everyone’s comfort level. Watch the POLY555 in action in the video, embedded below.
It’s not clear whether Westinghouse and IBM collaborated on the project, but given the inside knowledge of the dot-matrix printer’s assembly, it seems like they did. The first few minutes are occupied by an unidentified Westinghouse executive talking about design for assembly in general terms, and how it impacts the bottom line. Skip ahead to 3:41 if talking suits aren’t your thing.
Once the engineer gets going on the printer, though, things get really interesting. The printer’s guts are laid out before him, ready to be assembled. What’s notably absent from the table are tools — the Proprinter was so well designed that the only tool needed is a pair of human hands. And they don’t have to be particularly dexterous hands, either — the design favors motions that are straight down, letting gravity assist the assembly process and preventing assemblers from the need to contort their bodies. Almost everything is held in place by compliant mechanisms built into the plastic parts. There are a few gems in the film, like the plastic lead screw that drives the printhead, obviating the need to string a fussy timing belt, or the unique roller that twists to lock onto a long shaft, rather than having to be pushed to its center.
We found this film which we’ve placed below the break to be very instructive, and the fact that a device as complex as a printer can be assembled in just a few minutes without picking up a single tool is pretty illustrative of the power of designing for assembly. Slick designs that can’t be manufactured at scale are all too common in this age of powerful design tools and desktop manufacturing, so these lessons from the past might be worth relearning.
3D printing can be great for making enclosures, and following some simple guidelines can help the whole process go much smoother. 3D Hubs has an article on designing printed enclosures that has clear steps and tips to get enclosures coming out right the first time. 3D Hubs offers 3D printing and other services, and the article starts with a short roundup of fabrication methods but the rest is a solid set of tips applicable to anyone.
The first recommendation is to model the contents of the enclosure as a way to help ensure everything fits as it should, and try to discover problems as early as possible during the design phase, before anything gets actually printed. We’ve seen how a PCB that doesn’t take the enclosure into account risks needing a redesign, because there are some issues an enclosure just can’t fix.
The rest of their advice boils down to concrete design guidelines about wall thickness (they recommend 2 mm or more), clearances (allow a minimum of 0.5 mm between internal components and enclosure), and how to size holes for fasteners, clips, or ports. These numbers aren’t absolute minimums, but good baseline values to avoid surprises.
One final useful tip is that using a uniform wall thickness throughout the enclosure is general good practice. While this isn’t strictly necessary for successful 3D printing, it will make life easier if the enclosure ever moves to injection molding. Want to know more? Our own Bob Baddeley has an excellent primer on injection molding, and his been-there-done-that perspective is invaluable.
[Tweepy]’s TV stopped working, and the experience is a brief reminder that if a modern appliance fails, it is worth taking a look inside because the failure might be something simple. In this case, the dead TV was actually a dead LED backlight, and the fix was so embarrassingly simple that [Tweepy] is tempted to chalk it up to negligently poor DFM (design for manufacture) at best, or even some kind of effort at planned obsolescence at worst.
What happened is this: the TV appeared to stop working, but one could still make out screen content while shining a bright light on the screen. Seeing this, [Tweepy] deduced that the backlight had failed, and opened up the device to see if it could be repaired. However, the reason for the backlight failure was a surprise. It was not the power supply, nor even any of the LEDs themselves; the whole backlight wouldn’t turn on because of a cheap little PCB-to-PCB connector, and the two small spring contacts inside that had failed.
From the outside things looked okay, but wiggling the connector made the backlight turn on and off, so the connection was clearly bad. Investigating further, [Tweepy] saw that the contact points of the PCBs and the two little conductors inside the connector showed clear signs of arcing and oxidation, leading to a poor connection that eventually failed, resulting in a useless TV. The fix wasn’t to clean the contacts; the correct fix was to replace the connector with a soldered connection.
Using that cheap little connector doubtlessly saved some assembly time at the factory, but it also led to failure within a fairly short amount of time. Had [Tweepy] not been handy with a screwdriver (or not bothered to investigate) the otherwise working TV would doubtlessly have ended up in a landfill.
It serves as a good reminder to make some time to investigate failures of appliances, even if one’s repair skills are limited, because the problem might be a simple one. Planned obsolescence is a tempting doorstep upon which to dump failures like this, but a good case can be made that planned obsolescence isn’t really a thing, even if manufacturers compromising products in one way or another certainly is.
[Dan Royer] shared a tip about how to get a reliably tight fit between 3D printed parts and other hardware (like bearings, for example.) He suggests using crush ribs, a tried-and-true solution borrowed from the world of injection molding and repurposed with 3D printing in mind. Before we explain the solution, let’s first look at the problem a little more closely.
Imagine one wishes to press-fit a bearing into a hole. If that hole isn’t just the right size, the bearing won’t be held snugly. If the hole is a little too big, the bearing is loose. Too small, and the bearing won’t fit at all. Since a 0.1 mm difference can have a noticeable effect on how loose or snug a fit is, it’s important to get it right.
For a 3D printed object, a hole designed with a diameter of 20 mm (for example) will come out slightly different when printed. The usual way around this is to adjust printer settings or modify the object until the magic combination that yields exactly the right outcome is found, also known as the Goldilocks approach. However, this means the 3D model only comes out right on a specific printer, which is a problem for a design that is meant to be shared. Since [Dan] works on robots with 3D printed elements, finding a solution to this problem was particularly important.
The solution he borrowed from the world of injection molding is to use crush ribs, which can be thought of as a set of very small standoffs that deform as a part is press-fit into them. Instead of a piece of hardware making contact with the entire inside surface of a hole, it makes contact only with the crush ribs. Press fitting a part into crush ribs is far easier (and more forgiving) than trying to get the entire mating surface exactly right.
Using crush ribs in this way is a bit of a hack since their original purpose in injection molding is somewhat different. Walls in injection-molded parts are rarely truly flat, because that makes them harder to eject from a mold. Surfaces therefore have a slight cant to them, which is called a draft. This slight angle means that press fitting parts becomes a problem, because any injection-molded hole will have slanted sides. The solution is crush ribs, which — unlike the walls — are modeled straight. The ribs are small enough that they don’t have an issue with sticking in the mold, and provide the mating surface that a press-fit piece of hardware requires. [Dan] has a short video about applying this technique to 3D printed objects, embedded below.
There are more free 3D models online than one can shake a stick at, but what about paid models? Hosting models somewhere and putting a buy button in front of the download is certainly a solved problem, but after spending some time buying and printing a variety of non-free 3D models online, it’s clear that there are shortcomings in the current system.