Closet Door Locker

Yesterday I install a new closet door in our front entrance hall, and discovered a problem which I then solved with 3D Printing. The door is a standard bi-fold type, with pins in the top and bottom of one side for rotation, a central vertical hinge, and a track along the top to keep the far side in alignment.

     

The problem was – with the volume of coats we need to survive a the winter on the ice planet Hoth (Chicago) and the positioning of the hanger rail, the coats push the door out and prevent it from staying fulling closed. Given that this is immediately adjacent to the front door, not an ideal solution at all.

There are lots of types of locks/clasps/magnets designed to solve this problem, but the one I chose to emulated is this over-the-door babyproofing product. It’s essentially a c-channel of plastic that slides over the middle-hinge when the door is closed, to prevent it from swinging open. Genius.

I created my own variant in Fusion360, thinking about how to make the design rigid, printable, and aesthetically pleasing. I added ridges along the sides to increase its lateral strength, and little pull-tabs to make it easier to grip. I trussed-out the top to give it some additional strength and reduce weight. Here’s how it ended up after about an hour of drafting:

Printing took a little over 10 hours, and the final result works great. I selected a blue-green PLA+ for ease of printing and aesthetic considerations:

Thanks 3D printing!

3D Printing in the Home Workshop

With the bulk of the shelving and organization overhaul complete as of last week, I’ve spent the last week starting to personalize my home workshop space, mostly using my 3D Printer. This is definitely a situation of “when your favorite tool is a hammer, everything looks like a nail.” And the 3D printer is an awfully nice hammer…

There are some things that 3D printed plastic parts are perfect for, including:

  • Brackets to attach/connect unusual shapes
  • Containers/guides for specific materials and tools
  • Stands and supports for lightweight goods

But of course, there are some properties that 3D printed thermoplastics are always going to be underachievers in, like:

  • Brute strength (compared to metal or wood)
  • Tiny mechanical details (like screw threading)
  • Heat resistance

In my mind, an ideal setup picks and chooses the materials that are right for each job. There’s not much point in printing, say, a 24″ wide shelf when a wooden one with be stronger, cheaper, and easier to make or buy. Conversely, welding a microphone stand together out of metal would be a nightmare, where it’s easy to print an existing plastic design that will hold up just fine.

The thrust of this is that, with the ELFA shelving (wood and metal) providing the backbone of my setup, there’s lots of space to fill in the operational edges with 3D printing. I can’t possibly cover every print, but in no particular order, here are the new additions to the setup, and some most-useful oldies:

ELFA Corner Bumpers

I designed and printed these the same day I finished the shelving install, after my partner nearly beaned herself on the corner of a shelf by the doorway as she was getting up. They’re a tight enough fit that they stay out without adhesive or fasteners. The design is now on Thingiverse.

ELFA Cable Guides

With the number of things that plug into AC power on my bench, I figured cable management would be useful. I started by putting together an ELFA Shelf Hook Profile, which can be used as a basis for anything that hooks into the ELFA vertical standards. I then added an L-hook shape to one side of the profile, which captures any cable that are hooked into it before the piece is installed. This is the result.

ELFA/2020 Bracket

I’m trying out using a piece of 2020 extruded aluminum as a generic mounting rail for some desk equipment, including the camera arm below. Maybe I’m being precious because the shelving is still new, but I couldn’t bring myself to put holes into the front of the shelves to mount this rail in place. I designed and printed these brackets, which are a tight fit to both the front of an ELFA solid shelf and the 2020 piece, and further secure to the 2020 with a screw and a hammer nut. A small piece of blue-tak can be fitted to the slots on the underside to prevent the bracket from sliding off.

This will probably need a second draft, as I realized after installation that they don’t leave room for the LED lighting I intend to install under each shelf.

Lighting PSU Wall-Standoffs

I’ll get into the lighting for the room more once all the parts arrive on the slow boat and I can get it all installed. In the meantime, I’m starting by mounting the 30A, 12V PSU. The positioning of the vertical standards on my wall didn’t leave an obvious place to mount the PSU, but the unit does have four M4 threaded holes on the sides. I designed and printed these mounts to accept up to three drywall screws each, with a slot and countersink for an M4 screw.

Articulating Camera Arm

Having a semi-permanent camera on my desk has been useful for project documentation. This is an assembly of two prints by other makers – RaffoSan’s Universal Camera Mount and Felwats’ C920 Adapter. The adapter actually fully replaces a piece of metal that sits between the camera and its original hinged arm. The arm mounts to the 2020 rail previously mentioned, which is mounted on the front of the lowest shelves.

Oscilloscope Probe Holders

This design popped up on the FunctionalPrint subreddit just in time. I was struggling with what to do with my scope probes – coil them next to the scope, keep them in a bin and pull them as needed… this solves that problem. The design comes from JRucks and is now on Thingiverse.

‘Hot Shoe’ Microphone Mount

I’ve had this one kicking around for awhile to hold my cheapy Takstar SGC-598 microphone. It’s not the fanciest setup, but for my casual purposes it’s more than enough. The design comes from Asgeirom on Thingiverse.

Solder Roll Holder

I didn’t really see the point of having a solder-roll holder until I printed one. Never again will that 1 lbs roll go walking across the desk (or onto the floor) in the middle of a tricky joint. This design comes from Phredie on Thingiverse.

“Pencil Cups”

These multi-purpose cup was one of the first designs I ever printed, and it’s still my go-to print for sampling the color of a new filament. It’s meant to print in spiraled-contour mode, which means that the outer perimeter (after the base) prints in one continuous revolving motion, instead of stepping up layer by layer like a typical print. There are perhaps a dozen of these scattered around the apartment, but since the reorganization, most live just above my desk holding, individually: pens/pencils, colored sharpies, black/silver sharpies, screwdrivers, pliers, flush cutters, cutting tools, and misc tools.


The next improvement to my setup is definitely a lighting improvement – its not terribly bright in the room to start with, and the shade from the shelves doesn’t help. 3D printing will be involved.

I also put my new setup to the test for the first time last night as I laid out a version of a DMX shield for the Arduino Pro Mini. Having all my tools organized and close at hand, and plenty of space to work it, makes working in my new setup a joy. The cleaning, the organization, the installing of new systems and setups: all worth it. It’s now fun to sit at my workbench, instead of a kind-of cramped pain. Onward!

50W QRP Amplifier – 3D Printed Case Design and Livestream

  1.  With the 50W QRP amplifier project coming along nicely, I felt it was time to start thinking about a reproducible case for the project. And for custom, reproducible cases, 3D printing is my current tool of choice.

I ended up designing the case on a YouTube Livestream on Saturday night, to which a few great colleagues stopped by to ask questions and offer advice. The full video is below.

The case is in two parts – a box with standoffs for the PCB and holes for connectors, and a lid with labels. The standoffs and the attachment holes for the lid are meant to connect with M3 threaded-inserts and be held down with M3 machine screws.

This was my first time using Fusion 360’s Eagle Sync function – since Eagle PCB design software was acquired by AutoDesk in 2016, it makes sense that they’ve been working to integrate PCB design workflows into their other products. The sync was fair straightforward – open Fusion360, select Eagle Sync, select your board file in Eagle, and after a minute or two of importing, up pops your PCB in Fusion360. Neat! I’m still struggling with how to handle board cutouts in eagle, and I’m not sure how well they’ll be supported in Fusion, but that’s a project for another day.

Here’s the final design as it turned out in Fusion360:

amppic1

ampic4amppic

The PowerPole model was provided by Chris Wych, a theatrical propmaster who’s done some really interesting work with Fusion360, including using it to model some 2d-printable geodesic designs which then folded up into geometric shapes. Very cool!

First print of this design coming soon!

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This post is cross-posted to my ham-radio specific blog, kk9jef.wordpress.com.

Geared 7-Segment Display, Part 4 – Pinion Gears and First Rotation

This weekend I’ve added the pinion gears to the seven-segment display, and performed the first test rotation of the mechanism.

As previous noted, the arm gears are 6-tooth gears of module 4 (metric) – in clockmaking terms, these would be pinions. In the clockmaking world, where I’ve been doing quite a bit of research during this project, there doesn’t seem to be a hard dividing line between what’s considered a “gear” and what’s considered a “pinion,” except that gears are big and pinions are small. Fair enough. From this point forward I’ll be referring to the arm gears as arm pinions.

I printed 6 of the pinions in just over an hour, and fitted them to their axles, which are just hacked-off pieces of 1/8″ rod stock from the hardware store. With the tolerancing on the prints as it is, the pinions are a snug fit on the axles, so I’m not too concerned about slippage once I can get the whole thing turning smoothly.

Speaking of turning, here are the first (partial) rotations of the mechanism.

Right now, the biggest impediment seems to be that the frame lacks rigidity, and easy warps and slews far enough to drive the arm pinions out of mesh with the drive gears. I’m currently working on a two-part version of the frame with interlocking members that firmly affixes both halves on the frame so that they remain rigid and parallel.

I’d assumed when I started this project that the axles (arbors) would need to be made of metal rod or dowel stock, so that they were firm, perfectly round, and rigid. But this being a 3d printing project, I’m now experimenting with a fully3D printed arbor-and-arm-pinion assemblies. These have the advantage that there’s no need to manually locate the pinion on the arbor by sliding the arm pinons up and down the arbors – they’re all one piece. As a sample, I printed a C-Arm assembly in two different orientations, both vertically and horizontally:

The vertically-printed arbor and pinion came out much better – the axle on the horizontally-printed unit is limited in smoothness by the layer height of the print, while on the vertical print it’s limited by the X and Y resolution of the printer. Additionally, while there is significantly more support plastic on the vertically printed unit, it’s not touching any of the working surfaces of the pinion itself, making the post-processing and filing significantly simpler. Both seemed to rotate well in the axle holes, however; well enough that I plan to work up a full set of these and test them in the next version of the frame. That means the only non-3D printed part in the project would be the main axle, and possibly the G-Arm tubing.

Next steps are printing the stiffer frame and the pinion/arbor assemblies.

Geared 7-Segment Display, Part 3 – Drive Gear Interlocks

The heart of the seven segment display is the seven drive gears with select teeth, which share a common shaft and all rotate together. As I was developing the idea of the drive gears and conceiving of how the presence/lack of teeth could “signal” the arm gears to turn or not, I though of them as plain, 2-dimensional shapes. I had planned on spacing them out along their common shaft using 3D printed washers of a set thickness. As for aligning them at the appropriate relative rotation, I thought I might print a jig (some kind of tall internal gear) to hold all the drive gears in the right relationship. Then I would either affix the gears and washers with superglue, or drill an alignment hole through all 7 gears and insert a small alignment rod to maintain their orientation.

Here are the first three drive gears (A, B, C) with a 2mm-tall washer between each. Looking good!

But this is thinking like someone who only has access to subtraction manufacturing. Why carve out a hole and insert new material when we could print the holes and alignment rods as part of the gear themselves?

I took another pass through all the drive gears, and added two 3mm wide, 7mm long “pegs” to the front side of each one (except gear A, the front gear). I also carved out a matching “slot” in each gear to receive the pegs behind it, with 0.3mm of clearance in all dimensions. (0.3 is my standard clearance value when I want two mechanical parts to fit together with no problem at all – your experience may vary.) Additionally, I extruded the center portion of the gear an extra 3mm upward to eliminate the need for the spacing washers I’d previously planned on.

Here’s the new E gear as an example:

You can see the two protruding rectangular “pegs” on the top that fit into the D gear, and the two similar slots on the bottom that receives the pegs of the F gear.

So, here’s what all 7 interlocking gears look like on an axle:

I whipped up a couple of minimalist end-frames to hold the drive axle and the axles for the arm gears – with both front and back in place, the mechanism is starting to take shape:

These endframes are a good example of something I’ve noticed with mechanical objects and additive manufacturing – there are huge time paybacks for small investments in drafting time. I’d first conceived of these end-frames and simple, 2mm thick rectangles with 7 holes in them. Cura estimated that each of those plates would take around seven and a half hours to print. Oof! There goes the weekend. But another 15 minutes of casually cutting things away in Fusion360 and the resulting frame took about two hours and 45 minutes. That’s ten hours of printing time saved with a quarter hour of drafting, a massive return on time invested.

Next step will be to re-print the pinion arm gears with appropriate axle holes, and then test fit the gears together. Here goes nothing.

Geared 7-Segment Display – Part 2, More Gears

While time at home is scarce this week, I’ve stolen a couple moments late night to continue working on the design of the geared 7-segment display, including finishing the modelling of the 7 drive gears.

Each drive gear is based on a 30-tooth, involute gear of module 4. Each segment of 3 adjacent teeth represents a single transition of a segment (or lack there of) – if there are teeth in a segment, the associated arm gear will rotate, changing a segment from active to inactive for a given transition or vice versa.

As a side note, each gear has a even number of teeth remaining, and each segment makes an even number of transitions as the display makes a full cycle of ten digits. If a segment made an odd number of transitions, it would start the next “cycle” in a different state than on the previous cycle, causing the numbers to “look” different on each time a given number came up, which is clearly wrong. This served as a useful sanity check as I was working through each gear in turn.

Here is the mechanism in its current Fusion360 form (support plates, arms and mounts, and a drive mechanism yet to come):

 

The A, D, and G arm gears lie on the vertical axis of the mechanism. The A and G arm gears, as noted in my previous post, are currently intended to be co-axial, the shaft of the A segment being a small hollow tube which completely surrounds the shaft of the G segment. Of all the details in this mechanism, this one seems the most fiddly at the moment, since any tolerance issues are going to compound on each other.

The B, C, E, and F arm gears lie at ±50° from the vertical axis, which is just about as close to the vertical axis as they can be and still have their arms clear the axes of the A/D/G segments.

In contrast to what I said a the end of my last post, I’m thinking I’ll print each of the gears individually and then mount them on the center axle with spacer washers. The whole-gear-assembly-as-barrel has one fatal flaw: printability. That’s a lot of overhanging teeth to worry about. That said, the print-individual-gears approach means needing to worry about registering adjacent gears to each other, but that seems like a solvable problem.

Looking down the road, here’s a quick Vectorworks sketch of how close adjacent digit displays could be. It seems I could squeeze them to about 175mm (~7 inch) centers.

 

Currently, the plan is to build one digit and evaluate… but the only thing better than N mechanisms is N+1 mechanisms…

Designing 3-Way Initial Blocks [Video]

In my experiments  with Fusion360 recently and casting around for inspiration, I stumbled across my old copy of Godel, Escher, Bach: An Eternal Golden Braid, which has a curious cover design consisting of two objects that cast shadows of three different letters along three different axes. In the following video, I look at the process of designing one of these shapes with arbitrary letters for 3D printing.