Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
A discussion on the OpenSCAD mailing list about making a rectangular solid with rounded edges having different radii eventually produced this delightful result:
Basic Rounded Cube
Those guys make me feel dumb, because they’re generally solving problems I can’t even imagine, but I know what to do with this solution. One could slice it in half horizontally, emboss a height map defining a logo / picture into the top surface, print it out on your favorite 3D printer, maybe smooth / seal the surface a bit, define it to be a positive mold pattern, cast / pour flexible silicone around it, and get a negative mold for a pourable precious material such as, oh, chocolate.
You could make half a dozen of them, arrange them inside a suitable printed frame, pour the silicone, and get a multi-cavity mold for better manufacturing productivity.
The overall block lacks draft, because the problem it solves presumes you need a block of specific outside dimensions: it overlays three full-size rectangular blocks that define the dimensions. OpenSCAD constructs spheres such that they may be slightly smaller than the defined radius at the poles and, depending on their alignment, a face at the equator may reduce the outer dimension of a surrounding hull.
Given a sufficiently bendy silicone mold, you might not need any draft at all. If you do need draft and you don’t care about a very slightly undersized pattern, remove the internal blocks and increase the XY spacing of the lower four spheres by enough to make the draft come out right.
The grayscale logo / image should have nice smooth transitions that produce suitable draft for the fine details; a bare black-and-white image might not work well. Shallow is good, but that conflicts with 3D printing’s crappy resolution: 1 mm = 10 layers, tops. That might not matter in practice.
You’re supposed to temper the chocolate, but that’s probably more relevant for Fine Art molds.
Our Larval Engineer’s new camera uses Canon NB-6LH batteries, which have exactly the same nominal capacity as the NB-5L batteries for my camera, despite being not quite the same size. I cannot imagine any reason for that, other than brand fractionation, but there it is.
That hideous Powerpole thing came from one of the AA cell packs I’d been using to power the HTs on the bikes, before switching to lithium battery packs. It’s easier to harvest something suitable than to build a new thing, particularly for such a low duty cycle gadget.
This view of the solid model shows the contact pins, with the lid floating over its alignment pegs (made from snippets of 1.75 mm filament):
NB-6L Holder – fit layout
The pegs simplify gluing the lid in place, a process for which you can never have enough clamps:
Canon NB-6L holder – lid gluing
A cutaway shows the stepped holes around the contact pin, with the coil springs being the largest cylinder to the right of the solid-looking plug:
NB-6L Holder – show layout
The contact pins look like this, at least after one remembers to slide on all the parts before soldering the wires in place:
Canon NB-6L holder – contact pin detail
I filed off the inevitable solder bumps, rounded the butt ends with gentle suasion, and generally tidied the pins up so they’re smooth and symmetrical. The springs don’t have a lot of oomph, so wasting any force on friction or binding is a Bad Thing.
The holes require reaming with twist drills for a nice slip fit around the pins. The OpenSCAD script prints out the relevant diameters and depths:
ECHO: "Contact pin tip dia: 1.6"
ECHO: "Drill depth to taper end: 24.1 -- Dia: 2.4"
ECHO: " to ferrule end: 15 -- Dia: 3.1"
ECHO: " to plug end: 4 -- Dia: 5.2"
Grab the proper drill in a pin punch, adjust so that length protrudes, and have at it. Making the holes about 0.2 mm larger than nominal works well, although your mileage will definitely vary.
The build layout includes extra retaining plugs, as they tend to go walkabout under the bench:
NB-6L Holder – build layout
Add a dab of PVC cement with THF inside the holes and the plugs push firmly into place:
A few months ago I fired the Thing-O-Matic, only to have it wake up dead. Not exactly dead, but spitting out checksum errors on simple G-Code files sent from Pronterface, which used to work just fine. Trying a bit of this-and-that to no avail, I proposed to The Mighty Thor that I could loan the carcass to Squidwrench, reanimate it with a less bizarre set of hardware and firmware than the much-hacked Makerbot menagerie under the hood, and use it as an exemplar in my 3D Printing classes.
Fortunately, that particular Thing-O-Matic has the most well-documented hardware evah…
Matt suggested an Azteeg X3 controller, because it has thermocouple inputs that match the existing sensor, Thor ordered one, and I tinkered up a first-pass version of Marlin that could read the inputs and twiddle the motors. The firmware is on Github, not that you’ll need it for anything you’re doing; more on that later.
Here’s the Official Doc for the microstepping jumpers hidden under the driver boards:
Azteeg X3 – microstep jumpers
That’s XYZE = 16 16 8 4, respectively, with a spare slot (and spare driver, not installed) for the second extruder it’ll never have.
The extruder’s Type K thermocouple connects to the TC1 port on the shield, exactly reversed from the way you see the test thermocouple there: the red lead is to the left, the yellow lead is to the right. If you get it backwards, the indicated temperature goes down when you touch the bead. The printer’s thermocouple has some backstory.
The 10 kΩ thermistor bead connects to the BED port on the main board and isn’t polarized. The Heated Build Platform has a bit of backstory, too.
The gutted TOM286 carcass with the MBI hardware off to the side:
TOM286 – gutted electronics bay
After a few sessions, it looked pretty cheerful again:
This is what you see when looking down through the acrylic baseplate:
Azteeg X3 – inside TOM286
The blurry silver rectangle off to the left is an aluminum channel glommed to bottom of the acrylic baseplate with silicone snot to eliminate a nasty mechanical resonance.
The thermal cutout circuitry isn’t wired in yet; the ATX power supply has its -Power-On pin hotwired to the adjacent ground pin for now. The X3 gets its power directly from the +12 V supply, so there doesn’t seem to be any way to power the X3 from the +5 V Standby ouput, deliver +12 V to the motors, and switch the supply through the X3’s ATX output pin.
The heaters work fine, the motors turn properly, and the extruder feeds molten plastic; all the motor calibrations seem to be pretty close. The first test object was a total botch, of course, but the printer’s parts seem to work OK again.
A discussion on the Makergear Google Group about a heated enclosure prompted me to run the numbers for cooling stepper motors with water, rather than fans and finned heatsinks.
The general idea comes from my measurements of the air-cooled heatsink stuck to a stepper’s end cap. The metal-to-metal conductivity works surprisingly well and reduces the case temperature to slightly over ambient with decent airflow through the heatsink; epoxying a cold plate to the end cap should work just as well. A NEMA 17 stepper case is 42.3 mm square, so a standard 40 mm square CPU cooling plate will fit almost exactly.
The question then becomes: how much water flow do you need to keep the motors cool?
Some numbers:
Water’s heat capacity is 4.2 J/g·K
1 J = 1 W·s, 1 W = 1 J/s
NEMA 17 motors dissipate about 5 W (13 W if you’re abusing them)
We’ll cool all four motors in parallel, for a total of 20 W
Allow a 5 K = 5 °C temperature rise in each cold plate
Rub them all together:
(20 J/s) / (5 K * (4.2 J/g·K)) = 0.95 g/s
For water, 1 g = 1 cc, so the total flow is 1 cc/s = 3600 cc/h = 3.6 liter/h, which, here in the US, works out to a scant 1 gallon/hour. It’s tough getting a pump that small and cheap flowmeters run around 0.5 liter/m…
If you don’t want a pump. put an aquarium up on a (sturdy) shelf and drain it through the cold plates. A cubic foot of water, all eight gallons and sixty-some-odd pounds of it, will last 8 hours, which should be enough for most printing projects.
If you want reliability, drain the coolers into a sump with a float switch (high = on), put another float switch (high = off) on the aquarium, and have the pump top up the aquarium. If the pump fails, your steppers stay cool for the next 8 hours. Heating the water about 5 °C during 8 hours won’t require active cooling.
Now, managing the hoses leading to the X axis stepper may be challenging, but a cable drag chain would control the rest of the wiring, too.
Browning HP Mag Blocks – stainless and plastic – side
It’s actually bronze-infused stainless steel powder, so it’s not exactly solid steel. The parts spend a day rattling around in a vibratory polisher that slightly rounds off their edges and smooths the surface, but (as with all 3D printed objects) you must learn to love the results; it’s certainly more photogenic than the black plastic version from my M2.
The bottom view shows the hole I added to reduce the metallic volume; they charge a bit under $0.01/mm3, which encourages airy design:
Browning HP Mag Blocks – stainless and plastic – bottom
A cross-section view of the solid model shows the interior structure:
The vent pipes are somewhat larger than in the plastic version and, obviously, I didn’t include the yellow support structures in the model I sent to Shapeways.
Their specs give a minimum wall thickness of 3.0 mm, which I’m definitely pushing on some of the internal features. The pipes came out perfectly, as nearly as I can tell, although some polishing media did get wedged in the smaller hole. Air passes freely across the top, which is the important part.
Although the specs list a ±2 mm (!) tolerance, a comment in a Shapeways forum said that applies to larger objects, with 0.2 mm being typical for smaller objects. The steel and plastic parts match within 0.2 mm of the nominal model dimensions, so that lower tolerance seems about right; I have no idea how consistent it is.
Another comment recommended carbide tools for secondary operations and that’s definitely true; I wrecked a perfectly good HSS tap trying to thread the central hole. Fortunately, I made the block slightly smaller outside and slightly larger inside, specifically to avoid having a deep thread; I intend to ram a standard M3x0.5 SHCS into that hole and epoxy it in place without worrying about thread damage.
That image has desaturated red to suppress the camera’s red burnout. It looks better in the realm of pure math:
Planetary Gear Bearing – Kurled – solid model
Reducing the tolerance parameter to 0.4 produced a surprisingly rigid, yet freely turning, bearing that required no cleanup: it popped off the plate ready to roll!
The heavy lifting in the OpenSCAD source code remains emmitt’s work. I replaced the outer cylinder with a knurl and simplified his monogram to stand out better amid the diamonds. This is the affected section:
Santa delivered a pair of helmets that will require mirror mounts and a mic boom before the spring riding season kicks in. The visor has tabs that snap into sockets on each side of the helmet:
Bell Helmet Visor Mount – socket
It occurred to me that I could make an interposer between the helmet and the visor that could anchor the mic boom, with a tab for the helmet and a socket of some sort for the visor. While that’s still on the to-do list, the tab looks like this:
Bell Helmet Visor Mount
Those are 1 mm cubes on 10 mm centers, so this is a teeny little thing.
I don’t have a good idea for the corresponding socket, because those little grippers seem much too small for 3D printing, but now I have some tabs to play with:
Bell Helmet Visor Mount – OEM vs 3D Printed
The OpenSCAD source code puts the tab atop an oval base plate, but it’ll eventually stick out of the boom mount:
The Smell of Molten Projects in the Morning 