Posts Tagged CNC
There’s a good reason this was the last pneumatic tee fitting on the rack:
The center fitting should be a male 1/4 inch NPT connection, but it’s completely un-machined. Alas, I no longer have a 1/4 NPT die in my tool chest, so it’s not an easy fix.
The two female connections are fine, so it must have been one of those rare QC escapes.
Lowe’s marked it down to $0.47 on clearance and I still couldn’t justify buying the thing.
The cover for Mary’s favorite seam ripper cracked long ago, has been repaired several times, and now needs a replacement:
The first pass (at the top) matched the interior and exterior shapes, but was entirely too rigid. Unlike the Clover seam ripper, the handle has too much taper for a thick-walled piece of plastic.
The flexy thinwall cover on the ripper comes from a model of the interior shape:
It’s not conspicuously tapered, but OpenSCAD’s perspective view makes the taper hard to see. The wedge on top helps the slicer bridge the opening; it’s not perfect, just close enough to work.
A similar model of the outer surface is one thread width wider on all sides, so subtracting the handle model from the interior produces a single-thread shell with a wedge-shaped interior invisible in this Slic3r preview:
The brim around the bottom improves platform griptivity. The rounded top (because pretty) precludes building it upside-down, but if you could tolerate a square-ish top, that’s the way to go.
Both models consist of hulls around eight strategically placed spheres, with the wedge on the top of the handle due to the intersection of the hull and a suitable cube. This view shows the situation without the hull:
The spheres overlap, with the top set barely distinguishable, to produce the proper taper. I measured the handle and cover’s wall thicknesses, then guesstimated the cover’s interior dimensions from its outer size.
The handle’s spheres have a radius matching its curvature. The cover’s spheres have a radius exactly one thread width larger, so the difference produces the one-thread-wide shell.
Came out pretty nicely, if I do say so myself: the cover seats fully with an easy push-on fit and stays firmly in place. Best of all, should it get lost (despite the retina-burn orange PETG plastic), I can make another with nearly zero effort.
The Basement Laboratory remains winter-cool, so I taped a paper shield over the platform as insulation from the fan cooling the PETG:
The shield goes on after the nozzle finishes the first layer. The masking tape adhesive turned into loathesome goo and required acetone to get it off the platform; fortunately, the borosilicate glass didn’t mind.
The OpenSCAD source code as a GitHub Gist:
I’ve been using YAGV (Yet Another G-Code Viewer) as a quick command-line Guilloché visualizer, even though it’s really intended for 3D printing previews:
Oddly (for a command-line program), it (seems to) lack any obvious keyboard shortcut to bail out; none of my usual finger macros work.
A quick hack to the main
/usr/share/yagv/yagv file makes Ctrl-Q bail out, thusly:
diff yagv /usr/share/yagv/yagv 18a19 > import sys 364a366,367 > if symbol==pyglet.window.key.Q and modifiers & pyglet.window.key.MOD_CTRL: > sys.exit()
I tacked the code onto an existing issue, but yagv may be a defunct project. Tweaking the source works for me.
The Ubuntu 18.04 LTS repo has what claims to be version 0.4, but the yagv GitHub repository (also claiming to be 0.4) includes code ignoring G-Code comments. Best to build the files from source (which, being Python, they already are), then add my Ctrl-Q hack, because my GCMC Guilloché generator adds plenty of comments.
Flushed with success from engraving a hard drive platter for the 21HB5A tube, I bandsawed an acrylic square from a scrap sheet and unleashed the diamond drag bit on it:
That’s side-lit against a dark blue background. The long scratch and assorted dirt come from its protracted stay in the scrap pile.
If you look closely, you’ll see a few slightly wider loops, which came from a false start at Z=-0.1 mm.
Engraving at -0.5 mm looked pretty good:
Despite an angular resolution of 2°, the curves came out entirely smooth enough. The gritty scratchiness resulted in a pile of chaff covering the engraved area; perhaps some oil or lube or whatever would help.
Rescaling the pattern to fit a CD platter worked fine, too:
Polycarbonate seems to deform slightly, rather than scratch, leaving the final product with no chaff at all:
In this case, the doubled lines come from the reflection off the aluminized lower surface holding all the data.
That CD should be unreadable by now …
[Update: It seems I interchanged “em” and “de” throughout this post. ]
Up to this point, I’ve been labeling printed parts with
emdebossed legends that look OK on the solid model:
Alas, the recessed letters become lost in their perimeter threads:
Raising the legend above the surface (“
deembossing”) works reasonably well, but raised letters would interfere with sliding the battery into the holder and tend to get lost amid the surface infill pattern.
The blindingly obvious solution, after far too long, raises the letters above a frame embossed into the surface:
Which looks OK in the real world, too:
The frame is one thread deep and the legend is one thread tall, putting the letters flush with the surrounding surface and allowing the battery to slide smoothly.
The legend on the bottom surface shows even more improvement:
An OpenSCAD program can’t get the size of a rendered text string, so the fixed-size frame must surround the largest possible text, which isn’t much of a problem for my simple needs.
Adapting the NP-BX1 battery holder to use SMT pogo pins worked well:
The next step is to add sockets for those 14 AWG wires:
Start by reaming / hand-drilling all the holes to their nominal size and cleaning out the pogo pin pocket.
Solder wires to the pogo pins and thread them through the holder and lid:
That’s nice, floppy silicone-insulated 24 AWG wire, which may be a bit too thick for this purpose.
The pogo pins will, ideally, seat with the end of the body flush at the holder wall. Make it so:
Dress the wires neatly into their pocket:
Butter the bottom of the lid with epoxy, clamp in place, set it up for curing, then fill the recess:
While it’s curing, make a soldering fixture for the 14 AWG wires:
The holes are on 5 mm centers, in the expectation other battery holders will need different spacing.
Solder it up and stick the wires into the base:
Jam a battery in and It Just Works™:
- Green = supply current at 20 mA/div
- Yellow = LED driver transistor base voltage
- Purple = other transistor collector voltage
- White = base – collector voltage = capacitor voltage
The measurement setup was a bit of a hairball:
For completeness, here’s the schematic-and-layout diagram behind the circuitry:
I love it when a plan comes together!
The OpenSCAD source code as a GitHub Gist:
The pips are 100 mm apart at (-50,-50) and (+50,50). Astonishingly, the laser aligner batteries are in fine shape.
I should have protected the platter before drilling all those holes:
All’s well that ends well:
It looks even better in the dark, although you’d never know it from this picture:
I wish I could engrave those patterns on already-drilled platters, but dragging a diamond point into a hole can’t possibly end well. I could deploy the Tiny Sandblaster with a vinyl mask, if I had enough artistic eptitude to lay out a good-looking mask.