Posts Tagged M2
One of the octal tubes in my collection has a broken spigot / key post that lets some light in through the bottom of the normally opaque Bakelite base:
Perhaps drilling out the base would let more light pass around the evacuation tip, but that requires a shell drill to clear the tip. Some doodling suggested a drill with 12 mm OD and 8 mm ID, which was close enough to one of the smaller homebrew drills in my collection that I decided to see how it worked:
You (well, I) can’t freehand such a hole, particularly with a glass tip in the middle, so I needed a way to clamp the tube in either the drill press or the Sherline. A pad for the clamp screw in a V-block seemed appropriate:
The screw hole sits at the 1/3 point to put more pressure near the pin end of the base. Maybe that matters.
The setup looks like this, with a small red laser dot near the front of the base:
The tube rests on a random scrap of plastic, with the hope that the drill won’t apply enough pressure to break the glass envelope.
In normal use, the V-block would be oriented the other way to let you cross-drill the cylinder. In this end-on orientation, drilling torque can rotate the tube; compliant padding for more traction may be in order.
The OpenSCAD source code as a GitHub Gist now includes a module that spits out the clamp:
The original plate cap, even without fins, seemed entirely too large for the 21HB5A tube. There’s not much wasted space inside and, after trimming the outside a bit, this is about as small as seems possible:
PETG doesn’t bridge well and, after cleaning out the wire hole, the remaining shell didn’t hold the brass tube very securely. Epoxying tubes into two caps at once, with a longer brass tube holding them in alignment, worked well:
The tube eliminates vertical tilt and you (well, I) can eyeballometrically align the caps and tubes in azimuth. The thin ring of JB Kwik epoxy around the brass tube isn’t visible, so it’s all good:
This project may eventually force me to try epoxy coating, high-build primer, and good paint…
After drilling the platter for a Noval tube, I finally made a fixture to hold the platters firmly, but gently, in the proper position for drilling:
The platter sits more-or-less flush with the surface, where credit-card plastic pads work fine. Thinner platters may require compliant padding.
The solid model has locating pips at ±50 mm from the center and airspace below the platter for the drill bit:
The 1.16 inch hole spacing matches the Sherline’s tooling plate. The center hole seemed like a Good Idea, although it has no purpose right now.
The OpenSCAD source code is the same as before; just set
Layout = PlatterFixture; and it’ll produce the right thing.
An old friend asked for a copy of the Smithsonian’s Apollo 11 Command Module. I started with a tiny 1:80 version to check feasibility:
It’s obviously not printable in one piece without a ton of support, so I chopped off the heatsink and printed the parts separately in the obvious orientation:
And glued them back together:
That worked well enough, even without locating pins, to give me confidence that it’d come out all right.
There’s plenty of gimcrackery surrounding the upper airlock:
Most of which simply vanished at 1:80 scale:
I made another cut just below the top of the capsule and ran off a 1:40 scale version that came out somewhat better, but it was still ugly:
Much to my astonishment, the grab rail over the side hatch, between the two parachute motars, came out well every time.
The giant 1:20 scale version would require something over 24 hours of printing, so I went with 1:30 in three pieces:
The top had pretty good detail:
Gluing the parts together made it ready for cleanup / finishing / painting:
Which he’s better at than I ever will be…
Natural PETG probably isn’t the right plastic for that kind of model, but it’s what I had on hand.
After smashing one of the cord pulls between the sash and the frame:
The glittery PETG looks surprisingly good in the sunlight that will eventually change it into dullness. The black flecks come from optical effects in the plastic, not the usual burned PETG snot.
The solid model is basically a hull around two “spheres”, truncated on top & bottom:
The interior has a taper to accommodate the knot, but they’re chunky little gadgets:
I thought the facets came out nicely, even if they’re mostly invisible in the picture.
Each pull should build separately to improve the surface finish, so I arranged five copies in sequence from front to back:
If you’re using an M2, the fans hanging off the front of the filament drive housing might come a bit too close for comfort, so rotate ’em upward and out of the way.
If you remove the interior features and flip ’em upside down, they’d work well in Spiral Vase mode. You’d have to manually drill the top hole, though, because a hole through the model produces two shells.
The OpenSCAD source code as a GitHub Gist:
I picked up a horsehair dust brush from eBay as a lightweight substitute for the Electrolux aluminum ball, discovered that an adapter I’d already made fit perfectly, did the happy dance, and printed one for the brush. That worked perfectly for half a year, whereupon:
It broke about where I expected, along the layer lines at the cross section where the snout joins the fitting. You can see the three perimeter shells I hoped would strengthen the part:
That has the usual 15% 3D Honeycomb infill, although there’s not a lot area for infill.
There’s obviously a stress concentration there and making the wall somewhat thicker (to get more plastic-to-plastic area) might suffice. I’m not convinced the layer bonding would be good enough, even with more wall area, to resist the stress; that’s pretty much a textbook example of how & where 3D printed parts fail.
That cross section should look like this:
Anyhow, I buttered the snout’s broken end with JB Kwik epoxy, aligned the parts, and clamped them overnight:
The source code now has a separate solid model for the dust brush featuring a slightly shorter snout;
if when the epoxy fails, we’ll see how that changes the results. I could add ribs and suchlike along the outside, none of which seem worth the effort right now. Fairing the joint between those two straight sections would achieve the same end, with even more effort, because OpenSCAD.
The OpenSCAD source code as a GitHub Gist:
The topic of function generators came up at Squidwrench a while ago (Sophi was tinkering with LCD shutters) and I finally picked up one of those JYE Tech FG085 DDS function generators to see how they work:
Short answer: adequate, if you’re not too fussy.
The board arrived with a bizarre solder defect. It seems a solder stalk yanked one terminal off a ceramic SMD caps:
The schematic and adjacent parts suggested the victim was a 10 uF cap, so I replaced it with one from my stash that worked fine.
However, after soldering enough of the switches to do something useful, the board wouldn’t power up. With a bit of poking around, I discovered the power jack had +15 V from the wall wart, but the center terminals on the DPDT power switch that should have been connected to the jack showed maybe 0.3 V. Jumpering around the failed via and a short trace on the bottom surface let the board power up correctly:
If you’re building one of these, solder one pin of each switch, push all the switch caps in place, shove the faceplate over all of them, tape it to the PCB, make sure all the switches are push-able, then solder the remainder of the switch pins. If you do them one by one, you’re certain to end up with a few mis-aligned switches that will either prevent the faceplate from sliding over them or wedge firmly against the side of their assigned hole. Just sayin’.
It lives in a case from Thingiverse:
I tweaked the dimensions slightly to fit the (slightly larger, possibly new, maybe tolerance-eased) front panel, but the bottom mounting screw hole spacing depends on the front panel size, not a specific set of dimensions, leading me to relocate those holes by abrasive adjustment. I didn’t bother with the lid (which doesn’t clear the BNC jack anyway) or the printed plastic feet (having a supply of silicone rubber feet).
The fancy vent gridwork along the sides printed surprisingly well, even in PETG. I’d have gone with larger slots, although I doubt the thing really needs vents in the first place.
The DDS sine wave output is rough, to say the least:
The spectrum shows oodles of harmonic content:
A closer look:
Stepping back a bit shows harmonics of (and around) the 2.5 MHz DDS sampling frequency:
For comparison, my old Fordham FG-801 analog function generator has nice smooth harmonics:
Of course, that crusty old analog dial doesn’t provide nearly the set-ability of a nice digital display.