Posts Tagged M2
Five single-thread thinwall boxes scattered across the platform had an average height of 2.99 mm, with a range of +0.04 mm, -0.06 mm:
The wall widths work out to 0.39 mm, with a range of +0.2 mm, -0.01 mm.
Close enough, given that I can’t recall the last time I tweaked the platform height. I update the filament diameter setting in Slic3r every now & again as the printer gradually works through the spool, but, with one exception, this cyan PETG has been quite consistent and my tweaks didn’t really amount to much.
Frankly, given that any of the measurements may be off by ±0.02, the best I can hope for is an overall warm fuzzy feeling. When the printed results stop looking good, these results will (probably) provide some indication of whatever just changed.
The raw measurement data, such as it is:
A revision to my Fundamental Calibration Object adds some variations …
The classic thinwall open box:
A solid box:
A solid box with text embossed on the lower surface:
You must consider how the slicer settings interact with the solid model parameters, particularly now that slicers can produce adaptive infill for small gaps between perimeter threads. Previewing the slicer’s output will show you what assumptions it makes and prevent surprising results out there on the platform.
A single-thread wall comes out properly:
The results look just like the preview, with firmly bonded layers and no fluff:
This wall should be two threads wide, but Slic3r inserts very very thin infill thread:
I think that’s a result of forcing the two perimeter threads to sit with their centers exactly one thread width apart, making the (nominal, ideal) inner walls tangent to each other. Setting the wall to 1.9 mm eliminates the hair-fine infill thread, at the cost of producing an object 0.1 mm smaller than it looks.
Unfortunately, that fine infill doesn’t produce enough plastic flow for a continuous thread. The PET I’m using accumulates on the nozzle until enough of a glob forms to stick on the previous layer, but hair-fine strands connect those globs to each other and the nozzle, producing awful results:
A triple-thread wall allows Slic3r to produce a fatter infill thread that works the way you’d expect:
The threads bond firmly in all directions:
It’s not obvious from that picture, but the bond between successive infill threads produces a glass-clear vertical plastic slab that relays images from the bottom to the top. The perimeter threads are also firmly bonded, albeit with not quite the same optical quality.
To use these boxes:
- Set the OpenSCAD extrusion parameters to match whatever the slicer will use
- Set the wall height and thickness to whatever you like
- Compile-and-render, export the result as a solid model in STL / AMF / whatever
- Feed the solid model into your favorite slicer and save the G-Code
- Feed the G-Code into your printer, watch it magically create a little box
- Measure the printed results and compare with the ideal settings
- Change the slicing configuration and iterate until satisfied
Verify these measurements before adjusting anything else:
- Filament diameter: actual vs. nominal will be different
- Extruder steps per millimeter: mark 100 mm on filament, extrude 100 mm, compare
Then you can verify / adjust some finicky settings:
- Extrusion multiplier: does the actual single wall width match slicer’s nominal value?
- Infill density: 100% infill should perfectly fill the solid box
- Initial Z offset: does actual height match the model setting?
- Platform alignment: print five boxes at platform center + corners, verify heights
- First layer adhesion: if these don’t stick, the platform has weak adhesion
- Minimum time per layer: if the walls slump, you’re printing too fast
- Extrusion temperature: good bonding and no delamination along any axis
The OpenSCAD source code as a GitHub gist:
Two more Scli3r improvements calculate thin-wall and gap infill based on the available space, then vary the extrusion width to make the answers come out right for a given nozzle diameter. As a result, infill between close-set perimeter walls works much better than before; some of my long-held assumptions became invalid.
The only differences between the sheets: tweaking the
SheetSize parameters. The links recalculate themselves around those values.
The OpenSCAD source code as a GitHub gist:
After taking the incandescent lamp socket off its base, I drilled the tapped (yeah, in plastic) 6-32 holes out to a firm press fit for the knurled 6-32 inserts, buttered the inserts with epoxy, and pressed them firmly in place:
Fast forward a day and they’re stuck in there like they were glued. You can see a bit of the epoxy around the right rim of the insert; I wiped a bit more off around the other one.
Putting The Right Amount of epoxy on the insert requires dialing back my “The bigger the blob, the better the job” enthusiasm, but wasn’t all that difficult. It’s certainly more tedious than just ramming the inserts into a printed hole and might actually produce better retention. I doubt that will make the least difference for (almost) anything I build.
On the whole, they look good…
Mounting an octal tube socket in a CD requires nothing more than printing one from the same OpenSCAD code that produced the Noval socket:
I totally forgot about the raised ring around the central hole, so the OpenSCAD source code now moves the screws outward to 47 mm OC for a bit of head clearance. The 6-32 screws don’t look nearly so large next to that big Bakelite base.
The 2.36 mm tube pins fit perfectly into the (square!) socket holes without reaming.
This 6SN7GTB would definitely benefit from a ersatz plate cap with an LED shining down on the mica spacer; fortunately, the getter flash is on the side, not the top. You can see the plate cap atop the adjacent duodecar tube diffracted in the grooves, so a CD “chassis” will add some pizzazz to a rather drab tube:
In person, you see distinct RGB spots, not a continuous spectrum.
This tube has a completely broken-off base spigot (the keyed cylinder around the evacuation tip), so (I think) more light gets through the base than from a cut-off spigot end. Perhaps the plate cap will add enough light to turn the base LEDs into an accent.
The green phase looks nice, too:
Those screws are too big.
The getter flash covers the entire top of the tube; shining an LED down through the evacuation tip won’t work and even a laser doesn’t do much. That saves me the trouble of trying to create a cap that doesn’t wreck the tube’s good looks.
I originally planned to use white / natural PETG for the socket, but the more I see of those things, the more I think black is the new white. The sockets should vanish into the background, to let the tubes (and their reflections) carry the show.
The (yet to be designed) base must vanish under the platter edge, too, which puts a real crimp on its overall height. I’m not sure how to fit an Arduino Pro Mini and an FTDI board beside the existing socket; perhaps this calls for a unified socket-base design held on by those screws, rather than a separate socket inside a base enclosure.
Even though I know the tubes are inert and cool, I still hesitate before removing them from their sockets with the Neopixels running: you simply do not unplug a hot, powered device!
Replacing the hex nut traps with knurled insert cylinders slims the ends of the socket:
Making the raised part of the socket fit the 25 mm ID of a hard drive platter swells the midsection of the socket
, but the platter won’t need any machining or punching:
The octal and duodecar sockets will require a punch to open up the platter hole and all sockets require two drilled clearance holes for the screws. Given that I’ll eventually do this on the Sherline, maybe milling the hole for the bigger tubes will be faster & easier than manually punching them.
I moved the screw centers to 35 mm (from the historically accurate 28 mm) to accommodate the larger center, not that anybody will ever notice, and enlarged the central hole to 7.5 mm (from 5.0 mm) to let more light into the tube base.
The support structures inside the (now much smaller) knurled insert cylinders might not be strictly necessary, but I left them in place to see how well they built. Which was perfectly, as it turns out, and they popped out with a slight push:
They’re just the cutest little things (those are 0.100 inch grid squares in the background):
Anyhow, the knurled inserts pressed into their holes with a slight shove:
The chuck jaws were loose on the screw cutoff stud and stopped at the surface, putting the knurled inserts perfectly flush with the socket:
The surface looks very slightly distorted around the inserts, although it’s still smooth to the touch, and I think the PETG will slowly relax around the knurls. Even without heat or epoxy, they’re now impossible to pull out with any force I’m willing to apply to the screws threaded into them. Given that the platter screws will (be trying to) pull the inserts through the socket, I think a dry install will suffice for my simple needs.
Match-mark, drill #27 6-32 clearance holes, and the screws drop right in:
Those stainless steel pan-head 6-32 screws seem a bit large in comparison with the socket. Perhaps I should use 4-40 screws, even though they’re not, ahem, historically accurate.
The tube pin holes get hand-reamed with a #53 drill = 1.5 mm. That’s a bit over the nominal 1.1 mm pin diameter, but seems to provide both easy insertion and firm retention. For permanent installation, an adhesive would be in order.
Buff off the fingerprints, stick the tube in place, and it looks pretty good:
Yeah, those screws are too big. Maybe a brace of black M3 socket head screws would look better, despite a complete lack of historicity.
Now to wire it up and ponder how to build a base.
The OpenSCAD source code as a GitHub Gist: