Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
My decrepit Zire 71 PDA (remember PDAs?) has a cute little joystick dingus that, when pressed, displays the clock. That’s great, except that it stands proud of the surface by just enough to be constantly pressed by my pants fabric. Hence, the need for a button shield… which, after all these years, snapped at an obvious high-stress spot:
Broken Zire button shield
A dab of solvent glue, a few minutes of finger pressure, and let it cure overnight. That was easy.
But then it occurred to me that this was a broken plastic part and I had a 3D printer…
The fan on the dummy load that consumes the required minimum current to keep the ATX power supply happy wasn’t starting up reliably. That’s not surprising: I connected it to 5 V rather than the rated 12 V, because the load heatsink needs just a whisper of air flow to stay barely above room temperature, so it’s barely turning over and has no spare torque at all.
It turns out the heatsink really doesn’t need any forced air flow, despite having the fins oriented crosswise. Without the fan, it stabilizes just above comfortable-to-the-touch, a bit hotter than I’d prefer.
While I had the hood up for the HBP rebuild, though, I swapped in another fan and the heatsink is now cool to the touch. I did clean that dust off the fins, too.
If this one also fails at +5 V, I’ll fiddle the wiring to put it across the +12 V and +5 V supplies, where it’ll see 7 V. That should improve its disposition…
After a decade of stacking the plates in the dishwasher the same way every time, the flexible coating over the steel rods has worn through:
Dishwasher rack abrasion
We can’t stack them the other way, because the rotor spray rattles them unmercifully, and a fix is in order. Apparently, one can purchase touchup paint for this very purpose, but what’s the fun in that? Besides, I’d expect it to wear through even faster than the original coating, if only because adhesion is never as good as you’d expect from reading the label.
So this little dingus fits around a vertical pin and rests atop the horizontal rod, with the edge of the plate nestled into the joint between the two cylinders:
Dishwasher rack protector – solid model
Being very small, they build best in large groups:
Dishwasher rack protectors – on build platform
The horizontal half-cylinders require internal support, shown here adjacent to the protector for easy viewing:
Dishwasher rack protector – support model
Those fins just barely clear the interior of the horizontal cylinder, so the two parts don’t bond together very well (that’s the ideal condition, of course). The flat plate glues the support fins firmly to the build platform, which is easier to see on these somewhat shorter prototypes with a layer or two of orange filament on their bottoms:
Dishwasher rack protectors – support
The support chops out neatly with a repurposed nail set punch:
Dishwasher rack protector – removing support
Actually, I stood each one vertically on an aluminum chunk, held the punch in place with finger pressure, and whacked it with a small brass hammer. The OpenSCAD code now adds a small tab each end to help align the punch for the first whack.
The rod (vertical) hole came out just about exactly the right size (admittedly, with a 0.4 mm HoleFinagle adjustment), but required a pass with a drill in a pin vise to clear out the Reversal Zittage. The result slides easily over undamaged pins, but some pins had rust at either the top or bottom that required a bit of cleanup. This is a trial fit:
Dishwasher rack protectors – trial fit
I put a blob of acrylic caulk on the abraded spots to (attempt to) seal them from further damage, then squished the protectors in place. The dishwasher demonstrated that it’s perfectly capable of blasting an unglued protector (without a plate) up and off the pin, ingesting it into the trash grinder, chewing it up, and spitting the pieces down the drain. Lost a couple of prototypes before I figured that out, too.
Ya learn something new every day…
The OpenSCAD source code:
// Dishwasher rack protector
// Ed Nisley KE4ZNU - Jan 2012
Layout = "Show"; // Show Build Support
Support = true; // true to add support inside rod half-cylinder
include </home/ed/Thing-O-Matic/lib/visibone_colors.scad>
//-------
//- Extrusion parameters must match reality!
// Print with +0 shells
// Infill = 1.0, line, perpendicular to Bar axis on first bridge layer
// Multiply = at least four copies to prevent excessive slowdown
ThreadThick = 0.25;
ThreadWidth = 2.0 * ThreadThick;
HoleFinagle = 0.4;
HoleFudge = 1.00;
function HoleAdjust(Diameter) = HoleFudge*Diameter + HoleFinagle;
Protrusion = 0.1; // make holes end cleanly
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
function IntegerMultipleMin(Size,Unit) = Unit * floor(Size / Unit);
//-------
// Dimensions
PinDia = 4.0 + 0.5; // upright pin diameter + clearance
PinRadius = PinDia/2;
PinSpace = 35.0; // pin spacing along bar
PinOC = 3.4; // bar center to pin center
PinTubeLength = 15.0; // length of upright tube along pin
BarDia = 4.7 + 0.2; // horizontal bar diameter + clearance
BarRadius = BarDia/2;
BarTubeLength = PinSpace - 5.0; // length of horizontal half tube along bar
TubeWall = 4*ThreadWidth; // wall thickness -- allow for fill motion
TubeSides = 4 * 4; // default side count for tubes (in quadrants)
$fn = TubeSides;
SupportClear = 0.85; // support structure clearance fraction
//-------
module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
FixDia = Dia / cos(180/Sides);
cylinder(r=HoleAdjust(FixDia)/2,h=Height,$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//--------
// Support under bar tube shells
module SupportStructure() {
color("cyan")
difference() {
union() {
for (Index=[-4:4])
translate([Index*(BarTubeLength/8.5),0,0])
rotate([0,90,0])
rotate(180/TubeSides)
cylinder(r=SupportClear*BarRadius,h=2*ThreadWidth,center=true);
rotate([0,90,0])
rotate(180/TubeSides)
cylinder(r=SupportClear*BarRadius,h=10*ThreadWidth,center=true);
translate([0,0,ThreadThick])
cube([(BarTubeLength + 4*ThreadWidth),BarRadius,2*ThreadThick],center=true);
}
translate([0,0,-(BarRadius + Protrusion)/2])
cube([(BarTubeLength + 2*Protrusion),
BarDia,
(BarRadius + Protrusion)],center=true);
}
}
//-------
// Put it together
module Protector() {
difference() {
union() {
translate([0,PinOC,0])
rotate(180/TubeSides)
cylinder(r=(PinDia + 2*TubeWall)/2,h=PinTubeLength);
translate([-BarTubeLength/2,0,0])
rotate([0,90,0])
rotate(180/TubeSides)
cylinder(r=(BarDia + 2*TubeWall)/2,h=BarTubeLength);
}
translate([0,PinOC,-Protrusion])
rotate(180/TubeSides)
PolyCyl(PinDia,(PinTubeLength + 2*Protrusion),TubeSides);
translate([-BarTubeLength/2,0,0])
rotate([0,90,0])
rotate(180/TubeSides)
translate([0,0,-Protrusion])
cylinder(r=BarRadius,h=(BarTubeLength + 2*Protrusion));
translate([0,0,-(BarRadius + TubeWall + Protrusion)/2])
cube([(BarTubeLength + 2*Protrusion),
BarTubeLength,
(BarRadius + TubeWall + Protrusion)],center=true);
}
}
//-------
// Build it!
ShowPegGrid();
if (Layout == "Support")
SupportStructure();
if (Layout == "Show") {
Protector();
translate([0,-10,0])
SupportStructure();
}
if (Layout == "Build")
rotate(90) {
if (Support)
SupportStructure();
Protector();
}
The basic problem with the heater on the Heated Build Platform is that the SMD pads must both make electrical contact to the Molex-style connector and withstand mechanical stress from the dangling wires & cables as the platform moves along the X and Y axes. Rather than replace the entire heater, I attached pigtail leads to the PCB, anchored those leads to the wood platform under the heater, and routed the cables through the deck under the Y axis stage a bit differently.
However, attaching pigtail leads to the PCB poses a problem, because ordinary electronic hookup wire has thermoplastic insulation that melts or deforms at temperatures well under my usual 110 °C platform heat setting; shorting the heater wires would be a Very Bad Thing.
Some concerted rummaging in the Big Box o’ Multiconductor Cable turned up a hank of Teflon-insulated shielded two-wire cable that, as nearly as I can tell, has pure silver conductors and shield braid: the ends were tarnished like silver and there’s nary a trace of copper in the fresh cuts. It must be military surplus and, based on a vague recollection, was most likely cough salvaged by my father, who worked as an avionics tech at Olmstead AFB in the mid-60s. Ya gotta have stuff, right?
[Update: Alas, it’s not pure silver, as shown in the comments.]
The general idea is to scuff up the shiny PCB surface enough to anchor blobs of JB Industro Weld epoxy that surround brass tubes holding the cables. A pair of tubes secure each cable and provide strain relief; the cable is free to move, but not by very much. The thermistor cable has a long arch that will, I hope, keep the cable at the platform temperature and reduce its cooling effect on the thermistor:
Thermistor rewiring – heat cure
The alligator clips connect to a bench power supply that delivered 4 V @ 2 A = 8 W that heated the PCB to about 40 °C in the rather chilly Basement Laboratory and encouraged the epoxy to cure in less time than forever.
The final result looked like this, with Anderson Powerpoles now attached to the heater cable:
Rewired HBP
The 24 AWG conductors in the cable may seem scanty for 6 A of heater current, but, hey, they’re silver.
The three-pin connector on the end of the thermistor cable is a pure kludge, built from a 4-pin header to match the CD-ROM audio pinout on the new cable from the Extruder Controller. I kept the default pinout on this end to provide some protection against plugging it in backwards:
Kludged HBP thermistor connector
With all that in hand, I screwed the PCB to the aluminum sub-plate, bolted it to the plywood platform, and stuck the cables onto the platform with adhesive clamps:
Rewired HBP – front
Reaming out the hole between the red and black Powerpole shells provided just enough room for an M3 screw to anchor them to the HBP: they won’t flop around under acceleration.
The thermistor cable exits to the left, the rest to the right, and I’m unhappy with the overall routing. I added a small bumper (made from bent steel shim stock) to keep the thermistor cable out of the gap between the Y axis stage and the left side wall:
The platform is holding level within ±0.05 mm across build plates 1 and 2, somewhat better than before. On the other paw, the whole thing doesn’t have many hours on it…
With the heater off for repair, I added a strip of self-adhesive stainless steel tape to the top of the plywood platform, directly under the heater. This should reduce the wood temperature and maybe, just maybe, reduce the thermal expansion that shifts the X axis location of the Z-minimum platform height switch.
HBP heat shield
It’s stainless steel because that’s what was in the Tape Lookaside Buffer; a hunk of aluminum tape, even a pair of 2 inch / 50 mm strips would work just fine.
Not shown here is the M3 screw through the front-center hole (invisible under the tape) that will eventually anchor the new heater connector.
While I was rebuilding the HPB heater wiring, I drilled / countersunk / tapped a 4-40 hole in the middle of the aluminum sub-plate for a screw to secure the middle of the heater PCB:
HBP center attachement screw – top
Remember: this plate is firmly secured to the plywood build platform with three leveling screws over springs. Another aluminum plate, with Kapton tape as the build surface, sits on top, providing an absolutely flat build platform. If you’re using a single plate, you could backfill the hole with a dab of JB Industro Weld epoxy atop a lightly greased screw, then file the top flush with the plate.
A flat-head screw harvested from a chunk of electronic junk came from the Drawer o’ Short 4-40 Screws and fit perfectly:
HBP center attachment screw – bottom
Mirabile dictu, the screw was short enough that it didn’t require any trimming to stay below the top surface.
Securing the center of the PCB to the aluminum plate cuts the heater’s free span in half: the PCB originally had screws only along the left and right edges. Its thermal expansion visibly bowed it away from the plate and I hope this will reduce that problem. Of course, now the PCB’s expansion has nowhere to go and those thermal stresses will probably begin chewing up the mounting holes.
While I was at it, I removed the MBI “heat spreader” tape from the PCB. I’d been reluctant to do that, for fear of peeling the traces right off the board, but the surface was in fine shape. Whew!
More on the wiring and epoxy blobbed brass tube later…
Unlike that pattern, this OpenSCAD program produces an STL file that gets sliced in the usual manner, so that the end result shows exactly how the first layer of all other objects gets laid down.
Thread Thickness Test – solid model
It’s two threads wide and one thread thick: customize the OpenSCAD code to match the settings in Skeinforge (or Slic3r or whatever you’re using) to make it build properly.
The two tabs mark the +X and +Y directions. The bottom surface will be wonderfully shiny from the build plate, so the symmetry along the diagonal shouldn’t pose a problem.
Should the thickness vary more-or-less linearly along any of the bars, then you know which way to level the platform. If it varies non-uniformly, then either the build plate isn’t flat or the printer has other problems.
The actual width depends on the actual thickness, of course: a too-low nozzle will create a too-wide pattern regardless of the extrusion settings. The thickness should be uniform across the entire pattern, so you can still adjust the platform leveling screws.
If you’re using a Z-minimum platform height sensor, now’s the time to adjust the switch touch-off height to make the thread thickness come out right.
When the thread thickness comes out right, then the width should match the extrusion settings: the bottom layer will be exactly like all the others. That’s the ideal situation, anyway.
The Smell of Molten Projects in the Morning 