Tag: Improvements

Making the world a better place, one piece at a time

Zire 71 Protector: Some Things Last

This ABS slab emerged from the Thing-O-Matic in early 2012:

Zire 71 protector in place

The Zire would power on whenever the switches clicked or that little joystick moved, which happened regularly enough to be annoying.

Mary made a small case that matched the other pouches I carry around:

Belt pack – camera case – PDA case

She made the case to fit an HP48 calculator, but it was close enough for the Zire.

Time passed, the Zire died, I started carrying a Kindle Fire in another pocket, but the ABS slab provided a convenient stiffener between some Geek Scratch Paper and the various pencils / pens / markers / screwdrivers / flashlight filling the available space.

Unfortunately, minus the backup of an electronic slab, the protector finally failed along an obvious stress riser:

Zire 71 protector – cracked

I cut a similar rectangle from a sheet of unknown flexy plastic, rounded the corners, clipped the pencils & whatnot to it, and maybe it’ll survive for a while.

2017-05-13
XTC-3D Epoxy Coating: Results

Having figured the mixing ratios, found the mixing trays, and donned my shop apron, I buttered up several iterations of the badge reel case to see how XTC-3D epoxy works on the little things around here.

In all cases, I haven’t done any sanding, buffing, or primping, mostly because I’m not that interested in the final surface finish.

A single coat produces a glossy finish with ripples from the printed threads:

XTC-3D – Hilbert – reflective

Seen straight on, without the glare, a little speck toward the lower right corner shows that cleanliness is next to impossible around here:

XTC-3D – lines – direct

An additional coat atop a Hilbert-curve upper surface comes out somewhat smoother:

XTC-3D – Hilbert – reflective 2

Another view, with less glare, shows the pattern a bit better:

XTC-3D – Hilbert – reflective 1

With no glare, the 3D Honeycomb infill shows through the surface:

XTC-3D – Hilbert – direct

Coating the surface with epoxy definitely makes it more transparent / less translucent by filling in the air gaps.

The sides of that part have only one coat and still show typical 3D printed striations.

Three coats wipe out the striations, along with all other surface detail:

XTC-3D – Bezel – front oblique

The bolt head recesses collected enough epoxy to require reaming / milling, which certainly isn’t what you want in that situation. The bolt holes also shrank, although my usual hand-twisted drill would probably suffice to clear the epoxy.

Another view shows a glint from the smooth surface filling the upper-right recess:

XTC-3D – Bezel – front

Three coats definitely hides the 3D printed threads, although you can see some ridges and edges:

XTC-3D – heavy – oblique

The epoxy isn’t perfectly self-leveling, probably due to my (lack of) technique:

XTC-3D – heavy – reflection

Blowing out the contrast shows the surface finish:

XTC-3D – heavy – direct – boost

Those scratches come from fingernails, after the overnight curing time. The surface is hard, but not impervious to scratching, which is about what you’d expect for a clear epoxy.

Slightly over-thinning the XTC-3D with denatured alcohol in a 0.7 : 0.3 : 0.3 by weight ratio produced a watery liquid that penetrated directly into the surface:

XTC-3D – thinned – oblique

The finish depends critically on what’s below the surface and how much epoxy you apply. I tried to spread it uniformly with a foam brush, but the center came out somewhat rougher than the outer edge:

XTC-3D – thinned – oblique

The striations along the sides filled in a bit, but surely not enough to satisfy anybody who worries about such things.

A specular reflection shows the changing surface smoothness:

XTC-3D – thinned – oblique reflective

Perhaps two coats of thinned epoxy would produce a watertight / airtight part, without changing the overall dimensions by very much. The mechanical properties depend almost entirely on the plastic-to-plastic bond, so I doubt a thin epoxy layer would improve its pressure-handling capabilities.

Few of the parts I make will benefit from an epoxy coating and I definitely don’t want to get into post-processing the parts just to improve their looks!

2017-05-09
Wearable LED vs. Astable Multivibrator vs. Dead Lithium Cells

Mashing the wearable LED from the completely dead CR2032 cell with a classic astable multivibrator circuit and a not-dead-yet CR123 cell produced a pure-analog desktop blinky:

CR123A Astable – front

Of course, I managed to swap the base resistors, which meant the LED stayed on most of the time, which accounts for the slightly off-kilter brown resistor just under the LED.

It doesn’t look like much with the LED off:

CR123A Astable – top – off

Running from a 2.8 V (= dead) lithium cell, the LED lights a dark room at 3 mA:

CR123A Astable – top – on

The LTSpice schematic gives the details:

Astable Multivibrator – CR2032 – schematic

The LED definitely didn’t come from Nichia and the 2N3704 transistors aren’t the 2N3904s found in the LTSpice library, but, by and large, this is the kind of circuit where nearly anything will work.

The actual LED current obviously depends critically on the particular LED and the cell voltage, so this represents more of a serving suggestion than an actual prediction:

Astable Multivibrator – CR2032 – waveform

Indeed, a Tek current probe clamped around one of those 10 AWG copper wires shows a much more enthusiastic LED current (1 mA/div):

Astable – CR123A 2.8 V – 1 mA -green

I don’t trust the baseline very much. The simulation & back of the envelope agree: the LED-off current should be around 400 µA (which doesn’t depend on the LED at all), so it’s in the right ballpark.

Your mileage will definitely differ.

It runs without a trace of software, which everybody at Squidwrench thought was wonderful …

2017-05-08
XTC-3D Epoxy Coating

The striations inherent in the DIY-grade 3D printing process don’t bother me all that much, but I got some XTC-3D epoxy to see what I’ve been missing. The impressive scrap pile from the badge reel holder provided test pieces:

XTC-3D Epoxy – test pieces – holders

If I were serious, I’d figure out a better way to hold the parts. For now, I jammed a watch crab into the back and trapped the bezel on a watch holder, but … ick.

Weighing the components seems the least-awful way to get the small quantities I need. The instructions recommend 100:43 by weight of resin (A) : hardener (B):

XTC-3D Epoxy – weighing pan

For these tiny parts, 2 g + 0.9 g was way too much and 1 g + 0.4 g seemed entirely adequate. If you slowly drool resin into the pan, drool slightly less than half that much hardener, and it’ll be about as close as you can get. The hardener is much less viscous than the resin: drool carefully.

The stuff might be self-leveling on larger parts, but on these small surfaces it’s better (IMO) to dry-brush multiple layers: you can see thicker and thinner sections in the first picture. The recoat time runs about 1-½ h.

The instructions recommend acetone or denatured alcohol as a thinning agent, at 10 to 25% of the resin volume, with curing times up to 24 h. Alcohol seems less likely to produce Bad Results, because it won’t evaporate instantly. Neither will affect PETG, but if you’re using another plastic, keep its solvent list in mind.

I tried alcohol with a by-weight amounts around 0.7 : 0.3 : 0.3 g, obviously overshooting both the hardener and the alcohol by a few drops. The end result resembled thick water, brushed on easily, and penetrated the surface easily.

A first coat of thinned epoxy should fill voids and unify the surface without changing the dimensions very much, with subsequent coats leveling the striations.

More pix after more layers and more curing …

2017-05-04

Badge Lanyard Reel Mount

A certain young engineer of my acquaintance now carries an ID badge and, so I hear, works in a PCB design & test venue. Seeing as how her favorite color is purple, this seemed appropriate:

Badge Lanyard Reel - front - overall — Badge Lanyard Reel – front – overall

The guts came from Circuit Breaker Labs in the form of a recycled PCB trapped in acrylic resin atop a plastic housing with a spring-loaded reel inside.

It arrived with a plastic bullet at the end of the lanyard:

Badge Lanyard Reel - plastic bullet link — Badge Lanyard Reel – plastic bullet link

Which I immediately replaced with brass, because Steampunk:

Badge Lanyard Reel - bullet cross-drill — Badge Lanyard Reel – bullet cross-drill

That made the plastic housing look weak, so, in a series of stepwise refinements, I conjured a much better case from the vasty digital deep:

Badge Lanyard Reel - iterations — Badge Lanyard Reel – iterations

All of the many, many critical dimensions lie inside the case, where they can’t be measured accurately, so each of those iterations could improve only one or two features. The absolutely wonderful thing about OpenSCAD is having it regenerate the whole model after loosening, say, the carabiner slot by two thread thicknesses; you can do that with a full-on relational CAD drawing, but CAD drawings always seems like a lot of unnecessary work if I must figure out the equations anyway.

The back sports my favorite Hilbert Curve infill with a nicely textured finish:

Badge Lanyard Reel - rear - oblique — Badge Lanyard Reel – rear – oblique

It’d surely look better in solid brass with Hilbert curve etching.

Black PETG doesn’t photograph well, but at least you can see the M2 brass inserts:

Badge Lanyard Reel - lower interior — Badge Lanyard Reel – lower interior

The first prototype showed the inserts needed far more traction than the usual reamed holes could provide, so I added internal epoxy grooves in each hole:

Badge Lanyard Reel Mount - show — Badge Lanyard Reel Mount – show

Recessing the screw heads into the top plate made them more decorative and smoother to the touch. Button-head screws would be even smoother, but IMO didn’t look quite as bold.

After seeing how well the grooves worked, I must conjure a module tabulating all the inserts on hand and automagically generating the grooves.

The yellow star holds up the roof of the reel recess in the build layout:

Badge Lanyard Reel Mount - build layout - bottom — Badge Lanyard Reel Mount – build layout – bottom

Slic3r produced the rest of the support material for the carabiner exit slot:

Badge Lanyard Reel Mount - bottom - Slic3r support — Badge Lanyard Reel Mount – bottom – Slic3r support

Those two support lumps on the right don’t actually support anything, but tweaking the support settings to disable them also killed the useful support on the left; come to find out Slic3r’s modifier meshes don’t let you disable support generation.

The top plate required support all the way around the inside of the bezel:

Badge Lanyard Reel Mount - top - Slic3r support — Badge Lanyard Reel Mount – top – Slic3r support

I carved the original plastic housing in half, roughly along its midline, and discarded the bottom section with the belt clip (it’s on the far left of the scrap pile). The top section, with PCB firmly affixed, holds the lanyard reel and anchors the retracting spring in a central slotted peg. No pictures of that, as it’s either a loose assembly of parts or a spring-loaded bomb and I am not taking it apart again.

The lanyard passes through an eyelet that pays it out to the rotating reel. I’d definitely do that differently, were I building it from scratch, because mounting the eyelet in exactly the proper position to prevent the lanyard from stacking up on the reel and jamming against the inside of the housing turned out to be absolutely critical and nearly impossible.

The top plate presses the original housing against the carabiner, with the cut-off section inside the carabiner’s circular embrace, which just barely worked: the PCB bezel is a millimeter smaller than the shoulder of the housing.

All in all, I think it came out really well for a 3D printed object made by a guy who usually builds brackets:

Badge Lanyard Reel - front - oblique — Badge Lanyard Reel – front – oblique

I hope she likes it …

The OpenSCAD source code as a GitHub Gist:

	// Badge Lanyard Reel Mount
	// Ed Nisley KE4ZNU April 2017
	// Reel center at origin, lanyard exit toward +X

	Layout = "Show";

	Support = true;

	//- Extrusion parameters must match reality!

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.05; // make holes end cleanly

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	//———————-
	// Dimensions

	ID = 0; // for round things
	OD = 1;
	LENGTH = 2;

	Carabiner = [30.7,35.3,3.5]; // metal carabiner around original reel
	Latch = [6.0,-15,8.0]; // wire spring latch: offset from OD + thickness
	LatchAngle = 60; // max deflection angle to center from -X direction

	LatchPoints = [[0,0],
	[Latch[1]/tan(LatchAngle),0],
	[Latch[1]/tan(LatchAngle),-Latch[1]]]; // polygon in as-cut orientation

	echo(str("Latch polygon: ",LatchPoints));

	Screw = [2.0,3.8 + 0*ThreadWidth,10.0]; // M2 screw: ID = clear, OD = head
	ScrewHeadLength = 2.0;
	ScrewSides = 8;
	ScrewRecess = 5*ThreadThick;

	MountSides = ScrewSides; // suitably gritty corners

	MountThick = Screw[LENGTH] / cos(180/MountSides) + ScrewRecess + 2.0;

	Insert = [Screw[ID],3.4,4.0]; // brass insert for screws

	BCD = Carabiner[OD] + 2.5*Insert[OD];

	BoltAngles = [20,110]; // ± angles to bolt holes

	Reel = [5.3,25.5 + 2ThreadWidth,6.0 + 2ThreadThick]; // lanyard cord reel
	ShimThick = 2*ThreadThick; // covers open side of reel for better sliding

	Bezel = [31.0,32.0,7.5]; // PCB holder + shell, LENGTH = post + shell
	BezelSides = 6*4;
	BezelBlock = [5.5,7.5,3.6] + [ThreadWidth,ThreadWidth,ThreadThick]; // block around lanyard eyelet

	Eyelet = [3.5,4.5,3.0];

	Bullet = [2.0,6.5,2.0]; // brass badge holder, LENGTH = recess into mount

	//———————-
	// Useful routines

	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=(FixDia + HoleWindage)/2,
	h=Height,
	$fn=Sides);
	}

	//– Lanyard reel mockup

	module Reel() {

	cylinder(d=Reel[OD],h=Reel[LENGTH],center=true,$fn=6*4);

	}

	// Carabiner metal mockup
	// Some magic numbers lie in wait

	module Beener() {

	difference() {
	hull() {
	cylinder(d=Carabiner[OD],
	h=Carabiner[LENGTH] + 2*ThreadThick,
	center=true,$fn=BezelSides);
	translate([-Carabiner[OD]/2,0,0])
	cylinder(d=Carabiner[OD] – 2.0,
	h=Carabiner[LENGTH] + 2*ThreadThick,
	center=true,$fn=6*4);
	}
	cylinder(d=Carabiner[ID],
	h=2*Carabiner[LENGTH],
	center=true,$fn=BezelSides);
	translate([Carabiner[ID]/4,0,0])
	cube([Carabiner[ID],7.0,2*Carabiner[LENGTH]],center=true);
	}
	}

	// mockup of PCB holder atop remains of old mount with reel post
	// Z = 0 at midline of case

	module BezelMount() {

	rotate(180/BezelSides) {
	PolyCyl(Bezel[ID] + HoleWindage,MountThick,BezelSides); // PCB punches through mount
	PolyCyl(Bezel[OD] + HoleWindage,Bezel[LENGTH] – Reel[LENGTH]/2,BezelSides);
	}

	translate([Reel[OD]/2,0,BezelBlock[2]/2])
	scale([2,1,1])
	cube(BezelBlock,center=true);
	}

	// Main mount around holder & carabiner

	module Mount(Section="All") {

	render()
	difference() {
	hull() {
	for (a = BoltAngles) // spheres defining corners
	for (i=[-1,1])
	rotate(i*a)
	translate([BCD/2,0,0])
	sphere(d=MountThick,$fn=MountSides);
	cylinder(d=Carabiner[OD] + 4*ThreadWidth,
	h=MountThick,center=true); // capture carabiner ring
	}

	for (a = BoltAngles) // screw & insert holes, head recess
	for (i=[-1,1])
	rotate(i*a)
	translate([BCD/2,0,0])
	rotate(0i180/ScrewSides) {
	translate([0,0,-(Insert[LENGTH] + 2*ThreadThick)])
	PolyCyl(Insert[OD],
	Insert[LENGTH] + 2*ThreadThick + Protrusion,ScrewSides);
	for (k = [-2:2]) // epoxy retaining grooves
	translate([0,0,-(k3ThreadThick + Insert[LENGTH]/2)])
	PolyCyl(Insert[OD] + 1*ThreadWidth,
	2*ThreadThick,ScrewSides);
	PolyCyl(Screw[ID],Screw[LENGTH],ScrewSides);
	translate([0,0,MountThick/2 – ScrewRecess]) // recess screw heads
	PolyCyl(Screw[OD],Screw[LENGTH],ScrewSides);
	}

	translate([0,0,-1*ThreadThick]) // Minkowski Z extends only top surface!
	minkowski() { // space for metal carabiner
	Beener();
	// cube([ThreadWidth,ThreadWidth,2*ThreadThick]);
	cylinder(d=ThreadWidth,h=2*ThreadThick,$fn=6);
	}

	rotate([0,90,0]) rotate(180/6) // cord channel = brass tube clearance
	PolyCyl(Bullet[ID],Carabiner[ID],6);

	translate([Eyelet[LENGTH] + 2.0,0,0]) // eyelet, large end inward
	rotate([0,90,0]) rotate(180/6)
	PolyCyl(Eyelet[OD] + HoleWindage, Reel[OD]/2,6);

	if (false)
	translate([Reel[OD]/2 + Eyelet[LENGTH]/2,0,0]) // eyelet, small end outward
	rotate([0,90,0]) rotate(180/6)
	PolyCyl(Eyelet[ID],Eyelet[LENGTH],6);

	translate([(BCD/2 + MountThick/2)*cos(BoltAngles[0]) – Bullet[LENGTH],0,0]) // bullet recess
	rotate([0,90,0]) rotate(180/6)
	PolyCyl(Bullet[OD],Carabiner[ID],6);

	BezelMount(); // PCB holder clearance

	Reel(); // reel clearance

	translate([0,0,-(Reel[LENGTH] + ShimThick)/2]) // sliding plate on open side of reel
	cylinder(d=Reel[OD],h=ShimThick,center=true,$fn=6*4);

	translate([-Carabiner[OD]/2 + Latch[0],Latch[1],0])
	linear_extrude(height=Latch[2],center=true)
	polygon(LatchPoints);

	if (Section == "Upper") // display & build section cutting
	translate([0,0,-2*Carabiner[LENGTH]])
	cube(4*Carabiner,center=true);
	else if (Section == "Lower")
	translate([0,0,2*Carabiner[LENGTH]])
	cube(4*Carabiner,center=true);

	}

	if (Support) { // Completely ad-hoc support structures
	color("Yellow", Layout == "Show" ? 0.3 : 1.0) {
	if (false && Section == "Upper") {
	Spokes = BezelSides;
	Offset = 6*ThreadWidth;
	for (i = [2:Spokes – 2])
	rotate(i * 360/Spokes)
	translate([Offset,-ThreadWidth,0*(Carabiner[LENGTH]/2)/2])
	cube([Carabiner[OD]/2 – Offset – 0*ThreadWidth,
	2*ThreadWidth,
	Carabiner[LENGTH]/2],center=false);
	for (i = [0:Spokes – 1])
	rotate(i * 360/Spokes)
	translate([Offset,-ThreadWidth,0])
	cube([Bezel[OD]/2 – Offset,
	2*ThreadWidth,
	Bezel[LENGTH] – Reel[LENGTH]/2 – 2*ThreadThick],center=false);
	Bars = 7;
	render()
	difference() {
	union() {
	for (i = [-floor(Bars/2) : floor(Bars/2)])
	translate([-Carabiner[ID]/2,i*Carabiner[OD]/Bars,Carabiner[LENGTH]/4])
	cube([Carabiner[ID]/3,2*ThreadWidth,Carabiner[LENGTH]/2],center=true);
	translate([-Carabiner[ID]/2,0,ThreadThick/2])
	cube([Carabiner[ID]/3,Carabiner[ID],ThreadThick],center=true);
	}
	cylinder(d=Carabiner[ID] + 2*ThreadWidth,h=Carabiner[LENGTH]);
	}
	}
	if (Section == "Lower") {
	translate([0,0,-(Reel[LENGTH]/4 + ShimThick/2 – ThreadThick/2)])
	for (i = [0:8])
	rotate(i * 360/8)
	cube([Reel[OD] – 2*ThreadWidth,
	2*ThreadWidth,
	Reel[LENGTH]/2 + ShimThick – ThreadThick],center=true);
	if (false) {
	Bars = 7;
	render()
	difference() {
	union() {
	for (i = [-floor(Bars/2) : floor(Bars/2)])
	translate([-Carabiner[ID]/2,i*Carabiner[OD]/Bars,-Carabiner[LENGTH]/4])
	cube([Carabiner[ID]/3,2*ThreadWidth,Carabiner[LENGTH]/2],center=true);
	translate([-Carabiner[ID]/2,0,-ThreadThick/2])
	cube([Carabiner[ID]/3,Carabiner[ID],ThreadThick],center=true);
	}
	translate([0,0,-Carabiner[LENGTH]])
	cylinder(d=Carabiner[ID] + 0*ThreadWidth,h=Carabiner[LENGTH]);
	}
	}
	}
	}
	}

	}



	//———————-
	// Build it

	if (Layout == "Beener")
	Beener();

	if (Layout == "Mount")
	Mount();

	if (Layout == "Reel")
	Reel();

	if (Layout == "BezelMount")
	BezelMount();

	Gap = 25;
	if (Layout == "Show") {
	translate([0,0,Gap/2])
	Mount("Upper");
	translate([0,0,-Gap/2])
	Mount("Lower");
	color("Green",0.3)
	Beener();
	color("Brown",0.3)
	Reel();
	color("Red",0.3)
	translate([0,0,-(Reel[LENGTH] + ShimThick)/2])
	cylinder(d=Reel[OD],h=ShimThick,center=true,$fn=6*4);
	}

	if (Layout == "Build") {
	translate([(BCD + MountThick)/2,0,0])
	rotate(180)
	Mount("Upper");
	rotate([180,0,0])
	translate([-(BCD + MountThick)/2,0,0])
	Mount("Lower");
	}

	if (Layout == "BuildUpper")
	Mount("Upper");

	if (Layout == "BuildLower")
	rotate([180,0,0])
	Mount("Lower");

view raw Badge Lanyard Reel Mount.scad hosted with ❤ by GitHub

2017-04-28

Microscope 60 LED Ring Light Adapter

The Barbie-themed microscope light I built from an angel eye LED ring worked fine for the last six years (!), but a much brighter ring with 60 aimed 5 mm LEDs for $17 delivered from a US seller caught my eye:

Microscope 60 LED ring light - in use — Microscope 60 LED ring light – in use

Although this ring looks much more professional, it didn’t quite fit the microscope, being designed for a round snout rather than a squarish one. This snout has a 47-ish mm threaded ring intended for filters & suchlike, so I built an adapter between that and the 60 mm ID of the LED ring:

Microscope 60 LED Ring Light Adapter - top - Slic3r — Microscope 60 LED Ring Light Adapter – top – Slic3r

The ring came with three long knurled screws which I replaced with much tidier M3 socket-head screws going into those holes:

Microscope 60 LED ring light - assembled - top — Microscope 60 LED ring light – assembled – top

The part going into the snout threads is deliberately (honest!) a bit small, so I could wrap it with soft tape for a good friction fit. The Barbie Ring didn’t weigh anything and I wound up using squares of double-sticky foam tape; it could come to that for this ring, too.

The adapter features a taper on the bottom for no particularly good reason, as the field-of-view tapers inward, not outward:

Microscope 60 LED Ring Light Adapter - bottom - Slicer — Microscope 60 LED Ring Light Adapter – bottom – Slicer

Seen from the bug’s POV, it’s a rather impressive spectacle:

Microscope 60 LED ring light - assembled - bottom — Microscope 60 LED ring light – assembled – bottom

The control box sports a power switch and a brightness knob. Come to find out the ring is actually too bright at full throttle; a nice problem to have.

That was easy!

The OpenSCAD source code as a GitHub Gist:

	// LED Ring Light Mount – 60 mm ID ring
	// Ed Nisley KE4ZNU April 2017

	//- Extrusion parameters must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	//———————-
	// Dimensions

	ID = 0;
	OD = 1;
	LENGTH = 2;

	ScopeThread = [43.0,46.5,4.0]; // scope snout thread, ID = minimum invisible

	LEDRing = [ScopeThread[ID],60.0,8.0];
	LEDScrewOffset = 4.0;
	LEDScrewOD = 3.0;
	LEDScrews = 3;

	OAH = ScopeThread[LENGTH] + LEDRing[LENGTH];

	NumSides = 34LEDScrews; // get symmetry for screws

	//———————-
	// Useful routines

	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=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
	}

	//———————-
	// Build it

	difference() {
	rotate(180/NumSides)
	union() {
	cylinder(d=ScopeThread[OD],h=OAH,$fn=NumSides);
	cylinder(d=LEDRing[OD],h=LEDRing[LENGTH],$fn=NumSides);
	}

	translate([0,0,-Protrusion])
	rotate(180/NumSides)
	cylinder(d=ScopeThread[ID],h=OAH + 2*Protrusion,$fn=NumSides);

	translate([0,0,-Protrusion])
	rotate(180/NumSides)
	cylinder(d1=LEDRing[OD] – 26ThreadWidth,
	d2=ScopeThread[ID],
	h=LEDRing[LENGTH] + Protrusion,$fn=NumSides);

	for (i=[0:LEDScrews-1])
	rotate(i*360/LEDScrews)
	translate([LEDRing[OD]/2 – LEDScrewOD,0,LEDRing[LENGTH] – LEDScrewOffset])
	rotate([0,90,0]) rotate(180/6)
	cylinder(d=LEDScrewOD,h=LEDScrewOD + Protrusion,$fn=6);
	}

view raw LED Ring Light Mount – 60 mm.scad hosted with ❤ by GitHub

2017-04-25

3D Printer Design Conversation: Part 5

The final installment of musings about building a large-format 3D printer …

(Continued from yesterday)

Perhaps they saw your blog post?

The old-old (original) high-resistance Kysan motor costs something like $45 and, apart from minor cosmetic differences, looks /exactly/ the same as the old-new low-resistance motor. If you were picking motors and didn’t quite understand why you needed a low-resistance winding, which would you pick? Hence, my insistence on knowing the requirements before plunking down your money.

To be fair, I didn’t understand that problem until the Thing-O-Matic rubbed my nose in it. With all four motors. Vigorously.

So, yeah, I think I had a part in that.

comes back to the same numbers over and over

The new-new leadscrews have something like half the pitch of the old-new and old-old threads; I don’t recall the number offhand. In any event, that gives you twice the number of motor steps per millimeter of motion and roughly twice the lifting force. This is pretty much all good, even though it may reduce the maximum Z axis speed (depends on your settings & suchlike).

When it moves upward by, say, 5 mm and downward by 5 mm, you’re measuring position repeatability. That level of repeatability is pretty much a given (for the M2, anyhow), but it doesn’t involve stiction & suchlike.

Can you move the platform up by 0.01 mm, then down by 0.01 mm, and measure 0.01 mm change after each motion?

Do larger increments track equally well in both directions?

Move upward a few millimeters, then step downward by 0.01 mm per step. Does the measurement increase by 0.01 mm after each step?

Repeat that by moving downward, then upward in 0.01 mm increments.

If the platform moves without backlash & stiction in both directions with those increments, it’s a definite improvement.

I wish I knew more
everything you learned is burned into your head forever

The way to learn more is exactly what you’re doing.

Two things I learned a long time ago:

1. Whenever you have two numbers, divide them and ask whether the ratio makes sense.

2. Whenever you don’t understand a problem, do any part of it you do understand, then look at it again.

Also, write everything down. When you come back later, you won’t remember quite how you got those results.

Which is precisely why I have a blog. I search with Google (site:softsolder.com microstepping) and /wham/ I get a quick refresher on what I was thinking. That’s why I keep link-whoring URLs: that’s my memory out there!

You’ll sometimes find scans of my scrawled notes & doodles. They won’t mean anything to you, but they remind me what I do to get the answers in that blog post.

modern controllers utilize much higher voltage and current bursts

More or less. Microstepping drivers apply a relatively high voltage, far in excess of what the winding can tolerate as a DC voltage, then regulate the current to a value that produces the appropriate waveform.

This may be helpful:

https://softsolder.com/2011/05/05/thing-o-matic-mbi-stepper-motor-analysis/

The mass of the bed APPEARS to be cancelling out any magnetic or mechanical stiction.

That can’t be true in both directions: the gravity vector points downward and the results aren’t symmetric. I think you’re reading noise. If the sequences of motions I described don’t produce the results I described, then you’re /definitely/ measuring noise.

From back in the Thing-O-Matic days:

https://softsolder.com/2011/05/22/thing-o-matic-z-axis-resolution-repeatability-backlash/

E3D hot end setups vs MakerGear’s?

No opinion.

I’d want that groovemount post in an all-metal socket, though, rather than the traditional plastic, to get solid positioning and tolerance control. Makergear has the right idea with the aluminum V4 heater block mount.

2017-04-21

Tag: Improvements

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