Category: Machine Shop

Mechanical widgetry

Ham It Up Noise Source Enable Switch

Some rummaging produced a tiny DPDT switch that actually fit the holes intended for a pin header on the recently arrived Ham It Up board, at least after I amputated 2/3 of the poor thing’s legs:

Ham-It-Up – noise source switch – B

The new SMA noise output jack sits in the front left, with the white “noise on” LED just left of the switch:

Ham-It-Up – noise source switch – A

There’s no way to measure these things accurately, at least as far as I can tell, but the holes came out pretty close to where they should be. The new SMA connector lined up horizontally with the existing IF output jack and vertically with the measured / rounded-to-the-nearest-millimeter on-center distance:

Ham It Up – noise SMA drilling

The Enable switch doesn’t quite line up with the LED, so the holes will always look like I screwed up:

Ham-It-Up – noise source switch – case holes

That’s OK, nobody will ever notice.

Now, to stack up enough adapters to get from the SMA on the Ham It Up board to the N connector on the spectrum analyzer …

2016-01-20
Lithium Battery Pack Teardown

For reasons not relevant here, I tore down a battery pack containing three 18650 lithium cells. After a major struggle that involved drilling access holes into the side of the case and hammering the cells free of their silicone potting restraint, I was confronted with this:

Li-ion cell – unwrapped

Battery may explode or fire if mistreated. Yeah, that could happen.

Having pretty well ignored all the warnings, the damaged cells spent two days in the cold on the patio:

Li-ion cells – safety layout

They seem unchanged, so I’ll dispose of them at the next electronics recycling event.

As it turns out, the gadget containing the pack subsequently died of a whoopise while trying to figure out how the pack’s boost regulator worked, so it joined the cells on the outgoing pile.

So it goes …

2016-01-19

Microscope Stage Positioner

Given the vanishingly small depth of field provided by a cheap USB camera peering through the stereo zoom microscope, I’ve always wanted a better way of moving objects by small increments. The rehabilitated micropositioner didn’t have the right orientation or end effector:

So I rearranged the axis slides and added a small table:

That frees up the magnetic base and husky angle bracket, plus a few odds & ends, for future adventures.

The clear base is a random chunk of acrylic, bandsawed to the proper length, then tediously squared and drilled on the Sherline:

Microscope Stage Positioner - base squaring — Microscope Stage Positioner – base squaring

I briefly thought of printing the base, but came to my senses: there are better ways to make big flat surfaces.

The little aluminum table has a nubbly spray coating that came straight from the heap and looks surprisingly good after squaring & drilling. The X axis block puts it below the platform and one screw head above the desk when the Y axis arm sits flat on the acrylic base.

One solid model view arranges things in more-or-less the proper layout to check the alignment:

Microscope Stage Positioner - solid model - Show layout — Microscope Stage Positioner – solid model – Show layout

The build layout reduces the platform space:

Microscope Stage Positioner - Slic3r preview — Microscope Stage Positioner – Slic3r preview

You’re looking at four hours of PETG print time at 0.2 mm layer thickness with 15% infill and Hilbert Curve surfaces.

All of the screws have UNF fine-pitch threads (4-48, 6-40, 8-36, stuff like that), so the solid model includes the spacing required to reuse the original screws: those big holes in the Y axis arm end in little clearance holes for the tiny screws. Some of the screws bottom out with barely two millimeters of thread engagement in the slides, while others could jam against the racks. I didn’t want to cut that many screws from my Brownell’s gun screw assortment unless I absolutely had to. So far, so good.

I spent quite a while doodling the layout to convince myself that it would actually work:

Microscope Stage Positioner - layout doodle — Microscope Stage Positioner – layout doodle

Memo to self: Next time, use a larger scale!

Although the whole lashup works as intended, those metal hunks are way too heavy for the plastic block that fits between the Z axis drive pillar and the X axis slide: that long Y axis arm drooped toward the front by about 5 mm. A small shim raised the front of the Z axis footprint enough to level the arm, but I think the right answer is a metal upright with a bigger footprint that spreads the load.

All that mass hanging out in mid-air turns the plastic pieces into springs: you can’t keep your fingers on the knobs. Fortunately, everything returns to the same position after you release the knob, so it’s easy to move in precise increments if you close your eyes until the view settles down.

There’s a reason optical equipment uses cast iron, steel, and brass… but I’ll settle for plastic.

The OpenSCAD source code as a GitHub gist:

	// Microscope Stage Positioner
	// Ed Nisley KE4ZNU January 2016

	Layout = "Build"; // Show Build
	// Base ZStand YMount XMount

	Gap = 0.0;

	//- 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

	SlipFit = 0.1;

	ZDrive = [26.0,19.6,75.0]; // stationary part of Z drive
	ZDriveOffset =[0,0,22.0]; // left front corner of stationary Z base
	ZWall = 4.0; // thickness of edge wrapped around Z columns

	YStageBlock = [25.0,61.0,17.0]; // Y stage mount + slide
	YStageOffset = [-6.0,4.0,0.0]; // offset to inner corner of Y stage holder

	YArm = [10.0,93.0,17.0]; // mount to stationary part of Y stage

	ZStage = [24.0,9.7,85.0]; // moving part of Z drive
	ZYArm = [(2*ZWall + ZStage[0]),10.0,YArm[2]]; // attaches to ZStage, same thickness as YArm

	XStageBlock = [25.0,20.0,12.0]; // X stage mount + slide
	XStageOffset = [-95.0,-15.0,-26]; // offset to rear left bottom corner of X stage slide

	XTray = [25,25,5]; // X tray attached to bottom of X 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);
	}


	//– Z Stand

	module ZStand() {

	Holes = [12.0,41.5,68.0];
	HoleOD = 3.5;
	HolesOC = 15.0;

	echo(str("Z Stand holes OC: ",HolesOC));

	ZPlate = 6.0; // thickness of Z plate = max screw grab distance
	ZStandWrap = 2.0; // length of edge wrapped around Z column

	MaxY = 9.0;
	MinY = -14.0;

	difference() {
	union() {
	linear_extrude(height=ZDriveOffset[2])
	polygon(points=[
	[-ZWall,MaxY], // limited by Z slide rack
	[ZDrive[0] + ZWall,MaxY],
	[ZDrive[0] + ZWall,MinY], // limited by X slide rack
	[-ZWall,MinY]
	]);
	linear_extrude(height=(ZDrive[2] + ZDriveOffset[2]),convexity=4)
	polygon(points=[
	[-SlipFit,0],
	[ZDrive[0] + SlipFit,0.0],
	[ZDrive[0] + SlipFit,ZStandWrap],
	[ZDrive[0] + ZWall,ZStandWrap],
	[ZDrive[0] + ZWall,-ZPlate],
	[-ZWall,-ZPlate],
	[-ZWall,ZStandWrap],
	[-SlipFit,ZStandWrap]
	]);
	}

	for (i = [0:len(Holes) – 1]) // holes along Z stand
	translate([ZDrive[0]/2,ZDrive[1]/2,(Holes[i] + ZDriveOffset[2])])
	rotate([90,0,0])
	PolyCyl(HoleOD,ZDrive[1]);

	for (i = [-1,1]) // mounting screw holes
	translate([i*HolesOC/2 + ZDrive[0]/2, // center the holes from side to side
	(MaxY + MinY)/2, // moby hack to put holes on midline
	-Protrusion])
	PolyCyl(3.5,0.75*ZDriveOffset[2],6);
	}
	}

	//– Y Mounting arm
	// Polygon origin at inner corner nearest the Z stand column

	module YMount() {

	YHoles = [12.0,48.0,84.0]; // mounting holes along Y stage arm, from outside in
	YScrewLength = 4.0; // screw head to Y stage mount

	ZStageBase = [(ZDrive[0] – ZStage[0])/2,(ZDrive[1] + ZStage[1]),0.0] – YStageOffset; // local coordinates of Z slide left rear corner
	ZHoles = [26.5,55.0,71.0];

	ZStageWrap = 8.0; // length of edge wrapped around Z stage
	Trim = ZStageBase[1] – ZStageWrap;

	union() {
	difference() {
	linear_extrude(height=YArm[2],convexity=5)
	polygon(points=[
	[-Trim,0.0],
	[-YStageBlock[0],0.0],
	[-YStageBlock[0],-(YArm[1] + SlipFit)],
	[-(YStageBlock[0] + YArm[0]),-(YArm[1] + SlipFit)],
	[-(YStageBlock[0] + YArm[0]),Trim],
	[-Trim,(ZStageBase[1] + ZYArm[1])],
	[(ZStageBase[0] + ZStage[0]/2),(ZStageBase[1] + ZYArm[1])],
	[(ZStageBase[0] + ZStage[0] + ZWall),(ZStageBase[1] + 0*ZYArm[1])],
	[(ZStageBase[0] + ZStage[0] + ZWall),(ZStageBase[1] – ZStageWrap)],
	[(ZStageBase[0] + ZStage[0] + SlipFit),(ZStageBase[1] – ZStageWrap)],
	[(ZStageBase[0] + ZStage[0] + SlipFit),ZStageBase[1]],
	[(ZStageBase[0] – SlipFit),ZStageBase[1]],
	[(ZStageBase[0] – SlipFit),(ZStageBase[1] – ZStageWrap)],
	[0.0,(ZStageBase[1] – ZStageWrap)],
	[0.0,Trim]
	]);

	for (j=[0:len(YHoles) – 1]) { // Y stage mounting screws
	translate([-(YStageBlock[0] + YScrewLength),
	(-YArm[1] + YHoles[j] – 2*SlipFit),
	YArm[2]/2])
	rotate([0,-90,0]) rotate(180/6)
	PolyCyl(5.5,YArm[0],6);
	translate([-(YStageBlock[0] – Protrusion),
	(-YArm[1] + YHoles[j] – 2*SlipFit),
	YArm[2]/2])
	rotate([0,-90,0]) rotate(180/6)
	PolyCyl(2.5,2*YArm[0],6);
	}
	}
	if (true)
	difference() {
	linear_extrude(height=ZStage[2],convexity=5)
	polygon(points=[
	[(ZStageBase[0] – ZWall),(ZStageBase[1] + 5.0)],
	[(ZStageBase[0] + ZStage[0] + ZWall),(ZStageBase[1] + 5.0)],
	[(ZStageBase[0] + ZStage[0] + ZWall),(ZStageBase[1] – ZStageWrap)],
	[(ZStageBase[0] + ZStage[0] + SlipFit),(ZStageBase[1] – ZStageWrap)],
	[(ZStageBase[0] + ZStage[0] + SlipFit),ZStageBase[1]],
	[(ZStageBase[0] – SlipFit),ZStageBase[1]],
	[(ZStageBase[0] – SlipFit),(ZStageBase[1] – ZStageWrap)],
	[(ZStageBase[0] – ZWall),(ZStageBase[1] – ZStageWrap)],
	]);
	for (k=[0:len(ZHoles) – 1])
	translate([(ZStageBase[0] + ZStage[0]/2),0.0,ZHoles[k]])
	rotate([-90,0,0])
	PolyCyl(3.5,2*ZStageBase[1],6);
	}
	}
	}

	//– X Slide attachment
	// Origin at left rear bottom of mount

	module XMount() {

	XHoles = [6.0,18.0]; // from end of X slide
	XHolesOffset = 7.0; // from bottom of X slide

	TrayHolesOC = 10.0;
	echo(str("Tray holes OC: ",TrayHolesOC));

	BlockOAH = XStageBlock[2] – XStageOffset[2] – XTray[2]; // overall height of mount

	difference() {
	translate([XStageBlock[0],0,BlockOAH])
	rotate([0,90,180])
	linear_extrude(height=XStageBlock[0],convexity=2)
	polygon(points=[
	[0,0],
	[0.0,7.0],
	[(XStageBlock[2] + SlipFit),7.0],
	[(XStageBlock[2] + SlipFit),XStageBlock[1]],
	[BlockOAH,XStageBlock[1]],
	[BlockOAH,0.0],
	]);

	for (i=[0:len(XHoles) – 1]) // holes for X stage screws
	translate([XHoles[i],Protrusion,BlockOAH – XStageBlock[2] + XHolesOffset])
	rotate([90,0,0])
	PolyCyl(3.5,2*7.0,6);

	for (i=[-1,1]) // holes for tray mount
	translate([i*TrayHolesOC/2 + XStageBlock[0]/2,-XStageBlock[1]/2,-Protrusion])
	PolyCyl(2.5,0.75*(BlockOAH – XStageBlock[2]),6);
	}

	}

	//———————-
	// Build it

	if (Layout == "ZStand")
	ZStand();

	if (Layout == "YMount")
	YMount();

	if (Layout == "XMount")
	XMount();


	if (Layout == "Show") {

	color("lightgreen")
	ZStand();

	color("orange")
	translate(YStageOffset)
	YMount();

	color("lightblue")
	translate(XStageOffset + [0,0,-XStageOffset[2]])
	XMount();
	}

	if (Layout == "Build") {

	translate([20,0,0])
	ZStand();

	translate([YStageBlock[0]/2,0,0])
	YMount();

	translate([20,-30,0])
	XMount();
	}

view raw Microscope Stage Positioner.scad hosted with ❤ by GitHub

2016-01-18

Bathroom Light Switch: Contact Autopsy

The dual switch controlling the bathroom lights began requiring some fiddling, which was not to be tolerated. After replacing the switch, I cracked the old one open to see what’s inside…

The failed side of the switch controlled the lights over the sink:

Light switch contacts – lights

The side for the ceiling vent fan + light got much less use, still worked, and look a bit less blasted.

Light switch contacts – ceiling fan

Not much to choose between the two. It’s been running for nigh onto two decades, so …

2016-01-16

Olfa Rotary Cutter Spacer

At some point along the way, the bright yellow washer (they call it a “spacer”) on Mary’s 60 mm Olfa rotary cutter went missing. A casual search suggests that replacement washers come directly from Olfa after navigating their phone tree, but …

Judging from scuffs on the rear surface, the washer serves two purposes:

Hold the blade close to the handle against slightly misaligned cutting forces
Add more compression to the wave washer under the nut

This model is much more intricate than the stock washer:

Olfa Rotary Cutter - backing washer — Olfa Rotary Cutter – backing washer

The trench across the middle of the thicker part allows a wider compression adjustment range for the wave washer and provides more thread engagement at the lightest setting for my liking. The shape comes from the chord equation based on measurements of the wave washer:

Olfa Rotary Cutter - washer doodles — Olfa Rotary Cutter – washer doodles

The wave washer keys on the bolt flats: the whole affair rotates with the blade and gives the nut no inclination to unscrew. If you remove the trench, the remaining hole has the proper shape to key on the bolt and rotate with it; with the trench in place, the wave washer’s sides haul the plastic washer along with it.

The plain ring, just two threads thick, glues bottom-to-bottom on the thicker part to soak up the air gap and provide more blade stability. It’s not entirely clear that’s a win; it’s easy to omit.

It looks about like you’d expect:

Olfa Rotary Cutter - washer in place — Olfa Rotary Cutter – washer in place

The wave washer must go on the bolt with the smooth curve downward into the trench. That orientation that wasn’t enforced by the Official Olfa spacer washer’s smooth sides.

The nut sits upside-down to show the face that normally sits against the wave washer. I’d lay long odds that the recess around the threads originally held a conical compression spring with a penchant for joining the dust bunnies under the sewing table. You can insert the wave washer the wrong way, but it doesn’t store enough energy to go airborne unless you drop it, which did happen once with the expected result.

The OpenSCAD source code as a GitHub gist:

	// Olfa rotary cutter backing washer
	// Ed Nisley KE4ZNU January 2016

	Layout = "Build";

	//- Extrusion parameters must match reality!
	// Print with +1 shells and 3 solid layers

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

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

	Protrusion = 0.1; // make holes end cleanly

	//———————-
	// Dimensions

	WasherOD = 35.0;
	WasherThick = 1.5;

	WaveOD = 14.0; // wave washer flat dia
	WaveM = 1.8; // height of wave washer bend
	BendRad = (pow(WaveM,2) + pow(WaveOD,2)/4) / (2*WaveM); // radius of wave washer bend

	echo(str("Wave washer bend radius: ",BendRad));

	SpacerID = WaveOD + 2.0;
	SpacerThick = 2*ThreadThick;

	NumSides = 12*4;
	$fn = NumSides;
	//———————-
	// 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);
	}

	//———————-
	// Parts

	module Upper() {
	difference() {
	cylinder(d1=WasherOD,d2=(WasherOD – 2.0),h=WasherThick);
	translate([0,0,-Protrusion])
	intersection() {
	PolyCyl(8.2,2.0,8);
	cube([(6.0 + HoleWindage),10,2*WasherThick],center=true);
	}
	translate([-(WaveOD + 1.0)/2,0,BendRad])
	rotate([0,90,0]) rotate(0*180/16)
	PolyCyl(BendRad*2,(WaveOD + 1),16);
	}
	}

	module Spacer() {
	difference() {
	cylinder(d=WasherOD,h=SpacerThick);
	translate([0,0,-Protrusion])
	cylinder(d=SpacerID,h=2*SpacerThick);
	}
	}

	//———————-
	// Build it!

	if (Layout == "Show") {
	translate([0,0,SpacerThick])
	color("Cyan")
	Upper();
	color("LightCyan")
	Spacer();
	}

	if (Layout == "Build") {
	translate([-0.6*WasherOD,0,0])
	Upper();
	translate([0.6*WasherOD,0,0])
	Spacer();
	}

view raw Olfa Rotary Cutter.scad hosted with ❤ by GitHub

2016-01-13

Miniature Chain Mail: Handouts

I ran off a few patches of miniature chain mail for holiday handouts to a few folks who’d appreciate them:

Chain Mail Armor - 6x6 9.6 mm - top view — Chain Mail Armor – 6×6 9.6 mm – top view

A little patch like that makes a fondletoy that’s easier to pocket than, say, a planetary gear bearing and should be robust enough to withstand quite a bit of abuse.

Alas, it turned out that recent Slic3r development versions suffered a bridging regression. The stable 1.2.9 version does the right thing:

Slic3r 1.2.9 - good bridging — Slic3r 1.2.9 – good bridging

The hot-from-Github version goes diagonally, producing a pattern like an internal layer that normally sits atop the (omitted) bridge layer:

Slic3r 7c8b710 - diagonal bridging — Slic3r 7c8b710 – diagonal bridging

While that might barely work, the little bitty link bars will certainly fall into the abyss:

Slic3r 7c8b710 - diagonal bridging on links — Slic3r 7c8b710 – diagonal bridging on links

Given the complexity of slicing algorithms, I definitely can’t track down the problem; using the stable version for a while should suffice.

The OpenSCAD source code as a GitHub gist:

	// Chain Mail Armor Buttons
	// Ed Nisley KE4ZNU – December 2014

	Layout = "Build"; // Link Button LB Joiner Joiners Build PillarMod

	//——-
	//- Extrusion parameters must match reality!
	// Print with 1 shell and 2+2 solid layers

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

	//——-
	// Dimensions

	//- Set maximum sheet size

	SheetSizeX = 125; // 170 for full sheet on M2
	SheetSizeY = 125; // 230 …

	//- Diamond or rectangular sheet?

	Diamond = false; // true = rotate 45 degrees, false = 0 degrees for square

	BendAround = "X"; // X or Y = maximum flexibility around designated axis

	Cap = true; // true = build bridge layers over links
	CapThick = 4 * ThreadThick; // flat cap on link: >= 3 layers for solid bridging

	Armor = true && Cap; // true = build armor button atop (required) cap
	ArmorThick = IntegerMultiple(2.0,ThreadThick); // height above cap surface

	ArmorSides = 4;
	ArmorAngle = true ? 180/ArmorSides : 0; // true -> rotate half a side for best alignment

	//- Link bar sizes

	BarThick = 3 * ThreadThick;
	BarWidth = 3.3 * ThreadWidth;

	BarClearance = 3 * ThreadThick; // vertical clearance above & below bars

	VertexHack = false; // true to slightly reduce openings to avoid coincident vertices

	//- Compute link sizes from those values

	//- Absolute minimum base link: bar width + corner angle + build clearance around bars
	// rounded up to multiple of thread width to ensure clean filling
	BaseSide = IntegerMultiple((4BarWidth + 2BarWidth/sqrt(2) + 3(2ThreadWidth)),ThreadWidth);

	BaseHeight = 2*BarThick + BarClearance; // both bars + clearance

	echo(str("BaseSide: ",BaseSide," BaseHeight: ",BaseHeight));
	//echo(str(" Base elements: ",4BarWidth,", ",2BarWidth/sqrt(2),", ",3(2ThreadWidth)));
	//echo(str(" total: ",(4BarWidth + 2BarWidth/sqrt(2) + 3(2ThreadWidth))));

	BaseOutDiagonal = BaseSide*sqrt(2) – BarWidth;
	BaseInDiagonal = BaseSidesqrt(2) – 2(BarWidth/2 + BarWidth*sqrt(2));

	echo(str("Outside diagonal: ",BaseOutDiagonal));

	//- On-center distance measured along coordinate axis
	// the links are interlaced, so this is half of what you think it should be…

	LinkOC = BaseSide/2 + ThreadWidth;

	LinkSpacing = Diamond ? (sqrt(2)*LinkOC) : LinkOC;
	echo(str("Base spacing: ",LinkSpacing));

	//- Compute how many links fit in sheet

	MinLinksX = ceil((SheetSizeX – (Diamond ? BaseOutDiagonal : BaseSide)) / LinkSpacing);
	MinLinksY = ceil((SheetSizeY – (Diamond ? BaseOutDiagonal : BaseSide)) / LinkSpacing);
	echo(str("MinLinks X: ",MinLinksX," Y: ",MinLinksY));

	NumLinksX = ((0 == (MinLinksX % 2)) && !Diamond) ? MinLinksX + 1 : MinLinksX;
	NumLinksY = ((0 == (MinLinksY % 2) && !Diamond)) ? MinLinksY + 1 : MinLinksY;
	echo(str("Links X: ",NumLinksX," Y: ",NumLinksY));

	//- Armor button base

	ButtonHeight = BaseHeight + BarClearance + CapThick;
	echo(str("ButtonHeight: ",ButtonHeight));

	//- Armor ornament size & shape
	// Fine-tune OD & ID to suit the number of sides…

	TotalHeight = ButtonHeight + ArmorThick;
	echo(str("Overall Armor Height: ",TotalHeight));

	ArmorOD = 1.0 * BaseSide; // tune for best base fit
	ArmorID = 10 * ThreadWidth; // make the tip blunt & strong

	//——-

	module ShowPegGrid(Space = 10.0,Size = 1.0) {

	RangeX = floor(95 / Space);
	RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	for (y=[-RangeY:RangeY])
	translate([xSpace,ySpace,Size/2])
	%cube(Size,center=true);

	}


	//——-
	// Create link with armor button as needed

	module Link(Topping = false) {

	LinkHeight = (Topping && Cap) ? ButtonHeight : BaseHeight;

	render(convexity=3)
	rotate((BendAround == "X") ? 90 : 0)
	rotate(Diamond ? 45 : 0)
	union() {
	difference() {
	translate([0,0,LinkHeight/2]) // outside shape
	intersection() {
	cube([BaseSide,BaseSide,LinkHeight],center=true);
	rotate(45)
	cube([BaseOutDiagonal,BaseOutDiagonal,(LinkHeight + 2*Protrusion)],center=true);
	}

	translate([0,0,(BaseHeight + BarClearance + 0*ThreadThick – Protrusion)/2])
	intersection() { // inside shape
	cube([(BaseSide – 2*BarWidth),
	(BaseSide – 2*BarWidth),
	(BaseHeight + BarClearance + 0*ThreadThick + (VertexHack ? Protrusion/2 : 0))],
	center=true);
	rotate(45)
	cube([BaseInDiagonal,
	BaseInDiagonal,
	(BaseHeight + BarClearance + 0*ThreadThick + (VertexHack ? Protrusion/2 : 0))],
	center=true);
	}

	translate([0,0,((BarThick + 2*BarClearance)/2 + BarThick)]) // openings for bars
	cube([(BaseSide – 2BarWidth – 2BarWidth/sqrt(2) – (VertexHack ? Protrusion/2 : 0)),
	(2*BaseSide),
	BarThick + 2*BarClearance – Protrusion],
	center=true);

	translate([0,0,(BaseHeight/2 – BarThick)])
	cube([(2*BaseSide),
	(BaseSide – 2BarWidth – 2BarWidth/sqrt(2) – (VertexHack ? Protrusion/2 : 0)),
	BaseHeight],
	center=true);

	}

	if (Topping && Armor)
	translate([0,0,(ButtonHeight – Protrusion)]) // sink slightly into the cap
	rotate(ArmorAngle)
	cylinder(d1=ArmorOD,d2=ArmorID,h=(ArmorThick + Protrusion), $fn=ArmorSides);
	}

	}


	//——-
	// Create split buttons to join sheets

	module Joiner() {

	translate([-LinkSpacing,0,0])
	difference() {
	Link(false);
	translate([0,0,BarThick + BarClearance + TotalHeight/2 – Protrusion])
	cube([2LinkSpacing,2LinkSpacing,TotalHeight],center=true);
	}

	translate([LinkSpacing,0,0])
	intersection() {
	translate([0,0,-(BarThick + BarClearance)])
	Link(true);
	translate([0,0,TotalHeight/2])
	cube([2LinkSpacing,2LinkSpacing,TotalHeight],center=true);
	}

	}


	//——-
	// Build it!

	//ShowPegGrid();

	if (Layout == "Link") {
	Link(false);
	}

	if (Layout == "Button") {
	Link(true);
	}

	if (Layout == "LB") {
	color("Brown") Link(true);
	translate([LinkSpacing,LinkSpacing,0])
	color("Orange") Link(false);
	}

	if (Layout == "Build")
	for (ix = [0:(NumLinksX – 1)],
	iy = [0:(NumLinksY – 1)]) {
	x = (ix – (NumLinksX – 1)/2)*LinkSpacing;
	y = (iy – (NumLinksY – 1)/2)*LinkSpacing;
	translate([x,y,0])
	color([(ix/(NumLinksX – 1)),(iy/(NumLinksY – 1)),1.0])
	if (Diamond)
	Link((ix + iy) % 2); // armor at odd,odd & even,even points
	else
	if ((iy % 2) && (ix % 2)) // armor at odd,odd points
	Link(true);
	else if (!(iy % 2) && !(ix % 2)) // connectors at even,even points
	Link(false);
	}

	if (Layout == "Joiner")
	Joiner();

	if (Layout == "Joiners") {
	NumJoiners = max(MinLinksX,MinLinksY)/2;
	for (iy = [0:(NumJoiners – 1)]) {
	y = (iy – (NumJoiners – 1)/2)2LinkSpacing + LinkSpacing/2;
	translate([0,y,0])
	color([0.5,(iy/(NumJoiners – 1)),1.0])
	Joiner();
	}
	}

	if (Layout == "PillarMod") // Slic3r modification volume to eliminate pillar infill
	translate([0,0,(BaseHeight + BarClearance)/2])
	cube([1.5SheetSizeX,1.5SheetSizeY,BaseHeight + BarClearance],center=true);

view raw Chain Mail Square Armor.scad hosted with ❤ by GitHub

2016-01-11

Sienna Hood Rod Pivot: Failure Analysis

Our Larval Engineer returned the remaining chunk of the failed PLA hood rod pivot from “her” Sienna minivan:

$Sienna hood rod pivot - PLA fracture$
Sienna hood rod pivot – PLA fracture

A closer look at the top surface (facing you in the picture above) shows the threads didn’t fuse into a solid mass across the entire object:

$Sienna Hood Pivot - PLA fracture - top$
Sienna Hood Pivot – PLA fracture – top

The darker region in the middle comes from the infill pattern, which should have air gaps.

The bottom surface (on the platform during printing) shows how the threads spread out when the nozzle is closer to the platform than the layer thickness:

$Sienna Hood Pivot - PLA fracture - bottom right$
Sienna Hood Pivot – PLA fracture – bottom right

That’s more pronounced on the other side of the pivot:

$Sienna Hood Pivot - PLA fracture - bottom left 1$
Sienna Hood Pivot – PLA fracture – bottom left 1

The infill looks like a separate wall inside the two perimeter threads. That’s pretty much what you get in the space between two close-set walls: there’s not enough room for the full infill pattern.

A slightly different focus plane shows the mashed bottom layer, infill sitting atop the bottom layer, and fused perimeter threads:

$Sienna Hood Pivot - PLA fracture - bottom left 2$
Sienna Hood Pivot – PLA fracture – bottom left 2

Because 3D printing doesn’t (and really can’t) produce a solid block of plastic, the object will fail much more readily than an injection-molded part. The threads in the most highly stressed section fail first, after which the remainder will just rip apart. In this case, the hood rod provides a huge lever that easily overstresses the plastic; I’m surprised the original part lasted as long as it did.

We all knew PLA wasn’t the right material for the job, right from the start, so we’ll see how the enlarged PETG version works in the field.

2016-01-10