The New Hotness

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);

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The New Hotness

Miniature Chain Mail: Handouts