The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Machine Shop

Mechanical widgetry

Refrigerator Drawer Strut Tab: Now With Inserts

A spate of cleaning put the little tab that fixed the never-sufficiently-to-be-damned strut supporting the lower refrigerator drawers into my hands:

Refrigerator Drawer Strut – new tab in place

I discovered that 4-40 knurled inserts perfectly match the available space, so I drilled the 3D printed holes out to 11/16 inch (the OD of the smaller knurls) and rammed the inserts into place:

Refrigerator Drawer Strut Tab – knurled inserts

No epoxy, no heat, nothing but a friction fit.

Looks much better, ought to work just as well, and will definitely outlive the refrigerator; if I never take that thing apart again, it’ll be fine with me.

2016-04-08
Filament Drive Gear Calculations
Some equations relevant to indentations produced by a filament drive gear:

Filament Drive Gear Indentations

For reference, the smaller indentations are 0.25 mm deep and 1.3 mm across the bottom.

Variables:
- d = filament (a.k.a. circle) diameter
- r = filament radius
- m = chord depth (inward from circle)
- c = chord length
- Θ = angle across chord from circle center, degrees
- A = chord area (a.k.a. indentation face area)
The length of the chord at the bottom of the indentation, perpendicular to the filament axis:

c = 2 sqrt(2mr - m²)

The chord angle:

Θ = 2 arcsin(c/2r)

The chord area, which would be the indentation face if it were perpendicular, which it isn’t:

A = (r² / 2) x ((πΘ / 180) - sin(Θ))

If you measured Θ in radians, the π/180 factor would Go Away.

Some doodles showing that reducing the indentation from 0.25 to 0.15 reduces the chord area by a factor of two:

Filament Drive Gear – indentation doodles

The implication being that you must maintain fairly constant force on the drive bearing against the filament to prevent stripping the indentations.
2016-04-07
M2 Platform Alignment Check

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:

Thinwall open box – 1 thread walls

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:

Thinwall box measurements – 2016-04-01

2016-04-06

Thinwall and Solid Boxes for 3D Printer Calibration

A revision to my Fundamental Calibration Object adds some variations …

The classic thinwall open box:

Calibration Box - open - 1 thread - solid model — Calibration Box – open – 1 thread – solid model

A solid box:

Calibration Box - solid - solid model — Calibration Box – solid – solid model

A solid box with text embossed on the lower surface:

Calibration Box - solid text - solid model — Calibration Box – solid text – solid model

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:

Thinwall open box - 0.40 wall - Slic3r — Thinwall open box – 0.40 wall – Slic3r

The results look just like the preview, with firmly bonded layers and no fluff:

Thinwall open box - 1 thread walls — Thinwall open box – 1 thread walls

This wall should be two threads wide, but Slic3r inserts very very thin infill thread:

Thinwall open box - 0.80 wall - Slic3r — Thinwall open box – 0.80 wall – Slic3r

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:

Thinwall open box - 2 thread walls — Thinwall open box – 2 thread walls

A triple-thread wall allows Slic3r to produce a fatter infill thread that works the way you’d expect:

Thinwall open box - 1.20 wall - Slic3r — Thinwall open box – 1.20 wall – Slic3r

The threads bond firmly in all directions:

Thinwall open box - 3 thread walls — Thinwall open box – 3 thread walls

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:

	// Simple calibration boxes
	// Thin wall open box – verify Extrusion Multiplier
	// Solid box – verify infill settings
	// Ed Nisley – KE4ZNU
	// https://softsolder.com/

	Layout = "Open"; // Open Solid

	Texting = "Text!"; // text message on solid box or empty string to suppress

	//——-
	//- Extrusion parameters must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	Protrusion = 0.1; // make holes end cleanly

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

	//——-
	// Dimensions

	WallThick = 1.0 * ThreadWidth;
	echo(str("Wall thickness: ",WallThick));

	BoxSize = 20.0;
	echo(str("Overall size: ",BoxSize));

	NominalHeight = 3.0;
	echo(str("Nominal height: ",NominalHeight));

	Height = IntegerMultiple(NominalHeight,ThreadThick);
	echo(str("Actual height: ",Height));

	Rotation = 0; // 45 to exercise X and Y axis motors at same time

	CornerRadius = 2.0;
	CornerSides = 8*4;

	//——–

	module Solid() {

	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(BoxSize – 2CornerRadius)/2,j(BoxSize – 2CornerRadius)/2,0])
	cylinder(r=CornerRadius,h=Height,$fn=CornerSides);
	if (len(Texting))
	translate([0,0,-Protrusion/2])
	linear_extrude(height=3*ThreadThick + Protrusion)
	mirror([1,0,0])
	text(text=Texting,size=6,spacing=1.05,font="ITC Zapf Chancery:style=Italic",halign="center",valign="center");
	}
	}


	module Thinwall() {
	difference() {
	Solid();
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(BoxSize – 2CornerRadius)/2,j(BoxSize – 2CornerRadius)/2,-Protrusion])
	cylinder(r=(CornerRadius – WallThick),h=(Height + 2*Protrusion),$fn=CornerSides);
	}
	}


	//——-

	rotate(Rotation)
	if (Layout == "Open")
	Thinwall();
	else
	Solid();

view raw Calibration Boxes.scad hosted with ❤ by GitHub

2016-04-05

Kenmore 158.17032: Mystery Spring

This steel strip emerged from inside the arm of the Kenmore 158.17032 sewing machine that we’ve been reconditioning for one of Mary’s friends:

Kenmore 158.17032 – mystery spring

The ends show the granular fracture of hard steel:

Kenmore 158.17032 – mystery spring – end view

It’s 13.3 mm long, 1.0 mm thick, tapers slightly from 2.8 mm on the end that once said “Japan” to 2.76 mm on the other, and that’s all we know about it.

The sewing machine seems to work well enough without it (after some clean-and-lube action) and we haven’t found where the piece came from, but circumstantial evidence suggests it’s part of a spring somewhere inside the arm. It’s in a little bag with all the other random sewing machine parts I’ve collected along the way; perhaps some day we’ll know more and I can fabricate a replacement.

2016-03-31

Square Chain Mail Armor: Back From The Abyss

After a Slic3r commit fixed the bridging regression, I ran off chain mail patches to celebrate:

Square Chain Mail Armor - 3.3 3.5 4.0 thread bars — Square Chain Mail Armor – 3.3 3.5 4.0 thread bars

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 BarWidth and SheetSize parameters. The links recalculate themselves around those values.

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

2016-03-30

Recommended Screwdriver Set: Brownells Magna-Tip Super Set

More on the Kenmore 158.17032 that started all this appears elsewhere, but I found myself deploying several bits from my Brownells Magna-Tip screwdriver set:

Brownells Magna-Tip Super-Set on bench

The matrix of bits covers nine slot lengths (= screw head diameters) with four / five / six slot widths. This is the set with 44 bits; the 58 bit set fills the empty holes with 14 hex / square / Phillips bits that I already have in multiples.

I reserve these lovely hollow-ground bits for specialty screws that must not be goobered; most of the time ordinary drivers work just fine and there’s no reason to chew these up.

Even these tips won’t fit every screw in existence, but you’ll go a long way before this set isn’t the right hammer for the job at hand.

Highly recommended, even at today’s prices …

2016-03-26

Category: Machine Shop

Refrigerator Drawer Strut Tab: Now With Inserts

Filament Drive Gear Calculations

M2 Platform Alignment Check

Thinwall and Solid Boxes for 3D Printer Calibration

Kenmore 158.17032: Mystery Spring

Square Chain Mail Armor: Back From The Abyss

Recommended Screwdriver Set: Brownells Magna-Tip Super Set