M2 – Page 34 – The Smell of Molten Projects in the Morning

Mailing Tube End Caps

Faced with a need to send documents rolled up in a tube, rather than folded flat, I sawed off a suitable length of cardboard tube from the heap, then discovered a distinct lack of end caps.

Well, once again, it’s 3D printing to the rescue:

Mailing Tube Cap - top - Slic3r — Mailing Tube Cap – top – Slic3r

The small ribs probably don’t actually do anything, but seemed like a nice touch.

They’re somewhat less boring from the bottom:

Mailing Tube Cap - bottom - Slic3r — Mailing Tube Cap – bottom – Slic3r

The fancy spider supports that big flat top and provides some crush resistance. The flat flange should collect the edge of the packing tape wrapped around the ends.

A firm shove installs them, so the size worked out perfectly:

Mailing tube end cap - installed — Mailing tube end cap – installed

Add a wrap of tape to each end, affix the USPS label, and they went out with the next day’s mail, PETG hair and all.

The OpenSCAD source code as a GitHub Gist:

	// Mailing tube end cap
	// Ed Nisley KE4ZNU – June 2017

	Layout = "Build";

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

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

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//- Screw sizes

	inch = 25.4;

	TubeID = 2 * inch;
	TubeWall = 0.1 * inch;

	CapInsert = 15.0;
	CapRim = 1.0;
	CapWall = 3*ThreadWidth;

	NumFlanges = 3;
	FlangeHeight = 3*ThreadThick;
	FlangeWidth = ThreadWidth/2;
	FlangeSpace = CapInsert / (NumFlanges + 1);

	OAHeight = CapInsert + CapRim;

	NumRibs = 3*4;
	NumSides = 3*NumRibs;

	//- Adjust hole diameter to make the size come out right

	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);
	}

	module TubeCap() {

	difference() {
	cylinder(d=TubeID,h=OAHeight,$fn=NumSides);
	translate([0,0,CapWall])
	cylinder(d=TubeID – 2*CapWall,h=OAHeight,$fn=NumSides);
	}

	for (i=[1:NumFlanges])
	translate([0,0,i*FlangeSpace])
	difference() {
	cylinder(d=TubeID + 2*FlangeWidth,h=FlangeHeight,$fn=NumSides);
	translate([0,0,-Protrusion])
	cylinder(d=TubeID – 2CapWall,h=FlangeHeight + 2Protrusion,$fn=NumSides);
	}

	for (i=[0:NumRibs-1])
	rotate(i*360/NumRibs)
	translate([0,-ThreadWidth,CapWall + ThreadThick])
	cube([TubeID/2 – CapWall/2,2*ThreadWidth,CapInsert + CapRim – CapWall – ThreadThick],center=false);

	translate([0,0,CapInsert]) {
	difference() {
	cylinder(d=TubeID + 2*TubeWall,h=CapRim,$fn=NumSides);
	translate([0,0,-Protrusion])
	cylinder(d=TubeID – 32CapWall,h=2*CapRim,$fn=NumSides);
	}
	}
	}

	//- Build things

	if (Layout == "Show")
	TubeCap();

	if (Layout == "Build")
	translate([0,0,OAHeight])
	rotate([180,0,0])
	TubeCap();

view raw Mailing Tube Cap.scad hosted with ❤ by GitHub

2017-06-16

Proto Board Holder: Revised Screw Mounts

Improving the crystal tester’s (nonexistent) grounding requires a band of copper tape around the inside of the proto board holder. Rather than cut the tape lengthwise to fit the holder, a new one will be just tall enough:

Proto Board - 80x120 - revised inserts - Slic3r — Proto Board – 80×120 – revised inserts – Slic3r

While I was at it, I deleted the washer recesses, because those didn’t work out well, and fiddled the screw holes to put the inserts in from the bottom:

Proto Board - 80x120 - revised inserts - detail - Slic3r — Proto Board – 80×120 – revised inserts – detail – Slic3r

Although the overhang inside the holes will be ugly, I’ll epoxy the inserts flush with the bottom and nobody will ever know.

The copper tape now makes a tidy ground strap:

Crystal Tester - ground strap - rear — Crystal Tester – ground strap – rear

With a gap in the front to eliminate the obvious loop:

Crystal Tester - ground strap - front gap — Crystal Tester – ground strap – front gap

The OpenSCAD source code as a GitHub Gist:

	// Test support frame for proto boards
	// Ed Nisley KE4ZNU – Jan 2017
	// June 2017 – Add side-mount bracket, inserts into bottom

	Layout = "Frame";

	ClampFlange = true;

	Channel = false;

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

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

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//- Screw sizes

	inch = 25.4;

	Tap4_40 = 0.089 * inch;
	Clear4_40 = 0.110 * inch;
	Head4_40 = 0.211 * inch;
	Head4_40Thick = 0.065 * inch;
	Nut4_40Dia = 0.228 * inch;
	Nut4_40Thick = 0.086 * inch;
	Washer4_40OD = 0.270 * inch;
	Washer4_40ID = 0.123 * inch;

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

	Insert = [3.9,4.6,5.8];

	//- PCB sizes

	PCBSize = [80.0,120.0,1.6];
	PCBShelf = 1.0; // support rim under PCB

	Clearance = 2*[ThreadWidth,ThreadWidth,0];

	WallThick = 4.0;
	FrameHeight = IntegerMultiple(3/8 * inch,1.0);
	echo(str("Inner height: ",FrameHeight));

	ScrewOffset = 0.0 + Clear4_40/2;

	ScrewSites = [[-1,1],[-1,1]]; // -1/0/+1 = left/mid/right and bottom/mid/top

	OAHeight = FrameHeight + Clearance[2] + PCBSize[2];
	echo(str("OAH: ",OAHeight));

	FlangeExtension = 3.0;
	FlangeThick = IntegerMultiple(2.0,ThreadThick);
	Flange = PCBSize
	+ 2*[ScrewOffset,ScrewOffset,0]
	+ 2*[Washer4_40OD,Washer4_40OD,0]
	+ [2FlangeExtension,2FlangeExtension,(FlangeThick – PCBSize[2])]
	;

	echo(str("Flange: ",Flange));
	NumSides = 4*5;

	WireChannel = [Flange[0],15.0,3.0 + PCBSize[2]];
	WireChannelOffset = [Flange[0]/2,25.0,(FrameHeight + PCBSize[2] – WireChannel[2]/2)];

	//- Adjust hole diameter to make the size come out right

	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 things

	if (Layout == "Frame")
	difference() {
	union() { // body block
	translate([0,0,OAHeight/2])
	cube(PCBSize + Clearance + [2WallThick,2WallThick,FrameHeight],center=true);

	for (x=[-1,1], y=[-1,1]) { // screw bosses
	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);
	}

	if (ClampFlange) // flange for work holder
	linear_extrude(height=Flange[2])
	hull()
	for (i=[-1,1], j=[-1,1]) {
	translate([i(Flange[0]/2 – Washer4_40OD/2),j(Flange[1]/2 – Washer4_40OD/2)])
	circle(d=Washer4_40OD,$fn=NumSides);
	}
	}

	for (x=[-1,1], y=[-1,1]) { // screw position indexes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	-Protrusion])
	rotate(xy180/(2*6))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); // screw clearance holes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	-Protrusion])
	rotate(xy180/(2*6))
	PolyCyl(Insert[OD],OAHeight – PCBSize[2] – 3*ThreadThick + Protrusion,6); // inserts

	if (false)
	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2]])
	PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides); // washer recess
	}

	translate([0,0,OAHeight/2]) // through hole below PCB
	cube(PCBSize – 2[PCBShelf,PCBShelf,0] + [0,0,2OAHeight],center=true);

	translate([0,0,(OAHeight – (PCBSize[2] + Clearance[2])/2 + Protrusion/2)]) // PCB pocket on top
	cube(PCBSize + Clearance + [0,0,Protrusion],center=true);

	if (Channel)
	translate(WireChannelOffset) // opening for wires from bottom side
	cube(WireChannel + [0,0,Protrusion],center=true);
	}

	// Add-on bracket to hold smaller PCB upright at edge

	PCB2Insert = [3.0,4.9,4.1];
	PCB2OC = 45.0;

	if (Layout == "Bracket")
	difference() {
	hull() // frame body block
	for (x=[-1,1]) // bosses around screws
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);

	for (x=[-1,1]) // frame screw holes
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,-Protrusion])
	rotate(x180/(26))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6);

	for (x=[-1,1]) // PCB insert holes
	translate([x*PCB2OC/2,(Washer4_40OD + Protrusion),OAHeight/2])
	rotate([90,0,0])
	cylinder(d=PCB2Insert[OD],h=2*(Washer4_40OD + Protrusion),$fn=6);

	}

view raw Proto Board Holder.scad hosted with ❤ by GitHub

2017-06-13

AD8310 Log Amp Module: Sidesaddle Bracket

This little bracket attaches to a proto board holder, with holes for M3 inserts to mount the AD8310 log amp module:

PCB Side Bracket - 80x120 — PCB Side Bracket – 80×120

Thusly:

AD8310 module bracket on proto board holder - component side — AD8310 module bracket on proto board holder – component side

The OLED display looks a bit faded, which seems to be an interaction between matrix refresh and camera shutter: looks just fine in person!

Not much to see from the other side:

AD8310 module bracket on proto board holder - solder side — AD8310 module bracket on proto board holder – solder side

I should have included an offset to slide it a bit forward; then I could mount it on the other end with clearance for the Nano’s USB port. Maybe next time.

The OpenSCAD source code as a GitHub Gist:

	// Test support frame for proto boards
	// Ed Nisley KE4ZNU – Jan 2017
	// June 2017 – Add side-mount bracket

	Layout = "Bracket";

	ClampFlange = true;

	Channel = false;

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

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

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//- Screw sizes

	inch = 25.4;

	Tap4_40 = 0.089 * inch;
	Clear4_40 = 0.110 * inch;
	Head4_40 = 0.211 * inch;
	Head4_40Thick = 0.065 * inch;
	Nut4_40Dia = 0.228 * inch;
	Nut4_40Thick = 0.086 * inch;
	Washer4_40OD = 0.270 * inch;
	Washer4_40ID = 0.123 * inch;

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

	Insert = [3.9,4.6,5.8];

	//- PCB sizes

	PCBSize = [80.0,120.0,1.6];
	PCBShelf = 1.5;

	Clearance = 2*[ThreadWidth,ThreadWidth,0];

	WallThick = 4.0;
	FrameHeight = 8.0;

	ScrewOffset = 0.0 + Clear4_40/2;

	ScrewSites = [[-1,1],[-1,1]]; // -1/0/+1 = left/mid/right and bottom/mid/top

	OAHeight = FrameHeight + Clearance[2] + PCBSize[2];
	echo(str("OAH: ",OAHeight));

	FlangeExtension = 3.0;
	FlangeThick = IntegerMultiple(2.0,ThreadThick);
	Flange = PCBSize
	+ 2*[ScrewOffset,ScrewOffset,0]
	+ 2*[Washer4_40OD,Washer4_40OD,0]
	+ [2FlangeExtension,2FlangeExtension,(FlangeThick – PCBSize[2])]
	;

	echo(str("Flange: ",Flange));
	NumSides = 4*5;

	WireChannel = [Flange[0],15.0,3.0 + PCBSize[2]];
	WireChannelOffset = [Flange[0]/2,25.0,(FrameHeight + PCBSize[2] – WireChannel[2]/2)];

	//- Adjust hole diameter to make the size come out right

	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 things

	if (Layout == "Frame")
	difference() {
	union() { // body block
	translate([0,0,OAHeight/2])
	cube(PCBSize + Clearance + [2WallThick,2WallThick,FrameHeight],center=true);

	for (x=[-1,1], y=[-1,1]) { // screw bosses
	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);
	}

	if (ClampFlange) // flange for work holder
	linear_extrude(height=Flange[2])
	hull()
	for (i=[-1,1], j=[-1,1]) {
	translate([i(Flange[0]/2 – Washer4_40OD/2),j(Flange[1]/2 – Washer4_40OD/2)])
	circle(d=Washer4_40OD,$fn=NumSides);
	}
	}

	for (x=[-1,1], y=[-1,1]) { // screw position indexes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	-Protrusion])
	rotate(xy180/(2*6))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); // screw clearance holes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2] – Insert[LENGTH]])
	rotate(xy180/(2*6))
	PolyCyl(Insert[OD],Insert[LENGTH] + Protrusion,6); // inserts

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2]])
	PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides); // washers
	}

	translate([0,0,OAHeight/2]) // through hole below PCB
	cube(PCBSize – 2[PCBShelf,PCBShelf,0] + [0,0,2OAHeight],center=true);

	translate([0,0,(OAHeight – (PCBSize[2] + Clearance[2])/2 + Protrusion/2)]) // PCB pocket on top
	cube(PCBSize + Clearance + [0,0,Protrusion],center=true);

	if (Channel)
	translate(WireChannelOffset) // opening for wires from bottom side
	cube(WireChannel + [0,0,Protrusion],center=true);
	}

	// Add-on bracket to hold smaller PCB upright at edge

	PCB2Insert = [3.0,4.9,4.1];
	PCB2OC = 45.0;

	if (Layout == "Bracket")
	difference() {
	hull() // frame body block
	for (x=[-1,1]) // bosses around screws
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);

	for (x=[-1,1]) // frame screw holes
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,-Protrusion])
	rotate(x180/(26))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6);

	for (x=[-1,1]) // PCB insert holes
	translate([x*PCB2OC/2,(Washer4_40OD + Protrusion),OAHeight/2])
	rotate([90,0,0])
	cylinder(d=PCB2Insert[OD],h=2*(Washer4_40OD + Protrusion),$fn=6);

	}

view raw Proto Board Holder.scad hosted with ❤ by GitHub

2017-06-07

Bathroom Door Retainer

The weather got warm enough to open the windows before pollen season started, which led to the front bathroom door slamming closed in the middle of the night when a gusty rainstorm blew through town. After far too many years, I decided this was an annoyance up with which I need no longer put.

A few minutes with OpenSCAD and Slic3r produces the shape:

Bathroom Door Retainer - Slic3r — Bathroom Door Retainer – Slic3r

It’s basically an extrusion of a 2D shape with a rectangular recess for the door chewed out.

An hour later, it’s in full effect:

Bathroom Door Retainer - installed — Bathroom Door Retainer – installed

The model now sports a little ball to secure the retainer against the towel bar:

Bathroom Door Retainer - bump — Bathroom Door Retainer – bump

Maybe someday I’ll reprint it.

That was easy …

The cast-iron pig sometimes standing guard as a doorstop in the relatively narrow doorway poses a bit of a foot hazard, so he moves into a closet during the off season. He can now remain there, snug and comfy, until a need for ballast arises.

The OpenSCAD source code as a GitHub Gist:

	// Bathroom Door Retainer
	// Ed Nisley KE4ZNU – May 2017

	Layout = "Show"; // Show Build

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

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

	//——-
	// Dimensions

	TowelBarSide = 20.5; // towel bar across flat side
	TowelBarAngle = 45; // rotation of top flat from horizontal

	DoorOffset = 16.0; // from towel bar to door
	DoorThick = 36.5;

	WallThick = 4.0; // minimum wall thickness

	RetainerDepth = 10.0; // thickness of retaining notch

	NumSides = 6*4;
	CornerRad = WallThick;

	BarClipOD = TowelBarSidesqrt(2) + 2WallThick;
	BarClipRad = BarClipOD/2;

	OAH = RetainerDepth + WallThick;

	module LatchPlan() {

	union() {
	linear_extrude(height=OAH,convexity=4)
	difference() {
	union() {
	circle(d=BarClipOD,$fn=NumSides);
	hull()
	for (i=[0,1], j=[0,1])
	translate([i(BarClipRad + DoorOffset + DoorThick + WallThick – CornerRad),j(BarClipRad – CornerRad)])
	circle(r=CornerRad,$fn=4*4);
	}
	rotate(TowelBarAngle) // towel bar shape
	square(size=TowelBarSide,center=true);
	translate([0,-TowelBarSide/sqrt(2)]) // make access slot
	rotate(-TowelBarAngle)
	square(size=[2*TowelBarSide,TowelBarSide],center=false);
	}
	translate([0,-TowelBarSide/sqrt(2),OAH/2])
	rotate([90,0,45])
	sphere(r=TowelBarSide/25,$fn=4*3);
	}
	}

	module Latch() {

	difference() {
	LatchPlan();
	translate([BarClipRad + DoorOffset,-BarClipRad/2,-Protrusion])
	cube([DoorThick,BarClipOD,RetainerDepth + Protrusion],center=false);
	}
	}

	//——-
	// Build it!

	if (Layout == "Show") {
	Latch();
	}

	if (Layout == "Build") {
	translate([0,0,OAH])
	rotate([180,0,0])
	Latch();
	}

view raw Bathroom Door Retainer.scad hosted with ❤ by GitHub

2017-05-29

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 — 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 — XTC-3D – lines – direct

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

XTC-3D - Hilbert - reflective 2 — XTC-3D – Hilbert – reflective 2

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

XTC-3D - Hilbert - reflective 1 — XTC-3D – Hilbert – reflective 1

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

XTC-3D - Hilbert - direct — 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 — 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 — XTC-3D – Bezel – front

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

XTC-3D - heavy - oblique — XTC-3D – heavy – oblique

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

XTC-3D - heavy - reflection — XTC-3D – heavy – reflection

Blowing out the contrast shows the surface finish:

XTC-3D - heavy - direct - boost — 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 — 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:

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 — 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

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 — 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 — 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

Tour Easy Front Fender Clip: Heatshrink

So: jouncing over the larg(er) potholes / pavement discontinuities / debris on the roads around here wobbulates the front fender enough to pull the stays out of those tidy 18 mm = 6 diameter deep sockets on the fender clip.

Perhaps a generous application of heatshrink tubing will help:

Tour Easy Front Fender Clip - heatshrink hack — Tour Easy Front Fender Clip – heatshrink hack

Waving a heat gun around a 3D printed part seems fraught with peril, even with PETG’s glass transition temperature around 80 °C = 175 °F, as ordinary polyolefin tubing shrinks at 140-ish °C. Aiming the hot air stream more-or-less away from the clip (and the tire!) carried the day. PLA would surely have gotten bendy.

The proper solution surely involves screw clamps and suchlike. I really dislike fiddly hardware: I hope this hack survives.

2017-05-03

Tag: M2

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Tour Easy Front Fender Clip: Heatshrink