The New Hotness

We rode the Feeder Canal trail during a recent bike vacation in exotic Glens Falls NY:

Feeder Canal Park Trail - Branches — Feeder Canal Park Trail – Branches

The numerous downed branches along the trail and countless twigs on the trail came from a brush-clearing operation:

Feeder Canal Park Trail - Brush Clearing — Feeder Canal Park Trail – Brush Clearing

As luck would have it, a twig snagged between my front tire and fender, snapping the clips holding the fender in place:

Should it not be obvious, each ferrule formerly had two parallel jaws (on the left) gripping the fender, with the tiny screw digging into the fender. I affixed the fender to the broken clips with copious amounts of duct tape and we continued the mission.

It should be obvious why those ferrules are not suitable for 3D printing.

However, with the recent rear fender clip serving as inspiration, this didn’t take long:

Tour Easy - Front Fender Clip - Slic3r — Tour Easy – Front Fender Clip – Slic3r

The front fender fits a 20 inch wheel and is somewhat wider and flatter than the rear fender (I think they bent the same plastic strip around a smaller mandrel), so I did a quick copy-and-paste hack job on the OpenSCAD source code, rather than trying to parameterize the daylights out of the previous model.

The posts around the wire stays are 6 diameters deep and reamed to fit; the stays won’t be flopping around even without fiddly mechanical hardware retaining them. The holes extend about halfway into those posts to mimic the dimensions of the original ferrules.

All of us can predict where the next break will occur, right? That’s OK: I want this to break, instead of wrecking the fender, so the only question is how much abuse those simple joints can withstand. The printing orientation wraps the perimeter threads from the posts around the clip, making it about a strong as it can be.

The ferrules should splay outward by a few degrees to match the angle from the fender to the fork eyelets, but that’s in the nature of fine tuning.

The arch accommodates a strip of double-sided foam tape holding the clip in place along the fender curve, with those cute little hooks capturing the fender to keep the tape in compression:

Tour Easy Front Fender Clip - installed — Tour Easy Front Fender Clip – installed

I really must get some black foam tape …

The picture shows the fender sitting well away from the tire, due to the upper fender mount bending in response to the splash flap snagging on curbs and random debris; the wire stays didn’t seat completely into the posts.

The extender I made during the cracked fork episode remained perfectly straight, though:

Tour Easy - new fork - fender extender — Tour Easy – new fork – fender extender

So I re-bent the upper fender mount (not the extender!) to its original angle, thereby moving the bottom of the fender much closer to the tire. Now the stays seat fully, the clip holds the fender firmly in place with no rattles, and it’s all good.

The OpenSCAD source code as a GitHub Gist:

	// Tour Easy front fender clip
	// Ed Nisley KE4ZNU April 2017

	Layout = "Clip"; // Build Profile Ferrule Clip

	//- 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

	// special case: fender is exactly half a circle!

	FenderC = 51.0; // fender outside width = chord
	FenderM = 21.0; // height of chord

	FenderR = (pow(FenderM,2) + pow(FenderC,2)/4) / (2 * FenderM); // radius
	echo(str("Fender radius: ", FenderR));
	FenderD = 2*FenderR;

	FenderA = 2 * asin(FenderC / (2*FenderR));
	echo(str(" … arc: ",FenderA," deg"));

	FenderThick = 2.5; // fender thickness, assume dia of edge

	ClipHeight = 15.0; // top to bottom, ignoring rakish tilt
	ClipThick = 3.0; // thickness of clip around fender
	ClipD = FenderD; // ID of clip against
	ClipSides = 4 * 8; // polygon sides around clip circle

	BendReliefD = 2.5; // bend arch diameter
	BendReliefA = 2/3 * FenderA/2; // … angle from dead ahead
	BendReliefCut = 1.0; // factor to thin outside of bend

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

	StayDia = 3.3; // fender stay rod diameter
	StayOffset = 23.0; // stay-to-fender distance
	StayAngle = -5; // angle from stay to fender

	FerruleSides = 2*4;
	Ferrule = [StayDia,3FenderThick/cos(180/FerruleSides),6StayDia + StayOffset]; // ID = stay rod OD

	//———————-
	// 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);
	}

	//———————-
	// Clip profile around fender
	// Centered on fender arc

	module Profile(HeightScale = 1) {

	linear_extrude(height=HeightScale*ClipHeight,convexity=5) {
	difference() {
	offset(r=ClipThick) // outside of clip
	union() {
	circle(d=ClipD,$fn=ClipSides);
	for (i=[-1,1])
	rotate(i*BendReliefA) {
	translate([ClipD/2 + BendReliefD/2,0,0])
	circle(d=BendReliefD,$fn=6);
	}
	}
	union() { // inside of clip
	circle(d=ClipD,$fn=ClipSides);
	for (i=[-1,1])
	rotate(i*BendReliefA) {
	translate([ClipD/2 + BendReliefCut*BendReliefD/2,0,0])
	circle(d=BendReliefD/cos(180/6),$fn=6);
	translate([ClipD/2,0,0])
	square([BendReliefCut*BendReliefD,BendReliefD],center=true);
	}
	}
	translate([(FenderR – FenderM – FenderD/2),0]) // trim ends
	square([FenderD,2*FenderD],center=true);
	}

	for (a=[-1,1]) // hooks around fender
	rotate(a*(FenderA/2))
	translate([FenderR – FenderThick/2,0]) {
	difference() {
	rotate(1*180/12)
	circle(d=FenderThick + 2*ClipThick,$fn=12);
	rotate(1*180/8)
	circle(d=FenderThick,$fn=8);
	rotate(a * -90)
	translate([0,-2*FenderThick,0])
	square(4*FenderThick,center=false);
	}
	}
	}
	}


	//———————-
	// Ferrule body

	module FerruleBody() {

	translate([0,0,Ferrule[OD]/2 * cos(180/FerruleSides)])
	rotate([0,-90,0]) rotate(180/FerruleSides)
	difference() {
	cylinder(d=Ferrule[OD],h=Ferrule[LENGTH],$fn=FerruleSides,center=false);
	translate([0,0,StayOffset + Protrusion])
	PolyCyl(Ferrule[ID],Ferrule[LENGTH] – StayOffset + Protrusion,FerruleSides);
	}

	}

	//———————-
	// Generate entire clip at mounting angle

	module FenderClip() {

	union() {
	translate([FenderR,0,0])
	difference() { // angle and trim clip
	rotate([0,StayAngle,0])
	translate([-(FenderR + ClipThick),0,0])
	Profile(2); // scale upward for trimming
	translate([0,0,-ClipHeight]) // trim bottom
	cube(2*[FenderD,FenderD,ClipHeight],center=true);
	translate([0,0,ClipHeight*cos(StayAngle)+ClipHeight]) // trim top
	cube(2*[FenderD,FenderD,ClipHeight],center=true);
	}
	for (j = [-1,1])
	translate([Ferrule[OD]sin(StayAngle),j(FenderR – FenderThick + FenderThick/2),0])
	FerruleBody();
	}
	}

	//———————-
	// Build it


	if (Layout == "Profile") {
	Profile();
	}

	if (Layout == "Ferrule") {
	FerruleBody();
	}

	if (Layout == "Clip") {
	FenderClip();
	}

	if (Layout == "Build") {
	FenderClip();
	}

view raw Front Fender Clip.scad hosted with ❤ by GitHub

The New Hotness

Tour Easy Front Fender Clip