The New Hotness

In addition to sawing through the side of the cable ferrule, the front derailleur cable began breaking at the edge of the derailleur arm:

Tour Easy Front Derailleur Cable - frayed — Tour Easy Front Derailleur Cable – frayed

It wouldn’t have survived another ride!

Dan pointed out CNC machined aluminum cable clamps are a thing, but those are sized for larger frame tubes than the 1.0 inch steel used on our Tour Easy ‘bents and, although I’ve shimmed everything else on the frame, I wanted to tweak the cable angle to match the arm on the derailleur.

A bit of OpenSCAD wrangling produces a likely candidate:

Front Derailleur Cable Clamp - Slic3r — Front Derailleur Cable Clamp – Slic3r

That’s a bulked-up revision of the prototype:

Tour Easy Front Derailleur Cable Clamp - installed — Tour Easy Front Derailleur Cable Clamp – installed

Done up in orange PETG, it demonstrated the idea worked, but two perimeter threads wrapped around 15% infill isn’t quite up to the task. Note the split along the screw on the far half and various irregularities around the ferrule.

The cable angle isn’t quite right, either, as the proper compound angle would, alas, aim the cable into the pedal crank. The bulky bushings get in the way of putting the ferrule where it should be with the screws aligned in a tidy manner, so I must get used to the jaunty angle.

The bulkier version, done with 50% infill and four perimeter threads, has the same tilt angle, but the ferrule sits further from the screws:

Tour Easy Front Derailleur Cable Clamp V2 - rear quarter view — Tour Easy Front Derailleur Cable Clamp V2 – rear quarter view

The view from the left side shows the cable angles slightly to the rear, but the smaller angle should make it happier:

Tour Easy Front Derailleur Cable Clamp V2 - side view — Tour Easy Front Derailleur Cable Clamp V2 – side view

Probably should have used black PETG. Next time, for sure!

The OpenSCAD source code as a GitHub Gist:

	// Tour Easy Derailleur Cable Clamp
	// Ed Nisley KE4ZNU – June 2017

	/* [Build Options] */

	Layout = "Build"; // [Build, Show]

	/* [Extrusion] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40]

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

	/* [Hidden] */

	Protrusion = 0.01; // [0.01, 0.1]

	HoleWindage = 0.2;

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

	/* [Cable Clamp] */

	FrameOD = 25.7; // Tour Easy has hard inch tubing + paint

	Ferrule = [1.5,5.1,12.0]; // cable ferrule

	EntryPoint = [0,13,60]; // cable entry to derailleur, +Y to rear of bike

	CableTilt = -20; // tilt from parallel to frame tube
	CableTheta = 0; // rotation around clamp from +X axis

	/* [Screws and Inserts] */

	ClampScrew = [3.0,5.5,35.0]; // M3 button / socket head cap screw
	ClampWasher = [3.7,7.0,0.7]; // M3 washer
	ClampNut = [3.0,6.0,4.0]; // M3 nylock nut

	/*
	ClampScrew = [4.0,7.0,25.0]; // M4 button head cap screw
	ClampWasher = [4.5,9.0,0.8]; // M4 washer
	ClampNut = [4.0,8.0,5.0]; // M4 nylock nut
	*/

	NutShift = -0; // slide bushing toward nut for clearance

	//- Set clamp ring dimensions

	WallThick = 10.0;

	BushingSides = 8;

	Bushing = [ClampScrew[ID],
	// ClampWasher[OD]/cos(180/8) + 4*ThreadWidth,
	Ferrule[LENGTH]/cos(180/BushingSides),
	ClampScrew[LENGTH] – 2*ClampWasher[LENGTH] – ClampNut[LENGTH]];

	Ring = [FrameOD + HoleWindage,FrameOD + 2*WallThick,Ferrule[LENGTH]];

	ClampScrewOC = IntegerMultiple(FrameOD + ClampWasher[OD],1);
	echo(str(" screw OC: ",ClampScrewOC));

	ClampKerf = 0.75; // kerf between separated halves

	NumSides = 8*4;

	//- 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);
	}


	// Construct things

	module ClampRing() {
	difference() {
	union() {
	cylinder(d=Ring[OD],h=Ring[LENGTH],$fn=NumSides); // basic ring

	for (j=[-1,1]) // screw bushings
	translate([Bushing[LENGTH]/2 + NutShift,j*ClampScrewOC/2,Ring[LENGTH]/2])
	rotate([0,-90,0]) rotate(180/BushingSides)
	cylinder(d=Bushing[OD],h=Bushing[LENGTH],$fn=BushingSides);

	intersection() {
	rotate([CableTilt,0,CableTheta]) // reinforce cable ferrule
	translate([(Ring[ID] + Ring[OD])/4,0,Ferrule[LENGTH]/2])
	rotate(180/8)
	cylinder(d=3Ferrule[OD] + 0ThreadWidth,2*Ferrule[LENGTH],center=true,$fn=8);
	cylinder(d=2*Ring[OD],h=Ring[LENGTH],$fn=NumSides); // basic ring
	}
	}

	translate([0,0,-Protrusion]) // frame tube
	cylinder(d=Ring[ID],h=Ring[LENGTH] + 2*Protrusion,$fn=NumSides);

	rotate([CableTilt,0,CableTheta]) // cable ferrule
	translate([(Ring[ID] + Ring[OD])/4,0,-0.25*Ferrule[LENGTH]]) {
	rotate(180/8)
	PolyCyl(Ferrule[OD],Ferrule[LENGTH],8);
	rotate(-22.5)
	PolyCyl(Ferrule[ID],2*Ferrule[LENGTH],4);
	}

	for (j=[-1,1]) // screw holes
	translate([Ring[OD]/2,j*ClampScrewOC/2,Ring[LENGTH]/2])
	rotate([0,-90,0]) rotate(180/6)
	PolyCyl(Bushing[ID],Ring[OD],6);

	for (i=[-1,1], j=[-1,1]) // screw & nut seats
	translate([i(Bushing[LENGTH]/2) + NutShift,jClampScrewOC/2,Ring[LENGTH]/2])
	rotate([0,i*90,0]) rotate(180/BushingSides)
	cylinder(d=Bushing[OD],h=Bushing[LENGTH],$fn=BushingSides);

	translate([0,0,Ring[LENGTH]/2]) // slice it apart
	cube([ClampKerf,2Ring[OD],2Ring[LENGTH]],center=true);
	}
	}


	//- Build things

	if (Layout == "Show") {
	translate(EntryPoint)
	cube(1,center=true);
	ClampRing();
	}

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

view raw Derailleur Cable Clamp.scad hosted with ❤ by GitHub

The New Hotness

Tour Easy Front Derailleur Cable Clamp