The New Hotness

The throttle knob on our MTD snowthrower (a.k.a. snowblower) cracked apart around its metal shaft when I pulled it upward. A temporary fix involving duct tape and cable ties sufficed to start the engine, although the usual intense vibration shook the knob loose somewhere along the driveway during the next hour.

Update: Found it!

Although I have no photographic evidence, I did make a few quick measurements:

It fits an MTD model E6A4E, but I suspect nearly all their engines have identical throttle shafts:

Snowthrower Throttle Knob - stem end - solid model — Snowthrower Throttle Knob – stem end – solid model

The only practical way to build the thing has it standing on the shaft end, surrounded by a brim to improve adhesion, so I added (actually, subtracted) a pair of holes for music-wire reinforcements:

Snowthrower throttle knob - reinforcing wires — Snowthrower throttle knob – reinforcing wires

It definitely has a stylin’ look, next to the original choke control knob:

Snowthrower throttle knob - installed — Snowthrower throttle knob – installed

I omitted the finger grip grooves for obvious reasons.

The slot-and-hole came out slightly smaller than the metal shaft and, rather than wait for epoxy to cure, I deployed a 230 W soldering gun (not a piddly temperature-controlled iron suitable for electronics) on the shaft and melted it into the knob.

More snow may arrive this week and I printed another knob just in case …

The OpenSCAD source code as a GitHub Gist:

	// MTD Snowthrower Throttle Knob
	// Ed Nisley KE4ZNU 2020-12-18

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


	// Extrusion parameters
	/* [Hidden] */

	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

	Throttle = [17.0,1.85,6.5]; // blade insertion, thickness, width

	PaddleSize = [25,30,9];
	PaddleRound = 4.0;
	PaddleThick = 8.5;

	StemDia = 13.0;
	StemLength = 20.0;

	PinDia = 1.6;
	PinLength = PaddleSize.x + StemLength/2;
	echo(str("Pin: ",PinLength," x ",PinDia," mm"));

	//———————-
	// 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);
	}

	//———————-
	// Pieces

	module Paddle() {


	difference() {
	hull() {
	translate([PaddleSize.x/2,0,0]) {
	for (i=[-1,1], j=[-1,1])
	translate([i(PaddleSize.x – PaddleRound)/2,j(PaddleSize.y – PaddleRound)/2,0])
	sphere(d=PaddleRound,$fn=12);
	rotate([0,90,0]) rotate(180/12)
	cylinder(d=PaddleThick,h=PaddleSize.x,,center=true,$fn=12);
	}
	translate([-StemLength,0,0])
	rotate([0,90,0]) rotate(180/12)
	cylinder(d=StemDia,h=Throttle.x,center=false,$fn=12);
	}

	translate([-StemLength,0,0])
	cube([2*Throttle.x,Throttle.y,Throttle.z],center=true);
	translate([-(StemLength + Protrusion),0,0])
	rotate([0,90,0]) rotate(0*180/6)
	PolyCyl(2*Throttle.y,Throttle.x,6);

	for (j=[-1,1])
	translate([-StemLength/2,j*PaddleSize.y/6,0])
	rotate([0,90,0]) rotate(180/4)
	PolyCyl(PinDia,PinLength,4);
	}
	}




	//———————-
	// Build it

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


	if (Layout == "Build") {
	translate([0,0,StemLength])
	rotate([0,-90,0])
	Paddle();
	}

view raw Snowthrower Throttle Knob.scad hosted with ❤ by GitHub

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