The New Hotness

A pair of Step2 rolling garden seats (they have a new version) served in Mary’s gardens long enough to give their seat panels precarious cracks:

Step2 Seat - OEM seat — Step2 Seat – OEM seat

The underside was giving way, too:

Step2 Seat - cracks — Step2 Seat – cracks

We agreed the new seat could be much simpler, although it must still hinge upward, so I conjured a pair of hinges from the vasty digital deep:

Rolling Cart Hinges - solid model - bottom — Rolling Cart Hinges – solid model – bottom

The woodpile disgorged a slab of 1/4 inch = 6 mm plywood (used in a defunct project) of just about the right size and we agreed a few holes wouldn’t be a problem for its projected ahem use case:

Step2 Seat - assembled — Step2 Seat – assembled

The screw holes on the hinge tops will let me run machine screws all the way through, should that be necessary. So far, a quartet of self-tapping sheet metal (!) screws are holding firm.

Rolling Cart Hinges - solid model - top — Rolling Cart Hinges – solid model – top

A closer look at the hinges in real life:

Step2 Seat - top view — Step2 Seat – top view

The solid model now caps the holes; I can drill them out should the need arise.

From the bottom:

Step2 Seat - bottom view — Step2 Seat – bottom view

Three coats of white exterior paint make it blindingly bright in the sun, although we expect a week or two in the garden will knock the shine right off:

Step2 Seat - painted — Step2 Seat – painted

After the first coat, I conjured a drying rack from a bamboo skewer, a cardboard flap, and some hot-melt glue:

Step2 Seat - drying fixture — Step2 Seat – drying fixture

Three small scars on the seat bottom were deemed acceptable.

The OpenSCAD source code as a GitHub Gist:

	// Hinge brackets for rolling garden stool
	// Ed Nisley – KE4ZNU – 2019-06

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

	Support = true;

	/* [Hidden] */

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

	//———————-
	// Dimensions

	SeatThick = 6.0; // seat panel above cart body

	HingePin = [11.5,12.0,7.0]; // ID = tip OD = base

	HingeOffset = 8.0; // hinge axis above cart body (larger than radius!)
	HingeBolster = [5.0,24.0,SeatThick]; // backing block below hinge

	Block = [25.0,HingeOffset + 30.0,23.0]; // Z = above cart body

	Screw = [3.8,11.0,2.5]; // self-tapping #8 OD=head LENGTH=head thickness
	ScrewOC = 15.0; // spacing > greater than head OD
	ScrewOffset = Block.y/2 – (ScrewOC/2 + Screw[OD]/2 + HingeOffset); // space for head behind hinge

	BlockRadius = 7.0; // corner rounding

	//———————-
	// 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);
	}

	// Basic block shape
	// X axis collinear with hinge axes, hinge base at X=0

	module HingeBlock() {

	PinSides = 3*4;
	PinSupport = [HingePin[LENGTH] – 2ThreadWidth,0.6HingeOffset,HingePin[OD]]; // pre-rotated

	union() {
	translate([Protrusion,Block.y/2 – HingeOffset,HingeOffset])
	rotate([0,-90,0])
	rotate(180/PinSides)
	cylinder(d=HingePin[OD],h=HingePin[LENGTH] + Protrusion,$fn=PinSides);
	difference() {
	hull() {
	translate([Block.x – BlockRadius,-(Block.y/2 – BlockRadius),Block.z – BlockRadius])
	rotate(180/PinSides)
	sphere(r=BlockRadius/cos(180/PinSides),$fn=PinSides);
	translate([0,-(Block.y/2 – BlockRadius),Block.z – BlockRadius])
	rotate([0,90,0]) rotate(180/PinSides)
	cylinder(r=BlockRadius/cos(180/PinSides),h=Block.x/2,$fn=PinSides);
	translate([Block.x – BlockRadius,(Block.y/2 – BlockRadius),Block.z – BlockRadius])
	sphere(r=BlockRadius/cos(180/PinSides),$fn=PinSides);
	translate([0,(Block.y/2 – BlockRadius),Block.z – BlockRadius])
	rotate([0,90,0]) rotate(180/PinSides)
	cylinder(r=BlockRadius/cos(180/PinSides),h=Block.x/2,$fn=PinSides);
	translate([0,-Block.y/2,0])
	cube([Block.x,Block.y – HingeOffset,Block.z/2],center=false);
	translate([0,Block.y/2 – HingeOffset,HingeOffset])
	rotate([0,90,0]) rotate(180/PinSides)
	cylinder(r=HingeOffset/cos(180/PinSides),h=Block.x,$fn=PinSides);
	}
	translate([Block.x/2 + HingeBolster.x,0,(SeatThick – Protrusion)/2])
	cube([Block.x,2*Block.y,SeatThick + Protrusion],center=true);
	translate([0,-HingeBolster.y,(SeatThick – Protrusion)/2])
	cube([3*Block.x,Block.y,SeatThick + Protrusion],center=true);
	for (j=[-1,1])
	translate([Block.x/2,jScrewOC/2 + ScrewOffset,-4ThreadThick])
	rotate(180/8)
	PolyCyl(Screw[ID],Block.z,8);
	}
	}

	if (Support) { // totally ad-hoc
	color("Yellow") render(convexity=4)
	difference() {
	translate([-(PinSupport.x/2 + 2*ThreadWidth),Block.y/2 – PinSupport.y/2,HingeOffset])
	cube(PinSupport,center=true);
	translate([Protrusion,Block.y/2 – HingeOffset,HingeOffset])
	rotate([0,-90,0])
	rotate(180/PinSides)
	cylinder(d=HingePin[OD] + 2ThreadThick,h=2HingePin[LENGTH],$fn=PinSides);
	for (i=[-1:1])
	translate([i4ThreadWidth – HingePin[LENGTH]/2,
	Block.y/2 – (PinSupport.y + 1*ThreadThick),
	HingeOffset])
	cube([2ThreadWidth,2PinSupport.y,2*PinSupport.z],center=true);
	}
	}
	}

	module Blocks(Hand = "Left") {
	if (Hand == "Left")
	HingeBlock();
	else
	mirror([1,0,0])
	HingeBlock();
	}

	//- Build it

	if (Layout == "Block")
	HingeBlock();

	if (Layout == "Show") {
	translate([1.5*HingePin[LENGTH],0,0])
	Blocks("Left");
	translate([-1.5*HingePin[LENGTH],0,0])
	Blocks("Right");
	}

	if (Layout == "Build") {
	translate([0,-Block.z/2,Block.y/2])
	rotate([-90,0,0]) {
	translate([1.5*HingePin[LENGTH],0,0])
	Blocks("Left");
	translate([-1.5*HingePin[LENGTH],0,0])
	Blocks("Right");
	}

	}

view raw Rolling Cart Hinges.scad hosted with ❤ by GitHub

This original doodle gives the key dimensions, apart from the rounded rear edge required so the seat can pivot vertically upward:

Cart Hinge - dimension doodle — Cart Hinge – dimension doodle

The second seat looks just like this one, so life is good …

The New Hotness

Step2 Garden Seat: Replacement Seat