Category: Machine Shop

Although it’s common practice to exchange your empty 20 pound propane tank for a full one, I vastly prefer to keep my own tanks: I know where they’ve been, how they’ve been used, and can be reasonably sure they don’t have hidden damage. Two of my tanks have old-style threaded connections, but the barby has a quick-disconnect fitting on the regulator and I’ve been using an adapter on those tanks.

The adapter comes with a plastic tool that you use to install it in the tank valve. In principle, you insert the tool into the adapter, thread the adapter into the valve, then tighten with a wrench until the neck of the plastic tool snaps, at which point you eject the stub and the adapter becomes permanently installed. I don’t like permanent, so I carefully tightened the adapter to the point where the O-ring seals properly and the tool didn’t quite break. I’ve always wanted a backup tool, just in case the original broke, and now I have one:

It fit into both the adapter body and the 5/8 inch wrench (the OEM tool is 9/16 inch) without any fuss at all:

The solid model has a few improvements over the as-printed tool above:

• Shorter wrench flats
• More durable protrusions to engage the locking balls

It took about an hour to design and another 45 minutes to print, so it’s obviously not cost-effective. I’ll likely never print another, but maybe you will.

The OpenSCAD source code:

// Propane tank QD connector adapter tool
// Ed Nisley KE4ZNU November 2012

include </mnt/bulkdata/Project Files/Thing-O-Matic/MCAD/units.scad>
include </mnt/bulkdata/Project Files/Thing-O-Matic/Useful Sizes.scad>

//- Extrusion parameters must match reality!
//  Print with +1 shells and 3 solid layers

ThreadThick = 0.25;
ThreadWidth = 2.0 * ThreadThick;

HoleWindage = 0.2;

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

Protrusion = 0.1;			// make holes end cleanly

//----------------------
// Dimensions

WrenchSize = (5/8) * inch;		// across the flats
WrenchThick = 10;

NoseDia = 8.6;
NoseLength = 9.0;

LockDia = 12.5;
LockRingLength = 1.0;
LockTaperLength = 1.5;

TriDia = 15.1;
TriWide = 12.2;										// from OD across center to triangle side
TriOffset = TriWide - TriDia/2;		// from center to triangle side
TriLength = 9.8;

NeckDia = TriDia;
NeckLength = 4.0;

//----------------------
// 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);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

Range = floor(50 / Space);

	for (x=[-Range:Range])
	  for (y=[-Range:Range])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//-------------------
// Build it...

$fn = 4*6;

ShowPegGrid();

union() {

	translate([0,0,(WrenchThick + NeckLength + TriLength - LockTaperLength - LockRingLength + Protrusion)])
		cylinder(r1=NoseDia/2,r2=LockDia/2,h=LockTaperLength);

		translate([0,0,(WrenchThick + NeckLength + TriLength - LockRingLength)])
		cylinder(r=LockDia/2,h=LockRingLength);

	difference() {
		union() {

			translate([0,0,WrenchThick/2])
				cube([WrenchSize,WrenchSize,WrenchThick],center=true);

			cylinder(r=TriDia/2,h=(WrenchThick + NeckLength +TriLength));

			cylinder(r=NoseDia/2,h=(WrenchThick + NeckLength + TriLength + NoseLength));
		}

		for (a=[-1:1]) {
			rotate(a*120)
				translate([(TriOffset + WrenchSize/2),0,(WrenchThick + NeckLength + TriLength/2 + Protrusion/2)])
					cube([WrenchSize,WrenchSize,(TriLength + Protrusion)],center=true);
		}
	}
}