GCMC XY Axis Calibration Target

The CNC-3018XL drawing the scales on a Tek Circuit Computer disagreed with the MPCNC cutting the perimeter. The Y axis edges looked OK:

Tek CC - 2021-11 - Y detail
Tek CC – 2021-11 – Y detail

But the cut on the X axis edges went too close to the tips:

Tek CC - 2021-11 - X detail
Tek CC – 2021-11 – X detail

I conjured a calibration target to help measure the two machines:

Cal Target - CNC3018XL
Cal Target – CNC3018XL

The X- side of the plot gives the general idea:

CNC-3018XL - Backlash Test - 400step-mm
CNC-3018XL – Backlash Test – 400step-mm

The vertical lines consist of two halves, drawn in order from left to right on the top and right to left on the bottom, meeting in the middle at the Y=0 axis. If they do, in fact, meet in the middle, then there’s no problem with backlash.

The 25 mm distance between adjacent lines verifies the linear calibration; the total distance along the X and Y axes provides more travel for more error accumulation.

The circles provide some reassurance the machine can draw a smooth circle, because they come from GRBL’s (or whatever) G2 G-Code commands, not a linear approximation.

Spoiler: after a considerable amount of drawing, measuring, and muttering, the problem emerged from the CNC-3018XL’s X-axis leadscrew:

Cal Target - 400 step-mm - merged
Cal Target – 400 step-mm – merged

It’s half a millimeter short on each end!

More on this tomorrow …

The GCMC source code as a GitHub Gist:

(epilog begins)
(bCNC may regard plot as done before this returns)
(epilog ends)
view raw epilog.gcmc hosted with ❤ by GitHub
(prolog begins)
G17 (XY plane)
G21 (mm)
G40 (no cutter comp)
G49 (no tool length comp)
G80 (no motion mode)
G90 (abs distance)
G94 (units per minute)
(prolog ends)
view raw prolog.gcmc hosted with ❤ by GitHub
// Grid pattern to check XY scaling
// Ed Nisley KE4ZNU - 2021-11
// gcmc -P 4 --pedantic --prolog prolog.gcmc --epilog epilog.gcmc --output 'Scale Grid.ngc' 'Scale Grid.gcmc'
FALSE = 0;
// Define useful constants
SafeZ = [-,-,10.0mm]; // above all obstructions
TravelZ = [-,-,2.0mm]; // within engraving / milling area
PenZ = [-,-,-1.0mm]; // depth for good inking
PenSpeed = 2000mm;
// Overall values
PlotSize = [250mm,200mm,-];
comment("PlotSize: ",PlotSize);
GridSize = [25mm,25mm,-];
Margins = [5mm,5mm,-];
CenterOD = 5.0mm;
TextFont = FONT_HSANS_1_RS; // single stroke stick font
TextSize = 3.0 * [1.0mm,1.0mm];
// Draw it
comment("Draw title info");
tp = scale(typeset("Scale & Backlash Test Pattern",TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2,PlotSize.y/2 - GridSize.y/2,-];
tp = scale(typeset("Grid " + GridSize,TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2,PlotSize.y/2 - GridSize.y/2 - 1.5*TextSize.y,-];
tp = scale(typeset("F " + PenSpeed + "/min",TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2,PlotSize.y/2 - GridSize.y/2 - 3.0*TextSize.y,-];
tp = scale(typeset("Ed Nisley - KE4ZNU",TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2,-(PlotSize.y/2 - GridSize.y/2),-];
tp = scale(typeset("softsolder.com",TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2,-(PlotSize.y/2 - GridSize.y/2 + 1.5*TextSize.y),-];
comment("Mark center point");
comment("Label axes");
tp = scale(typeset("X+",TextFont),TextSize);
tp += [GridSize.x + 0.5*TextSize.x,-TextSize.y/2,-];
tp = scale(typeset("Y+",TextFont),TextSize);
tp += [-TextSize.x/2,GridSize.y + 0.5*TextSize.y,-];
comment("Draw left-to-right");
tp = scale(typeset("L to R →",TextFont),TextSize);
tp += [-PlotSize.x/2 + GridSize.x/2 - tp[-1].x/2,GridSize.y/2,-];
goto([-(PlotSize.x/2 + Margins.x),GridSize.y,-]);
for (p=[-PlotSize.x/2,GridSize.y,-] ; p.x <= PlotSize.x/2 ; p.x += GridSize.x ) {
comment(" p: ",p);
comment("Draw right-to-left");
tp = scale(typeset("R to L ←",TextFont),TextSize);
tp += [PlotSize.x/2 - GridSize.x/2 - tp[-1].x/2,-GridSize.y/2,-];
goto([(PlotSize.x/2 + Margins.x),-GridSize.y,-]);
for (p=[PlotSize.x/2,-GridSize.y,-] ; p.x >= -PlotSize.x/2 ; p.x -= GridSize.x ) {
comment(" p: ",p);
comment("Draw bottom-to-top");
tp = scale(typeset("B to T ↑",TextFont),TextSize);
tp += [-GridSize.x/2 - tp[-1].x/2,-(PlotSize.y/2 - TextSize.y),-];
goto([-GridSize.x,-(PlotSize.y/2 + Margins.y),-]);
for (p=[-GridSize.x,-PlotSize.y/2,-] ; p.y <= PlotSize.y/2 ; p.y += GridSize.y ) {
comment(" p: ",p);
comment("Draw top-to-bottom");
tp = scale(typeset("T to B ↓",TextFont),TextSize);
tp += [GridSize.x/2 - tp[-1].x/2,(PlotSize.y/2 - 1.5*TextSize.y),-];
goto([GridSize.x,(PlotSize.y/2 + Margins.y),-]);
for (p=[GridSize.x,PlotSize.y/2,-] ; p.y >= -PlotSize.y/2 ; p.y -= GridSize.y ) {
comment(" p: ",p);
comment("Draw circles");
maxr = (PlotSize.x < PlotSize.y) ? PlotSize.x/2 : PlotSize.y/2;
for (r=GridSize.x/2 ; r <= maxr ; r += GridSize.x) {
comment(" r: ",r);
view raw Scale Grid.gcmc hosted with ❤ by GitHub

ShopVac Nozzle Caddy

Shortly after acquiring the Greatest ShopVac, I zip-tied half a foot of cardboard tube to the handle to corral the nozzle and keep the ungainly hose from sprawling across the floor. While disembowling the Ottlite into a mini-lathe light, the plastic trim joining the baseplate to the vertical tube cried out to become a nozzle caddy:

ShopVac Nozzle Caddy - front view
ShopVac Nozzle Caddy – front view

It was exactly the right size and shape (by my admittedly slack standards) to hold the nozzle, plus being destined for the trash, so all it needed was a pair of clamp brackets conjured from the vasty digital deep:

ShopVac Nozzle Caddy - solid model
ShopVac Nozzle Caddy – solid model

The bosses fit into a tapered slot along what was the rear side, with a pair of 4 mm holes at each end for screws into threaded brass inserts epoxied into the brackets:

ShopVac Nozzle Caddy - clamps mounted
ShopVac Nozzle Caddy – clamps mounted

They obviously descend from the many clamp mounts I’ve made for everything from garden hoses to bike running lights. A pair of 4 mm SHCS squish the clamp around the handle, with a strip of electrical tape improving plastic-to-metal griptivity:

ShopVac Nozzle Caddy - side view
ShopVac Nozzle Caddy – side view

The clearance just barely allows a nylock nut atop a washer and you’ll want to trim those 40 mm screws to an exact fit, but it came out pretty well.

The original dimension doodle with some modeling ideas that didn’t survive more thinking:

ShopVac Nozzle Caddy - Dimension Doodle 1
ShopVac Nozzle Caddy – Dimension Doodle 1

A more detailed doodle with brass inserts instead of the nylock nuts and an aluminum spreader plate that was obviously not necessary:

ShopVac Nozzle Caddy - Dimension Doodle 2
ShopVac Nozzle Caddy – Dimension Doodle 2

In retrospect, the inserts would make more sense.

The angle doodles convinced me not to bother modeling either the slot’s taper along its length or its mold draft.

Kinda looks like it grew there and makes one wonder why they don’t include a caddy as a standard option.

The OpenSCAD source code as a GitHub Gist:

// ShopVac Nozzle Caddy
// Ed Nisley KE4ZNU 2022-02
Layout = "Show"; // [Handle,Block,Show,Build]
HandleOD = 20.0;
//- Extrusion parameters must match reality!
/* [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);
ID = 0;
OD = 1;
// Dimensions
// Handle lies along X axis
Handle = [200,HandleOD,HandleOD]; // X = longer than anything else
WallThick = 5.0; // Thinnest printed wall
Screw = [4.0,7.0,25.0]; // M4 socket head cap screw
Washer = [4.5,9.0,0.8]; // M4 washer
Insert = [4.0,5.9,10.0]; // M4 brass insert
Block = [15.0,Handle.y + 4*WallThick + 2*Screw[ID],HandleOD + 2*WallThick]; // overall clamp block
echo(str("Block: ",Block));
Bosses = [[Block.x,9.5,13.0],[Block.x,15.0,9.0]];
ScrewOC = Handle.y + 2*WallThick + Screw[ID];
Kerf = 1.0; // cut through middle to apply compression
Gap = 1.25;
CornerRadius = Washer[OD]/2;
// 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(d=(FixDia + HoleWindage),h=Height,$fn=Sides);
// Shopvac handle
module Handle() {
// Clamp block
module ClampBlock(BossID=0) {
difference() {
union() {
for (i=[-1,1], j=[-1,1]) // rounded block
translate([i*(Block.x/2 - CornerRadius),j*(Block.y/2 - CornerRadius),-Block.z/2])
translate([0,0,-(Block.z/2 + Bosses[BossID].z/2 - Protrusion)])
for (j = [-1,1]) // screw holes
translate([0,j*ScrewOC/2,-(Block.z/2 + Protrusion)])
PolyCyl(Screw[ID],Block.z + 2*Protrusion,6);
translate([0,0,-(Handle.z/2 + Insert[LENGTH])])
// Splice block less handle bore
module ShapedBlock() {
difference() {
// Build them
if (Layout == "Handle")
if (Layout == "Block")
if (Layout == "Show") {
xofs = -((len(Bosses) - 1)/2 * Gap*Block.x);
for (i=[0:len(Bosses) - 1])
translate([xofs + i*Gap*Block.x,0,0])
if (Layout == "Build") {
yofs = -((len(Bosses) - 1)/2 * Gap*Block.y);
for (j=[0:len(Bosses) - 1])
translate([0,yofs + j*Gap*Block.y,0])

Fluorescent Shop Light Ballast Caps

It never ceases to amaze me that these capacitors appear in the AC power line circuits inside old-school fluorescent shop lights:

Shop light ballast cap
Shop light ballast cap

It really is a capacitor:

Shop light ballast cap A - test
Shop light ballast cap A – test

Its sibling from the other end of the fixture had more ESR:

Shop light ballast cap B - test
Shop light ballast cap B – test

Both were likely within spec, whatever that means.

I have no idea what’s lurking inside the tidy LED tubes now living in that same fixture, of course.

Sheath Your Blades!

Trigger warning: gore.

A week ago I milled a stack of cursor blanks, then engraved a test hairline on a scrap cursor to make sure everything was ready:

Cursor V-bit setup
Cursor V-bit setup

After raising the spindle a few inches, I reached across the table, peeled the tape, and, as I pulled my hand back with the finished cursor, snagged the back of my left index finger on the V bit.

So. Much. Blood.

Urgent Care PA: “You may have nicked the tendon. Get thee hence to the Hospital Trauma Center.”

Trauma Center MD: “See that white fiber down in there? That’s the extensor ligament. Looks OK and should heal fine.”

Me: “Urp.”

Trauma Center MD: “Unless you’re one of the 20% who get an infection.”

Me: “Unless I’m one of the few who contract an MRSA infection, then just up and die.”

Trauma Center MD: “Well, yes, there’s that. If the wound swells or smells bad, come back here quickly.”

Dutchess County is now on the trailing edge of the Omicron wave, but the Trauma Center is attached to the Emergency Room and had a steady stream of customers arriving by ambulance. While being entirely content to not be their most urgent case, I had plenty of time to examine the wide variety of instruments parked in the room with me:

Nameless Hospital Cart
Nameless Hospital Cart

I’m on a ten-day regimen of surprisingly inexpensive Amoxicillin + Clavulanate Potassium capsules, which is apparently what it takes to knock down a potential infection these days.

Five days later, it looks like I should pull through:

Lacerated Left Index Finger
Lacerated Left Index Finger

So I hereby swear a mighty oath on the bones of my ancestors to always sheath my blades. You should, too.

But we all knew that last week, didn’t we?

Underwriter’s Knot

Found inside a fluorescent desk lamp being salvaged for possible use as an LED task lamp:

Fluorescent Desk Lamp - Underwriters Knot
Fluorescent Desk Lamp – Underwriters Knot

It’s one of the few Underwriter’s Knots I’ve ever seen in the wild. Many recent (i.e., built in the last half-century) lamps pass the cords through a plastic clamp or depend on simple bushings, with some just ignoring the problem.

This anonymous lamp sports the usual Made in China sticker, but also features a genuine-looking UL sticker complete with elaborate holograms, so it may well have been sold by a reputable company. IIRC, it came from a trash can in a Vassar College hallway, back when in-person meetings were a thing; perhaps Vassar required known-good electrical hardware.

CNC-3018XL: Improved X-Axis Home Switch Mount

A few months of inactivity left the CNC-3018XL table parked in its homed position where the gentle-but-inexorable pressure of the switch lever displaced the foam holding the plastic actuator tab on the X-axis bearing enough that it would no longer operate reliably:

3018 CNC - Y axis endstop
3018 CNC – Y axis endstop

Putting foam tape in a highly leveraged position produces the same poor results as in finance.

The fix requires reorienting the switch so a solid block on the bearing can push directly on the actuator lever:

CNC-3018 X Home Switch - bottom view
CNC-3018 X Home Switch – bottom view

The block must curve around the bearing to give the tape enough surface area for a good grip:

CNC-3018 X Home Switch - oblique view
CNC-3018 X Home Switch – oblique view

The solid model for the new X-axis mount looks about like you’d expect:

CNC-3018 X Home Switch Mount - solid model
CNC-3018 X Home Switch Mount – solid model

I increased the home switch pulloff to 2 mm, although it’s not clear that will make any difference in the current orientation.

The OpenSCAD source code as a GitHub Gist:

// 3018-Pro Mount for Makerbot Endstop PCB
// Ed Nisley KE4ZNU - 2019-07 (using OEM machine axes)
// 2022-02-02 rotate X block (after renaming axes to match new layout)
/* [Build Options] */
Layout = "Show"; // [Build, Show]
/* [Hidden] */
ThreadThick = 0.25; // [0.20, 0.25]
ThreadWidth = 0.40; // [0.40]
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
Protrusion = 0.01; // [0.01, 0.1]
HoleWindage = 0.2;
ID = 0;
OD = 1;
//- Shapes
// Basic PCB with hole for switch pins
// origin at switch actuator corner, as seen looking at component side
SwitchClear = [15.0,5.0,2.0]; // clearance around switch pins
SwitchOffset = [12.5,9.0,0.0]; // center of switch pins from actuator corner
PCB = [26.0,16.4,2*SwitchClear.z]; // switch PCB beyond connector, pin height
//XBlock = [PCB.x + 10.0,PCB.y,20.0];
XBlock = [PCB.x,PCB.y,10.0];
XBearing = [10.0,26.5,28.5];
XPin = [10.0,20.0,10.0];
module XMount() {
if (false) // side-push switch tended to slip
difference() {
cube(XBlock + [0,2*Protrusion,0],center=false);
translate(SwitchOffset + [0,0,10.0 - SwitchClear.z/2])
cube(SwitchClear + [0,0,Protrusion],center=true);
else {
difference() {
translate(SwitchOffset + [0,0,XBlock.z - SwitchClear.z/2])
cube(SwitchClear + [0,0,Protrusion],center=true);
difference() {
cube(XPin + [0,0,XBearing[OD]/4],center=false);
translate([-Protrusion,XPin.y/2,XPin.z + XBearing[OD]/2])
cylinder(d=XBearing[OD],h=XPin.x + 2*Protrusion,center=false);
cube(XPin + [2*Protrusion,0,0],center=false);
YBlock = [PCB.x,PCB.y,5.0];
module YMount() {
difference() {
translate(SwitchOffset + [0,0,YBlock.z - SwitchClear.z/2])
cube(SwitchClear + [0,0,Protrusion],center=true);
ZBlock = [PCB.x,PCB.y,6.0];
ZPin = [20.0,10.0,5.5];
module ZMount() {
difference() {
translate(SwitchOffset + [0,0,ZBlock.z - SwitchClear.z/2])
cube(SwitchClear + [0,0,Protrusion],center=true);
difference() {
cube(ZPin + [0,2*Protrusion,0],center=false);
//- Build things
if (Layout == "Show") {
translate([0,-(ZBlock.y + XBlock.y)])

Inkjet Refilling: End of an Era

Just before the turn of the millennium, I bought what turned out to be a never-sufficiently-to-be-damned HP 2000C inkjet printer that served as my introduction to refilling inkjet cartridges. A few years later, a Canon S630 printer joined the stable and worked fine for perhaps five years before succumbing to a printhead death. An Epson R380 that might have cost fifteen bucks after rebate took over, drank maybe a gallon of knockoff ink through a continuous ink supply system during the next thirteen years, and finally suffered progressive printhead failure during the last year.

Something recently changed in the inkjet market: Epson (among others) now touts their “Ecotank” printers featuring large internal reservoirs refilled by 70 ml bottles of color ink priced at perhaps 20¢/ml, obtained direct from Epson via Amazon. They proudly note you can save 90% off the cost of cartridges (“Kiss Expensive Cartridges Goodbye”), without mentioning how their previous extortionate cartridge business made that possible. Of course, Ecotank printers cost far more than cartridge-based printers, but that seems reasonable to me.

Because the ink bottles fit neatly into the printer through a push-to-flow valve interlock, I can finally retire this relic:

Inkjet refilling towel
Inkjet refilling towel

That’s maybe fifteen years of accumulated splotches.

I hope my refusal to buy their cartridges helped immanentize their eschaton, just a little.

Good riddance.