Machine Shop – Page 99 – The Smell of Molten Projects in the Morning

CNC-3018XL X-Axis Recalibration

Plotting the backlash / calibration target on both the CNC-3018XL and the MPCNC quickly showed, contrary to what I expected, the MPCNC was dead-on accurate, albeit with some wobbulation and a trace of backlash:

MPCNC - Backlash test - detail — MPCNC – Backlash test – detail

Although it looks ug-u-lee, the (lower speed) drag knife cuts come out nice and, because the entry and exit moves match the main cut, the minimal backlash wasn’t a problem.

Turns out only the X axis on the 3018XL had a problem:

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

Apparently the longer leadscrew I installed as part of the “XL” conversion has a small thread pitch error: about 1 mm short in every 250 mm of travel. I don’t have any (definite, non-handwavy) method to measure the pitch directly, other than by running the follower nut and measuring the results, but it’s consistently short.

Quite some time ago (after blowing up the OEM controller board), I set up the Protoneer CNC board in 1:8 microstep mode, making the GRBL $100 setting a nice, round 400 step/mm for a two-start leadscrew with 2 mm pitch and 4 mm lead:

400 step/mm = (200 step/rev * 8 µstep/step) / 4 mm

After a few more measurements suggesting the leadscrew actually traveled 249.2 mm, the correct value will be:

401.28 step/mm = 400 step/mm × 250 mm / 249.2 mm

To verify I understood the problem and solution, I set $100 to a few integer values around the goal:

Cal Target - stacked - 399-402 step-mm — Cal Target – stacked – 399-402 step-mm

The top image shows the leftmost line at the 10 mm mark on the scale, because it’s easier for me to match the ink line with an engraved line, rather than the non-line at the end of the ruler.

The other images show the results for $100 set to 399, 400, 401, and 402 step/mm, respectively. The results last two results bracket the desired 250 mm outcome, with 401 step/mm being Close Enough™. GRBL accepts a floating point step/mm value, so I set $100 to 401.28, but I was unable to convince myself the result came out consistently different than 401.00.

Plotting both the tick marks (green) and the knife path (red) on the 3018XL, then cutting the bare paper on the MPCNC, showed the two machines now agree on where the knife should fall. The outer end of the tick marks extends 1 mm beyond the cut line to ensure small misalignments do not produce an obvious white gap around the edge of the deck.

The Y axis continues to match:

Tek CC - 2022-02-14 - Y detail — Tek CC – 2022-02-14 – Y detail

And now the X axis looks just as good:

Tek CC - 2022-02-14 - X detail — Tek CC – 2022-02-14 – X detail

The drag knife corners are rounded, as you’d expect. The cut seems slightly offset from a small origin touch-off error, but the scales now match.

2022-03-01

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:

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)
	M2
	(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'

	include("engrave.inc.gcmc");

	FALSE = 0;
	TRUE = !FALSE;

	//—–
	// 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

	feedrate(PenSpeed);

	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,-];
	engrave(tp,TravelZ.z,PenZ.z);

	tp = scale(typeset("Grid " + GridSize,TextFont),TextSize);
	tp += [-PlotSize.x/2 + GridSize.x/2,PlotSize.y/2 – GridSize.y/2 – 1.5*TextSize.y,-];
	engrave(tp,TravelZ.z,PenZ.z);

	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,-];
	engrave(tp,TravelZ.z,PenZ.z);

	tp = scale(typeset("Ed Nisley – KE4ZNU",TextFont),TextSize);
	tp += [-PlotSize.x/2 + GridSize.x/2,-(PlotSize.y/2 – GridSize.y/2),-];
	engrave(tp,TravelZ.z,PenZ.z);

	tp = scale(typeset("softsolder.com",TextFont),TextSize);
	tp += [-PlotSize.x/2 + GridSize.x/2,-(PlotSize.y/2 – GridSize.y/2 + 1.5*TextSize.y),-];
	engrave(tp,TravelZ.z,PenZ.z);

	comment("Mark center point");
	goto(SafeZ);
	goto([CenterOD/2,0,-]);
	move(PenZ);
	circle_cw([0,0]);

	comment("Label axes");

	tp = scale(typeset("X+",TextFont),TextSize);
	tp += [GridSize.x + 0.5*TextSize.x,-TextSize.y/2,-];
	engrave(tp,TravelZ.z,PenZ.z);

	tp = scale(typeset("Y+",TextFont),TextSize);
	tp += [-TextSize.x/2,GridSize.y + 0.5*TextSize.y,-];
	engrave(tp,TravelZ.z,PenZ.z);

	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,-];
	engrave(tp,TravelZ.z,PenZ.z);

	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);
	goto(p);
	move(PenZ);
	move_r([-,-GridSize.y,-]);
	goto(TravelZ);
	}

	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,-];
	engrave(tp,TravelZ.z,PenZ.z);

	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);
	goto(p);
	move(PenZ);
	move_r([-,GridSize.y,-]);
	goto(TravelZ);
	}

	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),-];
	engrave(tp,TravelZ.z,PenZ.z);

	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);
	goto(p);
	move(PenZ);
	move_r([GridSize.x,-,-]);
	goto(TravelZ);
	}

	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),-];
	engrave(tp,TravelZ.z,PenZ.z);

	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);
	goto(p);
	move(PenZ);
	move_r([-GridSize.x,-,-]);
	goto(TravelZ);
	}

	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);
	goto([-r,0,-]);
	move(PenZ);
	circle_cw([0,0,-]);
	goto(TravelZ);
	}

	goto(SafeZ);
	goto([0,0,-]);

view raw Scale Grid.gcmc hosted with ❤ by GitHub

2022-02-28

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:

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;
	LENGTH = 2;

	//———-
	// 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 + 4WallThick + 2Screw[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() {

	rotate([0,90,0])
	translate([0,0,-Handle.x/2])
	rotate(180/(4*8))
	PolyCyl(Handle.y,Handle.x,4*8);
	}



	// Clamp block

	module ClampBlock(BossID=0) {

	difference() {
	union() {
	hull()
	for (i=[-1,1], j=[-1,1]) // rounded block
	translate([i(Block.x/2 – CornerRadius),j(Block.y/2 – CornerRadius),-Block.z/2])
	cylinder(r=CornerRadius,h=Block.z,$fn=8);
	translate([0,0,-(Block.z/2 + Bosses[BossID].z/2 – Protrusion)])
	cube(Bosses[BossID],center=true);
	}

	for (j = [-1,1]) // screw holes
	translate([0,j*ScrewOC/2,-(Block.z/2 + Protrusion)])
	rotate(180/6)
	PolyCyl(Screw[ID],Block.z + 2*Protrusion,6);

	cube([2Block.x,2Block.y,Kerf],center=true);

	Handle();

	translate([0,0,-Block.z])
	rotate(180/6)
	PolyCyl(Screw[ID],Block.z,6);

	translate([0,0,-(Handle.z/2 + Insert[LENGTH])])
	rotate(180/6)
	PolyCyl(Insert[OD],Handle.y,6);
	}
	}

	// Splice block less handle bore

	module ShapedBlock() {
	difference() {
	ClampBlock();
	Handle();
	}
	}




	//———-
	// Build them

	if (Layout == "Handle")
	Handle();

	if (Layout == "Block")
	ClampBlock(BossID=0);

	if (Layout == "Show") {
	color("Green",0.25)
	Handle();
	xofs = -((len(Bosses) – 1)/2 * Gap*Block.x);
	for (i=[0:len(Bosses) – 1])
	translate([xofs + iGapBlock.x,0,0])
	ClampBlock(i);
	}

	if (Layout == "Build") {
	yofs = -((len(Bosses) – 1)/2 * Gap*Block.y);
	for (j=[0:len(Bosses) – 1])
	translate([0,yofs + jGapBlock.y,0])
	translate([0,0,Block.x/2])
	rotate([0,90,0])
	ClampBlock(j);
	}

view raw ShopVac Nozzle Caddy.scad hosted with ❤ by GitHub

2022-02-25

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:

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.

2022-02-24

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:

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:

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:

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?

2022-02-17

Underwriter’s Knot

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

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.

2022-02-11

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;
	LENGTH = 2;

	//- 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() {
	translate([-10.0,0,0])
	cube(XBlock,center=false);
	translate([0,-Protrusion,10.0])
	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() {
	cube(XBlock,center=false);
	translate(SwitchOffset + [0,0,XBlock.z – SwitchClear.z/2])
	cube(SwitchClear + [0,0,Protrusion],center=true);
	}

	translate([1.25*XBlock.x,0,0])
	difference() {
	cube(XPin + [0,0,XBearing[OD]/4],center=false);
	translate([-Protrusion,XPin.y/2,XPin.z + XBearing[OD]/2])
	rotate([0,90,0])
	cylinder(d=XBearing[OD],h=XPin.x + 2*Protrusion,center=false);
	translate([-Protrusion,-XPin.y/2,XPin.z])
	cube(XPin + [2*Protrusion,0,0],center=false);
	}
	}
	}

	YBlock = [PCB.x,PCB.y,5.0];

	module YMount() {

	difference() {
	cube(YBlock,center=false);
	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() {
	cube(ZBlock,center=false);
	translate(SwitchOffset + [0,0,ZBlock.z – SwitchClear.z/2])
	cube(SwitchClear + [0,0,Protrusion],center=true);
	}

	translate([1.25*ZBlock.x,0,0])
	difference() {
	cube(ZPin,center=false);
	translate([ZPin.x/2,-Protrusion,4.0])
	cube(ZPin + [0,2*Protrusion,0],center=false);
	}
	}

	//- Build things

	if (Layout == "Show") {
	translate([0,XBlock.y,0])
	YMount();
	translate([0,-XBlock.y/2])
	XMount();
	translate([0,-(ZBlock.y + XBlock.y)])
	ZMount();
	}

view raw Home Switch Mounts.scad hosted with ❤ by GitHub

2022-02-10