Machine Shop – Page 97 – The Smell of Molten Projects in the Morning

Expedient Caster Wrench

Cranked down as far as it would go, a new adjustable height workbench in Mary’s sewing room turned out to be just slightly higher than the other work surfaces adjoining it, so I replaced its 3 inch casters with 2 inch versions:

Sewing bench - 2 vs 3 inch casters — Sewing bench – 2 vs 3 inch casters

The bench arrived as a kit and included the 17 mm flat wrench required to snug the hex head on the 3/8-16 threaded stem atop the 3 inch caster against the bottom of the bench foot. The 2 inch caster also has a threaded stem, but of course it has a 14 mm hex head.

I traced around a 14 mm open-end wrench on a scrap of aluminum and introduced the outline to Tiny Bandsaw:

Improvised 14 mm caster wrench - rough cut — Improvised 14 mm caster wrench – rough cut

A little belt sander action cleaned up the outside, some hand filing matched the wrench to the hex, and it came out OK, even before I scrubbed the dirt off its white-ish pebble-finish coating:

Improvised 14 mm caster wrench - finished — Improvised 14 mm caster wrench – finished

The bare steel wrench arrived with the bench and has 13 and 17 mm openings. I briefly considered embiggening the 13 mm end, but came to my senses.

Aluminum isn’t a particularly good metal for wrench duty, but this one had to apply maybe 1/3 of a turn to each of four stems, stopping when snug, and it performed just fine. It’s now sleeping in the wrench drawer, dreaming of another job that may never arrive.

The smaller casters lowered the bench by about an inch, whereupon cranking the surface up a bit less than half an inch aligned it perfectly.

2022-03-07

Work Glove Security Tags

Having worn my work glove collection to exhaustion, the fanciest two pairs in a new selection came with elaborate security tags:

Finding a standard tag inside inside the fancy shell shouldn’t come as any surprise, but I’m surprised the retail loss ratio for a pair of $20 gloves can support that much hardware.

I went through the self-checkout area and didn’t do anything special, so either those lanes don’t have tag scanners or the tags are security theater.

2022-03-03

Gidget II Sewing Table: Temporary Juki Insert

Mary’s new sewing table just arrived, but the laser-cut acrylic insert fitting around her Juki sewing machine is still a month or two away. Until then, a simple cardboard replacement must suffice to fill the gap:

The rectangle just to the left of the needle is a hatch for bobbin changes. Sheer faith and an interference fit between layers of Kapton tape holds it in place with surprising force.

I wanted to tape the cardboard edges to the machine and the table to smooth out the transitions, but her Supreme Slider slippery sheet may solve the problem without adhesives:

Juki temporary table insert - Super Slider — Juki temporary table insert – Super Slider

The “insert” is a 1/4 inch thick double-layer corrugated cardboard sheet, utility-knifed from a huge box. She layers cardboard under the wood chips in her Vassar Farms garden paths to discourage the weeds; this seemed like a perfectly reasonable diversion.

2022-03-02

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);
	}