Category: Machine Shop

Mechanical widgetry

CNC 3018-Pro: Probe Camera Case for Anonymous USB Camera

The anonymous USB camera I used with the stereo zoom microscope not only works with VLC, but also with bCNC, and it has a round PCB with ears:

CNC 3018-Pro - Probe Camera - PCB — CNC 3018-Pro – Probe Camera – PCB

Which suggested putting it in a ball mount for E-Z aiming:

CNC 3018-Pro - Probe Camera - ball mount — CNC 3018-Pro – Probe Camera – ball mount

Black filament snippets serve as alignment pins to hold the ball halves together while they’re getting clamped. They’re epoxied into the upper half of the ball, because who knows when I’ll need to harvest the camera.

The clamp mount descends from the Tour Easy Daytime Running Lights, with more screws and less fancy shaping:

USB Camera - Round PCB Mount - solid model - build — USB Camera – Round PCB Mount – solid model – build

The clamp pieces fit around the ball with four M3 screws providing the clamping force:

USB Camera - Round PCB Mount - solid model sectioned — USB Camera – Round PCB Mount – solid model sectioned

The whole affair sticks onto the Z axis carrier with double-sided foam tape:

CNC 3018-Pro - Probe Camera - alignment — CNC 3018-Pro – Probe Camera – alignment

It barely clears the strut on the -X side of the carriage, although it does stick out over the edge of the chassis.

After the fact, I tucked a closed-cell foam ring between the lens threads and the ball housing to stabilize the lens; the original camera glued the thing in place, but some fiddly alignment & focusing lies ahead:

Alignment mirror - collimation — Alignment mirror – collimation

It’s worth noting that the optical axis of these cheap cameras rarely coincides with the physical central axis of the lens. This one requires a jaunty tilt, although it’s not noticeable in any of the pictures I tried to take.

All in all, this one works just like the probe camera on the MPCNC.

The OpenSCAD source code as a GitHub Gist:

	// CNC 3018-Pro Probe Camera mount for anonymous USB camera
	// Ed Nisley KE4ZNU – August 2019

	Layout = "Show"; // [Show, Build, Ball, Clamp, Bracket, Mount]

	//——-
	//- Extrusion parameters must match reality!
	// Print with 2 shells

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

	inch = 25.4;

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

	//——-
	// Dimensions

	//– Camera

	PCBThick = 1.2;
	PCBDia = 25.0;

	KeySize = [28.0,8.5,IntegerMultiple(PCBThick,ThreadThick)];
	KeyOffset = [0.0,2.0,0.0];

	KeyRadius = IntegerMultiple(sqrt(pow(KeySize.y – KeyOffset.y,2) + pow(KeySize.x/2,2)),0.01);
	echo(str("Key radius: ",KeyRadius));

	Lens = [14.0,18.0,25.0];

	BallID = PCBDia;
	BallOD = IntegerMultiple(2*KeyRadius,5.0);
	echo(str("Ball OD: ",BallOD));

	WallThick = 3.0;

	CableOD = 3.75;

	NumPins = 3;
	Pin = [1.75,1.8,5.0];

	Screw = [
	3.0,6.8,25.0 // M3 ID=thread, OD=washer, LENGTH=below head
	];

	RoundRadius = IntegerMultiple(Screw[OD]/2,1.0); // corner rounding

	ClampSize = [BallOD + 2WallThick,BallOD + 2WallThick,20.0];
	echo(str("Clamp: ",ClampSize));

	MountSize = [5.0,BallOD,25.0];
	MountClearance = 1.0; // distance between clamp and mount

	Kerf = 2*ThreadThick;

	ScrewOC = [ClampSize.x – 2RoundRadius,ClampSize.y – 2RoundRadius];
	echo(str("Screw OC: ",ScrewOC));

	Insert = [ // brass insert: body, knurl,length
	3.9,4.9,8.0
	];
	UseInsert = false;

	NumSides = 12*4;

	//——-

	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);
	}


	//——-
	// Components

	module CamBall(Section="Both") {

	Offset = (Section == "Both") ? 0 :
	(Section == "Upper") ? BallOD/2 :
	(Section == "Lower") ? -BallOD/2 :
	0;

	render(convexity=4)
	intersection(convexity = 3) {
	difference() {
	sphere(d=BallOD,$fn=NumSides);

	sphere(d=BallID,$fn=NumSides); // interior

	PolyCyl(CableOD,2*BallOD,8); // cable & lens holes
	translate([0,0,-Lens[LENGTH]])
	PolyCyl(Lens[OD],Lens[LENGTH],NumSides);

	translate([0,0,-PCBThick])
	PolyCyl(PCBDia,PCBThick,NumSides);

	translate(KeyOffset + [0,-KeySize.y/2,-PCBThick/2]) // PCB key
	cube(KeySize,center=true);

	for (i=[0:NumPins – 1])
	rotate(i*360/NumPins)
	translate([0,-(BallID + BallOD)/4,-Pin[LENGTH]/2])
	PolyCyl(Pin[OD],Pin[LENGTH],6);
	}
	translate([0,0,Offset])
	cube([BallOD,BallOD,BallOD] + 2*[Protrusion,Protrusion,0],center=true);
	}
	}

	module Clamp(Section="Both") {

	Offset = (Section == "Both") ? 0 :
	(Section == "Upper") ? ClampSize.z/2 :
	(Section == "Lower") ? -ClampSize.z/2 :
	0;

	render(convexity=4)
	intersection() {
	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([iScrewOC.x/2,jScrewOC.y/2,0])
	cylinder(r=RoundRadius,h=ClampSize.z,$fn=NumSides,center=true);

	sphere(d=BallOD + 2*HoleWindage,$fn=NumSides); // space around camera ball

	for (i=[-1,1], j=[-1,1]) // screws
	translate([iScrewOC.x/2,jScrewOC.y/2,-ClampSize.z])
	PolyCyl(Screw[ID],2*ClampSize.z,6);

	if (UseInsert)
	for (i=[-1,1], j=[-1,1]) // inserts
	translate([iScrewOC.x/2,jScrewOC.y/2,-(ClampSize.z/2 + Protrusion)])
	PolyCyl(Insert[OD],Insert[LENGTH] + Protrusion,8);

	cube([2ClampSize.x,2ClampSize.y,Kerf],center=true); // clamping gap

	}
	translate([0,0,Offset])
	cube([ClampSize.x,ClampSize.y,ClampSize.z] + 2*[Protrusion,Protrusion,0],center=true);

	}
	}

	module Bracket() {

	translate([ClampSize.x/2 + MountSize.x/2 + MountClearance,0,MountSize.z/2 – ClampSize.z/2])
	cube(MountSize,center=true);

	translate([ClampSize.x/2 + MountClearance/2,0,-(ClampSize.z + Kerf)/4])
	cube([MountClearance + 2*Protrusion,MountSize.y,(ClampSize.z – Kerf)/2],center=true);

	}


	module Mount() {

	union() {
	Clamp("Lower");
	Bracket();
	}

	}



	//——-
	// Build it!

	if (Layout == "Ball")
	CamBall();

	if (Layout == "Clamp")
	Clamp();

	if (Layout == "Bracket")
	Bracket();

	if (Layout == "Mount")
	Mount();

	if (Layout == "Show") {
	difference() {
	union() {
	color("Purple")
	Clamp("Upper");
	Mount();
	color("LimeGreen")
	CamBall();
	}
	rotate([0,0,45])
	translate([-ClampSize.x,0,0])
	cube(2*ClampSize,center=true);
	}
	}

	if (Layout == "Build") {
	Gap = 0.6;
	translate([-GapBallOD,GapBallOD,0])
	CamBall("Upper");

	translate([-GapBallOD,-GapBallOD,0])
	rotate([0,180,0])
	CamBall("Lower");

	translate([GapClampSize.x,-GapClampSize.y,ClampSize.z/2])
	rotate([0,180,0])
	Clamp("Upper");

	translate([GapClampSize.x,GapClampSize.y,ClampSize.z/2]) {
	rotate(180)
	Mount();
	}
	}

view raw USB Camera – Round PCB Mount.scad hosted with ❤ by GitHub

2019-09-03

CNC 3018-Pro: Probe Camera Case for Logitch QuickCam Pro 5000

The ball-shaped Logitch QuickCam Pro 5000 has a rectangular PCB, so conjuring a case wasn’t too challenging:

Probe Camera Case - Logitech QuickCam Pro 5000 - bottom — Probe Camera Case – Logitech QuickCam Pro 5000 – bottom

That’s more-or-less matte black duct tape to cut down reflections.

The top side has a cover made from scuffed acrylic scrap:

Probe Camera Case - Logitech QuickCam Pro 5000 - top — Probe Camera Case – Logitech QuickCam Pro 5000 – top

The corners are slightly rounded to fit under the screw heads holding it in place.

The solid model shows off the internal ledge positioning the PCB so the camera lens housing rests on the floor:

3018 Probe Camera Mount - solid model — 3018 Probe Camera Mount – solid model

The notch lets the cable out, while keeping it in one place and providing some strain relief.

I though if a camera was recognized by V4L2 and worked with VLC, it was good to go:

Logitech QuickCam Pro 5000 - short focus — Logitech QuickCam Pro 5000 – short focus

Regrettably, it turns out the camera has a pixel format incompatible with the Python opencv interface used by bCNC. This may have something to do with running the code on a Raspberry Pi, rather than an x86 box.

The camera will surely come in handy for something else, especially with such a cute case.

The OpenSCAD source code as a GitHub Gist:

	// Probe Camera Mount for CNC 3018-Pro Z Axis
	// Ed Nisley – KE4ZNU – 2019-08

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

	Support = false;

	/* [Hidden] */

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

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

	inch = 25.4;

	//———————-
	// Dimensions

	PCB = [45.0,38.0,1.5]; // Logitech QuickCam Pro 5000 ball camera

	PCBLip = 1.0; // max non-component border
	PCBChamfer = 3.0; // cut along XY axes for corner bevel

	PCBClearTop = 15.0; // cables & connectors
	PCBClearSides = [0.5,0.5]; // irregular edges & comfort zone
	PCBClearBelow = 5.0; // lens support bracket rests on floor

	Lens = [11.5,14.2,3.0]; // LENGTH = beyond PCBClearBelow bracket
	LensOffset = [-1.5,0.0,0]; // distance from center of board

	CableOD = 4.5;

	BaseThick = Lens[LENGTH];

	Screw = [
	3.0,6.8,18.0 // M3 OD=washer, LENGTH=below head
	];

	RoundRadius = IntegerMultiple(Screw[OD]/2,1.0); // corner rounding

	ScrewOC = [PCB.x + 2sqrt(Screw[OD]),PCB.y + 2sqrt(Screw[OD])];
	echo(str("Screw OC: ",ScrewOC));

	Lid = [ScrewOC.x,ScrewOC.y,1.0/16.0 * inch]; // top cover plate
	echo(str("Lid: ",Lid));

	BlockSize = [ScrewOC.x + 2RoundRadius,ScrewOC.y + 2RoundRadius,
	BaseThick + PCBClearBelow + PCB.z + PCBClearTop + Lid.z];
	echo(str("Block: ",BlockSize));

	NumSides = 234;

	//———————-
	// 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 shapes

	// Overall block

	module Block() {

	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([iScrewOC.x/2,jScrewOC.y/2,0])
	cylinder(r=RoundRadius,h=BlockSize.z,$fn=NumSides);

	for (i=[-1,1], j=[-1,1]) // corner screws
	translate([iScrewOC.x/2,jScrewOC.y/2,BlockSize.z – Screw[LENGTH]])
	cylinder(d=Screw[ID],h=2*Screw[LENGTH],$fn=8); // cylinder = undersized

	translate(LensOffset + [0,0,-Protrusion]) // lens body
	PolyCyl(Lens[OD],2*BlockSize.z,NumSides);

	translate([0,0,BlockSize.z/2 + BaseThick]) // PCB lip on bottom
	cube([PCB.x – 2*PCBLip,PCB.y,BlockSize.z],center=true);

	translate([0,0,BlockSize.z/2 + BaseThick + PCBClearBelow]) // PCB clearance
	cube([PCB.x + 2PCBClearSides.x,PCB.y + 2PCBClearSides.y,BlockSize.z],center=true);

	translate([0,0,BlockSize.z – Lid.z/2]) // lid recess
	cube(Lid + [0,0,Protrusion],center=true);

	translate([0,Lid.y/2 – CableOD/2,BaseThick + PCBClearBelow + PCB.z]) // cable exit
	hull()
	for (j=[-1,1])
	translate([0,j*CableOD/4,0])
	rotate(180/8)
	PolyCyl(CableOD,BlockSize.z,8);
	}

	}


	//- Build it

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

	if (Layout == "Show") {
	Block();

	}

	if (Layout == "Build") {
	Block();
	}

view raw 3018 Probe Camera Mount – QC Pro 5000.scad hosted with ❤ by GitHub

2019-09-02

CNC 3018-Pro: Platter Fixtures

Up to this point, the Sherline has been drilling 3.5 inch hard drive platters to serve as as reflecting bases for the vacuum tubes:

LinuxCNC - Sherline Mill - Logitech Gamepad — LinuxCNC – Sherline Mill – Logitech Gamepad

The CNC 3018-Pro has a work envelope large enough for CD / DVD platters, so I mashed the Sherline fixture with dimensions from the vacuum tube code, added the 3018’s T-slot spacing, and conjured a pair of fixtures for a pair of machines.

Because I expect to practice on scrap CDs and DVDs for a while:

Platter Fixtures - CD on 3018 — Platter Fixtures – CD on 3018

And a 3.5 inch hard drive platter version:

Platter Fixtures - hard drive platter on 3018 — Platter Fixtures – hard drive platter on 3018

The holes sit at half the 3018’s T-slot spacing (45 mm / 2), so you can nudge the fixtures to the front or rear, as you prefer.

The alignment dots & slots should help touch off the XY coordinate system on the Sherline, although it can’t reach all of a CD. Using bCNC’s video alignment on the hub hole will be much easier on the 3018.

After fiddling around with the 3018 for a while, however, the CD fixture doesn’t have many advantages over simply taping the disc to a flat platen. Obviously, you’d want a sacrificial layer for drilling, but it’s not clear the OEM motor / ER11 chuck would be up to that task.

The OpenSCAD source code as a GitHub Gist:

	// Machining fixtures for CD and hard drive platters
	// Ed Nisley KE4ZNU February … September 2016
	// 2019-08 split from tube base models

	PlatterName = "CD"; // [3.5inch,CD]

	CNCName = "3018"; // [3018,Sherline]

	PlateThick = 5.0; // [5.0,10.0,15.0]

	RecessDepth = 4.0; // [0.0,2.0,4.0]

	//- 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);

	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);
	}


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

	//———————-
	// Dimensions

	P_NAME = 0; // platter name
	P_ID = 1; // … inner diameter
	P_OD = 2; // … outer diameter
	P_THICK = 3; // … thickness

	PlatterData = [
	["3.5inch", 25.0, 95.0, 1.75],
	["CD", 15.0, 120.0, 1.20],
	];

	PlatterSides = 345; // polygon approximation

	B_NAME = 0; // machine name
	B_OC = 1; // … platform screw OC, use small integer for slot
	B_STUD = 2; // … screw OD clearance

	BaseData = [
	["3018", [5.0, 45.0], 6.0], // slots along X axis
	["Sherline", [1.16inch,1.16inch], 5.0], // tooling plate

	];

	//———————-
	// Drilling fixture for disk platters

	module PlatterFixture(Disk,Machine) {

	PI = search([Disk],PlatterData,1,0)[P_NAME]; // get platter index
	echo(str("Platter: ",Disk));
	Platter = [PlatterData[PI][P_ID],
	PlatterData[PI][P_OD],
	PlatterData[PI][P_THICK]];

	BI = search([Machine],BaseData,1,0)[B_NAME]; // get base index
	echo(str("Machine: ",Machine));

	AlignOC = IntegerMultiple(Platter[OD],10);
	echo(str("Align OC: ",AlignOC));
	AlignSlot = [3ThreadWidth,10.0,3ThreadThick];

	StudClear = BaseData[BI][B_STUD]; // … clearance

	StudOC = [IntegerMultiple(AlignOC + 2*StudClear,BaseData[BI][B_OC].x), // … screw spacing
	BaseData[BI][B_OC].y];
	echo(str("Stud spacing: ",StudOC));
	NumStuds = [2,1 + 2*floor(Platter[OD] / StudOC.y)]; // holes only along ±X edges
	echo(str("Stud holes: ",NumStuds));

	BasePlate = [(20 + StudOC.x*ceil(Platter[OD] / StudOC.x)),
	(10 + AlignOC),
	PlateThick];
	echo(str("Plate: ",BasePlate));
	PlateRound = 10.0; // corner radius

	difference() {
	hull() // basic plate shape
	for (i=[-1,1], j=[-1,1])
	translate([i(BasePlate.x/2 – PlateRound),j(BasePlate.y/2 – PlateRound),0])
	cylinder(r=PlateRound,h=BasePlate.z,$fn=4*4);

	for (i=[-1,0,1], j=[-1,0,1]) // origin pips
	translate([iAlignOC/2,jAlignOC/2,BasePlate.z – 2*ThreadThick])
	cylinder(d=4*ThreadWidth,h=1,$fn=6);

	for (i=[-1,1], j=[-1,1]) { // alignment slots
	translate([i*(AlignOC + AlignSlot.x)/2,
	j*Platter[OD]/4,
	(BasePlate.z – AlignSlot.z/2 + Protrusion/2)])
	cube(AlignSlot + [0,0,Protrusion],center=true);
	translate([i*Platter[OD]/4,
	j*(AlignOC + AlignSlot.x)/2,
	(BasePlate.z – AlignSlot.z/2 + Protrusion/2)])
	rotate(90)
	cube(AlignSlot + [0,0,Protrusion],center=true);
	}

	for (i=[-1,1], j=[-floor(NumStuds.y/2):floor(NumStuds.y/2)]) // mounting stud holes
	translate([iStudOC.x/2,jStudOC.y/2,-Protrusion])
	rotate(180/6)
	PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);

	translate([0,0,-Protrusion]) // center clamp hole
	rotate(180/6)
	PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);

	translate([0,0,BasePlate.z – Platter[LENGTH]]) // disk locating recess
	rotate(180/PlatterSides)
	linear_extrude(height=(Platter[LENGTH] + Protrusion),convexity=2)
	difference() {
	circle(d=(Platter[OD] + HoleWindage),$fn=PlatterSides);
	circle(d=Platter[ID] – HoleWindage,$fn=PlatterSides);
	}

	translate([0,0,BasePlate.z – RecessDepth]) // drilling recess
	rotate(180/PlatterSides)
	linear_extrude(height=(RecessDepth + Protrusion),convexity=2)
	difference() {
	circle(d=(Platter[OD] – 10),$fn=PlatterSides);
	circle(d=(Platter[ID] + 10),$fn=PlatterSides);
	}
	}

	}


	//———————-
	// Build it

	PlatterFixture(PlatterName,CNCName);

view raw Platter Fixtures.scad hosted with ❤ by GitHub

2019-08-30

Printer Filament Millifiori

I finally decommissioned my old Thing-O-Matic, as it’s been far surpassed by the current generation of dirt-cheap Prusa-style 3D printers, and must now figure out what to do with about 10 kg of 3 mm ABS filament. Yes, 3 mm filament from back in the Bad Old Days.

Also back in the day, our Larval Engineer made millifiori creations in glass (at school) and polymer clay, building up the final piece from murrine canes, which suggested a similar technique using filament strands:

Filament Millefiori – 160C pipe – slice detail

Well, maybe it’s not exactly art …

Just to see how it might work, I packed a random length of conduit with filament snippets and jammed a thermocouple into the middle:

Filament Millefiori – packed conduit

Which went into the shop’s sacrificial Dutch oven over low heat:

Filament Millefiori – conduit heating

For lack of anything smarter, I slowly heated it to 250 °C, well above what the Thing-O-Matic used for extrusion, let it soak for a few minutes, then let the tube cool on the counter.

Some persuasion with a hammer and drift punch extracted the fused filament:

Filament Millefiori – 250C results

Obviously, the concept needs more work, but the bottom side looks promising:

Filament Millefiori – 250C results – bottom

Wrapping the bundle with silicone tape should keep the filament from sticking to the tube and provide uniform compression:

Filament Millefiori – 235C silicone wrap

I forced it into the tube and wrapped the whole affair with aluminum foil to confine the hot ABS stench:

Filament Millefiori – 235C heating

I held this one at 235 °C for a few minutes, cooled, unwrapped, and discovered the silicone wrap worked as expected:

Filament Millefiori – 235C thermocouple blob

OK, the blob on each end wasn’t expected, but at least the thermocouple came out with gentle persuasion. The compressed filament looked like it should be edible:

Filament Millefiori – 235C results

The molten filament oozed out of the wrap inside the tube, over there toward the right.

The filament snippets have a distinct curvature, brought on by years spent snuggled around a spool’s core, so I wondered if they could be straightened by application of somewhat less heat. Wikipedia lists the glass transition temperature for various ABS compositions as around 105 °C, so I packed the tube with more snippets and affixed the thermocouple with silicone tape:

Filament Millefiori – 100C setup

Wrap with foil, heat to 100 °C, let cool, and they’re definitely straighter than the unheated white strand at the bottom:

Filament Millefiori – 100C results

Having learned my lesson with a thermocouple inside the strands, the straightened strands get a looser silicone wrap with the thermocouple secured to the outside of the bundle:

Filament Millefiori – 160C setup

Heat to 160 °C:

Filament Millefiori – 160C setup

Let cool and (easily!) slide the compressed bundle out of the tube:

Filament Millefiori – 160C cooling

The silicone wrap definitely mushed the strands together, as shown by the larger diameter on the uncompressed end:

Filament Millefiori – 160C results

Bandsawing the bundle reveals nicely fused filaments inside, along with melty ends that stuck out of the wrap:

Filament Millefiori – 160C cut end

Thinking shorter lengths might pack better without straightening, I faced the ends of a thick aluminum pipe and stuffed as many snippets into it as would fit. This is the point where a real artist would arrange the filaments in a pleasing pattern, if not a picture, but I was content with a random layout:

Filament Millefiori – 160C pipe – cable in pipe

That’s what the ends looked like after heating to 160 °C: somewhat glazed, reasonably fused, but certainly not compacted. The other end pointed upward and definitely felt the heat:

Filament Millefiori – 160C pipe – cable melty end detail

With a PCV pipe “collet” holding the cable / cane / murrina in the chuck, I faced the end:

Filament Millefiori – 160C pipe – cable facing

After taking this picture, I came to my senses and bandsawed the slice instead:

Filament Millefiori – 160C pipe – cutoff tool

Parting the slice in the lathe might have worked, but it just seemed like a really really bad idea when I looked at the setup.

A PVC pipe spacer kept the slice lined up in the chuck jaws while facing the bandsawed end:

Filament Millefiori – 160C pipe – slice facing

The slice and the cable:

Filament Millefiori – 160C pipe – slice and cable

Although the filament snippets fuse together without a silicone tape compression wrap, the gaps collect plenty of swarf during the cutting & facing:

Filament Millefiori – 160C pipe – cable end detail

The snippets along the outside, closest to the pipe, obviously got hotter than the ones in the middle and fused more solidly.

The pipe has a 35 mm ID for an area 136 times larger than a 3 mm filament. I packed about 100 snippets into the pipe, a 0.73 packing fraction, which looks to be in the right ballpark for the high end of the Circle Packing Problem. If they were straighter, maybe a few more would fit, but twisting the lot into a cable seemed to align them pretty well.

Perhaps filling the gaps with pourable epoxy before cutting the slices would help? A completely filled interior might require pulling a good vacuum on the whole thing.

A hexagonal pipe would produce slices one could tile into a larger sheet.

All in all, a useful exercise, but … it ain’t Art yet!

2019-08-29
CNC 3018-Pro: DRV8825 Hack for 1:8 Microstep Mode
The CAMTool V3.3 board on the CNC 3018-Pro hardwires the three DRV8825 stepper driver chips in 1:32 microstep mode by pulling all three Mode pins high. Unlike most CNC boards, it does not include jumpers to let you select different microstep modes; the designers know you want as many microsteps as you can possibly get.

As it turns out, 1:32 microstep mode requires 1600 steps for each millimeter of travel and, because GRBL tops out around 30 k step/s, the maximum speed is about 18.75 mm/s = 1125 mm/min. Which isn’t at bad, but, because I intend to use the thing for engraving, rather than the light-duty machining it’s (allegedly) capable of performing, running at somewhat higher speeds will be desirable.

For sure, a 3018-Pro does not have a physical resolution of 625 nm.

If you’re willing to settle for a mere 400 step/mm = 2.6 µm, then you can just ground the Mode 2 pin to get 1:8 microstep mode:

DRV8825 – Stepper Motor Controller – Microstep Modes

Rewiring the CAMTool board isn’t feasible, but hacking the DRV8825 carrier PCB doesn’t require much effort.

So, we begin.

Clamp the PCB in a vise, grab the Mode 2 pin with a needle-nose pliers, apply enough heat to melt the solder completely through the board, and yank that pin right out:

CAMTool V3.3 – DRV8825 M2 pin removed

I do wonder how the layout folks managed to reverse the “N” for the Enable pin. Perhaps it’s a Cyrillic И in a dead-simple font?

With that done, add a snippet of wire from M2 to the GND pin in the opposite corner to complete the job:

CAMTool V3.3 – DRV8825 wired for 8 ustep mode

Despite that picture, remember to plug the DRV8825 boards into the CAMTool V3.3 board with the heatsink downward and the twiddlepot on the top, as shown in the little instruction book you got with the hardware:

SainSmart Genmitsu CNC Router 3018PRO-User Manual – DRV8825 orientation

Recompute the step/mm value in 1:8 microstep mode:
```
400 step/mm = (200 full step/rev) × (8 microstep/full step) / (4 mm/rev)
```
Then set the corresponding GRBL parameters:
```
$100=400
$101=400
$102=400
```
The 3018-Pro should work exactly like it did before, maybe a little noisier if your ears are up to the task.

Moah Speed comes later …
2019-08-28
CNC 3018-Pro: CAMTool V3.3 USB Power Diode

The CAMTool V3.3 board dispenses with fancy USB power switching circuitry:

CAMTOOL CNC-V3.3 schematic – USB Power Entry

The NUP2201 is an ESD clamp diode / suppressor IC, which is a nice touch, but FU1, a simple 300 mA polyfuse, is the only thing standing between the USB cable and the on-board +5 V regulator. In real life, it looks like this:

CAMTool V3.3 – USB power fuse

It’s the little black rectangle between the USB jack and the CH340 USB-to-serial chip. The

The far end of the USB cable plugs into a Raspberry Pi, a device known for unseemly fussiness about USB power, so I unsoldered the fuse and installed a diode:

CAMTool V3.3 – USB power diode

It’s a BAT54 Schottky diode, pointed toward the right to prevent current from the board getting to the Pi. Pin 2 (toward the bottom) isn’t connected to anything inside the package, either, so it’s all good.

I suppose if one were a stickler for detail, one could gimmick the diode in series with the fuse, but I figured that’s a solution for a problem well down on the probability list …

2019-08-27
DRV8825 Stepper Driver: Fast vs. Mixed Decay Current Waveforms
Herewith, a look at CNC 3018-Pro stepper motor current waveforms as a function of supply voltage, PWM decay mode, and motor speed.

The scope displays X and Y axis motor current at 1 A/div, with sensing through a pair of Tektronix Hall effect current probes:

CNC 3018-Pro – XY axes – Tek current probes

The X axis driver is an unmodified DRV8825 PCB operating in default mixed-decay mode. The Y axis DRV8825 has its DECAY pin pulled high, thereby putting it in fast decay mode.

The scope timebase varies to match the programmed feed rate. Because the X and Y axes move simultaneously, each axis moves at 1/√2 the programmed speed:
```
G1 X10 Y10 F100 → 71 mm/min on X and Y
```
The motor generates minimal back EMF at slow speeds, so the winding sees nearly the full supply voltage. As described in the previous post, the basic problem arises when the current rises too fast during each PWM cycle:
```
V = L di/dt
di/dt = 24 V / 3 mH = 8 kA/s
```
The first 1:32 microstep away from 0 calls for 5% of max current = 50 mA at a 1 A peak. The DRV8825 datasheet says the PWM typically runs at 30 kHz = 33 µs/cycle, during which the current will change by 270 mA:

267 mA = 8 kA/s × 33.3 µs

Notice how the current slams to a nearly constant, much-too-high value just after the first microstep. The incorrect current level decreases with lower supply voltage, because the rate-of-change decreases and the commanded current level reaches the actual (incorrect) current sooner.

Varying the motor voltage at a constant 10 mm/min:

3018 XY – Mixed Fast – 24V – 10mm-min 1A-div

3018 XY – Mixed Fast – 20V – 10mm-min 1A-div

3018 XY – Mixed Fast – 15V – 10mm-min 1A-div

3018 XY – Mixed Fast – 12V – 10mm-min 1A-div

3018 XY – Mixed Fast – 10V – 10mm-min 1A-div

Note that reducing the supply voltage doesn’t change the motor winding current, because the DRV8825 controls the current during each microstep, at least to the best of its ability.

Also note that the current overshoots the target for those microsteps, even when the motor is stopped, because there’s no back EMF, so the power dissipation is too high even at rest.

Enough back EMF appears at 100 mm/min to begin tamping down the current overshoot at 24 V:

3018 XY – Mixed Fast – 24V – 100mm-min 1A-div

The current waveform looks good at 12 V:

3018 XY – Mixed Fast – 12V – 100mm-min 1A-div

The back EMF at 1000 mm/min nearly eliminates the overshoot at 24 V, with fast decay in the Y axis causing some PWM ripple:

3018 XY – Mixed Fast – 24V – 1000mm-min 1A-div

Both decay modes look good at 12 V:

3018 XY – Mixed Fast – 12V – 1000mm-min 1A-div

At 1500 mm/min, the highest reasonable speed for the thing, and a 24 V supply, both waveforms still look good:

3018 XY – Mixed Fast – 24V – 1500mm-min 1A-div

However, the back EMF is now high enough to buck the 12 V supply, preventing the current from decreasing fast enough in mixed decay mode (top trace):

3018 XY – Mixed Fast – 12V – 1500mm-min 1A-div

Tweaking the GRBL config to allow 2000 mm/min feeds shows the waveforms starting to become triangular, even at 24 V:

3018 XY – Mixed Fast – 24V – 2000mm-min 1A-div

And a 12 V supply opposed by the back EMF simply can’t change the current fast enough to keep up with the DRV8825 microstep current levels:

3018 XY – Mixed Fast – 12V – 2000mm-min 1A-div

Bottom line: a +12 V motor supply and DRV8825 drivers modified to run in fast decay mode look like the best setup for the 3018-Pro: good current control at low speeds with enough moxie to handle higher speeds.

I should hack the DRV8825 boards into 1:8 microstep mode to reduce the IRQ rate by a factor of four, then see what happens to the back EMF at absurd speeds.
2019-08-26