Improvements – Page 94 – The Smell of Molten Projects in the Morning

CNC 3018-Pro: Table Riser

With the 3018-Pro used for drag engraving on CDs and hard drive platters, there’s no need for all the clearance below the Z-axis carriage required for the OEM motor and ER11 collet chuck. A chunk of laminate countertop and a hunk of Celotex foam insulation produce a nicely flat surface 47 mm above the platform:

It’s surprisingly flat:

Table Flatness Measurement - 2019-08-30 — Table Flatness Measurement – 2019-08-30

Those are millimeters of clearance between the gray plastic clamp around the diamond drag tool holder (about which, more later) and my trusty bench block, measured at 50 mm intervals across the platform. The lower figures appeared after tightening the upper-left screw by a little over 1/6 turn = 0.2 mm, making the entire platform flat & aligned within ±0.1 mm.

Yeah, not bad for a scrap countertop!

The four M6 socket head cap screws pass through the stack into T-nuts in the platform:

CNC 3018 Table Riser - screw clearance — CNC 3018 Table Riser – screw clearance

The countertop was thick enough to allow countersinking the screws slightly below the surface:

CNC 3018 Table Riser - screw countersink — CNC 3018 Table Riser – screw countersink

I transfer-punched the screw clearance hole locations into the Celotex and drilled it with an ordinary twist drill. It wasn’t pretty, but nobody will ever notice.

Two sheets, maybe 1 mm thick, of closed-cell foam below the Celotext provide enough squish to align the top surface without straining anything. The screws are firmly tight, so they shouldn’t work their way loose under minimal engraving loads.

Taping the CDs to the surface works well for now, although a simpler version of the fixture may be in order.

2019-09-04

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

Monthly Science: Weight

Another two months of dots for the record:

Weight Chart 2019-08 - Ed — Weight Chart 2019-08 – Ed

The eyeballometric slope continues at 1 lb/month.

I started low-key upper-body strength training in June with encouraging results: my biceps no longer require exotic instrumentation for detection and my abs may soon transition from “throw pillow” to “two-pack”.

This is, however, the season of bounteous garden harvests, including delicious corn-on-the-cob and summer squash …

2019-09-01

Rt 376: Clearcut From Red Oaks Mill to Maloney Rd

NYS DOT Region 8 Dutchess South recently did enough over-the-rail clearcutting to make Rt 376 bicycle-able from Red Oaks Mill to Maloney Rd!

To the best of our memories and judging from the tree stumps along the rail, it’s been a decade since DOT last clearcut that section; the Japanese Knotweed has definitely taken over since then.

Here’s what the Knotweed looked like in June, just north of Maloney Rd, after a trimming in May:

Rt 376 at Maloney - knotweed overgrowth - 2019-06-07 — Rt 376 at Maloney – knotweed overgrowth – 2019-06-07

Now, it’s not nearly so snug out there:

Rt 376 Clearcut - 20 - 2019-08-29 — Rt 376 Clearcut – 20 – 2019-08-29

Here’s a slide show starting with Dutchess North’s routine grass mowing in Red Oaks Mill and ending with Dutchess South’s clearcut just north of Maloney Rd:

The Wappinger Creek bridge seems to be a no man’s land between the two Residencies, but we can generally take the lane:

Rt 376 Clearcut - 03 - 2019-08-29 — Rt 376 Clearcut – 03 – 2019-08-29

We hope Dutchess South’s over-the-rail maintenance will become an annual event and prevent the brush from taking over again.

2019-08-31

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

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 — 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 — 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 — 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 — 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

Tag: Improvements

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