Software – Page 62 – The Smell of Molten Projects in the Morning

MPCNC: GCMC Text vs. Speed

GCMC includes single-stroke fonts derived from Hershey fonts, so I added a legend to the Spirograph Shakedown generator:

MPCNC - GCMC Text - 3000 mm-min — MPCNC – GCMC Text – 3000 mm-min

Obviously, plotting 2.5 mm tall characters at 3000 mm/min = 50 mm/s isn’t a Good Idea on a less-than-absolutely-rigid CNC machine.

Slowing down to 250 mm/min = 4.2 mm/s produces much better results:

MPCNC - GCMC Text - 250 mm-min — MPCNC – GCMC Text – 250 mm-min

A closer look, albeit with less-than-crisp focus:

MPCNC - GCMC Text - 250 mm-min - detail — MPCNC – GCMC Text – 250 mm-min – detail

This isn’t a conclusive test, but it reminds me that Speed Kills.

The green plotter pen started life with a standard 0.3 mm felt nib, but it’s worn somewhat wider over the intervening ~~years~~ decades. Those 2.5 mm characters would look better coming from a narrow ceramic pen, which would require a pen change before doing the legend; using 4 mm characters would produce better results.

The line spacing is 110% of the font X height, which obviously isn’t quite enough. Something on the order of 150% should look better.

This GCMC code (including those mods) produces the legend:

feedrate(250mm);

textsize = [4.0mm,4.0mm];
textat = [0.5*PlotSize.x/2,-PlotSize.y/2 + 2*textsize.y];

textpath = typeset("Seed: " + PRNG_Seed + "  Stator: " + StatorTeeth + "  Rotor: " + RotorTeeth,FONT_HSANS_1);
scalepath = scale(textpath,textsize);
placepath = scalepath + textat;
engrave(placepath,1.0mm,-1.0mm);

textpath = typeset("Offset: " + L + "  Lobes: " + Lobes + "  Turns: " + Turns,FONT_HSANS_1);
scalepath = scale(textpath,textsize);
placepath = scalepath + textat + [-,-1.5*textsize.y];
engrave(placepath,1.0mm,-1.0mm);

2017-12-20

MPCNC: Spirograph Exerciser

Both bCNC and GCMC include Spirograph generators with more-or-less fixed patterns and sizes, because the code serves to illustrate the software’s capabilities:

MPCNC - bCNC Spirograph patterns — MPCNC – bCNC Spirograph patterns

I wanted to exercise my MPCNC’s entire range of travel, familiarize myself with some new GCMC features, and, en passant, mimic the actual gears in a classic Spirograph, so, of course, I had to write a Spirograph emulator from scratch:

MPCNC - Full-platform Spirograph - multicolor — MPCNC – Full-platform Spirograph – multicolor

The perspective makes a 29×19 inch sheet of paper (made from three B sheets and one A sheet) look not much larger than the 17×11 inch B size sheets in the first two pictures. IRL, it’s a billboard!

My GCMC code uses notation and formulas from a paper (tidy PDF) on a Gnuplot spirograph generator, with a dash of error checking from the GCMC source.

The code enumerates the possible gear tooth counts in a pair of vectors from which you select the desired stator and rotor gears using integer subscripts. Because I eventually scale the results to fit the plot area, there’s no need to keep track of actual gear pitch diameters.

Similarly, the pen offset from the center of the rotor gear is a pure number, which you can think of as the ratio of the offset to the rotor diameter. It can have either sign and may exceed unity, as needed, either of which would be difficult with a physical gear.

Figuring the number of rotor turns required to complete the pattern requires reducing the gear ratio to a fraction with no common factors, so I wrote a Greatest Common Divisor function using Euclid’s algorithm adapted for GCMC’s bitwise tests and shifts.

With those values in hand, a loop iterates around the entire pattern to produce a list of XY coordinates in normalized space. Because the formula doesn’t have the weird properties of the Superformula I used with the HP 7475 plotter, I think there’s no need to prune the list to eliminate tiny moves.

Scaling the entire plot requires keeping track of the actual extents along both axes, which happens in the loop generating the normalized coordinates. A pair of gears producing an odd number of lobes can have different extents in the positive and negative directions, particularly with only a few lobes (3, 5, 7 …):

Spirograph - 3 lobes - QnD Simulator — Spirograph – 3 lobes – QnD Simulator

So I accumulate all four, then scale based on the absolute maximum; I added scalar min() and max() functions.

Converting the list of scaled points into G-Code turns out to be a one-liner using GCMC’s tracepath() library function. Previewing the results in a Web-based simulator helps weed out the duds.

The code needs cleanup, in particular to let a Bash script set various parameters, but it’s a good start.

The GCMC source code as a GitHub Gist:

	// Spirograph simulator for MPCNC plotter
	// Ed Nisley KE4ZNU – 2017-12
	// Spirograph equations:
	// https://en.wikipedia.org/wiki/Spirograph
	// Loosely based on GCMC cycloids.gcmc demo:
	// https://gitlab.com/gcmc/gcmc/tree/master/example/cycloids.gcmc

	include("tracepath.inc.gcmc");

	//—–
	// Greatest Common Divisor
	// https://en.wikipedia.org/wiki/Greatest_common_divisor#Using_Euclid's_algorithm
	// Inputs = integers without units

	function gcd(a,b) {
	local d=0;

	// message("gcd(" + a + "," + b + ") = ");

	if (!isnone(a) \|\| isfloat(a) \|\| !isnone(b) \|\| isfloat(b)) {
	warning("Values must be dimensionless integers");
	}

	while (!((a \| b) & 1)) { // remove and tally common factors of two
	a >>= 1;
	b >>= 1;
	d++;
	}

	while (a != b) {
	if (!(a & 1)) {a >>=1;} // discard non-common factor of 2
	elif (!(b & 1)) {b >>= 1;} // … likewise
	elif (a > b) {a = (a – b) >> 1;} // gcd(a,b) also divides a-b
	else {b = (b – a) >> 1;} // … likewise
	}

	g = a*(1 << d); // form gcd
	// message(" " + g);
	return g;

	}

	//—–
	// Max and min functions

	function max(x,y) {
	return (x > y) ? x : y;
	}

	function min(x,y) {
	return (x < y) ? x : y;
	}
	//—–
	// Spirograph tooth counts mooched from:
	// http://nathanfriend.io/inspirograph/

	Stators = [96, 105, 144, 150];
	Rotors = [24, 30, 32, 36, 40, 45, 48, 50, 52, 56, 60, 63, 64, 72, 75, 80, 84];

	//—–
	// Set up gearing

	s = 1; // index values should be randomized
	r = 6;

	StatorTeeth = Stators[s]; // from the universe of possible teeth
	RotorTeeth = Rotors[r];

	message("Stator: ", StatorTeeth);
	message("Rotor: ", RotorTeeth);

	L = 0.90; // normalized pen offset in rotor

	message("Pen offset: ", L);

	g = gcd(StatorTeeth,RotorTeeth); // reduce teeth to ratio of least integers
	StatorN = StatorTeeth / g;
	RotorM = RotorTeeth / g;

	K = to_float(RotorM) / to_float(StatorN); // normalized rotor dia

	Lobes = StatorN; // having removed all common factors
	Turns = RotorM;

	message("Lobes: ", Lobes);
	message("Turns: ", Turns);

	AngleStep = 2.0deg;

	//—–
	// Crank out a list of points in normalized coordinates

	Path = {};
	Xmax = 0.0;
	Xmin = 0.0;
	Ymax = 0.0;
	Ymin = 0.0;

	for (a=0.0deg ; a <= Turns*360deg ; a += AngleStep) {
	x = (1 – K)cos(a) + LKcos(a(1 – K)/K);
	if (x > Xmax) {Xmax = x;}
	elif (x < Xmin) {Xmin = x;}

	y = (1 – K)sin(a) – LKsin(a(1 – K)/K);
	if (y > Ymax) {Ymax = y;}
	elif (y < Ymin) {Ymin = y;}

	Path += {[x,y]};
	}

	message("Max X: ", Xmax, " Y: ", Ymax);
	message("Min X: ", Xmin, " Y: ", Ymin); // min will always be negative

	Xmax = max(Xmax,-Xmin); // odd lobes can cause min != max
	Ymax = max(Ymax,-Ymin); // … need really truly absolute maximum

	//—–
	// Scale points to actual plot size

	TableSize = [25in,18in]; // largest possible plot area

	PaperSize = 0 ? [17.0in,11.0in] : TableSize;
	Margins = [0.5in,0.5in] * 2;

	Boundary = PaperSize – Margins;
	message("Boundary: ",Boundary);

	PlotScale = [Boundary.x / (2Xmax), Boundary.y / (2Ymax)];
	message("Plot scale: ", PlotScale);

	Points = scale(Path,PlotScale); // fill page, origin at center

	//—–
	// Produce G-Code

	feedrate(6000.0mm);

	safe_z = [-,-,25.0mm];
	plotz = -1.0mm;

	goto([0,0,10.0mm]);
	tracepath(Points, plotz);

	goto(safe_z);

view raw Spirograph Shakedown.gcmc hosted with ❤ by GitHub

2017-12-19

MPCNC: GCMC Spirograph Shakedown

The MPCNC instructions recommend running it for a while, taking it apart, then putting it back together, so all the parts have a chance to relax and get used to working together. To that end, I figured doing some full platform plots would run the rollers over the entire length of the rails:

MPCNC - Full-platform Spirograph - first pass — MPCNC – Full-platform Spirograph – first pass

I taped three B-size sheets together, with an A-size sheet in the far right corner, into a 29×19 inch sheet to put borders around the MPCNC’s 28×18 inch work area. The tape is on the top surface to prevent embarrassing accidents where the pen snags on an edge, at the cost of blurry lines where the ink doesn’t stick quite right.

The far left corner of the paper washes up on the tool length probe’s base, but the pen position turns out to be so repeatable (it should be!) you can swap them with gleeful abandon and get good results:

The pen rumbles along at 12000 mm/min = 200 mm/s = 7.8 inch/s with no hint of wobblulation. Most likely, those big loops aren’t particularly challenging, although watching the big central assembly whip around a tight curve can be startling.

I modified the pen holder for 3-point support, as the recess for the pen flange isn’t quite deep enough:

MPCNC - Pen holder - 3 point grip — MPCNC – Pen holder – 3 point grip

Good old masking tape holds the pens securely enough for now.

The glass plate I’d been using for B-size plots doesn’t cover the full area, but I’d set the Z axis limit switch to trip just before the bottom of the rails whacked into the glass. Extending the travel by 5 mm required a snippet of black tape:

MPCNC - Z axis switch - table limit — MPCNC – Z axis switch – table limit

The patterns come from a scratch-built Spirograph generator, because I wanted to review what’s new in GCMC. More on the software tomorrow …

2017-12-18

MPCNC: GCMC Configuration

The default GCMC prolog(ue) spits out some G-Codes that GRBL doesn’t accept, requiring tweaks to the incantation.

A first pass at a useful prolog, minus the offending codes:

cat ~/.config/gcmc/prolog.gcmc 
(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)

Including any of the usual “end of program” M-Codes in the epilog(ue) causes GRBL to pause before exiting the program, so leave only a placeholder:

cat ~/.config/gcmc/epilog.gcmc 
(epilog begins)
(M2) (allow program to continue)
(epilog ends)

Having done a git clone into /opt/gcmc before building the program, the GCMC library routines live in:
/opt/gcmc/library

Limiting numeric values to two decimal places makes sense:
-P 2

With all that in hand, unleashing the compiler on an unsuspecting source file requires this jawbreaker:

gcmc -P 2 -I /opt/gcmc/library \
-G ~/.config/gcmc/prolog.gcmc \
-g ~/.config/gcmc/epilog.gcmc \
-o cycloids.ngc \
cycloids.gcmc

One might, of course, tuck all that into a little script, rather than depend on extracting it from the bash history as needed.

The resulting G-Code file looks about right:

head cycloids.ngc
(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)
F2500.00
[pi@MPCNC tmp]$ head -25 cycloids.ngc
(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)
F2500.00
G0 Z1.00
(-- tracepath at Z=-1.00mm --)
G0 X-145.50 Y-30.00
G1 Z-1.00
G1 X-145.51 Y-29.93

... vast snippage ...

G1 X175.50 Y30.00
G1 Z1.00
G0 Z25.00
(epilog begins)
(M2)
(epilog ends)

Then it’s just a matter of tweaking cycloids.gcmc to make interesting things happen:

2017-12-14

MPCNC: Re-Improved Endstop Switch Mount

As part of entombing the endstop PCBs in epoxy, I tweaked the switch mounts to (optionally) eliminate the screw holes and (definitely) rationalize the spacings:

MPCNC MB Endstop Mount - No screws — MPCNC MB Endstop Mount – No screws

The sectioned view shows the cable tie slot neatly centered between the bottom of the switch terminal pit and the EMT rail, now with plenty of meat above the cable tie latch recess. The guide ramp on the other side has a more-better position & angle, too.

A trial fit before dabbing on the epoxy:

MPCNC - Endstop Mount for epoxy coating - trial fit — MPCNC – Endstop Mount for epoxy coating – trial fit

The 3M black foam tape works wonderfully well!

After the epoxy cures, it’s all good:

MPCNC - Epoxy-coated Endstop - Installed — MPCNC – Epoxy-coated Endstop – Installed

The OpenSCAD source code as a GitHub Gist:

	// MPCNC Endstop Mount for Makerbot PCB on EMT tubing
	// Ed Nisley KE4ZNU – 2017-12-04

	/* [Build Options] */

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

	Holes = false; // holes for switch screws

	Section = true; // show internal details

	/* [Extrusion] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40]

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

	/* [Hidden] */

	Protrusion = 0.01; // [0.01, 0.1]

	HoleWindage = 0.2;

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

	/* [Sizes] */

	RailOD = 23.5; // actual rail OD

	SwitchHeight = 8.0; // switch PCB distance from rail OD

	Strap = [5.5,50,2.0]; // nylon strap securing block to rail
	StrapHead = [8.2,3.0,5.5]; // recess for strap ratchet head

	Screw = [2.0,3.6,7.0]; // thread dia, head OD, screw length

	HoleOffset = [2.5,19.0/2]; // PCB mounting holes from PCB edge, rail center

	SwitchClear = [6.0,15,3.0]; // clearance around switch pins
	SwitchOffset = [6.0,0]; // XY center of switch from holes

	StrapHeight = (SwitchHeight – SwitchClear[2])/2; // strap center from rail

	Block = [16.4,26.0,RailOD/2 + SwitchHeight]; // basic block shape

	//- Adjust hole diameter to make the size come out right

	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);
	}

	//- Shapes

	// Main block constructed centered on XY with Z=0 at top of rail

	module PCBBlock() {
	difference() {
	translate([-Block[0]/2,-Block[1]/2,-RailOD/2])
	cube(Block,center=false);

	translate([(SwitchOffset[0] + HoleOffset[0] – Block[0]/2),
	SwitchOffset[1],
	(SwitchHeight – SwitchClear[2]/2 + Protrusion/2)])
	cube(SwitchClear + [0,0,Protrusion],center=true);

	if (Holes)
	for (j=[-1,1])
	translate([HoleOffset[0] – Block[0]/2,j*HoleOffset[1],(Block[2]/2 – Screw[LENGTH])])
	rotate(180/6)
	if (true) // true = loose fit
	PolyCyl(Screw[ID],Screw[LENGTH] + Protrusion,6);
	else
	cylinder(d=Screw[ID],h=Screw[LENGTH] + Protrusion,$fn=6);

	translate([0,0,StrapHeight])
	cube(Strap,center=true);

	translate([0, // strap head recess
	(Block[1]/2 – StrapHead[1]/2 + Protrusion),
	StrapHeight – Strap[2]/2 + StrapHead[2]/2])
	cube(StrapHead + [0,Protrusion,0],center=true);

	StrapAngle = atan((StrapHeight + RailOD/4)/Strap[2]); // a reasonable angle
	echo(str("Strap Angle: ",StrapAngle));
	translate([0,-(Block[1]/2 – Strap[2]/(2*sin(StrapAngle))),StrapHeight])
	rotate([StrapAngle,0,0])
	translate([0,-Strap[1]/2,0])
	cube(Strap,center=true);

	if (Section)
	translate([Block[0]/2,0,0])
	cube(Block + [0,2Protrusion,2Block[2]],center=true);
	}
	}

	module Mount() {

	difference() {
	translate([0,0,RailOD/2])
	PCBBlock();
	rotate([0,90,0])
	cylinder(d=RailOD,h=3*Block[0],center=true);
	}

	}

	//- Build things

	if (Layout == "Show") {
	Mount();
	color("Yellow",0.5)
	rotate([0,90,0])
	cylinder(d=RailOD,h=3*Block[0],center=true);
	}

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

	if (Layout == "Build")
	translate([0,0,Block[2]])
	rotate([180,0,0])
	Mount();

view raw MPCNC MB Endstop Mount.scad hosted with ❤ by GitHub

2017-12-07

MPCNC: Endstop Mount, Now With Recess

There being nothing like a new problem to take your mind off all your old problems, now there’s a cable tie latch recess:

X min endstop - recessed cable tie latch — X min endstop – recessed cable tie latch

A sectioned view of the model shows the layout:

MPCNC MB Endstop Mount - latch recess — MPCNC MB Endstop Mount – latch recess

On the other side, a ramp helps bend the tie toward the MPCNC rail:

X min endstop - recessed strap — X min endstop – recessed strap

Which looks thusly in the realm of applied mathematics:

MPCNC MB Endstop Mount - strap recess — MPCNC MB Endstop Mount – strap recess

I’ll leave the OpenSCAD code to your imagination, because the endstop block turns out to be a bit small for the recesses. Eventually, they need a dust cover and some cleanup.

So, there!

2017-11-27

USPS Package Tracking: Huh?

This story unfolded over the course of three weeks:

After the package visited Poughkeepsie for the second time, I contacted the local delivery manager. He was absolute baffled as to what was going on, but promised to intercept it and give me a call when it returned.

When I called on 22 November, I got somebody else who was also completely baffled. However, she could view a scan of the package and noticed an odd mismatch:

The package tracking info showed my name and street address
The tracking info had my email address
The package label had somebody else’s name & address in Rensselaer

As best as I can follow the explanation, automated routing machinery at each facility scans each incoming package and shunts it to a conveyor belt filling a bin, thence to a truck, and away toward wherever it’s going. Alas, the (bogus) tracking info associated with this particular package aimed it toward me in Poughkeepise, but, when it arrived, a human read the actual label and tossed it in the bin headed toward Rensselaer.

Upon arriving in Renselaer, the automation fired it back toward Poughkeepsie.

Lather, rinse, repeat.

I buy plenty of “made in China” things, many shipped with tracking numbers, and tracking generally works the way you’d expect. Sometimes, however, the shipper does not tell me the tracking number and the first I learn of it is when tracking emails begin arriving from USPS. In other cases, no USPS facility along the way scans the package, whereupon the first notification I get happens when I open my mailbox and see the package.

In this case, I hadn’t bought anything close to the time when it would have been shipped and the tracking number didn’t correspond to any of my orders.

If this were an isolated incident, I’d shrug it off, but over the last year or two this is the third or fourth time this has happened, with packages from different Chinese sellers and another shipped from Arizona to Tennessee.

There was also a certified mail piece addressed to somebody at a nearby (easily typo-ed) address, delivered to our mailbox, but tracked as “handed to resident”. Whoops, indeed.

In all those cases, I got the tracking information from USPS, but the packages went directly to their destination. The extensive looping for this package was definitely a New Thing.

Nobody can explain how I (and my address!) get associated with these packages:

It’s obviously not a problem at the source, as I have no idea who the sellers / shippers are
To the best of my knowledge, they don’t know me, because their addresses aren’t familiar
The notices come directly from the USPS, so they’re associating me with a random package
It’s not a fault on my end, because I haven’t bought the items and don’t know they’re coming

Definitely a puzzlement …

2017-11-26