Improvements – Page 125 – The Smell of Molten Projects in the Morning

MPCNC: Tool Length Probe Station

Having a tool length probe station on the Sherline, I had to build one for the MPCNC:

MPCNC Tool Length Probe - plotter pen — MPCNC Tool Length Probe – plotter pen

It’s little more than a flange atop a wide base:

MPCNC Tool Length Probe - Slic3r preview — MPCNC Tool Length Probe – Slic3r preview

The flange offset puts the switch actuator on the midline of the base, not that that matters, and the base features rounded corners and a suitable legend, because I can.

I clipped the PCB’s through-hold leads nearly flush and stuck it to the flange with 3M permanent foam tape, which seems to work much better than screws & inserts for simple things that need never come apart.

The Protoneer CNC Shield includes a Probe input on the GRBL-compliant A5, although it took me a while to find the legend on the SCL pin in the I2C header. I moved the endstop power jumper to another header, then conjured a quick-and-dirty connector:

Protoneer CNC Shield - Tool Probe Wiring — Protoneer CNC Shield – Tool Probe Wiring

When I embed the endstop switch PCB in epoxy, I’ll add a drop to the connector while engaging in Magical Thinking. The whole Arduino + CNC Shield must go into an enclosure after I finish measuring the motor currents.

To forestall discussions about switch repeatability and accuracy, suffice it to say the MPCNC doesn’t claim to be much more than a woodworking router, so those switches seem Good Enough.

The OpenSCAD source code as a GitHub Gist:

	// MPCNC Tool Length Probe Station
	// Ed Nisley KE4ZNU – 2017-12-08

	/* [Extrusion] */

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

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

	/* [Hidden] */

	Protrusion = 0.1; // [0.01, 0.1]

	HoleWindage = 0.2;

	/* [Sizes] */

	EndstopPCB = [40.0,16.5,1.6]; // endstop PCB
	ComponentHeight = 6.0; // max component height above PCB

	SwitchOffset = [35.0,21.0,4.75]; // touch point center from lower left PCB corner
	SwitchTravel = 2.5; // first touch to switch actuation

	TapeThick = 1.0; // foam mounting tape

	WallThick = 4.0; // basic wall & floor thickness

	BaseRadius = 5.0;

	Base = [IntegerMultiple(EndstopPCB[0] + 2*BaseRadius,20),
	IntegerMultiple(EndstopPCB[2] + TapeThick + WallThick + 2BaseRadius,225),
	2.0];

	NumSides = 8*4;

	TextDepth = 2*ThreadThick;

	//- Build it

	union() {
	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(Base[0]/2 – BaseRadius),j(Base[1]/2 – BaseRadius),0])
	resize([0,0,Base[2]])
	intersection() {
	cylinder(r=BaseRadius,h=BaseRadius,$fn=NumSides);
	sphere(r=BaseRadius,$fn=NumSides);
	}
	translate([0,0,Base[2] – TextDepth])
	linear_extrude(height=TextDepth + Protrusion) {
	translate([0,-10,0])
	text(text="MPCNC",size=8,spacing=1.05,font="Arial:style=Bold",halign="center");
	translate([0,-18,0])
	text(text="Tool Probe",size=6,spacing=1.05,font="Arial:style=Regular",halign="center");
	}

	}
	translate([0,
	WallThick/2 + TapeThick + SwitchOffset[2],
	(EndstopPCB[1] – Protrusion)/2 + Base[2]])
	cube([EndstopPCB[0],WallThick,EndstopPCB[1] + Protrusion],center=true);

	}

view raw Tool Length Probe Station.scad hosted with ❤ by GitHub

The original doodles show a severely over-complexicated solution desperately searching for an actual problem:

MPCNC Tool Length Probe - doodles — MPCNC Tool Length Probe – doodles

Putting a large flat pan at the end of a relatively long lever arm, with the pivot arranged to put the pan level at the switch actuation point, made sense at the time. Give the relatively small tools I expect to use, directly ramming them into the switch lever should work just as well.

Putting all that complexity in harm’s way seemed like a Bad Idea when I sat down and looked at it in cold blood.

2017-12-13

Epson R380 Continuous Ink Supply Tubes

After fixing the yellow ink tube, the Epson R380 printer occasionally gave off a horrible clunk as the tubes slapped around inside the frame. This routing seems much quieter and, as you can see from the marks on the tubes, leaves much less free to flop around:

Epson R380 Printer - CISS tube routing — Epson R380 Printer – CISS tube routing

I cut a small collar (to the left of the white block with the red cable tie) to guide the tubing up over the edge of the ink cartridge holder, with a ramp from the upper edge and raised edges to hold the tubes in place, from a block of black closed-cell foam. It seems perfectly happy to do its job without anything other than the tubes holding it in place atop the cartridges.

There’s also a block of foam filling a gap under the printer’s top frame member (along the far left edge of the picture) to cushion the tubes as they whack against the edge.

So far, so good.

I’ve dumped a few more tanks of waste ink down the drain. When this printer eventually gives up, I’ll get a color laser and move on.

2017-12-10

MPCNC: Z Axis Upward Homing with Opto Proximity Sensor

Homing the MPCNC’s Z axis at the bottom end of its travel made no sense, but the Z stage lacks a convenient spot to mount / trigger a switch at the top of its travel, so this sufficed for initial tests & fiddling:

MPCNC - Z min endstop — MPCNC – Z min endstop

The EMT rail carrying the switch moves downward, tripping the lever when it hits the MPCNC’s central assembly.

Somewhat to my surprise, a TRCT5000-based optical proximity sensor (harvested from the Kenmore 158 Crash Test Dummy’s corpse) and a strip of black electrical tape work perfectly:

MPCNC - Z Axis Opto Proximity Endstop — MPCNC – Z Axis Opto Proximity Endstop

The PCB wears a shiny new epoxy coat:

MPCNC - Epoxy-coated Endstop - Opto Prox Sensor — MPCNC – Epoxy-coated Endstop – Opto Prox Sensor

I soldered the wires (harvested from the previous endstop) directly to the PCB, because the pinout isn’t the same and fewer connectors should be better.

The mount uses black PETG, rather than translucent orange, in hope of IR opacity, and wraps around the EMT rail at (roughly) the 2 mm standoff producing the peak response:

IR Reflective Sensor module - TCRT5000 - response vs distance — IR Reflective Sensor module – TCRT5000 – response vs distance

In truth, I set the gap by eyeballometric guesstimation to make the entire mount arc sit equidistant from the EMT:

MPCNC - Z Opto Prox Endstop - top view — MPCNC – Z Opto Prox Endstop – top view

The mount includes the 2 mm spacing around the EMT OD and puts the sensor tip flush with the arc OD, so it should be pretty close:

TCRT5000 Z Axis Endstop Mount - solid model — TCRT5000 Z Axis Endstop Mount – solid model

A strip of 3M permanent tape, cut to clear the 608 bearings, affixes the mount to the MPCNC’s central assembly. The solid model now includes a midline reference notch, with a height rounded up to the next-highest multiple of 2.0 mm. It needs a loop to anchor the cable.

The blue twiddlepot sets the comparator threshold midway between the response over black tape (incorrectly on = too low) and bare EMT (incorrectly off = too high), in the hope of noise immunity. The range spanned nearly half of the pot rotation, so I think it’s all good.

The sensor doesn’t trip when the edge of the tape exactly meets its midline, which meant I had to trim a strip of tape to suit. As part of setting the twiddlepot, I shut off the Z axis motor and laid some test strips on the EMT:

MPCNC - Z Axis Opto Prox Endstop - Test Tape — MPCNC – Z Axis Opto Prox Endstop – Test Tape

I spun the leadscrew with one hand, held the sensor with the other, twiddled the trimpot, trimmed the upper and lower ends of the tape, and generally had a fine time. The sensor responds equally well to a half-wide strip of tape (in the upper picture), with the distinct advantage of not encroaching on the 608 bearing tracks.

The GRBL setup now homes Y and Z toward the positive end of their travel, with X still toward the negative end while a set of extension cables remains in transit around the planet.

The OpenSCAD source code as a GitHub Gist:

	// TCRT5000 Z Axis Endstop Mount
	// Ed Nisley KE4ZNU – 2017-12-04

	/* [Build Options] */

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

	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

	OptoPCB = [32.5,14.2,1.6]; // prox sensor PCB
	ComponentHeight = 5.0; // max component height above PCB

	OptoSensor = [5.8,10.2,10.5]; // sensor head below PCB
	OptoOffset = 3.0; // sensor head center from PCB edge
	OptoRange = 2.0; // sensor to rail distance

	TapeThick = 1.0; // foam mounting tape

	WallThick = 4.0; // basic wall thickness

	Block = [WallThick + OptoRange + RailOD/2 + (OptoPCB[0] – OptoOffset),
	RailOD/2 + OptoRange + OptoSensor[2] – TapeThick,
	IntegerMultiple(OptoPCB[1] + 2*WallThick,2.0)]; // basic block shape

	echo(str("Block: ",Block));

	NumSides = 6*4;

	//- 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 with PCB along X, opto sensor at Y=0

	module PCBBlock() {
	difference() {
	translate([-(WallThick + OptoRange + RailOD/2),
	(-Block[1] + RailOD/2 + OptoRange),
	-Block[2]/2])
	cube(Block,center=false);
	for (i=[-(RailOD/2 + OptoRange + WallThick),
	(OptoPCB[0] – OptoOffset)])
	translate([i,0,0])
	rotate([90,0,0]) rotate(45)
	cube([2ThreadWidth,2ThreadWidth,2*Block[2]],center=true);
	translate([0,(RailOD/2 + OptoRange),0])
	cylinder(d=(RailOD + 2*OptoRange),
	h=(Block[2] + 2*Protrusion),
	$fn=NumSides,center=true);
	rotate([90,0,0])
	cube(OptoSensor + [0,0,Block[1]],center=true);
	}
	}

	//- Build things

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

	if (Layout == "Show") {
	translate([0,-(RailOD/2 + OptoRange),0])
	PCBBlock();
	color("Yellow",0.5)
	cylinder(d=RailOD,h=2*Block[2],$fn=NumSides,center=true);
	}

	if (Layout == "Build")
	translate([0,0,OptoSensor[2] – TapeThick])
	rotate([90,0,0])
	PCBBlock();

view raw TCRT5000 Z Axis Endstop Mount.scad hosted with ❤ by GitHub

The original doodles, including a bunch of ideas left on the cutting room floor:

MPCNC Z Opto Proximity Sensor Endstop - doodles — MPCNC Z Opto Proximity Sensor Endstop – doodles

2017-12-08

MPCNC: Epoxy-Coated Endstop Switches

Using 3D printer style endstop switches has the advantage of putting low-pass filters (i.e. caps) at the switches, plus adding LED blinkiness, but it does leave the +5 V and Gnd conductors hanging out in the breeze. After mulling over various enclosures, it occured to me I could just entomb the things in epoxy and be done with it.

The first step was to get rid of the PCB mounting screws and use 3M permanent foam tape:

MPCNC - Epoxy-coated Endstop - Adhesive Tape — MPCNC – Epoxy-coated Endstop – Adhesive Tape

Get all the switches set up and level, mix up 2.8 g of XTC-3D (because I have way too much), and dab it on the switches until all the exposed conductors have at least a thin coat:

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

You should use a bit more care than I: the epoxy can creep around the corner of the switch and immobilize the actuator in its relaxed position. Some deft X-Acto knife work solved the problem, but only after firmly smashing the X axis against the nonfunctional switch.

Epoxy isn’t a particularly good encapsulant, because it cures hard and tends to crack components off the board during temperature extremes. These boards live in the basement, cost under a buck, and I have plenty of spares, so let’s see what happens.

At least it’s now somewhat more difficult to apply a dead short across the Arduino’s power supply, which comes directly from a Raspberry Pi’s USB port.

2017-12-06

MPCNC: Stepper Motor Power Control

GRBL responds to critical errors by disabling its outputs, which seems like a useful feature for a big-enough-to-hurt CNC machine like the MPCNC. Unlike the RAMPS 1.4 board, there’s no dedicated power-control pin, so I connected the Coolant output to the same DC-DC SSR I tried out with the RAMPS board:

MPCNC - CNC Shield - Power SSR — MPCNC – CNC Shield – Power SSR

With homing enabled, GRBL emerges from power-on resets and error conditions with the spindle and coolant turned off and the G-Code interpreter in a locked state requiring manual intervention, so turning the stepper power on fits right in:

$x – Unlock the controls
m8 – Coolant output on = enable stepper power
$h – Home all axes

The steppers go clunk as the power supply turns on, providing an audible confirmation. The dim red LED on the SSR isn’t particularly conspicuous.

Turning the stepper power off:

m9 – Coolant output off = disable stepper power

I think the A4988 drivers maintain their microstep position with the stepper power supply off, because their logic power remains on. In any event, you probably wouldn’t want to restart after an emergency stop without clearing the fault and re-homing the axes.

The board has Cycle Start, Feed Hold, and Abort inputs just crying out for big colorful pushbutton switches.

Unlike the RAMPS board, the Prontoneer CNC Shield does not feed stepper power to the underlying Arduino UNO, leaving it safely powered by USB or the coax jack.

2017-12-04

MPCNC: Z Axis Coupler Backlash Prevention

The MPCNC has the entire weight of the Z axis motor and stage resting on the leadscrew, so the instructions call for preloading the spring coupler by stretching it with the leadscrew butted against the motor shaft. The leadscrew end isn’t particularly flat, so I inserted a 1/4 inch ball bearing between the two before the stretch:

MPCNC - Z Axis leadscrew - coupler bearing — MPCNC – Z Axis leadscrew – coupler bearing

I’m reasonably sure the ball won’t make the slightest difference, but two slightly misaligned shafts can now pivot on a point, rather than grind against each other. There’s no evidence of misalignment; I feel better and that’s what counts.

2017-12-03

MPCNC: Belt Tensioners

The GT2 / GT3 belt specs call for 10-ish pounds of tension, but I don’t yet have a good feel for the actual MPCNC belt tension … and it’s hard to measure in-situ. So I picked up some spring tensioners and yanked one with a luggage scale:

GT2 Belt Tensioner - 4 kg — GT2 Belt Tensioner – 4 kg

You’re looking at 4 kg = 8-ish pounds of tension. When they’re relaxed, the arms sit at roughly right angles.

I installed them on the far end of the belts, although that’s a bit snug under the roller:

GT2 Belt Tensioner - installed — GT2 Belt Tensioner – installed

An endstop switch will eventually add some clearance and it’ll be all good.

Even though they’re neither linear nor precisely calibrated, they’ll serve as a reminder to check the tension every now and again.

Install them with the same casual disregard you reserve for fish hooks and you’ll emerge unscathed.

2017-12-02