The New Hotness

When in doubt, use an endstop switch:

MPCNC - Endstop Z probe - USB camera — MPCNC – Endstop Z probe – USB camera

The USB camera lurks in the upper right.

Just after that picture, I clipped off the NC switch terminal so I can wire this endstop in parallel with the tool length probe. Epoxy coating to follow.

The DW660 collet grabs a length of 1/8 inch drill rod jammed into a hole positioned to put the switch actuator directly in line with the spindle axis when it trips the switch, so as to measure a known and useful location:

Z Axis Height Probe - MBI endstop - Slic3r — Z Axis Height Probe – MBI endstop – Slic3r

After mulling things over for a while, I fired up the Sherline, drilled a #54 hole in the actuator, and epoxied a 3/32 inch bearing ball in the hole:

MPCNC - Endstop Z probe - bearing — MPCNC – Endstop Z probe – bearing

A #54 drill hole is half the diameter of the ball and, with a bit of luck, enough of the ball will stick through into the epoxy on the underside for a good grip:

MPCNC - Endstop Z probe - bearing - detail — MPCNC – Endstop Z probe – bearing – detail

The general idea is to convert the stamped steel actuator into a single, albeit not particularly sharp, contact point that can glide over the platform / PCB / sheet-of-whatever to measure the surface. The actuator pivots as it depresses, so the ball must slide horizontally just a bit. I prefer a rod-in-tube probe poking a linear button switch, but those weren’t getting me anywhere.

If I were really cool, I’d use a ruby ball. Maybe silicon nitride?

The OpenSCAD source code as a GitHub Gist:

	// MPCNC Z Axis Height Probe – MBI endstop in router collet
	// Ed Nisley KE4ZNU – 2018-02-17

	Layout = "Build"; // Build, Show

	/* [Extrusion] */

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

	/* [Hidden] */

	Protrusion = 0.1; // [0.01, 0.1]

	HoleWindage = 0.2;

	inch = 25.4;

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

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

	//- 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);
	}

	PCB = [40.0,1.6,16.5]; // endstop PCB, switch downward, facing parts

	Touchpoint = [4.8,4.8,-4.5]; // contact point from PCB edges, solder side

	TapeThick = 1.0; // foam mounting tape

	ShankOD = 0.125 * inch; // rod into tool collet
	ShankInsert = 3*ShankOD; // … insertion into switch holder

	WallThick = 3.0; // basic wall & floor thickness

	Mount = [PCB.x,
	(WallThick + TapeThick + Touchpoint.y) + (ShankOD/2 + WallThick),
	PCB.z + ShankInsert
	];

	NumSides = 2*4;

	//—–
	// Define shapes

	module SwitchMount() {

	difference() {
	translate([PCB.x/2 – Touchpoint.x, // overall block
	Mount.y/2 – (ShankOD/2 + WallThick),
	(PCB.z + ShankInsert)/2])
	cube(Mount,center=true);

	translate([0,0,-Protrusion]) // collet shank hole
	PolyCyl(ShankOD,2*Mount.z,NumSides);

	translate([PCB.x/2 – Touchpoint.x, // PCB recess
	-Mount.y/2 + TapeThick + Touchpoint.y,
	PCB.z/2 – Protrusion/2])
	cube([Mount.x + 2*Protrusion,
	Mount.y,
	PCB.z + Protrusion
	]
	,center=true);
	}

	}

	//—–
	// Build it

	if (Layout == "Show")
	SwitchMount();

	if (Layout == "Build") {
	translate([0,0,Mount.z])
	rotate([180,0,-90])
	SwitchMount();
	}

view raw Z Axis Height Probe – MBI Endstop.scad hosted with ❤ by GitHub

The New Hotness

MPCNC: Autolevel Probe, Endstop Edition