MPCNC: Autolevel Probe, Endstop Edition

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();
}