The New Hotness

As part of coaching a student (and his father!) on their incredibly ambitious build-a-plotter-from-scratch project, I suggested ~~stealing~~ using HP’s grit-wheel paper drive, rather than fiddling with guide rods to move either the pen carrier or the entire paper platform. Dremel sanding drums seem about the right size and they had an 8 mm shaft harvested from a defunct printer, so a pair of mounts moves the project along:

NEMA17 and Bearing Mounts - Slic3r preview — NEMA17 and Bearing Mounts – Slic3r preview

The motor mount code is a hack job from my old NEMA17 mount and the code has a lot not to like. The bearing mount puts the bearing on the proper centerline using brute force copypasta and depends on friction to hold it in place. The two models should be integrated into the same file, the shaft centerline shouldn’t involve the printed thread width, and blah blah blah:

I had him turn the shaft adapter from an aluminum rod in the mini-lathe: he’s hooked.

The OpenSCAD source code as a GitHub Gist:

	// Ball bearing mount
	// Ed Nisley KE4ZNU 2017-10-09

	//– Extrusion parameters

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2; // enlarge hole dia by this amount

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

	Protrusion = 0.1; // make holes look good and joints intersect properly

	//– Useful sizes

	inch = 25.4;

	Tap10_32 = 0.159 * inch;
	Clear10_32 = 0.190 * inch;
	Head10_32 = 0.373 * inch;
	Head10_32Thick = 0.110 * inch;
	Nut10_32Dia = 0.433 * inch;
	Nut10_32Thick = 0.130 * inch;

	// Bearing sizes

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

	Bearing = [8.0,22.0,7.0];

	ShaftHeight = IntegerMultiple(25.2,ThreadWidth); // arbitrary or copied from motor mount

	WallThick = 3.0;

	//– Mount Sizes

	MountSize = Bearing[OD] + 2*WallThick;

	BaseThick = max(WallThick,ShaftHeight – MountSize/2); // baseplate

	StandBoltHead = IntegerMultiple(Head10_32,2); // bolt head rounded up
	StandBoltClear = 1.25 * StandBoltHead;

	StandBoltOC = IntegerMultiple(MountSize + StandBoltClear,2);

	StandLength = StandBoltOC + StandBoltClear;
	StandThick = StandBoltClear + WallThick;
	StandHeight = MountSize + BaseThick;

	Cutout = (StandLength – MountSize)/2;

	echo(str("Stand Base: ",StandLength," x ",StandThick," x ",BaseThick));
	echo(str("Stand Bolt OC: ",StandBoltOC));
	echo(str("Shaft Height:",ShaftHeight));

	//———————-
	// 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);
	}

	//———————-
	// Put it together

	module BearingMount() {

	difference() {
	translate([BaseThick/2,0,StandThick/2])
	cube([StandHeight,StandLength,StandThick],center=true);
	translate([0,0,-Protrusion])
	PolyCyl(Bearing[OD],(StandThick + 2*Protrusion));
	for (j=[-1,1]) // cutouts over bolts
	translate([-(StandHeight/2 – ShaftHeight + WallThick),
	j*(StandLength/2 – Cutout/2 + Protrusion/2),
	(WallThick + StandThick/2)])
	cube([StandHeight,
	Cutout + Protrusion,
	StandThick],center=true);
	for (j=[-1,1]) // stand bolt holes – base
	translate([(MountSize/2 – Protrusion),
	j*StandBoltOC/2,
	WallThick + StandBoltClear/2])
	rotate([0,90,0])
	rotate(180/6)
	PolyCyl(Clear10_32,BaseThick + 2*Protrusion,6);
	for (j=[-1,1]) // stand bolt holes – back
	translate([0,j*StandBoltOC/2,-Protrusion])
	rotate(180/6)
	PolyCyl(Clear10_32,StandThick + 2*Protrusion,6);
	translate([0,-(MountSize/2 – ThreadWidth/2),(StandThick – WallThick)/2 + WallThick])
	rotate([90,180,0])
	linear_extrude(ThreadWidth,convexity=10)
	text(text=str(ShaftHeight),size=6,spacing=1.20,font="Arial",halign="center",valign="center");

	}

	}

	//———————-
	// Build it

	BearingMount();

view raw Bearing Mount.scad hosted with ❤ by GitHub

	// NEMA 17 stepper mount
	// Ed Nisley KE4ZNU August 2011
	// Tweaked & thinned 2017-10-09

	//– Extrusion parameters

	ThreadThick = 0.25;
	ThreadWidth = 0.4;

	HoleWindage = 0.3; // enlarge hole dia by this amount

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

	Protrusion = 0.1; // make holes look good and joints intersect properly

	//– Useful sizes

	inch = 25.4;

	Tap10_32 = 0.159 * inch;
	Clear10_32 = 0.190 * inch;
	Head10_32 = 0.373 * inch;
	Head10_32Thick = 0.110 * inch;
	Nut10_32Dia = 0.433 * inch;
	Nut10_32Thick = 0.130 * inch;



	NEMA17_ShaftDia = 5.0;
	NEMA17_ShaftLength = 24.0;
	NEMA17_PilotDia = 0.866 * inch;
	NEMA17_PilotLength = 0.080 * inch;
	NEMA17_BCD = 1.725 * inch;
	NEMA17_BoltDia = 3.5;
	NEMA17_BoltOC = 1.220 * inch;

	//– Mount Sizes

	MountWidth = IntegerMultiple(NEMA17_BCD,ThreadWidth); // use BCD for motor clearance
	MountThick = IntegerMultiple(4.0,ThreadThick); // for stiffness

	MountBoltDia = 3.0;

	StandThick = 3.0; // baseplate

	StrutThick = IntegerMultiple(3.0,ThreadWidth); // sides holding motor mount

	UprightLength = MountWidth + 2*StrutThick;

	StandBoltHead = IntegerMultiple(Head10_32,5); // bolt head rounded up
	StandBoltOC = IntegerMultiple(UprightLength + 2*StandBoltHead,5);

	StandLength = StandBoltOC + 2*StandBoltHead;
	StandWidth = 2*StandBoltHead;

	StandBoltClear = (StandLength – UprightLength)/2; // flat around bolt head

	MotorRecess = StandWidth – MountThick;

	ShaftHeight = IntegerMultiple(StandThick + MountWidth/2,ThreadWidth);

	echo(str("Stand Base: ",StandLength," x ",StandWidth," x ",StandThick));
	echo(str("Stand Bolt OC: ",StandBoltOC));
	echo(str("Shaft Height:",ShaftHeight));
	echo(str("Strut Thick: ",StrutThick));

	//———————-
	// 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);
	}

	//———————-
	// Model

	module MotorMount() {

	difference() {
	translate([StandThick/2,0,StandWidth/2])
	cube([(MountWidth + StandThick),StandLength,StandWidth],center=true);
	translate([-Protrusion/2,0,StandWidth – (MotorRecess – Protrusion)/2])
	cube([(MountWidth + Protrusion),MountWidth,(MotorRecess + Protrusion)],center=true);
	translate([0,0,-Protrusion]) // pilot hole
	PolyCyl(NEMA17_PilotDia,(MountThick + 2*Protrusion));
	for (i=[-1,1]) // motor bolt holes
	for (j=[-1,1])
	translate([iNEMA17_BoltOC/2,jNEMA17_BoltOC/2,-Protrusion])
	PolyCyl(MountBoltDia,(MountThick + 2*Protrusion),6);
	for (j=[-1,1]) // cutouts over bolts
	translate([-Protrusion/2,
	j*((StandLength – StandBoltClear)/2 + Protrusion/2),
	StandWidth/2])
	cube([(MountWidth + Protrusion),
	(StandBoltClear + Protrusion),
	(StandWidth + 2*Protrusion)],center=true);
	for (j=[-1,1]) // stand bolt holes
	translate([(MountWidth/2 – Protrusion),j*StandBoltOC/2,StandWidth/2])
	rotate([0,90,0])
	rotate(180/6)
	PolyCyl(Clear10_32,StandThick + 2*Protrusion,6);

	translate([0,-(UprightLength/2 – ThreadWidth/2),StandWidth/2])
	rotate([90,180,0])
	linear_extrude(ThreadWidth,convexity=10)
	text(text=str(ShaftHeight),size=6,spacing=1.20,font="Arial",halign="center",valign="center");

	}

	}

	//———————-
	// Build it

	MotorMount();

view raw NEMA17 Mount.scad hosted with ❤ by GitHub

The New Hotness

NEMA17 Motor and Bearing Mounts