Day: August 23, 2011

This mount will hold a NEMA 17 stepper firmly in place so I can attach things to the shaft:

The baseplate holes fit 10-32 screws, which work in the plastic sheet that will go below this thing, and the motor mount plate holes fits 3 mm bolts for the motors. Washers under the heads, of course. Build with three additional shells, three solid layers, and 0.25 fill for useful rigidity; the flanges came out completely solid.

Somewhat to my surprise, this didn’t show any signs of delamination due to the rather low 190 °C extrusion temperature. The flanges aren’t all that massive, though, so perhaps trouble still lies await.

The OpenSCAD solid model uses subtractive construction, for reasons that I’ll go into later:

The OpenSCAD source code:

// NEMA 17 stepper mount for dynamometer
// Ed Nisley KE4ZNU August 2011

include </home/ed/Thing-O-Matic/lib/MCAD/units.scad>

//-- Layout Control

Layout = "Build";				// Build Show

//-- Extrusion parameters

ThreadThick = 0.33;
ThreadWT = 2.0;
ThreadWidth = ThreadThick * ThreadWT;

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

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

//-- Useful sizes

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(8.0,ThreadThick);				// for stiffness

MountBoltDia = 3.0;

StandThick = IntegerMultiple(5.0,ThreadWidth);				// baseplate

StrutThick = IntegerMultiple(4.0,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 = IntegerMultiple(2*StandBoltHead,ThreadThick);

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

MotorRecess = StandWidth - MountThick;

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

//-- Convenience values

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

BuildOffset = 3 * ThreadWidth;

//----------------------
// 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);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  Range = floor(50 / Space);

	for (x=[-Range:Range])
	  for (y=[-Range:Range])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//----------------------
// Combined stand and mounting plate

module Combined() {

  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 (x=[-1,1])								// motor bolt holes
	  for (y=[-1,1])
		translate([x*NEMA17_BoltOC/2,y*NEMA17_BoltOC/2,-Protrusion])
		  PolyCyl(MountBoltDia,(MountThick + 2*Protrusion));
	for (y=[-1,1])								// cutouts over bolts
	  translate([-Protrusion/2,
				y*((StandLength - StandBoltClear)/2 + Protrusion),
				StandWidth/2])
		cube([(MountWidth + Protrusion),
			 (StandBoltClear + Protrusion),
			 (StandWidth + 2*Protrusion)],center=true);
	for (y=[-1,1])								// stand bolt holes
	  translate([(MountWidth/2 - Protrusion),y*StandBoltOC/2,StandWidth/2])
		rotate([0,90,0])
		  PolyCyl(Clear10_32,StandThick + 2*Protrusion,8);

  }

}

//----------------------
// Lash everything together

ShowPegGrid();

if (Layout == "Build") {
  translate([0,0,0])
	Combined();
}

if (Layout == "Show") {
  translate([-StandWidth/2,0,(StandThick + MountWidth/2)])
	rotate([0,90,0])
	  Combined();
}