OpenSCAD source code: Mini-lathe change gear generator with optional stacking

Mini-lathe stacked change gears.scad

// LMS Mini-Lathe
// Change gears with stacking
// Generate SVG outlines with Inkscape's Gear extension
// Ed Nisley - KE4ZNU
// 2020-05

/* [Gears] */

TopGear = 0;            // zero for single gear
BottomGear = 42;

/* [Hidden] */

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.2;

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

Protrusion = 0.1;           // make holes end cleanly

Dir = "";                   // empty string for current directory

/* [Dimensions] */

ShaftOD = 12.0;
ShaftSides = 4*3;

GearThick = 7.75;

Keyway = [3.5 + HoleWindage,3.0 + HoleWindage,3*GearThick];    // x on radius, y on perim, z on axis

LegendThick = 2*ThreadThick;
LegendZ = (TopGear ? 2*GearThick : GearThick) - LegendThick;

LegendRecess = [10,7,LegendThick];

LegendEnable = (TopGear == 0 && BottomGear > 41) || (TopGear > 41);


//----------------------
// Useful routines

// Enlarge holes to prevent geometric shrinkage
// based on nophead's polyholes
// http://hydraraptor.blogspot.com/2011/02/polyholes.html
// http://www.thingiverse.com/thing:6118

module PolyCyl(Dia,Height,ForceSides=0) {

  Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

  FixDia = Dia / cos(180/Sides);

  cylinder(r=(FixDia + HoleWindage)/2,
           h=Height,
		   $fn=Sides);
}

//-----------------------
// Build it!

union() {

  difference() {

    union() {
      linear_extrude(GearThick,center=false,convexity=5)
        import(file=str(Dir,"Change Gear - ",BottomGear," teeth.svg"),
              center=true);

      if (TopGear)
      translate([0,0,GearThick])
        linear_extrude(GearThick,center=false,convexity=5)
          import(file=str(Dir,"Change Gear - ",TopGear," teeth.svg"),
                center=true);
    }

    rotate(180/ShaftSides)
      translate([0,0,-Protrusion])
        PolyCyl(ShaftOD,3*GearThick);

    translate([ShaftOD/2,0,Keyway.z/2 - Protrusion])
      cube(Keyway,center=true);

    if (LegendEnable) {
      translate([0,1.1*ShaftOD,LegendZ + LegendRecess.z/2])
        cube(LegendRecess + [0,0,Protrusion],center=true);

      if (TopGear) {
        translate([0,-1.1*ShaftOD,LegendZ + LegendRecess.z/2])
          cube(LegendRecess + [0,0,Protrusion],center=true);
      }
    }

  }

  if (LegendEnable)
    translate([0,0,LegendZ - Protrusion])
      linear_extrude(height=LegendThick + Protrusion,convexity=10) {
          translate([-0*2.5,1.1*ShaftOD])
            rotate(-0*90)
              text(text=str(BottomGear),size=5,font="Arial:style:Bold",halign="center",valign="center");
        if (TopGear)
          translate([-0*2.5,-1.1*ShaftOD])
            rotate(-0*90)
              text(text=str(TopGear),size=5,font="Arial:style:Bold",halign="center",valign="center");
        }

}

More details on my blog at https://wp.me/poZKh-93z