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Mini-lathe Change Gear Generator: Redux

Because the BOSL2 library includes a gear generator, I can now avoid creating a gear outline in Inkscape and importing it into my stacked change gear generator.

The labels now snuggle closer to the shaft and (barely) fit on smaller gears:

Mini-lathe stacked change gears - 28T - solid model — Mini-lathe stacked change gears – 28T – solid model

The stacked B-C gears for the jack shaft work as before, with both labels on the top gear:

Mini-lathe stacked change gears - 28-50T - solid model — Mini-lathe stacked change gears – 28-50T – solid model

The admittedly flimsy motivation for all this was to make a 28 tooth gear to cut a 0.9 mm pitch, thus filling an obvious hole in the gear table.

My collection of gears could do 21-60-81-50, but the 81 T gear collides with the screw holding the 21 T gear. Rearranging it to 21-50-81-60 showed the B-C gears exceeded the space available.

Because it’s all ratios and a 28 T gear is 4/3 bigger than 21 T, reducing the rest of the train by 3/4 should work. In fact, it produced a reasonable 28-80-81-50 chain:

Mini-lathe change gears - 28T installed — Mini-lathe change gears – 28T installed

The fact that I do not anticipate ever needing to cut a 0.9 mm pitch has nothing whatsoever to do with it; that gear will surely come in handy for something.

While I was at it, I made a 27 T gear, because 27 = 21 × 9/7:

Mini-lathe stacked change gears - 27T - PrusaSlicer preview — Mini-lathe stacked change gears – 27T – PrusaSlicer preview

You can never have enough change gears. Right?

The OpenSCAD source code as a GitHub Gist:

	// LMS Mini-Lathe
	// Change gears with stacking
	// Ed Nisley – KE4ZNU
	// 2020-05 use Inkscape SVG gears
	// 2025-12 use BOSL2 gear generator

	include <BOSL2/std.scad>
	include <BOSL2/gears.scad>

	/* [Gears] */

	TopGear = 0; // zero for single gear
	BottomGear = 28;

	/* [Hidden] */

	ThreadThick = 0.20;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	/* [Dimensions] */

	ShaftOD = 12.0;

	GearThick = 7.75;

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

	LegendEnable = (TopGear == 0 && BottomGear > 27) \|\| (TopGear > 27);

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

	LegendSize = 5;
	LegendRecess = [8,6,LegendThick];
	LegendOffset = [0,LegendRecess.y/2 + ShaftOD/2 + HoleWindage,LegendZ + LegendRecess.z/2];



	//———————–
	// Build it!

	union() {

	difference() {

	union() {

	spur_gear(mod=1,teeth=BottomGear,thickness=GearThick,shaft_diam=ShaftOD + HoleWindage,anchor=BOTTOM);

	if (TopGear)
	spur_gear(mod=1,teeth=TopGear,thickness=2*GearThick,shaft_diam=ShaftOD + HoleWindage,anchor=BOTTOM);
	}

	right(ShaftOD/2)
	down(Protrusion)
	cube(Keyway,anchor=CENTER+BOTTOM);

	if (LegendEnable) {
	translate(LegendOffset)
	cube(LegendRecess + [0,0,Protrusion],anchor=CENTER);

	if (TopGear)
	zrot(180)
	translate(LegendOffset)
	cube(LegendRecess + [0,0,Protrusion],anchor=CENTER);
	}

	}

	if (LegendEnable)
	translate([0,0,LegendZ – Protrusion])
	linear_extrude(height=LegendThick + Protrusion,convexity=10) {
	translate([LegendOffset.x,LegendOffset.y])
	text(text=str(BottomGear),size=LegendSize,font="Arial:style:Bold",halign="center",valign="center");
	if (TopGear)
	zrot(180)
	translate([LegendOffset.x,LegendOffset.y])
	text(text=str(TopGear),size=LegendSize,font="Arial:style:Bold",halign="center",valign="center");
	}

	}

view raw Mini-lathe stacked change gears.scad hosted with ❤ by GitHub

2025-12-04