Tag: MK4

Prusa Mk 4 3D printer with MMU3 feeder

Dryer Vent Filter Snout: More Warping

I have unfairly maligned the TPU snout, because the PETG snout failed the same way:

Clothes Dryer Vent Filter Snout – warped PETG

Seen with the shock cord in place, it’s obvious that combining moderately high temperature with steady compression sufficed to bend the PETG enough to pop those tabs loose from the vent.

So the OpenSCAD model now produces a stiffening ring to be laser-cut from acrylic:

Clothes Dryer Vent Filter Snout – OpenSCAD stiffener

The whole snout builds as a single unit in the obvious orientation:

Clothes Dryer Vent Filter Snout – V2 – slicer

Because the part of the snout with the tabs is 7 mm tall, I glued a 4 mm acrylic ring to a 3 mm ring, with both of them glued to the snout:

Clothes Dryer Vent Filter Snout – acrylic gluing

That’s “natural” PETG, which I expected to be somewhat more transparent, but it’s definitely not a dealbreaker.

Mary will sew up another cheesecloth filter and we’ll see what happens to this setup.

As the saying goes, “Experience is what you get when you don’t get what you want.”

Fortunately, living in the future makes it easy to iterate on the design & implementation until experience produces what should have been obvious at the start.

2025-12-11
Smashed Glass Coaster: Rivers of Crack

Looking at that big smashed-glass coaster from a different angle showed interesting patterns:

Printed Fragment Coaster – 165mm – long cracks

Although the larger fragments were still holding together when I laid them in their recesses, they apparently consist of several sub-fragments with larger continuous cracks letting the epoxy flow / ooze inside.

Now that I know what to look for, the original picture also shows them, albeit less distinctly:

Printed Fragment Coaster 165mm – overview

They’re not obvious in the scanned image of the fragments, although I could convince myself I see some:

Fragments 165mm square – scan sample

The many smaller fragments I’ve been turning into coasters probably separated from similar large chunks along such cracks, which is why I’ve never seen rivers of crack before.

Apologies if you arrived here expecting a tirade concerning the drug trade … :grin:

2025-12-08

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

Sears Humidifier Bottle Cap Reinforcement

In the midst of the humidification season, I spotted this while refilling one of the ancient Sears Humidifier bottles:

Humidifier bottle cap reinforcement - crack — Humidifier bottle cap reinforcement – crack

While it’s possible to buy replacement caps, this seemed more appropriate:

Humidifier bottle cap reinforcement - installed — Humidifier bottle cap reinforcement – installed

It’s PETG-CF, of course:

Bottle cap reinforcement - solid model — Bottle cap reinforcement – solid model

The shape is a ring with a simplified model of the cap removed from the middle:

Bottle cap reinforcement - lid solid model — Bottle cap reinforcement – lid solid model

It fits snugly over the cap atop a thin layer of JB PlasticBonder that should hold it in place forevermore:

Humidifier bottle cap reinforcement - bottom view — Humidifier bottle cap reinforcement – bottom view

The other side shows the crack over on the right:

Humidifier bottle cap reinforcement - top view — Humidifier bottle cap reinforcement – top view

Close inspection showed a few smaller cracks, so that cap was likely an original.

I made another ring for the other cap, only to find it was slightly larger with a black washer inside: apparently a previous owner had replaced one of the caps. The OpenSCAD program has measurements for both, not that you have either.

The OpenSCAD source code as a GitHub Gist:

	// Humidifier bottle cap reinforcement
	// Ed Nisley – KE4ZNU
	// 2025-11-29

	include <BOSL2/std.scad>

	Layout = "Show"; // [Show,Build,Cap]

	/* [Hidden] */

	Protrusion = 0.1;

	//—–
	// Bottle cap/valve
	// Collects all the magic numbers in one place

	Left = false; // the caps are different, of course
	CapODs = Left ? [43.0,42.1] : [43.1,42.9]; // [0] = base of cap

	CapHeight = 10.0;

	Notch = [0.6,2.0,8.5 + Protrusion]; // Z + hack for slight angle
	NumRibs = 24;
	RibAngle = 90 – atan(CapHeight/((CapODs[0]-CapODs[1])/2));
	echo(RibAngle=RibAngle);

	$fn=2*NumRibs;

	module Cap() {

	difference() {
	cyl(CapHeight,d1=CapODs[1],d2=CapODs[0],anchor=BOTTOM);
	for (a=[0:NumRibs-1])
	zrot(a*360/NumRibs)
	right(CapODs[1]/2) down(Protrusion)
	yrot(RibAngle)
	cuboid(Notch,anchor=RIGHT+BOTTOM);
	}

	}

	//—–
	// Reinforcing ring

	RingThick = 3.0;

	module Ring() {

	render()
	difference() {
	tube(CapHeight,od=CapODs[0] + 2RingThick,id=CapODs[1] – 2Notch.x,anchor=BOTTOM);
	Cap();
	}

	}

	// Build things

	if (Layout == "Cap")
	Cap();


	if (Layout == "Build" \|\| Layout == "Show")
	Ring();

view raw Bottle cap reinforcement.scad hosted with ❤ by GitHub

2025-12-02

Large Smashed Glass Coaster
Those of long memory will recall our vermiculture setup in the basement that turns kitchen scraps into plant food. We accumulate scraps in plastic milk jugs, which jugs get recycled after they become grody.

I finally made a decorative coaster to keep the sometimes-wet jug off the counter:

Printed Fragment Coaster 165mm – in use

This used several of the larger smashed glass fragments from the collection:

Fragments 165mm square – scan sample

They all fit inside a 165 mm square, with the conformal perimeter disguising the outline:

Printed Fragment Coaster 165mm – overview

I printed the frame with the same blue PETG-CF that leaked epoxy the last time around. Using the correct filament setting (Extrusion Multiplier = 1.0) produced an epoxy-tight frame:

Printed Fragment Coaster 165mm – epoxy filling

The overall process:
- Run a bead of epoxy around the edge of each recess
- Fill in the center with a thin layer
- Squish the metallized paper reflector in place starting from one end to ease the bubbles out
- Cover the reflector with another layer of epoxy
- Lay the glass fragment down starting at one end
- Press gently down to get all the bubbles out
- Cover the glass with more epoxy
I dripped enough epoxy on each fragment to form a meniscus without having it go over the rim:

Printed Fragment Coaster 165mm – epoxy meniscus

The Basement Shop temperature is just over 60 °F, so I put a heating pad in a huge ziplock bag, laid an aluminum sheet atop it as a heat spreader, put some waxed paper on the aluminum just in case, then did the filling described above:

Printed Fragment Coaster 165mm – warming setup

A cardboard box on top helped the heating pad keep the coaster at a uniform 85 °F, slightly warmer than the epoxy instructions recommend, but it cured overnight with a wonderfully shiny surface.

Now that I have the process down, making glittery coasters is surprisingly easy.
2025-11-25
PolyDryer Humidity: White PETG

The white PETG filament started out at 39 %RH and 50 g of silica gel dragged it down to 23 %RH after a three days: still unusually high.

The beads weighed 54.6 g, a weight gain of 9 %, which is about as much as they’ll take. I replaced them with 50 g of new-from-the-bottle beads and the meter dropped to 14 %RH overnight.

Running the tiny fan for another day made no difference:

Polydryer Box desiccant tray – fan

Thereby confirming my suspicion that air circulation inside the box isn’t nearly as much of a problem as I expected.

So filament need not arrive bone-dry and, with enough surface area exposed to the air, silica gel beads can adsorb their limit of water vapor in a day or two.

2025-11-24

PolyDryer Humidity: November

The measurements:

	2025-11-04	2025-11-11				2025-11-19
Filament	%RH	%RH	Weight – g	Wt gain – g	Gain %	%RH
PETG White	39	39	27.4	2.4	9.6%	23
PETG Black	25	26	26.7	1.7	6.8%	14
PETG Orange	30	23	26.5	1.5	6.0%	23
PETG Blue	18	23	27.0	2.0	8.0%	10
PETG-CF Blue	25	25	26.5	1.5	6.0%	18
PETG-CF Black	22	22	26.3	1.3	5.2%	14
PETG-CF Gray	28	28	26.5	1.5	6.0%	18
Empty → PETG Clear	31	n/a	26.8	1.8	7.2%	18
TPU – Clear	28	29	26.3	1.3	5.2%	14
W empty → TPU – K	23	27	26.8	1.8	7.2%	18

All the boxes now have filament spools and 50 g of silica gel divided equally between the humidity meter and the tray in the bottom of the box:

Polydryer Box desiccant tray - installed — Polydryer Box desiccant tray – installed

The PETG White in the first row is the new spool loaded last month. I think the 39 %RH indicates the spools do not necessarily arrive bone-dry in their vacuum-sealed bags with a tiny desiccant packet.

Conversely, both the PETG Clear and TPU K filaments are new spools that seem reasonably dry out of their bags.

The auto-rewind spindle in the PETG Orange filament hasn’t been working quite right, so I opened the box a few times. It now has a new PETG-CF spindle.

2025-11-20

Tag: MK4

Dryer Vent Filter Snout: More Warping

Smashed Glass Coaster: Rivers of Crack

Mini-lathe Change Gear Generator: Redux

Sears Humidifier Bottle Cap Reinforcement

Large Smashed Glass Coaster

PolyDryer Humidity: White PETG

PolyDryer Humidity: November