Category: Machine Shop

Mechanical widgetry

Silica Gel Beads: Regeneration Damage
The silica gel beads I’ve been using in the PolyDryer boxes start out a uniform yellow / light brown:

Polydryer Box desiccant tray – top view

The humidity indicating chemical seems to be methyl violet, described as changing from yellow to green when saturated, which has never happened here. For example, these beads, retrieved from random corners of the workbench, have been sitting in 40-ish %RH basement air for weeks:

Silica gel beads – 36pctRH ambient

The fragment just left of center looks greenish, but the rest are, at best, various shades of brown. This may be due to the (relatively) low humidity in the basement, but putting them under a damp sponge for a few hours didn’t change their color.

The most recent regeneration session started with an open cast-iron pan on an induction cooktop:

Silica gel beads – drying

The variety of browns comes from various amounts of adsorbed water in the PolyDryer boxes, but AFAICT there really isn’t much correlation between the humidity level and the amount of adsorbed water.

The drying process went like this:
- 650 g at start
- 50% power for 2 hr → 200 °F
- Covered the pan & turned it off overnight
- 623 g at start
- 50% power for 2 hr → 220 °F
- 612 g
- 50% power for 1 hr → 236 °F
- 610 g
- 30% power for 30 min → 205 °F
- 35% power for 30 min → 200 °F
- 609 g
So about four hours at 50% power would get all but the laser few grams of water out of the silica gel.

After all that, the beads looked about the same in a white bowl for cooling:

Silica gel beads – damaged indicator dye

Each regeneration cycle leaves more dark brown beads in the mix, which may be due to poor temperature control, and they do not return to their original yellow / pale brown shade.

Apparently cooking silica gel beads over 120 °C = 250 °F (various sources give various temperatures) can damage their structure or the methyl violet indicator; for sure some of those beads have been abused.

Unsurprisingly, the bead temperature rises as they dry out. Although the induction cooktop has a temperature control, we’ve found the setting doesn’t match the pan temperature and the overall control is poor. I could set the gas oven to 200 °F, but I’m certain it doesn’t control the temperature all that closely, either.

The original jug held 2 pounds = 907 g of beads. Add the 609 g from this session to the 350 g of allegedly dry beads in seven of the PolyDryer boxes: my regeneration hand is weak.
2026-01-07

PolyDryer Humidity: December

The measurements:

	2025-12-29
Filament	%RH	Weight – g	Wt gain – g	Gain %
PETG White	18	53.8	3.8	7.6%
PETG Black	18	53.8	3.8	7.6%
PETG Orange	22	52.3	2.3	4.6%
PETG Natural	22	53.4	3.4	6.8%
PETG-CF Blue	18	54.1	4.1	8.2%
PETG-CF Gray	23	54.1	4.1	8.2%
PETG-CF Black	18	53.8	3.8	7.6%
PETG Blue	10	52.9	2.9	5.8%
TPU Clear	18	54.4	4.4	8.8%
TPU Black	18	55.1	5.1	10.2%

I used to think there was some correlation between the indicated humidity and the amount of water adsorbed by the silica gel, with the humidity rising as the gel absorbed more water. That is obviously not the case.

AFAICT, I’d been reading the chart wrong:

Instead of the adsorption being a function of the equilibrium humidity, it’s the other way around. With the humidity held constant (by adding water vapor), the silica gel will adsorb thus-and-so percentage of its weight and equilibrate at that humidity. If the filament was an infinite reservoir of dampness, then the equilibrium humidity would indicate how much the silica gel had coped with.

At least I think that’s how it goes. I have been wrong before.

Anyhow, IMO the right way to proceed is to just replace the silica gel every month and be done with it.

Also true: the humidity meters aren’t particularly accurate at the low humidity values in those boxes.

2026-01-06

Prusa MK4 Foam Feet

Along the same lines as the foam feet under the 3018XL plotter, the MK4 now has a bit of vibration isolation:

Prusa MK4 Foam Feet – installed

I’d stuck four exercise mat tabs (scraps of a flooring project) under the feet, but the loading was much too high:

Prusa MK4 Foam Feet – foam snippets

It was really an excuse for some non-critical cutting with the 3 inch lens in the laser cutter:

Prusa MK4 Foam Feet – assembled

The foam cut nicely, albeit with a 1.3 mm kerf, and the chipboard & plywood seemed about the same. They’re 30 mm square and, should they flatten out, I have enough foam scraps for a larger set.

Unlike the 3018 feet, my deflicted ears can’t tell the difference with these place, so I assume a standard MK4 squash-ball foot upgrade isn’t worth the filament.

2026-01-05
OMTech Laser vs. Ortur Rotary: 3 Inch Lens
The manual accompanying my OMTech 60 W CO₂ laser clearly states it has a 1.5 inch focus lens:

OMTech laser packing list – 1.5 inch focus lens

Which I had always assumed was the case, even though a short lens like that would typically be used for fine engraving due to its smaller spot size. One could argue the carton should have included a 1.5 inch lens in addition to whatever was in “its optics”, but it didn’t.

It has a 2 inch lens, as I confirmed while switching to a 3 inch lens to get more clearance over the Ortur rotary than the stock lens allows:

Ortur Chuck Rotary – 2 inch focus lens

The bottom of the lens (its planar surface) sits inside the nozzle at (about) the same level as the joint just above the assist air fitting:

OMTech laser – 3 inch lens focus distance

That’s the proper focus distance for the 3 inch lens, with the lens 3 inch = 3 × 25.4 = 76.2 mm above the platform. There’s obviously some room for quibbling about the optical center of the lens vs. the lower surface and so forth and so on, but a ramp test shows it’s Close Enough™:

Ramp Test – 3inch lens – 2025-12-29

Which adds an inch of clearance, enough to prevent obvious collisions:

Ortur Chuck Rotary – 3 inch focus lens

Changing the lens requires removing the air fitting, during which operation I also moved the clamp holding the focus pen. Because that changed where the switch trips, the Focus Distance also changed:
- 2 inch lens = 12.7 mm
- 3 inch lens = 12.7 + 25.4 = 38.1 mm
The clearance under the nozzle depends only on the lens:
- 2 inch lens = 18.5 mm
- 3 inch lens = 18.5 + 25.4 = 43.9
I’ve been using step gauges for manual focusing with the 2 inch lens:

OMTech focus pen – tripped vs nozzle

I figured a rod would be more appropriate for the 3 inch lens and, hey, now that I have a rotary, I can engrave it:

OMTech laser – 3 inch lens focus stick

Through no fault of mine at the lathe, that stick is exactly 43.9 mm long, but “44 mm” fit better.
2026-01-02

Ortur YRC-1: Conical Tailstock Centers

A conical (a.k.a. bullnose) center in the tailstock simplifies supporting cylindrical objects:

Ortur Chuck Rotary conical center - installed — Ortur Chuck Rotary conical center – installed

The spring-loaded tailstock bearing has a 5 mm bore. The bullnose rests against a small spacer on its 5 mm shaft to hold it away from the bearing’s mounting screws with some bearing spring compression. I turned the spacer from aluminum rod because lathe work is satisfying, but a printed spacer would work fine.

The bullnose is a cone with steps encouraging the cylinder to sit properly:

Ortur Rotary Conical Center - 10-50mm — Ortur Rotary Conical Center – 10-50mm

With both ends centered, the cylinder sits concentric with the chuck axis:

Ortur Chuck Rotary home switch - jaw position — Ortur Chuck Rotary home switch – jaw position

The chuck grabs the OD and the bullnose supports the ID, so removing crud from both ends is in order.

The bullnose won’t work for a solid rod, so a negative cone = cup center may come in handy:

Ortur Chuck Rotary cup center - installed — Ortur Chuck Rotary cup center – installed

Stipulated: A CO₂ laser will bounce right off a solid aluminum rod. Imagine I chucked up a wood dowel, OK?

A cup center is what remains afteryoinking a bullnose out of a cylinder:

Ortur Rotary Conical Centers - cup — Ortur Rotary Conical Centers – cup

Looks like I did exactly that:

Somewhat surprisingly, the two parts nest perfectly:

Ortur Chuck Rotary conical centers - nested — Ortur Chuck Rotary conical centers – nested

That’s without the shaft installed on the cup, so they won’t sit quite so neatly on the shelf.

Aligning the rotary axis along the laser’s X axis and setting the focus requires attention to detail, but a decent tailstock center makes that effort meaningful.

The OpenSCAD code as a GitHub Gist:

	// Ortur Rotary Conical centers
	// Ed Nisley – KE4ZNU
	// 2025-12-27

	include <BOSL2/std.scad>

	Style = "Bullnose"; // [Build,Cone,Bullnose,Cup,Cone]

	MinDia = 10.0;
	MaxDia = 50.0;

	/* [Hidden] */

	LayerThick = 0.2; // should match slicer thickness

	Ramp = 1.0;

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

	HoleWindage = 0.2;
	Protrusion = 0.1;

	NumSides = 834;
	$fn=NumSides;

	Gap = 5.0;

	WallThick = 2.0;

	TailBearing = [5.0,7.0,10.0]; // tailstock shaft, LENGTH = insert depth

	StepHeight = 2*LayerThick;

	NumSteps = (((MaxDia – MinDia)/2) / Ramp);
	ConeOAH = NumSteps * (Ramp + StepHeight);

	//—–
	// Bullnose shape

	module Bullnose() {

	difference() {
	union()
	for (i = [0:NumSteps – 1])
	up(i*(Ramp + StepHeight)) hull()
	cyl(StepHeight + Protrusion,r=(MaxDia/2 – i*Ramp),anchor=BOTTOM) position(TOP)
	cyl(Ramp,r1=(MaxDia/2 – iRamp),r2=(MaxDia/2 – (i+1)Ramp),anchor=BOTTOM);
	}


	}

	module Cone() {

	difference() {
	Bullnose();
	down(Protrusion)
	cyl(TailBearing[LENGTH] + Protrusion,d=TailBearing[ID],circum=true,anchor=BOTTOM);
	}

	}

	module Cup() {

	difference() {
	cyl(ConeOAH + TailBearing[LENGTH],d=MaxDia + 2*WallThick,anchor=BOTTOM);
	up(ConeOAH + TailBearing[LENGTH] + Protrusion)
	yrot(180)
	Bullnose();
	down(Protrusion)
	cyl(TailBearing[LENGTH] + 2*Protrusion,d=TailBearing[ID],circum=true,anchor=BOTTOM);
	}


	}


	//—–
	// Build things

	if (Style == "Bullnose")
	Bullnose();

	if (Style == "Cone")
	Cone();

	if (Style == "Cup")
	Cup();

	if (Style == "Build") {
	right(MaxDia/2 + Gap)
	Cone();
	left(MaxDia/2 + WallThick + Gap)
	Cup();
	}

view raw Ortur Rotary Conical Centers.scad hosted with ❤ by GitHub

2025-12-30

Ortur YRC-1: Adding a Home Switch

Stipulated: A chuck rotary doesn’t need a home switch.

With that in mind, a home switch seemed like it might come in handy and this is the simplest workable design:

Ortur Chuck Rotary home switch - installed — Ortur Chuck Rotary home switch – installed

The cover mimics the size & shape of the Ortur cover, minus the stylin’ rounding & chamfering along the edges:

Ortur Rotary Belt Cover - exterior - solid model — Ortur Rotary Belt Cover – exterior – solid model

It has a certain Cybertruck aspect, doesn’t it?

Two beads of hot melt glue hold the switch flush along the cover’s inside surface:

Ortur Chuck Rotary home switch - case exterior — Ortur Chuck Rotary home switch – case exterior

One might argue for a tidy cover over those terminals.

While contemplating the layout by holding the switch here & there, seeing the switch roller neatly centered on the pulley hub told me the Lords of Cosmic Jest favored this plan:

Ortur Chuck Rotary home switch - case interior — Ortur Chuck Rotary home switch – case interior

A simple cam lifts the roller:

Ortur Chuck Rotary home switch - pulley cam — Ortur Chuck Rotary home switch – pulley cam

That’s obviously laser-cut acrylic sitting on double-sided tape. Some finicky repositioning put the #1 chuck jaw on top after homing:

A more permanent adhesive under the cam may be in order.

Update: The switch triggers more reliably with a simple setscrew standing proud of the pulley hub:

Ortur Rotary Focus Pad - home trip setscrew — Ortur Rotary Focus Pad – home trip setscrew

Wiring the normally open switch contacts in parallel with the existing Y axis home switch lets both the gantry and the rotary trigger the controller. The front-panel switch ensures only one of those two can move:

Laser Rotary - control switch — Laser Rotary – control switch

With all that in place and the switch flipped, the chuck rotates happily and homes properly with the controller in normal linear mode.

Spoiler: A Ruida-ish KT332N controller ignores the Y-axis Home enable setting with Rotary mode enabled, because everybody knows a rotary has no need for a home switch.

The OpenSCAD code as a GitHub Gist:

	// Ortur Rotary belt cover
	// Ed Nisley – KE4ZNU
	// 2025-12-23

	include <BOSL2/std.scad>

	Layout = "Show"; // [Show,Build,Block,Shell]

	/* [Hidden] */

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

	HoleWindage = 0.2;
	Protrusion = 0.1;

	NumSides = 234;
	$fn=NumSides;

	Gap = 5.0;

	WallThick = 1.6; // OEM wall

	CoverOA = [81.5,50.5,23.0]; // open side down
	CoverRadius = 4.0;
	CoverTrimZ = 6.0;
	CoverTrimAngle = 45;

	BreakX = (CoverOA.z – CoverTrimZ)/tan(CoverTrimAngle);

	ScrewOC = [51.0,38.0];
	ScrewHoleID = 3.5;
	ScrewHeadRecess = [ScrewHoleID,7.0,1.8];
	ScrewOffset = 8.0; // cover edge to hole centerline

	SwitchOA = [21.0,20.0,6.5]; // X = body + roller, excludes terminals
	SwitchOffset = [0,0,17.0]; // nominal end = roller at centerline



	//—–
	// Overall cover shape

	module CoverBlock() {

	cuboid([CoverOA.x,CoverOA.y,CoverTrimZ],anchor=BOTTOM) position(TOP+LEFT)
	prismoid(size1=[CoverOA.x,CoverOA.y],size2=[CoverOA.x – BreakX,CoverOA.y],
	height=CoverOA.z – CoverTrimZ,shift=[–BreakX/2,0],anchor=BOTTOM+LEFT);
	}

	// Cover shell

	module CoverShell() {

	difference() {
	CoverBlock();
	down(Protrusion)
	resize(CoverOA – [2WallThick,2WallThick,WallThick – Protrusion])
	CoverBlock();
	}
	}

	// The complete cover

	module Cover() {

	difference() {
	union() {
	CoverShell();
	left((CoverOA.x – ScrewOC.x)/2 – ScrewOffset)
	for (i = [–1,1], j=[–1,1])
	translate([iScrewOC.x/2,jScrewOC.y/2,0])
	cyl(CoverOA.z,d=ScrewHoleID + 2*WallThick,anchor=BOTTOM);
	}
	left((CoverOA.x – ScrewOC.x)/2 – ScrewOffset) down(Protrusion)
	for (i = [–1,1], j=[–1,1])
	translate([iScrewOC.x/2,jScrewOC.y/2,0]) {
	cyl(CoverOA.z + 2*Protrusion,d=ScrewHoleID + HoleWindage,anchor=BOTTOM);
	up(CoverOA.z – ScrewHeadRecess[LENGTH])
	cyl(ScrewHeadRecess[LENGTH] + 2*Protrusion,
	d1=ScrewHeadRecess[ID] + HoleWindage,d2=ScrewHeadRecess[OD] + HoleWindage,
	anchor=BOTTOM);

	}
	translate(SwitchOffset) left(CoverOA.x/2 – WallThick – Protrusion)
	cuboid(SwitchOA,anchor=RIGHT+FWD);
	}

	}


	//—–
	// Build things


	if (Layout == "Block") {
	CoverBlock();
	}

	if (Layout == "Shell") {
	CoverShell();
	}

	if (Layout == "Show") {
	Cover();
	}

	if (Layout == "Build") {
	up(CoverOA.z)
	xrot(180)
	Cover();

	}

view raw Ortur Rotary Belt Cover.scad hosted with ❤ by GitHub

2025-12-29

OMTech Laser: It Was The Focus Pen Wire

Because the focus pen worked on the bench, I was certain this had to be true:

OMTech focus pen – failed 24V wire

There is a break somewhere along the blue wire carrying 24 V to the focus pen. The signal and 0 V wires are fine.

I updated the original post, because I’m going to use that picture a lot whenever the subject of laser machine wiring comes up.

2025-12-26

Category: Machine Shop

Silica Gel Beads: Regeneration Damage

PolyDryer Humidity: December

Prusa MK4 Foam Feet

OMTech Laser vs. Ortur Rotary: 3 Inch Lens

Ortur YRC-1: Conical Tailstock Centers

Ortur YRC-1: Adding a Home Switch

OMTech Laser: It Was The Focus Pen Wire