Category: Machine Shop

Mechanical widgetry

Prusa MK4: Mesh Bed Leveling Temperature vs. 0.8 mm Ruby Durozzle
After going through the ritual required to install the 0.8 mm nozzle and preload the filament, the hot end looks like this before installing the silicone sock:

Prusa MK4 hot end – 0.8 mm Durozzle ruby – front

The aluminum block doesn’t look nearly as awful as these pictures suggest; those plastic smears serve as reminders of a few previous printing mishaps.

The nozzle is a 0.8 mm Durozzle with a ruby tip suitable for abrasive filaments like PETG-CF, although this is gooey squishy “natural” TPU:

Prusa MK4 hot end – 0.8 mm Durozzle ruby – bottom

The first patio table foot test piece in TPU had terrible adhesion to the Textured Sheet, which I eventually tracked down to an excessively thick first layer. Given that the MK4 homes the axes and performs mesh bed leveling probes over the build area, this was difficult to believe, particularly because it had never been a problem with the Prusa 0.4 mm ObXidian hardened steel nozzle.

More poking around showed some of the plastic drool left on the outside of the nozzle from the previous print session (as shown in the two pictures above) could remain hardened or at least “not squishy” despite the nozzle being heated before homing and mesh probing. Because probing depends on having the nozzle touch the platform, anything between the nozzle and the steel sheet will raise the Z=0 position and cause all the layers to be too high.

As far as I can tell, ruby has a thermal coefficient around 40 W/m·K, roughly the same as steel. Both are considerably lower than the 200-ish W/m·K for the aluminum block surrounding the nozzle tube, suggesting most of whatever temperature gradient there may be occurs between the heater and the nozzle, not in the nozzle.

While puzzling that out, I noticed the nozzle heated to only 160 °C prior to homing and probing, which seemed low for a filament calling for 230 to 250 °C during printing. Ordinary PETG heated to 170 °C, so something was different.

More puzzling showed the Start G-Code section of the printer’s Custom G-Code sets the home / probe temperature, herein reformatted for readability:
```
M140 S[first_layer_bed_temperature] ; set bed temp

M104 T0 S{((filament_notes[0]=~/.*MBL160.*/) ? 160 : 
(filament_notes[0]=~/.*HT_MBL10.*/) ? (first_layer_temperature[0] - 10) : 
(filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : 
(filament_type[0] == "FLEX") ? 210 : 
(filament_type[0]=~/.*PET.*/) ? 175 : 
170)} ; set extruder temp for bed leveling

M109 T0 R{((filament_notes[0]=~/.*MBL160.*/) ? 160 : 
(filament_notes[0]=~/.*HT_MBL10.*/) ? (first_layer_temperature[0] - 10) : 
(filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : 
(filament_type[0] == "FLEX") ? 210 : 
(filament_type[0]=~/.*PET.*/) ? 175 : 
170)} ; wait for temp
```
The bursts of line noise after the M104 Set Extruder Temperature and M109 Set Extruder Temperature and Wait commands consist of nested ternary operators sifting placeholder variables defined in other parts of the slicer configuration.

I had set up the eSun TPU 95A filament parameters based on Prusa’s TPU definition. I eventually discovered that definition includes the text MBL160 in its Notes section, which satisfies the regex in the first ternary operator:
```
(filament_notes[0]=~/.*MBL160.*/) ? 160 : … snippage …
```
Which then emitted the M104 T0 S160 and M109 R160 commands into the G-Code to set the temperature.

After considerably more flailing around while figuring this out, I changed the filament Notes to read:
```
HT_MBL10 -- force higher probe temperature for Durozzle ruby nozzle
mbl160 -- disabled by lowercase
```
Which then falls through to the regex in the second ternary operator:
```
(filament_notes[0]=~/.*HT_MBL10.*/) ? (first_layer_temperature[0] - 10) : 
```
Which sets the temperature to 10 °C below the first layer temperature, which I had set to 230 °C, so the probing now occurs at 220 °C.

I am not making this up.

Although that may be a bit too hot, the drool on the nozzle softens nicely and smashes flat during probing, thus solving the immediate problem and, without further ado, produced good round and square TPU feet.
2026-06-09
Translucent vs. Transparent PETG Soap Dishes

In addition to printing bendy objects with TPU, the 0.8 mm nozzle 3D-prints PETG into thin walls with better transparency than the default 0.4 mm nozzle:

Clear PETG – 0.4 vs 0.8 mm nozzle – side view

The wall is now 1.0 mm thick, rather than 0.6 mm, and is much closer to being transparent. Those gray links from the RPi camera mount inside the dishes help show the difference.

The 2.0 mm thick base plate is also more transparent, but mostly just reveals the 0.4 mm thick infill layers:

Clear PETG – 0.4 vs 0.8 mm nozzle – top view

More study is needed, even if we already have far more soap dishes than strictly necessary.

2026-06-08
Prusa MK4: Nozzle Change Checklist
Both the round and square TPU patio table feet came from a 0.8 mm nozzle on the Prusa MK4, which produces results much faster than the venerable Makergear M2’s 0.35 mm nozzle. However, for unknown reasons a 0.8 mm nozzle is not compatible with the MMU3, so changing from and to the default 0.4 mm nozzle requires a somewhat complex ritual.

For context, the MK4 extruder and hot end:

Prusa MK4 – extruder overview

Because the MK4 automatically unloads the filament from the extruder (with help from auto-retracting filament spools) when using the MMU, the hot end doesn’t have any filament in it. Disconnect the PTFE tube from the fitting atop the extruder, insert the end of the TPU filament from its Polydryer box, and …

Change to 0.8 mm nozzle:
- Remove silicone sock from hot end
- Install fixture to hold the hot end in place
- Loosen the two knobs clamping the nozzle
- Loosen nozzle with 7 mm socket wrench
- Unscrew & remove nozzle by hand
- Install new nozzle by hand
- Tighten nozzle with wrench
- Tighten those two knobs
- Remove fixture
- Install silicone sock
Change MK4 settings using the LCD panel:
- Settings → MMU = Off
- Settings → Hardware → Printhead = 0.8 mm
Then, with the TPU filament poked into the top of the extruder:
- Filament → Load Filament =FLEX
You’ll want to extrude a few lengths just to settle everything in place.

Switching back to the 0.4 mm nozzle proceeds in the opposite direction, starting with:
- Filament → Unload Filament
Something of a nuisance, but not unbearable.
2026-06-04

Square Patio Table Feet

For a square patio table (with one missing foot), of course:

Patio Table Feet - installed — Patio Table Feet – installed

These are chunky enough to demonstrate they’re made of clear-ish TPU, at least when backlit:

Patio Table Feet - installed - backlit — Patio Table Feet – installed – backlit

The interior of the leg determines what fits into it:

Patio Table Feet - leg interior — Patio Table Feet – leg interior

I pried out another foot, scanned it, and blew out the contrast:

Patio Table Foot - scan — Patio Table Foot – scan

Importing that into LightBurn let me draw a rectangle matching the measured size, then node-edit the corners to approximate the shape:

Patio Table Foot - LightBurn layout — Patio Table Foot – LightBurn layout

Export that shape as an SVG, import into OpenSCAD, and turn it into a solid model:

Patio Table Foot - solid model - show view — Patio Table Foot – solid model – show view

That’s the Show view simulating the actual positions, which demonstrates why the pair of legs at each corner wear mirror-imaged feet. The Build view arranges the pair more sensibly for 3D printing:

Patio Table Foot - solid model - build view — Patio Table Foot – solid model – build view

The protrusions and their bumps went through several iterations on the way to being functional, with the black TPU prototype on the left being entirely too bendy and the first clear version requiring utility knife editing to fit the end posts inside the leg:

Patio Table Feet - prototypes — Patio Table Feet – prototypes

The original feet seem to be injection-molded ABS with a flat bottom intended to erode one corner against whatever the table stands on. However, the legs splay out at 5° from the vertical, which makes the flat bottom I used for the first few iterations obviously wrong:

Patio Table Feet - flat foot — Patio Table Feet – flat foot

Somebody who can math harder than I would resolve the two angles and all the measurements into a single transformation matrix, but I rotated the foot separately around the X and Y axes, trigged the lowest corner to the proper height, then chopped off everything below Z=0. Works for me.

The OpenSCAD source code as a GitHub Gist:

	// Patio Table Foot – rectangular legs
	// Ed Nisley – KE4ZNU
	// 2026-05-26

	include <BOSL2/std.scad>

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

	/* [Hidden] */

	HoleWindage = 0.2;
	Protrusion = 0.01;
	NumSides = 432*4;
	Gap = 5.0/2;

	$fn=NumSides;

	PadOA = [50,23.5,4.5];

	LegAngles = [5,5];

	EndStrut = [2.5 + 2.5,13.3 – 1.0,23.0];
	SideStrut = [12.0,5.5 – 1.0,13.0];

	Clearance = 0.5;

	StrutsOC = [44.0 – EndStrut.x,18.0 – SideStrut.y];



	//—–
	// Define it

	module Foot(angles = LegAngles) {

	difference() {
	up((PadOA.x/2)abs(sin(angles.x)) + (PadOA.y/2)abs(sin(angles.y)))
	xrot(angles.x) yrot(angles.y)

	union() {

	down(3*PadOA.z)
	linear_extrude(4*PadOA.z)
	left(PadOA.x/2) fwd(PadOA.y/2)
	import("Patio Table Foot – pad outline.svg",center=true);

	up(PadOA.z)
	for (i = [-1,1])
	right(i*StrutsOC.x/2)
	cuboid(EndStrut,anchor=BOTTOM) position(TOP)
	down(EndStrut.y/2) left(i*Clearance)
	pie_slice(r=(PadOA.x – StrutsOC.x)/2,ang=180,l=EndStrut.y,anchor=CENTER,spin=-i*90,orient=FRONT);

	up(PadOA.z)
	for (j = [-1,1])
	fwd(j*StrutsOC.y/2)
	cuboid(SideStrut,anchor=BOTTOM) position(TOP)
	down(SideStrut.x/2) zrot(90) right(j*Clearance)
	pie_slice(r=(PadOA.y – StrutsOC.y)/2,ang=180,l=SideStrut.x,anchor=CENTER,spin=j*90,orient=FRONT);

	}

	cuboid(4*PadOA,anchor=TOP);
	}

	}


	//—–
	// Build it

	if (Layout == "Show") {

	back(PadOA.y/2 + Gap)
	Foot();

	left(0.8*PadOA.x) fwd(PadOA.y) zrot(-90)
	yflip() Foot();

	}

	if (Layout == "Build") {

	union() {
	fwd(PadOA.y/2 + Gap)
	Foot();

	back(PadOA.y/2 + Gap)
	yflip() Foot();
	}
	}

view raw Patio Table Foot.scad hosted with ❤ by GitHub

2026-06-03

Round Patio Table Feet
For a round patio table, although you can’t tell from the picture:

Round patio table feet – installed

Also despite appearances, that’s 3D printed from clear-ish TPU, with its black appearance due to internal reflections from the leg’s dark interior.

The original hard-white-plastic feet had eroded enough to let the aluminum legs scrape the deck paint:

Round patio table feet – old vs new

The only way to extract each old foot was to hack out a segment with a razor knife, after which it slid out easily.

The ring around the top of the sections provides enough griptivity inside the leg to hold the foot in place:

Round Patio Table Foot – solid model

As with the TPU chains on the bike rack tray holder, I expect the compressed / bent segments will gradually relax inside the legs, but the feet ought not fall out in normal use.

The OpenSCAD source code isn’t quite a one-liner, but it’s close:
```
// Patio Table Foot - round legs
// Ed Nisley - KE4ZNU
// 2026-05-29

include <BOSL2/std.scad>

/* [Hidden] */

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

HoleWindage = 0.2;
Protrusion = 0.01;
NumSides = 4*3*2*4;
Gap = 5.0;

$fn=NumSides;

PadOA = [8.0,1*INCH,3.0];

SleeveOA = [13.0,21.7 - HoleWindage,12.0];

Kerf = 2.5;


//-----
// Build it

difference() {
  union() {
    tube(PadOA[LENGTH],od=PadOA[OD],id=PadOA[ID],anchor=BOTTOM) position(TOP)
      tube(SleeveOA[LENGTH],od=SleeveOA[OD],id=SleeveOA[ID],anchor=BOTTOM);
    up(PadOA[LENGTH] + SleeveOA[LENGTH] - 1.0)
      torus(d_maj=SleeveOA[OD],r_min=(PadOA[OD] - SleeveOA[OD])/2,anchor=TOP);
  }
  up(PadOA[LENGTH])
    for (a = [0,60,120])
      zrot(a)
        cuboid([PadOA[OD],Kerf,2*SleeveOA[LENGTH]],anchor=BOTTOM);
}
```
2026-06-02
Laser-Engraved Food
Having been nerd-sniped again, I had to try this:

Laser-toasted bread – engraving

It turned out reasonably well:

Laser-toasted bread

That’s at 100 mm/s and 40% of a 60 W CO₂ laser. Although the exhaust fumes smelled pretty good, the bread tasted burned rather than toasted.

Undaunted, I tried another sandwich layer:

Laser-engraved food – provolone – direct light

The patterns become more obvious in oblique light:

Laser-engraved food – provolone – angled light

Settings, all with 0.3 mm line interval:
- Top: 100 mm/s @ 40%
- Middle left: 100 mm/s @ 20%
- Middle right: 200 mm/s @ 20%
- Bottom: 200 mm/s @ 12.5%
It’s good stinky provolone, so its taste remained undamaged by the experience.

Laser engraving apparently works really well on hot dogs and their buns, but I am not going there …
2026-06-01
HQ Sixteen: Needle Bar Reorientation
The original needle bar orientation for Mary’s Handiquilter HQ Sixteen put the needle clamp screw (a black-oxide socket head cap screw with the end flattened) about 45° from the rear of the needle bar:

HQ Sixteen – original needle foot orientation

The hex driver passes through the sight hole letting you verify the needle is inserted all the way into the holder before tightening the screw.

It turns out needles fitting the HQ Sixteen come in two varieties, both with nominal 2.0 mm shanks. Mary’s stock has slightly different and entirely consistent diameters around their eyeballometric typical value:
- Round shank = 1.94 mm (-0.00 / +0.02 mm)
- Flatted shank = 2.04 mm (-0.02 / +0.04 mm)
The round shank needles fit easily into the needle holder, but most of the flatted needles simply would not go in. The difference felt like a burr somewhere inside the bore, rather than a uniformly too-small bore: a burr is easy to imagine around the threaded hole for the lock screw.

Orienting a round-shank needle is exceedingly fiddly, because the groove above the thread hole must be aligned exactly to the front of the needle bar to mesh properly with the bobbin mechanism, but snugging the screw invariably rotates the shank.

While you might think the locking screw would properly orient flatted-shank needles by tightening on the flat, you would be wrong. The flat is at the back of the machine when the groove and hole are properly oriented, which means the locking screw bears on the rounded part of the needle, right at the edge of the flat. Mary was generally unable to use even the few flatted needles that fit into the needle bar, because tightening the screw tended to grab the flat, rotate the needle, and lock it firmly in the wrong orientation.

It is worth nothing that all of the other machines around here have locking screws arranged exactly as you’d expect: tightening the screw onto the shaft flat correctly aligns the needle with zero fiddling.

Pictures of various HQ Sixteen machines found on the InterWebs show their needle bar and locking screw can be oriented anywhere from nearly in front to entirely in the back, suggesting:
- Whoever aligns those machines doesn’t care about needle orientation
- Everybody uses round-shank needles
- Anybody using flatted-shank needles is an outlier
I suggested rotating the needle bar to put the screw in back and, if possible, remove the burr inside the bore. After considerable discussion, my plan was approved.

The needle bar slides vertically in a machined block, driven by a link attached to the machine’s main shaft, shown here at Top Dead Center:

HQ Sixteen Handi-feet conversion – foot rod clamp

The surface of the needle rod has a yellow / amber color from the slick coating that must not be disturbed, to the extent the maintenance instructions require a plastic-lined clamp for adjustments.

The vertical position of the needle rod in the clamp determines the “timing” of the needle with respect to the hook on the whirling bobbin case where the magic happens. Setting the timing requires a Special Service Tool that I do not have and likely never will, so the vertical position must not change while rotating the rod in the clamp.

So, we begin.

Removing the machine cover requires removing the Control Pod electronics box with all its cables to get access to the last screw, so this is a nontrivial operation.

Position the shaft at Bottom Dead Center, then measure the distance from the ruler foot to the needle plate:

HQ Sixteen – Ruler foot clearance

The correct distance is 0.5 mm and the taper gauge shows it at 0.6 mm, but all I need here is putting it back at the same height after I remove the foot.

Ensure the shaft is exactly at Bottom Dead Center, then stack gauge blocks under the needle bar as shown in the top picture. For reference, the gauge block set showing which blocks went into that stack:

HQ Sixteen – gage blocks used

Although I didn’t need the absolute measurement, it’s 0.551 inch = 0.300 + 0.150 + 0.101 inch = 13.995 mm. It’s less than 0.552 inch = 14.021; I decided fiddling with the fourth decimal place would be counterproductive.

With the needle bar held at that height, stick a screwdriver through the hole intended for this purpose and loosen the clamp screw:

HQ Sixteen – needle bar clamp

Yes, the hole is slightly misaligned with the screw, presumably because aligning it properly would put the hole too close to the edge of the frame casting for comfortable drilling. You could make this adjustment without removing the cover, but I’m not that type of guy.

Rotate the needle bar to put the locking screw exactly at the back, verify the bottom of the bar rests on the gauge blocks, tighten the clamp screw, and verify the bottom of the bar rests on the gauge blocks:

HQ Sixteen – needle bar reoriented

Again, the hex driver shows the observation hole orientation.

Acceptance testing requires a practice quilt, but the machine lights up properly and moves smoothly with a needle in place, so it’s pretty close to being correct.

This was one of those jobs requiring about two hours of setup, twenty seconds of adjustment, and half an hour of put-away.
2026-05-26