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Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: MK4

Prusa Mk 4 3D printer with MMU3 feeder

Knitted Spider: Eyemaxxing
A 3D printed spider with a knitted texture seemed a sufficient oxymoron to justify its existence:

Knitted Spider – black eyes

But all-black looked rather somber, even for an All Hallow’s Eve decoration, so I used PrusaSlicer’s Multi-Material Painting to print the eyes in retina-burn orange:

Knitted Spider – orange eyes – wipe tower

The chunky wipe tower shows the cost of switching filaments for a quartet of little eyes. The new Prusa INDX extruder design reduces that waste, but I’m not going there.

You can see the block of painted-on support under the palps, which worked better than overenthusiastic automatic support generation.

The consensus suggested the spider suffered from insufficient eye, so I upleveled it to maximum spider spec:

Knitted Spider – 8 eyes – on platform

Which looks like evolution in action:

Knitted Spider – iteration

The additional eyes came from a trivial OpenSCAD / BOSL2 sphere:
```
include <BOSL2/std.scad>
spheroid(d=5.0,style="icosa");
```
Which is both small and large enough to have a useful number of facets:

Knitted Spider – 5mm icosa sphere eye model

Those facets will come in handy for Multi-Material Painting.

Adding the sphere to the spider model turned out to be trickier than I imagined, because PrusaSlicer requires object to sit flat on the platform, but merging the sphere and spider models got it done:

Knitted Spider – merged models

Then you can use the Move tool to haul the sphere into place:

Knitted Spider – eye positioning

Use the Scale tool to reduce it to a suitable size.

With the eye in place, copy-n-paste creates a duplicate Merged sphere at the same coordinates, which you chivvy into its proper spot. Repeat as needed for more eyes!

The sphere facets are far below the 0.4 mm nozzle’s resolution, but they simplify painting the eye with “Smart Fill” angle settings:

Knitted Spider – 8 eyes – slicer material painting

I had initially thought to just drop separate spheres in place and assign them to the orange extruder, but the slicer (quite properly) treats them as separate objects and creates balls sitting in sockets.

Instead, the eyes must become part of the spider’s shape, have their exterior surfaces painted, then get sliced. In order to do that, I exported the 8-eyed spider as a new STL file and imported it back for painting & slicing:

Knitted Spider – 8 eyes – slicer model

The original single-color spider prints in an hour and adding any number of eyes doubles the time, so those MMU3 tool changes are expensive. Although the printer is reliable, the auto-retract spools I set up sometimes retract the filament beyond the feed gear inside the MMU3, which the firmware detects and calls for manual intervention. It’s best to be puttering in the basement while the printer buzzes away.
2026-09-23
Printed Fragment Coaster: Delamination and Pinhole

Although “chipboard” is also known as “beer mat”, it’s not intended for long-term use under sweaty mugs. After a few weeks of daily use, this is obviously out of spec:

Printed Fragment Coaster – moisture damage

The aforementioned sweaty mug lifted part of a fragment off the coaster:

Printed Fragment Coaster – delamination

The chipboard is Quickboard from Makerstock, which is basically recycled-fiber chipboard with the advantage of being through-dyed in cheerful colors. It’s described as “2 mm-thick, three-layered board” and it looks like the core delaminated from the bottom layer.

Seeing as how it’s near the end of Sweaty Mug season, I smeared Elmer’s Glue Stick PVA adhesive over the fragment, stuck it back in place, and declared victory.

While doing that, however, I noticed a pinhole:

Printed Fragment Coaster – delamination detail

You may recall the outline came from hand-tracing a fragment of smashed glass in GIMP to get a path, then 3D printing a base to hold it:

Printed Coaster – Set C – oblique

Going back to the original GIMP tracing (storage being cheap, never delete anything), I missed a pixel:

Printed Fragment Set C – GIMP selection – errant pixel

Surely you can see it, particularly because you know exactly where it is. Right?

The (degenerate) path around that pixel becomes a tiny vector in LightBurn:

Printed Fragment Coaster – Set C – orphan vector

It’s easier to see there. Right?

Whereupon LightBurn dutifully punched a pinhole through the chipboard, because that’s what I asked it to do. It also punched that pinhole into the metallized paper reflector under the smashed glass fragment, but I didn’t notice it then, either.

Shrinking the GIMP selection by one pixel width, then growing it by one pixel would eliminate single-pixel selections: just another item on the to-do list while tracing fragments.

Ya learn something new every day around here …

2026-09-21
Another Snowflake Coaster Reaches EOL

Apparently a year in the bathroom under a cup with constant moisture is enough to ruin untreated wood inlaid in an acrylic coaster:

Mildew on wood snowflake coaster

A small 3D printed chipboard fragment coaster now enters service:

Printed Fragment Coaster – small

I recently ran into an interesting chipboard failure suggesting this one won’t last forever, so the clock is ticking.

About which, more later.

2026-09-18
Dog Paw Coaster
Start with a picture of a dog paw:

Dog Paw Coaster – starting picture

Rescale the paw to about 100 mm vertically to properly fit a normal-size glass / tumbler / mug. This may be considerably larger than life, but dog owners always want more dog, so it’ll work.

Generate an outline mask in GIMP:

Dog Paw Coaster – paw mask

Generate another mask for the pads & toenails:

Dog Paw Coaster – pad mask

Convert those into paths, save them as SVG files, and hand them to OpenSCAD:
```
include <BOSL2/std.scad>

/* [Hidden] */

PadThick = 1.2;
BaseThick = 2.0;

RimHeight = 0.4;
RimWidth = 0.8;
RimOffset = 1.0;

Clearance = 0.1;    // embiggen pad recesses

OutlineFN = "Dog Paw - Outline.svg";
PadFN = "Dog Paw - Pads.svg";

union() {


  linear_extrude(h=BaseThick)
    import(OutlineFN);

  color("Green")
    up(BaseThick)
      linear_extrude(h=PadThick)
        difference() {
          import(OutlineFN);
          offset(r=Clearance)
            import(PadFN);
        }

  
}
```
Which will get you a solid model like this:

Dog Paw Coaster – OpenSCAD model

Should you want decorative raised rims around the perimeter and pads:

Dog Paw Coaster – raised rim – OpenSCAD model

Then turn this on:
```
if (false)
  color("Red")
    up(BaseThick + PadThick)
      linear_extrude(h=RimHeight) {
        difference() {
          offset(r=RimOffset + RimWidth)
            import(PadFN);
          offset(r=RimWidth)
            import(PadFN);
        }
        difference() {
          offset(r=-RimOffset)
            import(OutlineFN);
          offset(r=-(RimOffset + RimWidth))
            import(OutlineFN);
        }
      }
```
Run the solid model through PrusaSlicer, send it to the MK4, and, while the printer is buzzing away, run the pads through an online nesting program to see how well that works:

Dog Paw Coaster – Pads nesting – LightBurn layout

While nesting didn’t save much material, it might come in handy for something more intricate and now I’ll be able to find it again.

Then get busy:
- Stick adhesive sheet to the chipboard
- Mirror the pads to cut adhesive side up
- Cut the pads, rescue a toenail from the chip tray
- Import the paw outline SVG
- Offset 0.75 mm inward
- Stick adhesive sheet on the cork
- Cut paw outline (adhesive up, but not mirrored!)
- Peel & stick
Which turned out pretty good:

Dog Paw Coaster – assembled

I used Concentric infill on the top to resemble the fur pattern, but it came out way too subtle.

The owner liked it, though, which made it all worthwhile.
2026-09-17
Prusa MK4 Camera Lighting: FAIL

Well, this didn’t take long:

Prusa MK4 – Extruder sidelight – COB LED failure

The upper five-LED string in the middle module failed open-circuit, which left the remaining two strings handling too much current. The five LEDs across the middle look like they’re running at War Emergency Power and the lower five are limping along:

COB LED failure – detail

The dark spots in the middle are overexposed pixels.

I soldered in a replacement from the same bag and it’s all good again, but I expect that won’t last very long.

2026-09-10
Bike Rack Tray Holder: Small Version

Mary wanted to haul seedlings started in half-gallon milk bottles to their destination and I figured they shouldn’t slide around while being transported:

Milk bottle seedling starter carrier

That’s a half-width drawer from the same salvaged collection that produced the Bike Rack Tray Holder and a few minutes with LightBurn adapted the wider cardboard bike rack mount to fit the narrower drawer:

Bike Rack Tray Holder – small – LightBurn layout

Basically, use Node Edit to delete the horizontal lines, move the sides inward by half the difference of the drawer widths, then draw a few short lines to close the gaps.

Hot-melt gluing four layers of cardboard with crossed corrugations, plus three flat bottom layers, got it done:

Bike Rack Tray Holder – small drawer – installed

Those are the same stretchy TPU straps, with an additional link on each rear chain to compensate for the slightly higher block mount and a slightly narrower front block to fit in the slightly narrower drawer handle:

Bike Rack Tray Holder – half-width drawer straps

Of course, the only way to know what didn’t fit was to make a pair of the original ones, try them on for size, then adapt the OpenSCAD code accordingly.

That was surprisingly easy …

2026-09-09

PolyDryer Humidity: September

After six months to see how much moisture entered from the 50%RH (±5%RH) basement air:

	2026-09-07
Filament	%RH	Weight – g	Wt gain – g	Gain %
PETG White	26	56.2	6.2	12.4%	Gel
PETG Black	28	57.3	7.3	14.6%	Gel
PETG Orange	34	54.1	4.1	8.2%	Alumina
PETG Clear	37	54.4	4.4	8.8%	Alumina
PETG-CF Blue	38	54.0	4.0	8.0%	Alumina
PETG-CF Gray	34	56.4	6.4	12.8%	Gel
PETG-CF Black	25	56.3	6.3	12.6%	Gel
PETG Blue	38	55.9	5.9	11.8%	Alumina
TPU Clear	34	56.3	6.3	12.6%	Alumina
TPU Black	32	55.2	5.2	10.4%	Alumina

Sorted by relative humidity:

PETG-CF Black	25	56.3	6.3	12.6%	Gel
PETG White	26	56.2	6.2	12.4%	Gel
PETG Black	28	57.3	7.3	14.6%	Gel
TPU Black	32	55.2	5.2	10.4%	Alumina
PETG Orange	34	54.1	4.1	8.2%	Alumina
PETG-CF Gray	34	56.4	6.4	12.8%	Gel
TPU Clear	34	56.3	6.3	12.6%	Alumina
PETG Clear	37	54.4	4.4	8.8%	Alumina
PETG-CF Blue	38	54.0	4.0	8.0%	Alumina
PETG Blue	38	55.9	5.9	11.8%	Alumina

Fairly obviously, there is no correlation between the humidity level and the amount of adsorbed water.

The silica gel beads were rather dark, not that that means much:

Silica Gel beads - 2026-09-07 — Silica Gel beads – 2026-09-07

All the boxes now contain 50 g of alumina beads.

2026-09-08

Tag: MK4

Knitted Spider: Eyemaxxing

Printed Fragment Coaster: Delamination and Pinhole

Another Snowflake Coaster Reaches EOL

Dog Paw Coaster

Prusa MK4 Camera Lighting: FAIL

Bike Rack Tray Holder: Small Version

PolyDryer Humidity: September