Tag: MK4

Prusa Mk 4 3D printer with MMU3 feeder

Gizo Spider Footpads
Given a 3% failure rate for the tiny footprint of Gizo spider legs, I added 5 mm pads to each foot:

Gizo Spider – footpads

A few rounds of successive approximation and one copypasta hit the right spots:
```
// Gizo spider footpads
// Ed Nisley - KE4ZNU
// 2024-10-26

pts = [
[24,-23],[28.5,-7],[29.5,14.5],[20,28],
[-24,-23],[-28.5,-7],[-29.5,14.5],[-20,28]
];

translate([14,0,2.8])
  import("/mnt/bulkdata/Project Files/Prusa Mk4/Models/Gizo Spider/GizoSpider.stl");

linear_extrude(height=0.2)
  for (pt = pts)
    translate(pt)
      circle(d=5,$fn=2*3*4);
```
Which was enough to stick the legs firmly to the build platform:

Gizo spider – white leg towers

Talk about blank looks:

Gizo spider – black on platform

White filament is particularly susceptible to charred globbing:

Gizo spider – white char inclusion

Which was, fortunately, completely hidden inside the shell.

Extensive testing showed the pads pushed the error rate below 1.5%:

Gizo spider pile

As before, dots of hot melt glue hold the eyes in place.

All’s well that ends well: just in time, too.
2024-10-30
Cart Coin Handle vs. Reality

This failed pretty much the way I expected:

Cart Coin – broken handle

The “carbon fiber” part of PETG-CF consists of very very short fibers, unlike the longer fibers in real carbon fiber materials, so the strength is nowhere near what you might expect from the marketing. I knew this going in and the break wasn’t surprising.

Round cart coins continue to work exactly like US quarters.

2024-10-29
Humidifier Lid Hinges
The humidifier that Came With The House™ had a lid with two broken plastic hinges that I figured I could never replace, but while cleaning out the fuzz for the upcoming season I found one missing piece stuck inside the lid. Given a hint, I glued it back in place:

Humidifier Hinge – outlined

There’s a strip of duct tape around the outside holding the fragment in place while the adhesive cured.

A manual curve fit to the image in Inkscape produced the red outline, which gets saved as a plain SVG and fed into OpenSCAD to create a solid model:

Humidifier Hinge – solid model

The cylinder doesn’t exactly fit the end of the hinge, but it’s close enough. The straightforward OpenSCAD code making that happen:
```
// Humidfier Hinge Replacement
// Ed Nisley KE4ZNU
// 2024-10-20

HingeThick = 10.0;
PinLength = 10.0;

ScrewOD = 2.0;

NumSides = 2*3*4;
Protrusion = 0.1;

difference() {
    union() {
        translate([0,0,HingeThick])
            cylinder(d=6.0,h=PinLength,$fn=NumSides);

        linear_extrude(height=10.0,convexity=5)
            translate([-3.1,-8.0])
                import("Humidifier Hinge - ouline.svg");
    }

    cylinder(d=ScrewOD,h=4*(HingeThick + PinLength),center=true,$fn=8);
}
```
The pin has a hole for a M2 screw, but contemplation of the broken pieces suggested the pin wasn’t the weakest link, which later experience confirmed.

Figuring I’d need only one hinge, I made a spare for fitting:

Humidifier hinge – on platform

The unmodified part fit just about perfectly, whereupon a completely ad-hoc fixture involving a pair of laser-cut MDF slabs, a craft stick epoxy mixer, and more duct tape held it in place while the adhesive cured:

Humidifier hinge – fixturing

The hinge pin turned out to be half a millimeter too long, which is easily fixed, and it worked fine:

Humidifier hinge – installed

That’s more duct tape wrapped around the perimeter to hold the pieces in place, should it break again.

Which, I regret to report, occurred on the way up the stairs from the Basement Shop™ when the lid slipped from my grasp, fell away from the rest of the humidifer’s top panel, and jammed open:

Humidifier hinge – break

The PETG-CF part held together, the adhesive remained bonded to both pieces, but the original plastic fractured just below the joint. A closer look from the other side shows the break:

Humidifier hinge – break detail

The other hinge broke about where it did before.

So the humidifier remains in service with the lid in status quo ante and a small bag inside holding the fragments for the next return to the shop.

Drat!
2024-10-28
Gizo Spiders: Leg Splice

This being the season for decorative spiders, two more appeared:

Gizo spider assortment

Wedding photographers have trouble getting the proper exposure for both the bride and the groom, too.

Only one of the 32 legs came loose from the platform:

Gizo spider – failed leg

The upper part of the leg captured the loose segment and glommed it into a blob:

Gizo spider – failed leg – detail

Fortunately, one of the clearance test pieces was an isolated leg and joint, so I amputated the grisly mess, matched the cut in the test piece, and hot-melt-glued the pieces together:

Gizo spider – spliced leg

Not quite perfect, but good enough for the purpose.

Given the 3% failure rate, I think the legs show such small contact areas really do justify a brim. Adding a brim to the main body would mess up the joints, but I think PrusaSlicer can add brims to specific parts. More study is needed.

Orange eyes for the win!

2024-10-21

Laser Cutter: Focus Ramp Fixture

After figuring out the Ruida focus settings, a focus ramp fixture seemed like a good thing to have around:

Ramp Test Fixture - setup — Ramp Test Fixture – setup

The solid model shows a bit more detail:

Laser Focus Ramp Fixture - solid model — Laser Focus Ramp Fixture – solid model

Centering the autofocus “pen” = switch on the peg in the back puts the beam dead-center in the fixture, with the notches as comfort marks. The top of the peg is flush with the center notch, so the machine should be properly focused at that level after a focus operation.

Obviously, your laser has a different pen location, as will this one the next time I fiddle with anything around the nozzle.

The general idea is to tape a target to the ramp, with some attention to flattening the paper (tape the edges in critical spots as needed) & putting its zero at the center marks, align the fixture to the laser path along the X axis & secure it with a few magnets, then burn a single line at low power along the length of the scale:

Ramp Test Fixture - laser line — Ramp Test Fixture – laser line

The mark will be thinnest in the region with the best focus, which should be centered around the 0.0 mark in the middle. In that photo, the thinnest section runs from about -2.0 to +1.0, although (at least for me) it does take some squinting to be sure.

The ramp has a 1:10 = 5.71° slope to spread 1 mm of vertical focus across 10 mm of horizontal distance. If you’re being finicky, you should rescale the targets to correct the 0.5% cosine error, but IMO it’s irrelevant for this purpose.

A few more tests varying the focus distance by a millimeter:

Ramp Test Targets - 15 16 mm — Ramp Test Targets – 15 16 mm

AFAICT, setting the controller’s Focus Distance to 16 mm is about right. That puts the focal point 18 mm below the nozzle, as shown in the earlier post, and is pretty much what I’ve been using all along.

The OpenSCAD code as a GitHub Gist, along with a simplified target layout in SVG format:

	// Laser Cutter Focus Ramp Fixture
	// Ed Nisley KE4ZNU
	// 2024-10-10

	FocusPenOffset = [-19,23,0];
	FocusPenOD = 10.0;

	RampHeight = 16.0;
	RampScale = 10;
	RampLength = RampScale * RampHeight;

	Magnet = [5.0,60.0,10.0];

	NumSides = 3*4;

	Protrusion = 0.1;

	RampAngle = atan(RampHeight/RampLength);
	echo(RampAngle=RampAngle);

	Slot = [(RampLength + 25.0),10.0,8RampHeight]; // very tall to cut through everything

	Body = [(Slot.x + 210.0),30.0,3RampHeight]; // extend Z to reach baseplate

	FocusPillarHeight = (RampHeight/2) + Body.z/3; // match Z at center of body

	BasePlate = [(Body.x + 2Magnet.x + 25.0),max(Magnet.y,FocusPenOffset.y + 2*5.0),3.0];
	BaseRound = 5.0;

	//—– Build it

	difference() {
	union() {
	translate(FocusPenOffset)
	cylinder(d=FocusPenOD,h=FocusPillarHeight,$fn=NumSides);

	difference() {
	union() {
	rotate([0,RampAngle,0])
	cube(Body,center=true);

	linear_extrude(height=BasePlate.z)
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(BasePlate.x/2 – BaseRound),j(BasePlate.y/2 – BaseRound)])
	circle(r=BaseRound,$fn=NumSides);
	}

	cube(Slot,center=true);

	translate([0,0,FocusPillarHeight]) {
	cube([0.5,2*Body.y,1.0],center=true);

	rotate([0,RampAngle,0])
	cube([2*Slot.x,0.5,1.0],center=true);
	}

	}
	}

	translate([0,0,-Body.z])
	cube(2*[BasePlate.x,BasePlate.y,Body.z],center=true);
	}

view raw Laser Focus Ramp Fixture.scad hosted with ❤ by GitHub

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view raw Target Layout – LightBurn.svg hosted with ❤ by GitHub

Contrary to what you might think, the targets are not laser cut, although you could use the crosshairs for LightBurn’s Print and Cut alignment.

2024-10-18

Printed Spiders

PETG gets remarkable traction on a Prusa Textured Powder-Coated Steel Sheet:

Gizo spider – starting build

The Gizo spider’s eight legs built right up to the top without incident:

Gizo spider – nearly complete

The Articulated Spider assembled from many flat pieces distributed over the sheet, with no excitement at all:

Articulated and Gizo spiders

The orange parts printed in a separate operation (the eyes push in and glue on, respectively), because multi-material printing doesn’t make sense unless there’s no other way.

Those were test cases of joint fit without any model adjustments. The Gizo prints fully assembled and, as with the Steamopus, all eight joints worked smoothly after a few careful break-in motions. Each of the Articulated Spider’s many joints snapped together without incident, but benefited from a dot of silicone grease apiece.

With the possible exception of the PETG-CF filaments, the MK4 prints accurately enough to not need much, if any, compensation.

2024-10-17
Seasonally Appropriate Teapot Knob
Long years ago, the Bakelite (or some such) lid on our rarely used teapot disintegrated, whereupon I replaced it with an aluminum sheet and metal knob. Admittedly, a metal knob was not the brightest idea I ever had, but it sufficed for a few uses over the intervening decades.

Mary hosted this month’s quilting bee and, after having someone else bring a larger teapot for the occasion, suggested I Make. A. Better. Knob. After a bit of searching, this statue seemed appropriate for the season:

Skull teapot knob

It’s printed with PETG filament that should easily withstand the no-more-than-boiling-water temperatures found atop a teapot.

I imported the original model into PrusaSlicer, shrank it to 50 mm tall and simplified the mesh, exported it as an OBJ file, imported it into OpenSCAD, mashed it together with a 1/4-20 threaded_nut from BOSL2, added the finger protector, and got a suitable model:

Teapot Knob – solid model bottom view

The as-printed threads were a bit snug with $slop=0, but running the screw in with a dot of silicone grease to ease the way worked fine.

I should rebuild the whole lid in PETG-CF sometime.

The OpenSCAD code stitches the parts together:
```
// Teapot Knob
// Ed Nisley - KE4ZNU
// 2024-10-11

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

StackHeight = 50.0;
ThreadLength = 25.0;
HeatbreakOD = 40.0;
HeatbreakThick = 3.0;

    intersection() {
        union() {
            cylinder(d=HeatbreakOD,h=HeatbreakThick,$fn=2*4*9);
            up(HeatbreakThick)
                translate([-121,-105])      // totally eyeballometric
                    import("stackofskulls - 50mm.obj",convexity=10);
        }

        union() {
            threaded_nut(100,INCH/4,ThreadLength,INCH/20,        // flat size, root dia, height, pitch
                                     bevel=false,ibevel=false,anchor=BOTTOM);
            up(ThreadLength)
                cylinder(d=100,h=StackHeight);
        }
    }
```
2024-10-16