The Smell of Molten Projects in the Morning

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

Tag: Laser Cutter

Laser Cutter: Fourth Corner Fix Summary
A discussion on the LightBurn forum about a large-format machine with a misaligned beam prompted me to think through the whole “Fourth Corner” problem and come up with this summary based on my beam realignment adventure:
Here’s what I think is going on, referring to the 4×8 foot (!) machine in that discussion and lightly edited to improve readability & fix minor errors …

Mirror 1 alignment gets the beam parallel to the Y axis, averaged over the gantry travel between front and rear. The path length variation on your machine is four feet.

Mirror 2 alignment gets the beam parallel to the X axis, averaged over the laser head travel from left to right. The path length variation on your machine is eight feet.

When the laser head is in the left rear corner, the total path length is maybe a foot or two. When it’s in the front right corner, the total path length is upwards of twelve feet.

The “Fourth Corner” problem comes from a slight angular misalignment of Mirror 1, because you (and I and everybody) must set it with a maximum path length around four feet (Mirror 1 to Mirror 2 with the gantry at the front end of the machine). But with the laser head in the right front corner, the path length (Mirror 1 to Mirror 3) is three times longer, so the error due to a slightly mis-set angle at Mirror 1 is correspondingly larger.

A tiny tweak to Mirror 1 changes the spot position at Mirror 2 by very little, but moves the spot at Mirror 3 by much more due to the longer path length.

Tweaking Mirror 1 cannot compensate for a warped machine frame, but it will get the beam alignment as good as it can be made.

The next point of contention was my “middle of the mirror” suggestion. AFAICT, the spot burned into the target at each mirror marks only the useful part of the beam with stray energy in a halo around it. Centering the spot keeps that stray energy away from the mirror mounts, so it doesn’t cause unnecessary heating. This will be particularly important with a high-power laser.

Angular adjustment of each mirror puts the beam parallel to the axes, but cannot also center it on the mirrors. After it’s aligned, the path from the laser tube through the nozzle depends on the position of the tube relative to the nozzle: moving the tube up/down and front/back moves the beam position on the mirrors and through the nozzle, but (in an ideal world) doesn’t change the angular alignment.

So after aligning the beam parallel to the axes, you must move the laser tube, the mirrors (up/down left/right front/back), and maybe the laser head to center the beam in the mirrors and also in the nozzle. Because we don’t live in an ideal world, moving any of those pieces wrecks their angular alignment, so it’s an iterative process.

The goal is to reach this point:

Beam Alignment – Mirror 3 detail – 2023-09-16

Those are five separate pulses, one each at the four corners and center of the platform.

The beam then goes pretty much through the center of the laser head and lens:

Beam Alignment – Focus detail – 2023-09-16

Works for me, anyhow.
2024-11-13
Layered Paper: Mariner’s Compass in Colors

Having recently shotgunned Amazon’s selection of colored art paper, this becomes possible:

Mariners Compass – inset browns

It’s the same geometry as the plain white layered version, with somewhat more attention to detail, and consists of a dozen layers glued and stacked on an assembly fixture.

The quilt-block version uses simple layering:

Layered Paper – Mariners Compass – Beyer 133

No commercial potential, but I like the effect.

2024-11-12
Curtain Rod Spring Pusher Block

Spotted during Autumn Window Cleaning:

Curtain rod pusher block – spring contortion

That’s the compression spring inside the curtain rod over the kitchen sink, intended to push the ends against the cabinets on either side. The screw slides along the outer rod and when tightened, backstops the spring against the inner rod.

The end of the spring is apparently intended to twist and jam inside the inner half of the rod, but that seemed so … unesthetic.

Being in the midst of setting up a Windows 11 box for the laser cutter, I used it as an excuse to fiddle with the RDP configuration to get LightBurn running in full screen mode on the monitor atop my desk; more about all that later.

The little pusher block is a hull around a pair of circles the same diameter as the smaller dimension of the inner rod, spaced apart enough to match its width, then laser-cut from a scrap of 1/4 inch acrylic:

Curtain rod pusher block – overview

Which assembles as you’d expect:

Curtain rod pusher block – installed

The spring seems much happier pushing against the block, doesn’t it?

Admittedly, this was completely unnecessary, but if you think of it as a side effect of the Win 11 thing, it makes at least a little sense.

2024-11-07
Laser Test Paper: Weathering

Three months of outdoor exposure suggest that laser test paper can survive use as a plant tag for one growing season, at least when it remains flat:

Laser test paper – small plant labels – 3 month exposure

The two upper tags demonstrated the paper has no flexibility worth mentioning, so it cannot become a tag wrapped around a stem.

The two lower labels spent their time tucked into a window frame where they got plenty of sun & rain without the benefit of a backing plate. Looks good to me!

Contrary to my expectation, the craft adhesive sheet behind this label survived intact, although the label itself took some damage, perhaps from the more direct sunlight out on the deck:

Laser test paper – plant marker – 3 month exposure

In any event, they look Good Enough™ for our simple needs and next year’s plants will be properly labeled.

2024-11-04
Leaf Engraving

A discussion about engraving leaves on the LightBurn forum prompted an experiment with a seasonally appropriate motif:

Engraved leaves

Those ran at 500 mm/s with 8 to 10% power, respectively the fastest speed & lowest power for my 60 W CO₂ laser.

The mmmm material has obvious irregularities and doesn’t lie flat:

Engraved leaf

A closer look:

Engraved leaf – detail

The line interval is an absurdly large 0.5 mm to keep the leaf from falling apart, as the laser burns almost completely through despite the low power.

I thought about scattering a bunch of these along the driveway, but came to my senses just in time …

2024-11-01
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
Laser Cutter: Focus Ramp Tests
A few ramp tests with various Focus Distance + Home Offset settings as noted:

Ramp Test Targets – 14-17 mm

The bottom test was at 15 mm, which (contrary to previous estimates) seems to center the narrow band round 0.0 mm. Given the depth of field, a millimeter one way or the other likely doesn’t matter, particularly given the mmm lack of flatness in many materials.

The controller settings making it happen:

KT332N Autofocus settings

What they mean:
- Home Offset = distance to retract after the autofocus “pen” = switch activates so the tip of the pen clears the material
- Focus Distance = distance beyond Home Offset to put the focal point at the surface of the material (or wherever you want)
- Enable Homing = makes autofocus work at the push of a button
- Homing Speed = how fast the platform moves while focusing
Getting the focus right really makes the laser cut like it should!
2024-10-24