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

OMTech 60 W Laser: Axis Scale Check
Laying out my longest engraved scale on the honeycomb:

OMTech Axis Cal – dot positioning

The zero-th step aligns the scale with the axis travel: slide one end of the scale to put the dot on the edge, jog to the other end, slide to put the dot on the edge, iterate until the dot is the same brightness on both ends.

The scale lines are a tidy 0.2 mm wide, the red laser dot might be 0.4 (it’s rectangular-ish), and a jog increment of 0.2 mm works well. I can manually align (pronounced “slide”) the scale on the honeycomb to center the dot within a line, whereupon moving the head a known distance to the other end of the scale and counting-while-jogging a few steps until the dot drops into the proper line gives the offset from the correct distance.

Jogging 590 mm along the X axis produced 589.8 mm of actual travel (one jog step short of the line 590 mm from the start), an error of -340 ppm.

Jogging 495 mm along the Y axis travels 494.4 mm, an error of 1212 ppm. That’s considerably more than I expected and required a few iterations until I believed it.

Both axes use steppers with 20 tooth pulleys and 3 mm pitch belts, so the laser head moves 60 mm per motor revolution. The stepper drivers are configured for 5000 steps/rev, so the axes should have a step length of 12 µm = 60 mm / 5000 step. Both axes arrived with Step Length values set to weird numbers very close to 12 µm, but, after a quick check showed incorrect travel distances, I reset them to 12 µm before making real measurements.

LightBurn provides access to the Ruida controller’s “Vendor Settings” (after a warning to not mess things up) and allows you to change them:

OMTech Laser – Axis step length settings

The values shown above come from multiplying 12 µm by the ratio of the actual to the intended distance:
- 11.9959 = 12 × 589.8 / 590
- 11.9855 = 12 × 494.4 / 495
Repeating the tests with those slightly smaller step sizes produces motions that are spot on to within my ability to measure them.

Neither of those changes was large enough to affect the outcome of cutting the Tek Circuit Computer decks, which are much smaller than the full extent of the axes and thus see much smaller errors.
2022-06-14
Laser Printer vs. Laser Cutter: Alignment & Scale

The setup for cutting the Tektronix Circuit Computer decks looks like this:

Tek CC – Bottom Deck cutting setup

Four neodymium bar magnets hold the corners flat against the honeycomb and the neo disk magnet pins the center down, thus ensuring the red alignment laser meets the cutting beam at its focal point on the surface.

The triangular shapes mark the OD of the perimeter (177.8 mm) plus twice the cut margin on each side (2×2 mm), with the tick mark in the upper right ensuring I slap every deck down in the proper orientation. Aligning the two right marks to the edge of the honeycomb frame (with a straightedge for some offset) aims the deck’s 0° index along the cutter’s X axis.

The cut pattern origin is, naturally enough, the center point of the deck, so aligning the red dot to the center cross should put the OD cut at the place all around the perimeter. For confirmation, I fire the laser (“A single ping, Comrade.”) and verify the hole is in the middle of the cross.

Before cutting the deck, the laser also marks the corner shapes, so this may come as some surprise:

Tek CC Middle Deck Corner Targets

The laser printer (a venerable HP LaserJet 1200) produced the dark triangles and the laser cutter (a new OMTech 60 W) burned the light brown marks. The picture is a composite of the four corners, with the blank center removed to concentrate on what’s important.

The scrawls give the edge-to-edge distances in both inches (because that was the scale at hand) and converted to millimeters (because that’s how it’s laid out), with the L suffix for the laser marks.

What’s of interest is that you can’t overlay the two sets of marks by a combination of scaling and rotation with the centers (not shown) of the two patterns pinned together.

The laser measurements differ from the ideal 181.8 mm by 0.1 mm vertically and 0.4 mm horizontally. This may require dinking with the scale factors in the firmware, which I recall having weird values.

The LaserJet is definitely not a precise instrument, off by 0.4 mm vertically and a millimeter horizontally, with considerable variation. I think this comes down to unrealistic expectations for toner stuck to a flexible sheet wrapped around rollers and heated enough to melt dust into the fibers.

More study is indicated …

2022-06-13
Laser Imaging: Glass vs. Titanium Dioxide

A stack of glass shelves has long awaited this fate:

Glass engraving – front overview

As with the paving tile, the image came from a grayscale photo run through a halftone filter. The leftmost four images were burned through a titanium dioxide layer poured / spread over the glass surface. The rightmost two were burned directly into the glass, serving as a reminder that glass absorbs infrared radiation. The power levels varied from 15% to 60%, although I wasn’t taking notes, with a 400 mm/s scan speed.

It looks much the same when viewed from the rear:

Glass engraving – back overview

Although the process is often described as blasting chips out of the glass, there’s definitely melting going on. A closer look at the middle image in the top row, with darker gray patches from titanium fused into the glass:

Glass engraving – partial TiO2 fusion

Some pits have only a tiny dot of titanium, almost invisible against the glare from the glass around the rim:

Glass engraving – plain detail

A very close look shows damaged glass, with titanium in some of the pits:

Glass engraving – TiO2 detail

Higher laser power fuses more titanium into contiguous areas that appear much darker, as in the middle bottom image:

Glass engraving – full TiO2 fusion

This is loosely based on commentary in two LightBurn forum threads about variations on what’s known as the Norton White Tile Method, with more examples on the V1 Engineering forum. Just applying TiO₂ seems less awful than various paints / primers / whatever, with the additional benefit of eliminating the overhead of spraying / cleaning up.

The secret seems to be having enough power to chip the glass and decompose the TiO₂ into darker titanium, while not blasting the result entirely off the surface. Fairly obviously, this will require more experimentation than I’ve done so far.

Minimal assist air protects the laser focus lens from the debris and plenty of ventilation air carries the abrasive result out of the cabinet.

Not something I foresee doing a lot of, but at least I know what happens.

2022-06-02
Laser Imaging: Paving Tile vs. Titanium Dioxide

Dump enough titanium dioxide powder into denatured alcohol to make a thin slurry, bloosh it onto a reasonably clean paving / floor / whatever tile, spread it out with a chip brush, let the alcohol evaporate, then try a few images with various laser power settings scanned at 400 mm/s:

Paving tile – TiO2 prep and engrave

Wash off the TiO₂ powder to leave the fused titanium behind:

Paving tile – TiO2 images

A closer look at the middle eye:

Paving tile – TiO2 images – detail

The small granules spread across the surface are glass chips that probably improve traction, so this must have been a paving or floor tile intended for wet areas. A small stack of whole tiles and fragments Came With The House™, they’ve come in handy over the years, and that’s all we know.

The darkest image was at 40% power (maybe 24 W) and the lightest at 15%, although my notes are a bit fuzzy, and it started as a grayscale image dithered into on/off dots.

Obviously, my imaging hand is weak, but it does verify that TiO₂ powder will produce some sort of image without all the bother and solvents associated with paints / primers and the removal thereof.

2022-06-01
Homage Tektronix Circuit Computer: Laser-Engraved Hairline Improvement

Entirely by accident, I discovered that engraving a hairline with LightBurn’s Dot Mode using 1 ms burns and 0.1 mm spacing produces a continuous trench, rather than the series of dots at 0.25 mm:

Tek CC – Cursor Hairline – 30pct 100u – oblique view

The left is at 20% power (12-ish W) and the right is at 30% (18-ish W), both filled with Pro Sharpie red ink.

The V-shaped groove is even more obvious when seen end-on:

Tek CC – Cursor Hairline – 30pct 100u – end view

In both cases, the travel speed seems to be about 10 mm/s regardless of the speed set in the cut layer parameters. The higher power level produces a slightly wider cut that doesn’t seem deeper, which I cannot explain.

Filled with red lacquer crayon, the hairline looks absolutely gorgeous:

Tek CC – Cursor Hairline – 30pct 100u – in place

Engraving the PETG sheet with the protective film in place produces a neat cut with the film edges fused to the plastic.

Cutting the outline and pivot hole in the same operation ensures everything remains perfectly aligned:

Tek CC – Cursor Laser Cutting

Scribble red crayon over the film, make sure the trench is completely filled, peel the film off with some attention to not smearing the pigment, and it’s about as good a hairline as you (well, I) could ask for:

Tek CC – Cursor Hairline – 30pct 100u – Width

The pigment in the trench is about 0.2 mm wide, with slight heat distortion along each side, and I’ll call it Plenty Good Enough.

Totally did not expect this!

Getting a good-looking hairline on a good-looking cursor turns out to be a major challenge, because there’s nowhere to hide the blunders. A few of the many dead ends along the way shows what’s involved:

https://softsolder.com/2020/05/06/tek-circuit-computer-cursor-hairline-scraping/

https://softsolder.com/2021/01/26/tek-circuit-computer-cursor-hairline/

https://softsolder.com/2021/02/16/tek-circuit-computer-sawed-hairline-fixture/

https://softsolder.com/2021/04/13/tek-cc-milled-cursor-vs-speed-vs-coolant/

https://softsolder.com/2021/04/15/tek-cc-milled-cursor-mvp/

Plenty of Quality Shop Time™ along the way, though …

2022-05-31
OMTech 60 W Laser: Kerf Sizing

The nominal 5.5 mm OD of the eyelet turns out to be 5.45 mm and fits neatly into a nominal 5.3 mm hole laser-cut into either PETG or laminated paper:

Laser cutter – hole size test

The holes are 5.1 mm on one end and increase by 0.1 mm.

The eyelet fits loosely into the 5.4 mm hole, snugly into 5.3 mm, and only into the 5.2 mm paper hole.

So the nominal 5.3 mm hole is really 5.45 mm, which means the beam adds 0.15 mm to the hole diameter, about 0.08 mm to each side.

Given that the eyelet isn’t quite round and the holes aren’t exactly glass-smooth, figuring a 0.2 mm kerf seems both reasonable and easier to remember.

Obviously, the results will differ depending on what’s being cut, how thick it is, and probably the phase of the moon.

Those are the easiest holes I’ve ever made …

2022-05-27
Laser-cut Pole Bean Ties

This is the season for erecting the structures upon which the pole beans will climb:

Garden Bean Poles – overview

They’re made from a dozen small trees and branches of larger trees harvested around the yard. They last for a few years, just long enough for the next crop to reach useful lengths.

We lash them together with fabric strips:

Garden Bean Poles – joint detail

My knot hand is weak, but seems sufficient to the task.

Mary formerly tore the strips from old jeans / pants / whatever, which required considerable effort, produced ragged edges, and filled the air with fabric dust. This year, I proposed an alternative:

Garden Bean Poles – laser cutting ties

The weird thing in the middle is a reflection of an overhead can light in the laser cabinet’s polycarb lid.

From starting the LightBurn layout to presenting the strips for final inspection required the better part of ten minutes. I scissors-cut along the main seams to get single fabric layers, with everything above the crotch seam wadded off the platform to the left.

As with my shop raglets, the layout depends on LightBurn’s overhead camera view to align the cuts with the fabric on the platform:

Bean Pole Ties – LightBurn layout

It’d be easier to see with lighter fabric, but that’s what came to hand in the scrap box and the beans won’t care. We do not anticipate complaints about the odor of charred fabric when they reach the top of the poles, either.

The strips must align with the fabric’s grain to put the warp threads along their length, which makes the main side seam parallel to the X-axis. Even I can handle that layout!

Yes, the strips have rounded corners and, no, it doesn’t matter.

2022-05-25