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
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
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
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
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
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 …

Paracord Hot Knife

An upcoming project calls for cutting dozens of lengths from a spool of 550 (pound tensile strength) all-nylon paracord, which means I must also heat-seal the ends. Cold-cutting paracord always produces wildly fraying ends, so I got primal on an old soldering iron tip:

Paracord cutting - flattened soldering iron tip
Paracord cutting – flattened soldering iron tip

Bashed into a flattish blade, it does a Good Enough job of hot-cutting paracord and sealing the end in one operation:

Paracord cutting - results
Paracord cutting – results

Setting the iron to 425 °C = 800 °F quickly produces reasonably clean and thoroughly sealed cut ends.

Obviously, I need more practice.

Yes, I tried laser cutting the paracord. Yes, it works great, makes a perfectly flat cut, and heat-seals both ends, but it also makes no sense whatsoever without a fixture holding a dozen or so premeasured lengths in a straight line. No, I’m not doing that.

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
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 …

Kenmore Gas Range Control: Solder Joint Failure

The entire control panel of our longsuffering Kenmore gas range became increasingly erratic, eventually reaching the condition where touching the upper right corner would blank the display, touching the lower right corner would restore it, and gently touching the temperature knob might elicit an F2 or F4 error code on the display. Given the symptoms, the old adage “It’s always the connectors” sprang unbidden to mind; I was pretty sure the oven temperature sensor had nothing to do with it.

Pulling the thing apart reveals the PCB across the back of the control panel:

Kenmore oven control - PCB overview
Kenmore oven control – PCB overview

Note that all of the external connections arrive on the white power supply PCB attached over the main PCB.

A closer look shows one of the two groups of wire interconnects between the two boards:

Kenmore gas range - rear PCB
Kenmore gas range – rear PCB

There’s a similar group hidden behind the hulking transformer.

Removing the two obvious screws and easing the PCB out of the red plastic latches made the problem instantly obvious:

Kenmore gas range - failed solder joint
Kenmore gas range – failed solder joint

Yeah, that broken solder joint would definitely be touch-sensitive!

The solder joints in the other group also show signs of fatigue:

Kenmore gas range - broken solder joints
Kenmore gas range – broken solder joints

It’s of interest only the upper joints on the power supply PCB have fractured. Perhaps those ends of the wires were hand-soldered separately from the other ends in the main PCB?

Resoldering both ends of all the wires restored perfect operation:

Kenmore gas range - resoldered joints
Kenmore gas range – resoldered joints

For the record, the Kapton tape I laid over the entire control panel 2-½ years ago continues to protect the slightly cracked membrane over the pushbutton switches:

Kenmore oven control - Kapton tape cover
Kenmore oven control – Kapton tape cover

Gotta love yet another zero-dollar appliance repair …

Laser-cut Pole Bean Ties

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

Garden Bean Poles - overview
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
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
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
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.

Homage Tektronix Circuit Computer: Laser-Engraved Hairline Tests

This worked out surprisingly well:

Tek CC - laser-etched cursor hairline
Tek CC – laser-etched cursor hairline

Not knowing what to expect, I peeled the protective plastic off the styrene PETG sheet before cutting the perimeter, thereby dooming myself to about five minutes of polishing with Novus 2 to remove the condensed vaopor and another five minutes restoring the shine with Novus 1. Next time, I’ll know better.

Eyeballometrically, the hairline is a lovely fine line, but it’s really a series of craters on 0.25 mm centers filled with red Pro Sharpie marker and wiped off with denatured alcohol:

Tek CC - laser-etched cursor hairline - detail
Tek CC – laser-etched cursor hairline – detail

That’s dot mode: 2 ms pulses at 20% power (about 12 W) with a line speed of 100 mm/s and 0.25 mm dot spacing. The craters look to be 0.15 mm in diameter, with a 0.15 mm blast radius merging into a line along the sides. The view is looking through the undamaged side of the cursor, so you’re seeing the craters from their tips.

I cut the cursor and engraved / etched the hairline in one operation, by just laying a rectangle on the honeycomb and having my way with it:

Tek CC Cursor - LightBurn layout
Tek CC Cursor – LightBurn layout

For a more systematic test I aligned a cursor engraving fixture I built for the Sherline atop the laser’s honeycomb platform and wedged it into place with eccentric stops, then dropped a cursor milled on the Sherline in place:

Tek CC Cursor - laser fixture alignment
Tek CC Cursor – laser fixture alignment

The six pips (small printed holes with ugly black outlines) intended for the Sherline’s laser aligner make this feasible, although the accuracy of the OMTech’s laser pointer requires precisely setting the focal point atop the fixture.

The corners of LightBurn’s tooling layer (the enclosing rectangle) match the corner pip positions, so framing the pattern should light up those four holes. Putting the Job Origin (small green square) at the center-left point lets me tweak the machine’s origin to drop the alignment laser into that pip.

AFAICT, burning a cute puppy picture pretty close to the middle of a slate coaster makes everybody else deliriously happy.

Setting up the cut layer parameters:

Tek CC Cursor - laser dot mode tests
Tek CC Cursor – laser dot mode tests

Burning through the protective film, peeling it off, filling with Sharpie, and wiping with alcohol produces interesting results against a 0.1 inch = 2.54 mm grid:

Tek CC Cursor - dot mode 1-2ms 10-20pct
Tek CC Cursor – dot mode 1-2ms 10-20pct

The angled top and bottom lines are the edges of the cursor, positioned with the craters on the top surface.

The bottom three lines at 10% power consist of distinct 0.10 mm craters incapable of holding much ink:

Tek CC Cursor - dot mode 2ms 10pct
Tek CC Cursor – dot mode 2ms 10pct

The top three lines at 20% power have 0.15 mm craters and look better:

Tek CC Cursor - dot mode 1ms 20pct
Tek CC Cursor – dot mode 1ms 20pct

The top line was a complete surprise: it seems a 20% duty cycle does not turn off completely between 1 ms dots spaced at 0.15 mm. I expected a row of slightly overlapping dots, which is obviously not what happens.

Punching the dots through the protective film eliminated the polishing operation, although I have yet to cut the perimeter with the film in place.

More experimentation is in order, but it looks like I can finally engrave good-looking and perfectly aligned hairlines on nicely cut cursors without all those tedious manual machining operations.

[Update: dot mode can produce a continuous trench that looks even better! ]

OMTech 60 W Laser: Key Lock FAIL

The orange indicator I added makes the key lock switch position on the OMTech 60 W laser perfectly obvious:

Laser Power Lock Indicator - installed
Laser Power Lock Indicator – installed

It is in series with the lower switch on the side panel:

OMTech Laser - rocker switch lit
OMTech Laser – rocker switch lit

Although I would have labeled those switches differently, the “Control Switch” handles the 120 VAC line voltage to the HV power supply. As you’d expect, when its light is ON, the power supply is also ON and the laser is ready to fire.

Those two pictures show the situation after I turned the laser power on a few days ago: key lock switch OFF, HV laser power supply stubbornly ON.

Whoops.

The “Control Switch” still does what it should, so I can shut the HV supply off when it’s not needed, but the key lock switch has definitely failed ON.

As far as I can tell, the moving contact bar jammed at the bottom of its travel against the terminals. Pulling the switch out of the laser jostled it enough to release the bar and it’s now at the top of its travel:

OMTech Laser - key lock - side view
OMTech Laser – key lock – side view

If it failed once, it’ll fail again.

OMTech’s Customer Support agrees it shouldn’t behave like that; a replacement should arrive in a few days.