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.

Author: Ed

Laser-cut Punched Cards

I just had to do this:

Laser-cut punched card samples

It took several iterations to convince me I can’t quite pull it off yet, but the idea shows promise; the GitHub repo includes useful links to other variations and techniques.

The top card starts with hole locations / column numbers preprinted by the inkjet, then (nearly but not exactly) aligned in the laser cutter for “engraving” the variable text and “punching” the corresponding holes. The other cards represent various steps along the way, all of which demonstrate why a 60 W laser is the wrong way to print text on cardstock:

Laser cutter – engraved punched card

Aligning a preprinted sheet in the laser cutter with sufficient accuracy to hit all the holes turns out to be a significant challenge: the red dot laser pointer hangs off the rear of the nozzle with the beam at a steep angle:

Magnetic Honeycomb Spikes – MDF

Which means the red dot coincides with the main laser beam only at the exact focal distance below the nozzle after painstaking (and easily disrupted) alignment. A red dot laser coaxial with the CO₂ tube / beam should produce much better results, but that’s not what I have.

It Would Be Nice If™ I could cut the card outlines with the laser, print the hole positions on the inkjet, then align the “blanks” for “punching”, but I have yet to find any combination of parameters amid the unsteady ziggurat of Linux / CUPS printing configurations to produce properly aligned results on a custom paper size:

Misaligned punched card printing

You might think telling the printer it’s handling a #10 envelope with the image of the text carefully positioned to land at the proper spot on the actual card should work. You (well, I) would be wrong.

I’m pretty sure this can be coerced into working, but it must marinate on the to-do list for a while.

2022-05-04
OMTech 60 W Laser: Improved COB LED Shades

Adding (fake) rivets to the COB LED shade brackets definitely improves their appearance:

Acrylic COB LED Shade – installed

I cut new shades from vintag e clear acrylic sheet, with more aluminized mylar attached to the lower surface: you can barely see the COB LED strip through the reflecting surface.

Depending on how you arrange all the hardware hanging on the nozzle, the shades can collide with something at the home position in the far right corner:

Acrylic COB LED Shade – X clearance

Definitely a step up from cardboard …

2022-05-03
OMTech 60 W Laser: Head Alignment Puzzle

Having established that the laser beam comes out of the lens perpendicular to the honeycomb platform surface, this seemed peculiar:

OMTech 60W beam alignment – head X plane

The mirror 3 + lens tube has a distinct tilt when seen from the +X direction (the right side of the machine, so it’s in the YZ plane, I suppose).

This is not matched when seen from the -Y direction (front):

OMTech 60W beam alignment – head Y plane

The tilt does not seen to correct for a misalignment in the X axis rail or the brackets attaching the head to the linear bearing.

The beam seems properly centered on the lens and nozzle, so I’m loath to twiddle the alignment just to see what happens. One of these days, for sure, that must happen …

2022-05-02
OMTech 60 W Laser: Improved MDF Spikes and Stops

A bit of tinkering suggested I needed a way to repeatably position stock sheets on the honeycomb, so I conjured stops that would be slightly taller than the magnetic spikes:

Improved MDF Honeycomb Spikes – first pass

Three of those form a corner into which you can tuck victims of the same general size:

Improved MDF Honeycomb Spikes – stock alignment

Those pointy MDF spikes should start with slightly rounded tops, because that’s what they’ll look like after a few uses:

Improved MDF Honeycomb Spikes – alignment stops

I also made a low-profile stop for victims lying directly on the honeycomb for engraving:

Please Close The Gate – engraved

The SVG images include a nested version to tile across random MDF leftovers.

The SVG images as a GitHub Gist:

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2022-04-29
OMTech 60 W Laser: Magnetic Honeycomb Spikes

When a cardboard base plate under metal spikes would pose a fire hazard, you can position magnetic spikes where they’re needed:

Magnetic Honeycomb Spikes – acrylic

The 12 mm neodymium magnet is slightly larger than a single honeycomb cell, so it wants to center itself atop a cell. The stainless steel button head screw sits in the magnet’s countersunk hole and protrudes just enough to make sure the spike doesn’t slide sideways unless you want it to:

Magnetic Honeycomb Spikes – parts detail

A cloud of combustible gas doesn’t pose a threat under there:

Magnetic Honeycomb Spikes – MDF

The thin red beam comes from the targeting laser on the back of the nozzle.

Storage is easy: just smush a handful of the things against the side of the laser cabinet:

Magnetic Honeycomb Spikes – storage

Buy all the parts in lots of 100 to have supplies for other adventures!

2022-04-28
Gentec ED-200 Optical Joulemeter: Oscilloscope Comparison
The little DSO-150 oscilloscope has a 1 MΩ || 20 pF input with a 200 kHz bandwidth that should be entirely adequate for the OMTech laser’s millisecond-scale modulation signals from the Gentec ED-200 Optical Joulemeter. There is, however, only one way to be sure:

Gentec ED-200 – scope test setup

The two scope inputs are in parallel, so the joulemeter over on the far right sees a 500 kΩ load, half of the specified 1 MΩ load, with at least twice the capacitance. If the two scopes display pretty much the same result, then it’s good enough.

A 50 ms pulse at half power looks the same on both scopes:
Gentec ED-200 – 50 ms – DSO-150
Gentec ED-200 – 50 ms – Siglent
A 50 ms pulse at full power doesn’t quite top out:
Gentec ED-200 – 11V 50ms – DSO-150
Gentec ED-200 – 11V 50ms – Siglent
Given that the pulse duration should be less than the detector’s 1.5 ms risetime, using a 50 ms pulse is absurd. Right now I’m just looking at the overall waveform and detector range, not trying to get useful numbers out of the poor thing.

All in all, the DSO-150 will do just fine.
2022-04-27
OMTech 60 W Laser vs. Gentec ED-200 Optical Joulemeter: Long Pulse Duration Power

The Gentec ED-200 Joulemeter is severely underqualified to measure the OMTech 60 W laser’s beam power, because the laser’s 1 ms minimum manual pulse width isn’t much shorter than the sensor’s 1.5 ms risetime and the maximum beam power is far too high for the sensor’s health. With that in mind, I set the PWM power to 50% = 30 W (grossly too high) and looked at the peak output voltage for a series of (far too long) pulse widths:

Rounding the detector sensitivity to 11 V/J says the 1.3 V peak at 5 ms corresponds to 120 mJ and 24 W:

Gentec ED-200 – 60W 50pct 5ms

The 3.3 V peak at 10 ms is 300 mJ and 30 W:

Gentec ED-200 – 60W 50pct 10ms

The 3.4 V peak at 15 ms is 310 mJ and 21 W suggests the PWM power output is not nearly as constant as one might expect, although the pulse width looks fine:

Gentec ED-200 – 60W 50pct 15ms

The 6 V peak at 20 ms is 550 mJ and 27 W, although the on-screen display obscures the top:

Gentec ED-200 – 60W 50pct 20ms OSD

Another 20 ms pulse without the OSD produces a peak eyballometrically close to 6.4 V for 580 mJ and 29 W:

Gentec ED-200 – 60W 50pct 20ms

The KT332N controller in the OMTech 60 W laser has a pulse duration setting showing tenths of a millisecond, but (based on some additional measurements) the beam power can vary by 25% for successive pulses in the low millisecond range, so the pulse width resolution doesn’t seem to provide useful control.

Despite the over-long pulses, the calculated power corresponds surprisingly well with the nominal laser output power.

The 1 ms pulses used in LightBurn’s Dot Mode are consistent enough to punch essentially identical 0.2(-ish) mm holes in manila paper to mark the graticule:

OMTech 60W laser – beam alignment – focus detail – 2022-03-22

They’re on 0.25 mm centers, with slight variations showing the difference between stepper resolution and positioning accuracy. The shorter graticule lines have three holes on one side of the center lines and four on the other, despite the design’s 1 mm length on both sides; I think there’s a missing dot on the side where the head starts the line, perhaps due to a picket-fence error.

The large beam hole came from two 10 ms pulses, one at the focal point and another 10 mm lower.

2022-04-26