OMTech 60 W Laser: Expanded Clutter Space

The OMTech laser manual specifically warns against allowing clutter to accumulate atop the cabinet:

It is highly recommended to have an extra work table nearby in order to avoid placing objects on or directly adjacent to the machine, which could become a fire or laser hazard.

OMTech USB570c Cabinet Laser Engraver User Manual

The Basement Shop lacks the floor space for their recommended “extra work table”, so the laser cabinet now sports a pair of wings:

OMTech Laser - side shelf - end view
OMTech Laser – side shelf – end view

They’re a pair of those battered maple shelves, cut to fit the length of the cabinet:

OMTech Laser - side shelf
OMTech Laser – side shelf

They’re a convenient 9 inches wide, just right for general clutter. That stubby screwdriver encroaching on the lid shows I haven’t been entirely successful.

Each white shelf bracket has three self-tapping machine screws driven into the wood and a single 4 mm SHCS through a hole drilled into the cabinet with a nyloc nut & washer on the inside. If I understand the somewhat abbreviated instruction sticker correctly, I installed them upside-down in order to put the longer end under the wood where it would do the most good; they’re entirely rigid enough for the purpose.

Some of the same indoor urethane finish I slobbered on the gate signs tidied the sawed ends.

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
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.

Kodak 750H Slide Projector: Tin Whiskers!

Mary’s folks asked me to figure out why the carousel on their Kodak 750H projector no longer turned. Some initial poking around suggested a problem with the solenoid, which only clunked when the projector was upside-down on the desk. I thought it might just have gummed up after all those years, but disassembling the thing (per the Service Manual and the usual Youtube videos) produced the root cause:

Kodak 750H Projector - broken solenoid link
Kodak 750H Projector – broken solenoid link

That explained the yellowish plastic fragments rattling around inside.

As predicted, it’s impossible to remove the solenoid without breaking the equally brittle focus gear in the process:

Kodak 750H Projector - stripped focus gear
Kodak 750H Projector – stripped focus gear

This is a sufficiently common projector to make repair parts cheap and readily available, at least for now.

Some of the interior sheet metal has a dark surface, likely heavy tin plating, covered with a thick coat of whiskers:

  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers
  • Kodak 750H Projector - tin whiskers

Touching a whiskered surface with masking tape captures the culprits, whereupon zooming the microscope and camera all the way in makes them just barely visible: they’re a few millimeters long and a few atoms wide:

Kodak 750H Projector - tin whiskers - detail
Kodak 750H Projector – tin whiskers – detail

I have surely contaminated the entire Basement Laboratory with tin whiskers. Makes me itchy just thinking about them …

April Fools Day

These seem appropriate for the day.

Whoever composed this wall of text knew the next person in line would update the placeholder:

HelloFresh Intro Offer Card - missed directions
HelloFresh Intro Offer Card – missed directions

As you can tell from the prices, this dates back to late last year. Since then, the two red LED panels on each side had at least one pinball panic and were replaced with much dimmer units:

Mobil gas price puzzle
Mobil gas price puzzle

And a friend pointed me at this bit of innocently twisted signage from a Twitter thread:

Refuse
Refuse

Meanwhile, back in the Basement Laboratory …

Vintage Acrylic

Concerted rummaging in the Basement Warehouse produced some rather old acrylic sheets:

Acrylic Stockpile
Acrylic Stockpile

Washing with detergent and denatured alcohol cleaned off a lot of grunge, but the yellow tint says it’s been around for a while. In fact, It Came With The House™ when we bought it three decades ago.

One sheet was a status board in an automobile machine shop:

Vintage Acrylic Sheet
Vintage Acrylic Sheet

So, yeah, that might be 70-year-old acrylic.

HP 09872-60066 Digitizing Sights

A long-delayed bench cleanup united these two HP 09872-60066 digitizing sights:

HP 09872-60066 Digitizing Sights
HP 09872-60066 Digitizing Sights

I’ve used the one on the right (above) with my HP 7475A plotters, but the other sight obviously won’t fit:

HP 09872-60066 Digitizing Sights - diameters
HP 09872-60066 Digitizing Sights – diameters

The metal-shell version is advertised as “09872-60066 Calibration Pen for fit HP DesignJet 2000CP 2500CP 2800CP 3000CP 3500CP 3800CP Original New” which makes absolutely no sense, as those were inkjet and laser printers with (AFAICT) no need for a “calibration pen”. Because nobody with those printers will buy (or even look for) a widget they can’t use, the price is surprisingly low, compared to the real ones occasionally found on eBay.

My guess: somebody halfway around the planet found a pile of Genuine HP plastic snap boxes, filled them with knockoff sights vaguely similar to the original (perhaps intended for a different plotter?), and marketed them with the usual (lack of) attention to veracity.

Anyhow, we find our contestants standing in the light on a micropositioner under the microscope:

HP 09872-60066 Digitizing Sights - test setup
HP 09872-60066 Digitizing Sights – test setup

The old sight (genuine HP plotter) has a clean field of view:

HP 09872-60066 Digitizing Sights - old full
HP 09872-60066 Digitizing Sights – old full

With a tidy dot in the middle:

HP 09872-60066 Digitizing Sights - old detail
HP 09872-60066 Digitizing Sights – old detail

The new (to me, anyhow) sight has rather coarse hexagonal light pipes with a gaps at the edges:

HP 09872-60066 Digitizing Sights - new full
HP 09872-60066 Digitizing Sights – new full

The spot at the middle is raggedly machined / drilled, with a bottom sufficiently un-flat to prevent focusing on the whole thing at once:

HP 09872-60066 Digitizing Sights - new detail
HP 09872-60066 Digitizing Sights – new detail

I have a vague project in mind to turn the new (craptastic) sight into an optical alignment punch, but the spot seems a bit too large for that.