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.

Category: Science

If you measure something often enough, it becomes science

Scanning Offset Adjustment: LightBurn vs. RDWorks
A protracted debugging session on the LightBurn forum produced an interest result, which I must yoink over here so I can recall my thoughts:

The test patterns will require power / speed tweakage to properly mark cardboard on other machines. The vector boxes are about 1.5 mm wide: these are small differences in small patterns.

The setup for both LightBurn 1.7 RC-13 and RDWorks 8.01.65:
- The engraved patterns run at 500 mm/s & 20% power
- The lines & letters run at 100 mm/s & 8% Min – 9% Max power
- All on white cardboard, with image contrast blown out
Scanning offset = 0.2 mm = the usual setting for my machine

In LightBurn:

Scanning Offset 0.2 – LightBurn

In RDWorks:

Scanning Offset 0.2 – RDWorks

The slight shift to the left in the LightBurn results shows LB does not shift the uni-directional pattern to line up with the vector shape as RDWorks does, which is what started the forum thread.

Scanning offset = 1.0 mm to accentuate the difference, while shredding the bi-direction pattern as expected.

LightBurn’s uni-directional engraved pattern is still in the same slightly leftward-shifted position relative to the vectors, showing the offset value has not been applied:

Scanning Offset 1.0 – LightBurn

RDWorks definitely applies the offset in both modes:

Scanning Offset 1.0 – RDWorks

I do not know why RDWorks did not output the final “l” over there on the right, but it did so on some (not all) of the patterns while setting things up. The jank is strong with it.

So having LightBurn apply the same offset value for both uni- and bi-directional engravings would fix the (slight) offset in my machine. I think it will also fix the much larger misalignment in [the other] machine in that forum discussion.

The whole problem seems to arise from the response time of the HV power supply / laser tube: the position of the left & right edges of the scanned output line depend critically on the rising and falling edges of the current applied to the tube and its power output.

Being me, of course, makes me want a different offset value applied to the uni-directional case, just for fine tuning. Which would require a duplicate offset-per-speed table and that looks like a UX disaster comin’ on strong.
2024-09-24
Pill Desiccant

One of my Old Guy medicines has an elaborate desiccant container:

Pill desiccant container

Being that type of Old Guy, I weighed the container when I emptied the bottle, then left it sit in the kitchen cabinet with the scale for a week as the weight slowly increased.

It started at 2.38 g and stabilized at 2.56 g, so it absorbed 0.18 g of water from the air after it got my attention.

Peeling the label revealed an obvious joint:

Pill desiccant – contents

Looks like HO-scale coal in there!

The desiccant weighs all of 1.20 g, so it absorbed something more than 10% of its weight. That’s less than I found with silica gel, but I don’t know the starting weight or how much moisture it already absorbed.

A newly opened pill bottle disgorged a container weighing 2.42 g. The initial weight obviously depends on many variables, none of which would be tightly controlled.

2024-09-19
Miniature Planetary Gear Bearings

Because it’s easy to scale solid models:

Small Planetary Gear Bearings – PETG PETG-CF

The small bearings are 25 mm OD, with correspondingly small clearances between their moving parts, but they all spun easily after a bit of breaking in.

As with their larger cousins, the orange PETG bearing has the most axial play and worked just fine right off the platform. The gray PETG-CF bearing was jammed and required concerted effort to get the gears rolling, but now has essentially no axial play while turning easily. The snappy-looking orange and black bearing has very little play and feels the best of the three.

The single-material bearings take about 20 minutes to print, while the mixed material one requires 80 minutes due to the extruder purging and nozzle clearing. The larger mixed material bearing took more than three hours, but time doesn’t scale as the cube of the size because changing materials runs at a constant time:

Small Planetary Gear Bearings – PETG PETG-CF with wipe towers

The smaller mixed gear produced the smaller wipe tower on the right, but changing materials remains an expensive process. Of course, if you were doing this in production, you’d make a couple dozen of the little things in one job: the machine would spend most of its time squirting out planetary gear bearings with the same number of material changes building the same size wipe tower.

They’re slightly too small for my fingers and surely pose a choking hazard to children, but they’re definitely cute.

2024-09-17
Revised Measuring Spoon Drainer

A small tweak to the venerable spoon drainer adds a configurable cutout adapting it to a slightly different dish drainer rack:

Measuring Spoon Drainer – solid model

Which lets it snuggle into the corner:

Measuring spoon drainer – installed

Both the old and new racks had coated steel loops stuck into rubberoid feet perfectly suited to collect water and eventually rust the loops. Given a new rack, I figured potting the feet in JB PlasticBonder urethane adhesive would help forestall the rust:

Rubbermaid dish drainer – foot potting

I wish it were white, rather than black, but the only other color choice is tan and I can’t wish nearly that hard.

Along those lines, however, the gray JB Weld epoxy coating on the cheese slicer and the smaller repairs on the big knife are doing fine after years of use. JB Weld is good stuff!

2024-09-16
DVD Coasters: Stress Cracking

A bit less than a year ago I engraved Guilloche patterns on a stack of DVDs, stuck foam on their data sides, and defined the result to be coasters:

Laser cut CDs – Foam vs MDF-cork backing – detail

Perhaps unsurprisingly, those grooves turned out to be excellent stress raisers, to the extent that the two most-used coasters (we’re not talking heavy use) have developed cracks:

Laser-engraved DVD A – stress cracks

The parallel lines are part of the logo / pattern / design printed on the label side of the disc, which seems to have wrinkled after being glued to the foam layer. The cracks radiate outward from the laser-scarred zone around the hub.

The other one is worse:

Laser-engraved DVD B – stress cracks

None of the discs glued to rigid backing plates show anything more than minor cracks, so I think a combination of stress raising and slight flexing is really bad for cheap coaster-like objects.

No great loss, easily outweighed by knowing what not to do next time …

2024-09-09
Anker A1215 PowerCore 13000 Power Banks: Five Years

After five years of powering the action cameras on our Tour Easy recumbents, the pair of Anker A1215 PowerCore 13000 USB power banks have about 8 A·hr of capacity with a 2 A load after a full charge:

Anker PowerCore 13000 – 20204-07-26

It seems I did not test them on arrival, so I have no idea what their original capacity might have been, but I’m certain it wasn’t the 13 A·hr implied by their name.

The sawtooth voltage output looks like the internal controller picks a constant boost (or buck) ratio based on the battery voltage, then adjusts it when the output voltage falls below the lower limit. You can imagine it desperately boosting the ratio as the battery voltage falls off a cliff near the end of the curve.

I have no idea why the two packs behave so differently, although the voltages are certainly within ordinary USB limits.

They’ll continue powering the camera on my bike for a while, after which I’m sure they’ll come in handy for something …

2024-08-06
Please Close The Gate Signs: One Year

They still look pretty good after a year:

Please Close The Gate – weathered acrylic – 2024-07-20

Which is to say: the orange acrylic hasn’t faded, the black paint’s still in place, and the gates seem to stay closed.

One might quibble about the missing wire snippet on the lower left corner, but on the whole it doesn’t get much better than that …

2024-08-02