Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Tag: Improvements
Making the world a better place, one piece at a time
Cut the painted sheets cut face-down atop magnetic spikes on the honeycomb platform, with tabs to keep the petals in place and 0.15 mm kerf compensation. A light touch with an Xacto knife severs the tabs, after which the petals press firmly into the frames. Spread yellow PVA wood glue across the bottom disk, align the perimeters and press together, lay parchment paper between the coasters, clamp the stack between plywood sheets, and they emerge perfectly flat the next day.
They’re too labor-intensive for any economic activity, but I like ’em:
Coaster assortment
The pale gray petals in a white frame looks remarkably like the washed-out color scheme on whatever device you’re reading this, doesn’t it?
A bedroom rearrangement displaced the Dell Sound Bar attached to the streaming music player from its accustomed perch, so I conjured a mount from the parts bin to hang it from a shelf:
Dell sound bar mount – installed
The sound bar originally fit below any Dell monitor with the appropriate lugs under the bezel, but a bit of bandsaw work and hand filing produced a reasonable facsimile from an aluminum sheet:
Dell sound bar mount – plate installed
The bar’s plastic bits require a few millimeters of clearance above the sheet, now provided by a matching plywood shape:
Dell sound bar mount – parts
A trial fit showed all the parts would fly in formation:
Dell sound bar mount – trial fit
A laser-cut cardboard template maintained alignment and spacing while I stood on my head screwing the mount in place.
It has a drain hole in the bottom that made this whole thing practical, because a PVC pipe hot-melt-glued atop the drain maintains the water level in the reservoir without any further attention:
Silonn icemaker – drain pipe
The water line from the laser, formerly run directly into the bucket, now goes into the reservoir and through the drain into the bucket. The bucket holds about five gallons of water, with the pump submerged in the bottom.
The icemaker pumps water from the reservoir into the little icemaker tray, freezes nine little ice bullets, and scrapes them into the reservoir:
Silonn icemaker – new ice dump
It does that about every eight minutes.
A plot of water temperature vs. time shows what happens:
Silonn icemaker – cooling water plot
It’s as exponential as you could want.
The ice bullets drop into the reservoir and melt there, the cooled water continuously flows into the bucket, and mixes with the rest of the water before being pumped back through the laser. As a result, there are no sudden water temperature changes and the laser remains perfectly happy.
Some numbers for an idea of the cooling capacity:
Freezing 28 pounds = 12.7 kg of ice a day (which, in normal use, would require me to babysit the thing overnight to empty the ice and refill the reservoir) works out to:
12.7 kg × 334 kJ/kg = 4.2 MJ
Spread across 24 hours, that’s 49 W of cooling power. There will be a bit more going into the chilled water surrounding the bullets, but most of the energy goes into the water-to-ice phase change.
Run another way, 5 gallons of water is 42 pounds. The initial cooling slope looks like 2 °C = 3.6 °F in 2 hr, which is 75 BTU/hr = 23 W. However, the water is cooling the laser (which was inert except for one brief cut) as well as the basement, plus (most importantly) there’s a water pump dissipating 20 W submerged in the bucket, so the icemaker is delivering at least 43 W, which is pretty much its rated performance.
It’s obviously incapable of keeping up with a laser doing full-time production work, but for my simple needs it seems better than dunking ice packs in the bucket.
More study (and maybe getting an air-cooled water pump) is in order …
Anything would be better than just taping some gel filters to the front of the bare photodiode package:
Laser output – photodiode kludge
Right?
I heaved the slab of ½ inch black acrylic left over from the Totally Featureless (WWVB) Clock into the laser cutter and, two passes at 90% power later, had a somewhat lumpy 32 mm donut with an 11 mm hole in the middle. Because acrylic is opaque to the IR light from a CO₂ laser (which is why it cuts so well) and black acrylic is opaque to visible light (which is what the photodiode is designed for), this is at least as good as an aluminum housing and much easier to make.
Chuck the donut into Tiny Lathe and bore out the hole:
PIN-10D photodiode filter holder – boring ID
When it’s a snug fit to ½ inch brass tube (about the same size as the photodiode’s active area), flip it around, and bore the other size out to fit the photodiode case.
Ram the tube in place, grab the large recess, and center the tube:
[Edit: Got that backwards: I bored the big recess first.]
Skim most of the OD down, then, because I am a dolt forgot to put a spacer in there, flip it around again, get it running true (the chuck aligns the flat side):
Even though they’re pretty much transparent to thermal IR, a focused IR laser beam cuts them just fine. The little tab at 6 o’clock (remember round clocks with hands?) keeps the cut circle from falling out.
Drill & tap for an M3 setscrew to hold the photodiode in place:
PIN-10D photodiode filter holder – parts
Put them all together:
PIN-10D photodiode filter holder – assembled
I must conjure a better mount for the thing, because this is way too precarious:
PIN-10D photodiode filter holder – test install
Early results suggest it works better than the previous hack job, without ambient light sneaking around the edges of the filter pack.
The red-dot pointer on the OMTech laser cutter has the same problem as my laser aligner for the Sherline mill: too much brightness creating too large a visual spot. In addition, there’s no way to make fine positioning adjustments, because the whole mechanical assembly is just a pivot.
The first pass involved sticking a polarizing filter on the existing mount while I considered the problem:
OMTech red dot pointer – polarizing filter installed
The red dot pointer module is 8 mm OD and the ring is 10 mm ID, but you will be unsurprised to know the laser arrived with the module jammed in the mount with a simple screw. Shortly thereafter, I turned the white Delrin bushing on the lathe to stabilize the pointer and installed a proper setscrew, but it’s obviously impossible to make delicate adjustments with that setup.
Making the polarizing filter involves cutting three circles:
OMTech red dot pointer – polarizing filter
Rotating the laser module in the bushing verified that I could reduce the red dot to a mere shadow of its former self, but it was no easier to align.
Replacing the Delrin bushing with a 3D printed adjuster gets closer to the goal:
Pointer fine adjuster – solid model
Shoving a polarizing filter disk to the bottom of the recess, rotating the laser module for least brightness, then jamming the module in place produces a low-brightness laser spot.
The 8 mm recess for the laser module is tilted 2.5° with respect to the Y axis, so (in principle) rotating the adjuster + module (using the wide grip ring) will move the red dot in a circle:
Improved red-dot pointer – overview
The dot sits about 100 mm away at the main laser focal point, so the circle will be about 10 mm in diameter. In practice, the whole affair is so sloppy you get what you get, but at least it’s more easily adjusted.
The M4 bolt clamping the holder to the main laser tube now goes through a Delrin bushing. I drilled out the original 4 mm screw hole to 6 mm to provide room for the bushing:
Improved red-dot pointer – drilling bolt hole
The bushing has a wide flange to soak up the excess space in the clamp ring:
Improved red-dot pointer – turning clamp bushing
With all that in place, the dimmer dot is visually about 0.3 mm in diameter:
Improved red-dot pointer – offset
The crappy image quality comes from excessive digital zoom. The visible dot on the MDF surface is slightly larger than the blown-out white area in the image.
The CO₂ laser hole is offset from the red laser spot by about 0.3 mm in both X and Y. Eyeballometrically, the hole falls within the (dimmed) spot diameter, so this is as good as it gets. I have no idea how durable the alignment will be, but it feels sturdier than it started.
Because the red dot beam is 25° off vertical, every millimeter of vertical misalignment (due to non-flat surfaces, warping, whatever) shifts the red dot position half a millimeter in the XY plane. You can get a beam combiner to collimate the red dot with the main beam axis, but putting more optical elements in the beam path seems like a Bad Idea™ in general.
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Applying a laser cutter to paper-like materials requires balancing two contradictory imperatives:
Hold the sheet flat to avoid distortions
Have nothing below to avoid schmutz on the bottom
This seemed like a good compromise:
Sheet Holder – Tek CC bottom deck
The orange 3D printed blocks hold aluminum miniblind blades:
Sheet Holder – steel sheet magnet pads
The curved slots hold the blades flush with the upper surface and align their top sides parallel to the laser beam, giving the beam very little blade to chew on near the focus point and allowing plenty of room below the sheet to dissipate cutting fumes.
The gold-ish squares are thin steel sheets covered with Kapton tape, painstakingly filed en masse from small snippets:
Sheet Holder – filed steel pads
The first iteration used precisely laser-cut refrigerator magnet pieces, in the expectation a crappy rubber magnet would provide just enough attraction to let a neodymium magnets hold the paper flat, without risk of blood blisters between fingers and steel:
Sheet Holder – ferrite magnet pads
As expected, contact with the neo magnet completely wiped away the alternating pole magnetism in the rubber sheet, leaving a weakly attractive non-metallic surface. Alas, the rubber had too little attraction through a laminated sheet of paper, so I switched to real steel and risked the blisters.
Most of the blocks are narrow:
Sheet Holder Bracket – solid model
The four corners are wider:
Sheet Holder Bracket – wide – solid model
They’re symmetric for simplicity, with recesses for the magnets / steel sheets on the top. The through-holes have recesses for M3 SHCS holding them to T-nuts in Makerbeam rails, with a slightly overhanging alignment ledge keeping them perpendicular to the rail.
The magnets come from an array of worn-out Philips Sonicare toothbrush heads:
Sheet Holder – magnet holders curing
They’re epoxied inside a two-piece mount, with the lower part laser-machined from 3 mm acrylic to put the two magnets in each assembly flush with the lower surface; the green area gets engraved 1 mm below the surface for the steel backing plate. The 1.5 mm upper frame fits around the plate and protrudes over the ends just enough for a fingernail grip:
Magnet Holder Cuts
The epoxy got a few drops of fuschia dye, because why not:
Sheet Holder – trimmed magnet holders
The garish trimmings came from slicing the meniscus around the lower part of the holder off while the epoxy was still flexy.
The holders must be flat for clearance under the focus pen:
Sheet Holder – focus probe clearance
Some experimentation suggests I can raise the pen by maybe 2 mm (with a corresponding increase in the Home Offset distance) , but the switch travel requires nearly all of the protruding brass-colored tip and there’s not much clearance under the nozzle at the trip point.
With all that in hand, it works fairly well:
Sheet Holder – Tek CC cutout
The lower deck has very little margin for gripping, which is why the four corner blocks must be a bit wider than the others.
The lamInator tends to curl the sheets around their width, so most of the clamping force should be along the upper and lower edges to remove the curl at the ends. This requires turning the whole affair sideways and deploying more magnets, which is possible for the smaller middle and upper decks:
Sheet Holder – Tek CC middle deck
Protruding SHCS heads on the four corners snug up against the edge of the knife-edge bed opening for Good Enough™ angular alignment.
Plain paper (anything non-laminated) seems generally flat enough to require no more than the corner magnets.
It’s definitely better than the honeycomb surface for fume control!
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The axis scale error, however, took me by surprise.The X axis travels on the order of 0.2 mm more along 250 mm, about 0.08%, than the Y axis, even after my tedious calibration. I must do that calibration again, because, as Miss Clavel observed in a different context, Something Is Not Right.
And, yes, that tiny difference is enough to misalign the last few fingers with their holes, to the extent of requiring somewhat more than Gentle Persuasion with a plastic mallet.
The Smell of Molten Projects in the Morning 