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.

Sheath Your Blades!

Trigger warning: gore.

A week ago I milled a stack of cursor blanks, then engraved a test hairline on a scrap cursor to make sure everything was ready:

Cursor V-bit setup
Cursor V-bit setup

After raising the spindle a few inches, I reached across the table, peeled the tape, and, as I pulled my hand back with the finished cursor, snagged the back of my left index finger on the V bit.

So. Much. Blood.

Urgent Care PA: “You may have nicked the tendon. Get thee hence to the Hospital Trauma Center.”

Trauma Center MD: “See that white fiber down in there? That’s the extensor ligament. Looks OK and should heal fine.”

Me: “Urp.”

Trauma Center MD: “Unless you’re one of the 20% who get an infection.”

Me: “Unless I’m one of the few who contract an MRSA infection, then just up and die.”

Trauma Center MD: “Well, yes, there’s that. If the wound swells or smells bad, come back here quickly.”

Dutchess County is now on the trailing edge of the Omicron wave, but the Trauma Center is attached to the Emergency Room and had a steady stream of customers arriving by ambulance. While being entirely content to not be their most urgent case, I had plenty of time to examine the wide variety of instruments parked in the room with me:

Nameless Hospital Cart
Nameless Hospital Cart

I’m on a ten-day regimen of surprisingly inexpensive Amoxicillin + Clavulanate Potassium capsules, which is apparently what it takes to knock down a potential infection these days.

Five days later, it looks like I should pull through:

Lacerated Left Index Finger
Lacerated Left Index Finger

So I hereby swear a mighty oath on the bones of my ancestors to always sheath my blades. You should, too.

But we all knew that last week, didn’t we?

Ottlite Conversion: Mini-Lathe LED Lighting

An ancient Ottlite fluorescent floor lamp (one of a pair bought during a closeout sale at a minute fraction of their absurd sticker price) finally aged out. Pondering what to do with the carcass led to this discovery:

Ottlite conversion - LED panel fit check
Ottlite conversion – LED panel fit check

Half of a Samsung (!) LED panel (presumably sheared by the surplus supplier) fit so perfectly in place of the fluorescent tube that I just had to make it happen.

The original fluorescent ballast mounted in the smaller compartment:

Ottlite conversion - OEM fluorescent driver
Ottlite conversion – OEM fluorescent driver

I like the air-cooled triac sticking off the side of the PCB.

The lamp originally mounted parallel to the flex arm, but I wanted it at a right angle, so the molded bracket had to go:

Ottlite conversion - bracket milling setup
Ottlite conversion – bracket milling setup

Which required a few minutes of manual jogging:

Ottlite conversion - bracket milled
Ottlite conversion – bracket milled

Some coordinate drilling on the Sherline converted a rectangle of aluminum sheet into a backing plate inside the base (visible through the original holes) to spread the stress over a larger area:

Ottlite conversion - flex arm mount
Ottlite conversion – flex arm mount

The new 24 V 1 A power supply mounts pretty much where the OEM ballast came from, although I had to hack out the molded screw bosses and perch the PCB atop four aluminum standoffs anchored in globs of high-temperature hot-melt glue:

Ottlite conversion - power supply
Ottlite conversion – power supply

You might think the white and black wires on the right are interchanged, because you’re not supposed to switch the neutral, but only if you also insist anybody cares about the colors of wires inside a molded cord. This one came from a nominally good-quality cord with an IEC connector now in the e-waste box: trust yet always always verify.

The LED panel sticks to the aluminum sheet with thermal tape and is clamped in place with a quartet of M2.5 standoffs:

Ottlite conversion - bottom view
Ottlite conversion – bottom view

I’ll eventually make a better cover than a strip of overhead projector film (remember overhead projectors?), as spattering the LEDs with cutting oil and random conductive swarf is Bad Practice™.

A little more cutting and drilling produced an angle bracket for the lathe backsplash panel:

Ottlite conversion - installed
Ottlite conversion – installed

Thing looks like it grew there, doesn’t it?

The end of the backsplash might need a 3D printed bracket to stabilize its right-angle bends and prevent wobbulation, although I’ll wait until that becomes a real problem before solving it.

The top of that stylin’ lamp shade tapers along its length and, unfortunately, appears directly in front of the MPCNC bench across the basement (out of sight at the top) as I stand at the lathe. Having the shade not align exactly parallel to the bench is more annoying than it really should be; perhaps I can get used to it after spending more time at the lathe.

I loves me some good LED lighting …

Bafang Battery Charge Port: Shell Drills

Continuing to mull the problem of removing a brass nugget fused to the center pin of the Bafang battery’s charge port without the risk of causing further damage suggested a shell drill fitting over the pin and guided by an insulating bushing:

Bafang battery - shell drill test fit
Bafang battery – shell drill test fit

That’s our undamaged battery, now sporting labels inspired by my friend’s mishap.

The first pass was a 3 mm (actually, 1/8 inch) brass tube rammed into a printed handle descending from the Sherline Tommy Bar handles:

Bafang battery - brass shell grinder - grit load
Bafang battery – brass shell grinder – grit load

The black stuff is coarse grinding compound held on by a dot of oil, with a pair of notches filed into the tip for a little griptivity.

This worked surprisingly well, at least if you weren’t in much of a hurry, although the grinding compound also erodes the drill:

Bafang battery - brass shell grinder - tip wear
Bafang battery – brass shell grinder – tip wear

I hadn’t thought this through enough to realize there’s no good way to convince the grit to not work its way up into the acetal bushing and jam the rod. While this might be good for final polishing, it’s not going to work well against the nugget, so it’s time for a harder drill with real teeth.

Drilling a 2.3 mm hole into the end of some non-hardened 3 mm (for real!) ground rod provided enough clearance for the charge port pin and a pair of cross-drilled holes laid the groundwork for a shell drill:

Bafang battery - steel shell drill - raw holes
Bafang battery – steel shell drill – raw holes

I filed the end off down to leave about 3/4 of the holes, then applied a Swiss pattern file with a safe edge to cut some relief behind the tips:

Bafang battery - shell drill detail
Bafang battery – shell drill detail

It would be better to harden the end of the rod, but this is a single-use tool.

Ram the shank into another printed handle:

Bafang battery - shell drill - guide
Bafang battery – shell drill – guide

The new drill is long enough to reach past the wounded end of the pin and short enough to not bottom out inside the connector.

A few minutes of twirling and re-filing the tiny teeth improved the cut enough to produce a convincing result in the simulated connector:

Bafang battery - shell drill - test results
Bafang battery – shell drill – test results

I’m reasonably sure the ID of the acetal bushing won’t fit over the nugget, but that’s easy enough to drill out while leaving an insulating shell.

The charge port’s center pin probably can’t withstand too much torque, so the drill must take small cuts.

Vacuuming out the chips while cutting will be critical, as you don’t want an accumulation of conductive chaff down in the hole!

Tube Turning Adapters

Finishing the PVC tubes reinforcing the vacuum cleaner adapters required fixtures on each end:

Dirt Devil adapter - pipe turning
Dirt Devil adapter – pipe turning

Because the tubes get epoxied into the adapters, there’s no particular need for a smooth surface finish and, in fact, some surface roughness makes for a good epoxy bond. The interior of a 3D printed adapter is nothing if not rough; the epoxy in between will be perfectly happy.

Turning the tubes started by just grabbing the conduit in the chuck and peeling the end that stuck out down to the finished diameter, because the conduit was thick-walled enough to let that work.

The remaining wall was so thin that the chuck would crunch it into a three-lobed shape, so the white ring in the chuck is a scrap of PVC pipe turned to fit the tube ID and provide enough reinforcement to keep the tube round.

The conduit ID isn’t a controlled dimension and was, in point of fact, not particularly round. It was, however, smooth, which counts for more than anything inside a tube carrying airborne fuzzy debris; polishing the interior of a lathe-bored pipe simply wasn’t going to happen.

The fixture on the other end started as a scrap of polycarbonate bandsawed into a disk with a hole center-drilled in the middle:

Pipe end lathe fixture - center drilling
Pipe end lathe fixture – center drilling

Stick it onto a disk turning fixture and sissy-cut the OD down a little smaller than the eventual tube OD:

Pipe end lathe fixture - turning OD
Pipe end lathe fixture – turning OD

Turn the end down to fit the tube ID, flip it around to center-drill the other side, stick it into the tube, and finally finish the job:

Dirt Devil adapter - pipe fixture
Dirt Devil adapter – pipe fixture

The nice layering effect along the tube probably comes from molding the conduit from recycled PVC with no particular concern for color matching.

A family portrait of the fixtures with a finished adapter:

Dirt Devil adapter - fixtures
Dirt Devil adapter – fixtures

A fine chunk of Quality Shop Time: solid modeling, 3D printing, mini-lathe turning, and even some coordinate drilling on the Sherline.

Micro-Mark Bandsaw: Acetal Upper Blade Guide

There being nothing like a good new problem to take one’s mind off all one’s old problems:

Micro-Mark Bandsaw - acetal upper blade guide installed
Micro-Mark Bandsaw – acetal upper blade guide installed

It’s basically the same as the lower blade guide, except coming from a stick of 5/8 inch acetal. A scant 6 mm stem goes into the vertical square rod, with a flat matching the setscrew coming up from the bottom to hold it in proper alignment.

I came within a heartbeat of cutting the slot parallel to the flat.

It worked OK while cutting a chunk of stout aluminum tube: so far, so good!

The impressive chunk of hardware is the OEM blade guide, with the brass tube for coolant flow all over the bearings. It’s mostly intended for use with the diamond blade, so I’ll swap it back in when I finally get around to cutting some slate for base plates.

Tour Easy Rear Running Light: LED Heatsink

Because the rear running light will have a higher duty cycle than the front light, I made the (admittedly too small) heatsink slightly longer, with a deeper recess to protect the lens from cargo on the rear rack:

Tour Easy Rear Running Light - boring LED recess
Tour Easy Rear Running Light – boring LED recess

Boring that nice flat bottom is tedious; I must lay in a stock of aluminum tubing to simplify the process.

Drilling the holes went smoothly:

Tour Easy Rear Running Light - drilling LED heatsink
Tour Easy Rear Running Light – drilling LED heatsink

Those two holes fit a pair of pins aligning the circuit plate, with a screw and brass insert holding it to the heatsink. Scuffing a strip across the aluminum might give the urethane adhesive (you can see uncured globs on the pins) a better grip:

Tour Easy Rear Running Light - circuit plate attachment
Tour Easy Rear Running Light – circuit plate attachment

The screw / insert /pins are glued into the plate to permanently bond it to the heatsink. The screw occupies only half of the insert, with the longer screw from the end cap pulling the whole affair together.

The two holes on the left pass both LED leads to one side of the circuit plate, where they connect to the current regulator and its sense resistor.