Acrylic Coasters: Edge Finishing, Round 2

Because the Sherline mill can’t cut all the way around a 4 inch OD coaster clamped to its table, I set up the 4-jaw chuck on the rotary table and centered the nicely round fixture:

Coaster Epoxy Rim - centering fixture plate
Coaster Epoxy Rim – centering fixture plate

Admittedly, the centering need not be so precise, but practice makes perfect.

A few strips of double-stick tape affixed the test coaster, with too many clamps applied to settle it in place:

Coaster Epoxy Rim - Sherline clamp setup
Coaster Epoxy Rim – Sherline clamp setup

A few sissy cuts demonstrated the tape lacked sufficient stickiness to hold the coaster in place against the milling cutter’s uplift. I managed to mill most of the perimeter with those clamps in place, moving each one from just ahead of the cutter to just behind the cutter.

That way lies both madness and organic damage.

There are better tapes and better adhesives, all trading off a really sticky fixture against difficulty extracting an undamaged part.

A more complex circular fixture with built-in mechanical edge clamps extending around a major part of the perimeter seems like entirely too much of a diversion for a couple of obscene-gerund coasters.

A live center in a lathe tailstock applies pressure in exactly the right place to hold a circular object against a fixture while slicing off the entire perimeter, with the only problem being centering the object.

Maybe shimming the fixture against one chuck jaw will suffice?

Acrylic Coasters: Edge Finishing, Round 1

Assembling acrylic pieces inside an epoxy-filled frame produces nice results:

Cut Acrylic Coaster - bottom
Cut Acrylic Coaster – bottom

The gotcha: epoxy oozes from between the layers to form a slobbery edge.

I tried introducing a similar coaster to Mr Disk Sander with reasonable results:

Coaster Epoxy Rim - disk sanded rim
Coaster Epoxy Rim – disk sanded rim

The coaster on the bottom has its original generous epoxy slobber around the acrylic disks.

Assembling the layers inside a mold seems fraught with messiness, particularly if I eventually want to get it out of the mold.

Using a finer abrasive disk would certainly help, but the whole process requires intense concentration and is utterly unforgiving of mistakes.

I figured I could attach the coaster to a lathe fixture and turn the rim, so I made a fixture from scrap acrylic:

Coaster Epoxy Rim - cutting fixture plate
Coaster Epoxy Rim – cutting fixture plate

The lathe chuck inside jaws fit inside the hole and I set up to turn the OD to a nice even diameter:

Coaster Epoxy Rim - turning fixture rim
Coaster Epoxy Rim – turning fixture rim

The fixture sat flush against the middle step of the jaws with plenty of clearance from the outer step, so I could turn the OD without whacking the carbide insert.

I planned to grab the OD and turn the ID to a (reasonably) concentric finish, but the outer jaws have an absolute diameter limit a few millimeters less than the 4 inch = 101.4 mm coaster OD.

After some increasingly desperate attempts, I concluded that, lacking a 4-jaw lathe chuck, there was no way to mount the coaster on the fixture and have it sit it even approximately centered on the spindle axis.

I do, however, have a 4-jaw chuck for the Sherline mill, normally used with the rotary table.

Next up: Round 2.

High Impact Art: Smashed Glass Coaster Meniscus Removal

After using the smashed glass coaster for a while, the beveled epoxy meniscus around the perimeter proved itself more annoying than expected:

Glass Coaster - second test
Glass Coaster – second test

So I clamped it to the Sherline’s tooling plate and milled off the rim:

Smashed Glass Coaster - meniscus removal
Smashed Glass Coaster – meniscus removal

Given the Sherline’s cramped work envelope, all the action took place along the rearmost edge, requiring eight reclampings indexed parallel to the table with a step clamp.

The cutter cleared off everything more than 0.3 mm above the surface of the glass chunks. I could probably have gone another 0.1 mm lower, but chopping the bit into the edge of a shattered glass fragment surely wouldn’t end well.

Polishing the dark gray milled surface might improve it slightly, at the risk of scuffing whatever poured epoxy stands slightly proud of the glass:

Smashed Glass Coaster - leveled edge
Smashed Glass Coaster – leveled edge

Perhaps if I define it to be a border, everybody will think it was intentional.

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.

[Update: dot mode can produce a continuous trench that looks even better! ]

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!