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Archive for July, 2019

Dell UG679 Lithium Battery Teardown

The battery pack on my ancient Dell E1405 laptop finally died, so I tore it apart to see what horrors might lurk within:

Dell UG679 Lithium Battery - teardown
Dell UG679 Lithium Battery – teardown

The case snaps apart without too much effort, although the delicate single-use latches won’t survive the operation. These certainly didn’t, which didn’t bother me at all, as I already had a replacement battery on order.

One of the cells (in the front) seems to have leaked ever so slightly inside its wrapper:

Dell UG679 Lithium Battery - leaky cell
Dell UG679 Lithium Battery – leaky cell

The three cells in that 3P section seem to have failed open: they pass no current at all.

The other pair of 3P slices, charged at 4.2 V with a 700 mA current limit until the current dropped under 10 mA, still have some life:

Dell UG679 3P sections
Dell UG679 3P sections

Perhaps recycling individual cells into LED glowies would be nice, as they have enough capacity remaining to run an Arduino for quite a while, and a 1S USB charger would make for a self-contained package.

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Mini-Lathe Cut-Off Tool Holder: Improved Clamp Screw

Apparently all mini-lathe cutoff tool holders suffer from the same problem:

Lathe Cutoff Tool - OEM swaged screw
Lathe Cutoff Tool – OEM swaged screw

The clamp tightening screw is made from butter-soft Chinese steel with a swaged hex socket. As you’d expect, the hex wrench eventually (as in, after a few dozen adjustments, tops) rips the guts right out of the socket.

The screw has a M6×1.0 mm threads, but the thread around the hex recess is left-handed. While I could, in principle, print a 127 tooth change gear, rebuild the lathe’s banjo to accommodate it, then single-point a backassward M6 thread, it’s easier to just use a standard socket head cap screw:

Lathe Cutoff Tool - rebuilt screw
Lathe Cutoff Tool – rebuilt screw

The clamp screw passes through the block at an angle:

Lathe Cutoff Tool - blade view
Lathe Cutoff Tool – blade view

Fortunately, the screw is perpendicular to the angled side over on the left, making it easy to clamp in the Sherline’s vise:

Lathe Cutoff Tool - aligning to screw
Lathe Cutoff Tool – aligning to screw

Using the laser aligner seemed like a good idea at the time, but the top of the screw wasn’t particularly well-centered on the hole’s axis. I couldn’t screw the left-hand part (with the socket) in from the bottom and center the block near its surface, because then I couldn’t extract the screw before proceeding.

I used a diamond burr to grind out a flat for the screw head:

Lathe Cutoff Tool - clearing screw recess
Lathe Cutoff Tool – clearing screw recess

The flat came from about twenty manual G2 I-2.5 full-circle passes, stepping down through the hard steel block 0.1 mm per pass, at a too-slow 4000 RPM and a too-fast 30 mm/min feed, with plenty of water squirted from one side into a shop vac snout on the other. The doodle in the background of the first picture shows a first pass at the layout, with the burr centered at X=-2.5; I actually did the grinding from X=+2.5 so most of the passes started in thin air.

The screw head started just shy of 10 mm OD and the burr just over 5.2 mm, so the ensuing 5 mm circles created a flat barely large enough. If the flat were perfectly centered on the screw axis, I wouldn’t have had to grind out another millimeter on the left side (toward the bottom of the tool holder body), but it worked out OK:

Lathe Cutoff Tool - 6 mm SHCS test fit
Lathe Cutoff Tool – 6 mm SHCS test fit

The trial fitting also showed the head stuck out ever so slightly beyond the far side of the block, where it would interfere with the blade, so I turned off 0.4 mm off its OD.

If I had a 50 mm SHCS in hand, I’d have used it. Instead, I extended the threads of a 75 mm screw, then lopped off the end to the proper length. I’ll spare you the ordeal, including the moment when I reached for the cutoff tool to shorten the screw. A bag of such screws will arrive shortly, in preparation for future need.

Now the [deleted] cut-off holder works the way it should have from the beginning.

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Mower FOD

For reasons not relevant here, the lawn mower suffered some Foreign Object Damage:

Lawn Mower - bent blade mount
Lawn Mower – bent blade mount

I’m sure the hard stop loosened the tolerances along the shaft, but the mower fired right up (with that new blade!) and has no more vibration than usual, despite the seriously bent blade mount.

I no longer have a deep emotional attachment to lawn mowers, which is apparently common, as the label advises me there’s no need to change the oil:

Mower Engine - never change the oil
Mower Engine – never change the oil

Drive it ’til it drops …

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Houses Are Trouble: Electrical Service Division

The ancient utility pole on the north side of our property fell over a few hours after a thunderstorm rolled through:

Fallen Utility Pole - end view
Fallen Utility Pole – end view

Fortunately, the wire clamps were upward and it just lay there without sparks or excitement. It feeds the vacant house out back, so restoring power wasn’t urgent.

Unfortunately, the lines neatly bisected Mary’s garden:

Fallen Utility Pole - garden view
Fallen Utility Pole – garden view

The utility crew arrived a few hours later, disconnected the triplex at the fallen pole, rolled it up, secured it to the source pole out front, and promised a different crew would replace the pole in a while:

Central Hudson truck - 2019-06-27
Central Hudson truck – 2019-06-27

We agreed restoring service to other folks who needed it should take priority.

Mary’s been ducking the various cable TV / phone / FiOS cables ever since.

The pole has been God’s own toothpick for quite some time, as shown by this picture from 2001:

CHGE pole - rear - top
CHGE pole – rear – top

Fortunately for us, its pole tag hadn’t fallen off in all those years:

CHGE Pole Tag - mid-north
CHGE Pole Tag – mid-north

That little tag may save us ten large during this exquisite little inconvenience …

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Step2 Garden Seat: Replacement Seat

A pair of Step2 rolling garden seats (they have a new version) served in Mary’s gardens long enough to give their seat panels precarious cracks:

Step2 Seat - OEM seat
Step2 Seat – OEM seat

The underside was giving way, too:

Step2 Seat - cracks
Step2 Seat – cracks

We agreed the new seat could be much simpler, although it must still hinge upward, so I conjured a pair of hinges from the vasty digital deep:

Rolling Cart Hinges - solid model - bottom
Rolling Cart Hinges – solid model – bottom

The woodpile disgorged a slab of 1/4 inch = 6 mm plywood (used in a defunct project) of just about the right size and we agreed a few holes wouldn’t be a problem for its projected ahem use case:

Step2 Seat - assembled
Step2 Seat – assembled

The screw holes on the hinge tops will let me run machine screws all the way through, should that be necessary. So far, a quartet of self-tapping sheet metal (!) screws are holding firm.

Rolling Cart Hinges - solid model - top
Rolling Cart Hinges – solid model – top

A closer look at the hinges in real life:

Step2 Seat - top view
Step2 Seat – top view

The solid model now caps the holes; I can drill them out should the need arise.

From the bottom:

Step2 Seat - bottom view
Step2 Seat – bottom view

Three coats of white exterior paint make it blindingly bright in the sun, although we expect a week or two in the garden will knock the shine right off:

Step2 Seat - painted
Step2 Seat – painted

After the first coat, I conjured a drying rack from a bamboo skewer, a cardboard flap, and some hot-melt glue:

Step2 Seat - drying fixture
Step2 Seat – drying fixture

Three small scars on the seat bottom were deemed acceptable.

The OpenSCAD source code as a GitHub Gist:

This original doodle gives the key dimensions, apart from the rounded rear edge required so the seat can pivot vertically upward:

Cart Hinge - dimension doodle
Cart Hinge – dimension doodle

The second seat looks just like this one, so life is good …

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MPCNC: Calculating Spring Rates

Calculate the spring rates for the drag knife, diamond engraver, and collet pen holders by measuring the downforce every 0.5 mm (or so):

LM12UU Collet Pen Holder - spring rate test
LM12UU Collet Pen Holder – spring rate test

Then plotting the data points and eyeballing a straight-line curve fit:

MPCNC - Drag Knife Holder - spring constant
MPCNC – Drag Knife Holder – spring constant

Doing it on hard mode definitely has a certain old-school charm. The graph highlights mis-measured data and similar problems, because, if you don’t see a pretty nearly straight line, something’s gone awry.

But we live in the future, so there’s an easier way:

Droid48 - Spring Rate - Linear Fit coefficients
Droid48 – Spring Rate – Linear Fit coefficients

Well, OK, it’s the future as of the early 1990s, when HP introduced its HP 48 calculators. I’m using the Droid48 emulator on my ancient Google Pixel: living in the past, right here in the future.

Start by firing up the STAT library (cyan arrow, then the 5 key), selecting Fit Data … from the dropdown list, then selecting the Linear Fit model:

Droid48 - Spring Rate - Linear Fit screen
Droid48 – Spring Rate – Linear Fit screen

Then tap EDIT and enter the data in a tiny spreadsheet:

Droid48 - Spring Rate - Linear Fit data
Droid48 – Spring Rate – Linear Fit data

My default “engineering mode” numeric display format doesn’t show well on the tiny screen. Tapping the WID→ key helps a bit, but shorter numbers would be better.

With the data entered, set an X value and tap the PRED key to get the corresponding Y value:

Droid48 - Spring Rate - Linear Fit prediction
Droid48 – Spring Rate – Linear Fit prediction

Tapping the OK button puts the line’s coefficients on the stack, as shown in the first picture. Write ’em on a strip of tape, stick to the top of the holder, and it’s all good:

LM12UU Collet Pen Holder - test plot - overview
LM12UU Collet Pen Holder – test plot – overview

Works for me, anyhow.

HP still has the HP 48g manuals online. The (unofficial) HP Museum has a page on the HP 48S. More than you want to know about the 48 series.

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MPCNC: Diamond Drag Engraving Speed Tests

The MPCNC isn’t the most stable of CNC machine tools, given its large masses and 3D printed structure. My early plotting pen tests suggested speeds around 250 mm/min were appropriate:

MPCNC - GCMC Text - 250 mm-min
MPCNC – GCMC Text – 250 mm-min

Diamond drag engraving produces a thinner line and makes the wobbulations more obvious:

MPCNC Engraving Speed Test A - 600-900 mm-min
MPCNC Engraving Speed Test A – 600-900 mm-min

Another test showed similar results:

MPCNC Engraving Speed Test B - 700-900 mm-min
MPCNC Engraving Speed Test B – 700-900 mm-min

Slowing down definitely reduces the shakes:

MPCNC Engraving Speed Test B - 100-300 mm-min
MPCNC Engraving Speed Test B – 100-300 mm-min

Producing the best results takes quite a while:

MPCNC Engraving Speed Test A - 50-200 mm-min
MPCNC Engraving Speed Test A – 50-200 mm-min

Similar results on another test:

MPCNC Engraving Speed Test C - 50-150 mm-min
MPCNC Engraving Speed Test C – 50-150 mm-min

Those “mm/s” labels are typos; they should read “mm/min”. Plotting at -1.0 mm on scrap CDs and DVDs produces a downforce around 200 g.

Eyeballometrically, 100 mm/min seems fine, but 50 mm/min (I’d likely use 60 for a nice round 1 mm/s) eliminates all the shakes.

Smooth curves, like Guillloché patterns, can run much faster, because they don’t have abrupt direction changes. This 3-½ inch hard drive platter has text engraved at 100 mm/min and the pattern at 600 mm/min, both at -3.0 mm for 300 g of downforce:

MPCNC Engraving - Guilloche drive platter test
MPCNC Engraving – Guilloche drive platter test

A closer look at the text:

MPCNC Engraving - hard drive platter - detail A
MPCNC Engraving – hard drive platter – detail A

And some digits:

MPCNC Engraving - hard drive platter - detail B
MPCNC Engraving – hard drive platter – detail B

When I want to brand an engraved CD, this will suffice:

MPCNC Engraving - CD attribution text
MPCNC Engraving – CD attribution text

All in all, the MPCNC engraves much better than I expected!

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