Posts Tagged Sherline

CNC 3018-Pro: Milling the CD Fixture

It turns out that the outer diameter of CD platters isn’t quite as perfectly controlled as you (well, I) might imagine, although the differences between CDs from different sources amounts to perhaps ±0.1 mm. Of course, instantly after putting the tape-down fixture into use, the next few discs atop my stack of scrap CDs were just large enough to not quite fit.

The Sherline’s workspace can’t maneuver the holder’s perimeter around the spindle, so embiggening the OD calls for the rotary table. The general idea is to clamp the center of the fixture to the rotary table, run a small end mill about 0.1 mm into the fixture’s OD, spin the table one revolution, and be done with it.

Of course, the rotary table’s 3/8-16 threaded center hole doesn’t match the fixture’s 6 mm center hole: we need an adapter. Start with a 1 inch long 3/8-16 stainless steel hex bolt, center drill the end, peel off the hex head, then turn to 6 mm OD, going down far enough so the threads don’t stick up out of the table too much:

CNC 3018-Pro - CD fixture milling - bolt turning
CNC 3018-Pro – CD fixture milling – bolt turning

The Sherline uses 10-32 screws, so poke a #16 drill 15 mm into the bolt to get maybe 25% thread depth (because it’s a blind hole into stainless steel for an application requiring minimal strength and I hate breaking taps), tap 10-32, clean out the hole, and call it All Good:

CNC 3018-Pro - CD fixture milling - rotary table adapter
CNC 3018-Pro – CD fixture milling – rotary table adapter

Find the trim plate from an old faucet to reach around the central boss, stack up enough flat washers to meet the nut, snug a Sherline spherical nut + washer set (because it’s within reach), chuck up a 1/8 inch mill, and have at it:

CNC 3018-Pro - CD fixture milling
CNC 3018-Pro – CD fixture milling

The fixture sits atop an aluminum plate cut to fit a smaller version of the table riser, but this requires zero fancy alignment. The 6 mm adapter centers the fixture on the rotary table and the cutter sits at a fixed radius from the center wherever it contacts the fixture rim; just spin the table and it cuts a neatly centered circle.

A test fit showed the oversize discs fit perfectly:

CNC 3018-Pro - CD fixture milling - test fit
CNC 3018-Pro – CD fixture milling – test fit

Bonus: a nice new adapter for the rotary table!

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CNC 3018-Pro: Platter Fixtures

Up to this point, the Sherline has been drilling 3.5 inch hard drive platters to serve as as reflecting bases for the vacuum tubes:

LinuxCNC - Sherline Mill - Logitech Gamepad
LinuxCNC – Sherline Mill – Logitech Gamepad

The CNC 3018-Pro has a work envelope large enough for CD / DVD platters, so I mashed the Sherline fixture with dimensions from the vacuum tube code, added the 3018’s T-slot spacing, and conjured a pair of fixtures for a pair of machines.

Because I expect to practice on scrap CDs and DVDs for a while:

Platter Fixtures - CD on 3018
Platter Fixtures – CD on 3018

And a 3.5 inch hard drive platter version:

Platter Fixtures - hard drive platter on 3018
Platter Fixtures – hard drive platter on 3018

The holes sit at half the 3018’s T-slot spacing (45 mm / 2), so you can nudge the fixtures to the front or rear, as you prefer.

The alignment dots & slots should help touch off the XY coordinate system on the Sherline, although it can’t reach all of a CD. Using bCNC’s video alignment on the hub hole will be much easier on the 3018.

After fiddling around with the 3018 for a while, however, the CD fixture doesn’t have many advantages over simply taping the disc to a flat platen. Obviously, you’d want a sacrificial layer for drilling, but it’s not clear the OEM motor / ER11 chuck would be up to that task.

The OpenSCAD source code as a GitHub Gist:

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Kinesis Freestyle 2: Steel Tactile Bumps

Adding tape bumps to the worn Kinesis keyboard demonstrated I really need tactile home keys, so I popped the tops and fired up the Sherline mill:

Kinesis keyboard - 2 mm drilling
Kinesis keyboard – 2 mm drilling

That’s a genuine 2 mm carbide end mill, poked 1 mm into the key cap, snuggled right up against the front edge.

Two epoxy dabs and some wiping later:

Kinesis keyboard - 2 mm tactile bearings
Kinesis keyboard – 2 mm tactile bearings

The careful alignment on the F key tells you I did it first; obviously, I should make better fixtures.

The holes could be slightly larger and maybe slightly deeper, but the bearings feel just right.

Indeed, they work so well a ball now distinguishes the far-flung Delete and Backspace keys:

Kinesis keyboard - 2 mm bearing - Delete key
Kinesis keyboard – 2 mm bearing – Delete key

Now, to see how long the epoxy lasts …


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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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Drag Knife Blade Ejector Handle

The LM12UU drag knife holder buries the blade ejector pin deep inside the machinery:

Drag Knife - LM12UU ground shaft - assembled
Drag Knife – LM12UU ground shaft – assembled

So a handle with a pin makes sense:

LM12UU Drag Knife Ejector Pin Pusher
LM12UU Drag Knife Ejector Pin Pusher

It’s a variant Sherline tommy bar handle, so there’s not much to say about it.

The dark butt end comes from the traces of the black filament I used for the previous part. Even after flushing half a meter of orange through the hot end, you’ll still see some contamination, even with the same type of plastic. Doesn’t make much difference here, though.

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Sony NP-FM50 Battery Disassembly

Having won an eBay action for a known-dead Sony DSC-F717 at $0.99 (plus $15 shipping, the seller being no fool), I now have a possibly salvageable camera, a Genuine Sony AC supply, and two more NP-FM50 batteries for about the price of any one of the components.

One battery arrived stone-cold dead, suggesting the camera had been put away with the battery installed for a very long time and they died companionably. The camera still charges a (good) battery, even though it doesn’t turn on, and perusing the schematics suggests checking the power switch, because it’s always the switch contacts. That’s for another day, though.

For the record, the battery status:

NP-FM50 - 2019-03-30
NP-FM50 – 2019-03-30

The red and green traces come from the two batteries I’ve been cycling through the camera since, um, 2003, so they’re getting on in years and correspondingly low in capacity.

The fourth battery (2019 D, the date showing when it arrived, not its manufacturing date) went from “fully charged” to “dead” in about three seconds with a 500 mA load, producing the nearly invisible purple trace dropping straight down along the Y axis.

Sawing the dead battery case around its welded joint at a depth of 0.75 mm, then prying with a small chisel, exposed the contents without histrionics:

Sony NP-FM50 battery - cell label
Sony NP-FM50 battery – cell label

Now, there’s a name to conjure with. Turns out Sony sold off its Fukushima battery business a while back, so these must be collectibles. Who knew?

The lower cell is lifeless, the upper cell may still have some capacity. Three pairs of 18500 lithium cells are on their way, in the expectation of rebuilding the weakest packs.

After desoldering the battery tab on the right from the PCB, it occurred to me I needed pictures:

Sony NP-FM50 battery - PCB exposed
Sony NP-FM50 battery – PCB exposed

Yeah, that’s a nasty melted spot on the case, due to inept solder-wickage.

Unsoldering the three tabs closest to the case releases the cells + PCB from confinement:

Sony NP-FM50 battery - PCB overview
Sony NP-FM50 battery – PCB overview

I’m still bemused by battery packs with a microcontroller, even though all lithium packs require serious charge controllers. At least this is an Atmel 8-bitter, rather than 32-bit ARM hotness with, yo, WiFi.

The cells have shaped tabs which will require some gimmicking to reproduce:

Sony NP-FM50 battery - cell tabs
Sony NP-FM50 battery – cell tabs

Now, if only I could reboot the camera …



Multimeter Probe Cable: FAIL

A reasonably good silicone-wire multimeter probe set arrived last spring and has worked well enough (I thought, anyhow) for the usual voltage measurements, but recently failed while measuring a small current. We all know how this will turn out, but the details may be of some interest.

Measuring the resistance from tip to plug located the fault to the black probe, after which I poked a pin through the insulation near the plug:

Multimeter probe - diagnosis

Multimeter probe – diagnosis

The two leads near the bottom go to my shiny Siglent bench multimeter. Despite their similarity to the failed probes, I’m pretty sure Siglent has better QC (well, mostly).

The probe’s resistance was near zero from the tip (offscreen to the left) to the pin and megohms from pin to plug (on the right). Figuring the wire worked loose, I pulled it away from the plug:

Multimeter probe - disassembly 1

Multimeter probe – disassembly 1


Although I wouldn’t have trusted those probes anywhere near their alleged 1 kV rating, seeing that exposed copper-like substance was disconcerting.

Hacking off the strain relief bushing around the wire got closer to the fault:

Multimeter probe - disassembly 2

Multimeter probe – disassembly 2

And, finally, the problem becomes obvious:

Multimeter probe - disassembly 3

Multimeter probe – disassembly 3

Yet Another Cold Solder Joint:

Multimeter probe - cold solder joint

Multimeter probe – cold solder joint

Pulling a black banana plug from the heap, I decided to drill a proper hole to anchor the wire:

Multimeter probe - drilling plug

Multimeter probe – drilling plug

Which looked like this afterward:

Multimeter probe - soldered plug

Multimeter probe – soldered plug

And produced a strongly mismatched pair:

Multimeter probe - repaired

Multimeter probe – repaired

Ain’t it amazing how much fun you can have for a few bucks, all delivered by eBay? [sigh]

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