Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
All eight cells were within 3 mV of each other, so I sorted them by voltage and picked two from the middle of the lineup. Shorting them together in parallel produced a few microamps of current, so they’re as well matched as seems reasonable.
Rather than attempt to solvent-bond the case back together, I wrapped a layer of Kapton tape around the whole thing. The case doesn’t have quite enough meat to bond, anyway, because the width of the slitting saw turned that much plastic into dust.
A bunch of cutouts along the bottom edge key it into the charger, so I cut out the tape over those sections. Despite what it looks like, the small metal tab between the two terminals (on the top) is not covered in tape; that’s the snazzy InfoLithium contact that tells the camera that this is a valid battery.
The camera reported the pack had about 15 minutes of life remaining, which makes sense given that the cells spent quite a while in transit. I ran it down to empty, put it in the charger, and it seems to be perfectly happy. I’ll do a capacity test after a round or two of picture-taking.
I doubt the tape will prove to be a permanent fix, but as far as the camera is concerned, that slick Kapton makes it go in and out like anything…
I’ve been mulling over adding a tool length probe for a while and finally decided that the simplest approach might be the best: a momentary-contact pushbutton switch that pulls a parallel port input pin to ground.
The motivation is that a simple switch seems to be repeatable enough for tool length probing and it’s cheap enough that I won’t form a deep emotional bond to it. When a probe crashes the switch, I can just pop another one in place without any heartache or putzing around for a day or three to build another over-elaborate probe station.
The catch is that the Sherline motor driver box doesn’t include connections for any of the parallel port input pins.
The choices seem to boil down to:
Adding a breakout board between the parallel port and the driver box or
Hacking the driver box to get access to the port pins
Well, I’ve already pretty well hacked up my controller, as I wrote up in Circuit Cellar magazine (Aug & Oct 2004), so I don’t have much to lose… and the box is already in the shop!
Probe to port pin 15
This picture shows the connection to pin 15 of the parallel port on the Sherline driver PCB. The driver doesn’t use that input pin (or any of the others, for that matter), which means the PCB doesn’t have a trace leading anywhere convenient. I ran the new wires through the connector mounting hole, rather than around the edge, and soldered them directly to the connector pins on the bottom of the board.
The jack is an ordinary 1/8″ (3.5 mm, these days) stereo (3 conductor) jack, with lah-dee-dah gratuitous gold-flavored flashed plating; anything similar will work just fine.
Connections:
Sleeve -> driver box
Ring -> circuit ground (pin 19 is convenient)
Tip -> pin 15, the probe input
The cable shield connects only at the plug into the driver box, not at the switch end. That ensures there’s no current flowing through it and it can do a marginally better job of shielding the two conductors within. I’m reasonably sure that makes no difference whatsoever in this application.
The cable got chopped out of an AV-interconnect dingus with all sorts of fancy connectors on the other end. It’s a surplus find, cost maybe a buck, and has the redeeming feature of sporting molded plugs that I don’t have to solder.
The switch connections are soldered and insulated with heat stink shrink tubing. The general idea is that the driver box provides all the power, there’s no electrical contact with the mill table or spindle, and thus no reason to use fancy circuitry to solve a problem that’s not there.
I did not add a capacitor across the switch contacts, figuring that I’d solve that problem when it happened. The common practice of putting a honkin’ big cap across switch contacts is bad practice: it effectively shorts the power supply across the contacts for a brief moment every time the switch closes. Some stored energy is good (it keeps the contacts clean), too much simply burns them away. ‘Nuff said.
Probe jack – inside
I marked a hole on the front panel symmetric with the LED, eased the circuit board out of the case and wrapped it in a shop rag to keep the swarf out, propped the case on the drill press table, and rammed a 1/4″ hole through the spot marked X with a step drill. Yeah, hand-held on the table, just like you’re never supposed to do.
The force is strong with me…
The (well, my) Sherline.hal file connects pin 15 to the probe sense input (maybe I defined that when I set things up; I don’t recall now), but it assumes the pin will be high when active. The parallel port pin has a built-in pullup resistor and a switch to ground makes it active when low. These two lines in my custom_postgui.hal file disconnect the high-active pin signal and connect the low-active pin signal.
unlinkp parport.0.pin-15-in
net probe-in parport.0.pin-15-in-not
You do it that way to avoid changing the Sherline.hal file, which will be overwritten if you ever run the automagic configuration program again.
If you’re doing this from scratch, just configure the whole thing using the configuration tool, it’ll set the HAL file properly and you won’t need any of that fiddling around.
Tweak the Sherline.ini file to add support for tool changing with the G30 command:
[EMCIO]
TOOL_CHANGE_AT_G30 = 1
Button everything up, then do a quick
G91 G38.2 Z-10 F10
and poke the button while the Z axis is in motion. The Z axis should stop instantly. If not, check your wiring.
Now, some Orc Engineering is in order: I need a low-budget fixture to put the switch in harm’s way.
Went to roll the bike out of the garage and the rear tire was dead flat. You don’t even need to look at the tire, you just instantly know something’s wrong: the bike feels funny with a flat tire.
The picture shows the problem: a pinhole in the tube. Nothing penetrated the tire, nothing went wrong with the tire liner (you can see this was a few mm from the edge, so it’s not an abrasion flat), there are no problems anywhere. Just a tiny hole in the tube.
As nearly as I can tell, the tube simply failed at that point, without any external aggravation.
Popped in another tube and it’s all good, but … I guess it’s time to buy some new tubes: the new one came from a box dated May 90.
Finding a flat in the garage is much much better than finding a flat on the road.
So Mary was going to apply the long-disused Sears Craftsman electric hedge trimmer to the decorative grasses she’d planted on either side of the (equally disused) front entry, but when I deployed the thing it didn’t run. A quick walk through the debugging tree: GFI green, extension cord OK, so it must be the trimmer.
Off to the Basement Laboratory Repair Wing…
Two tricks to getting it apart, after removing all the obvious screws:
The handle comes out of the sockets after great persuasion
Remove two of the three hex-head-with-lockwasher screws on the bottom and the case pops apart. The third screw holds the motor plate into that half of the case.
The switch is, of course, not intended to be repairable, but that’s something of a motivator around here. It uses those awful poke-and-pray spring clamps, which you could, in principle, release with a small screwdriver, but I cut the wires on the motor side of the switch, leaving plenty of room to graft connectors onto them.
Next time, I’ll be able to release the wires more easily.
Congealed grease on switch contacts
A rivet holds the switch together, but attacking it with a drill removed enough of the head that I could whack the rest of the body out with a drift punch. A 2-56 machine screw fits neatly into the hole and there’s enough clearance on both sides for the screw head and a nut; hack the screw to length with a Dremel abrasive cutoff wheel.
Notice that the switch trigger button visible from outside the case acts on a push rod that slides the movable contacts (in the top part in the picture) back-and-forth atop the copper contacts (with the wires). A pair of springs loads the movable contacts against the copper strips.
The problem turned out to be, as expected, congealed grease inside the switch. The black gunk on the right halves of the copper contacts was essentially solid; you can see that it formed a nice insulating layer. I cleaned that out, polished up the moving contacts, reassembled it, and … the switch still didn’t work.
At least I discovered that with an ohmmeter, before reassembling the entire trimmer!
Switch contact slider
The movable switch contacts have a small ramp, just about in the middle, that rides up on the black hump between the copper strips when the trigger button is released. That mechanically breaks the connection, but also allowed the grease to congeal in the air gap. The grease also formed a lump that prevented the movable contacts from pressing firmly against the copper strips, despite the springs.
I gnawed out that crud with a small screwdriver, dabbed on more contact oxidation prevention grease, buttoned it up again, and now the switch works perfectly again.
New switch wires
I spliced in somewhat longer lengths of hookup wire with butt-splice connectors I’ve had for years and it’s all good.
The post with the screw hole just below the wires matches another in the opposite half of the case; the post actually fits inside the ring you see here, so it doesn’t crunch the wire. However, the wire must be pushed in far enough to avoid interfering with the switch action rod.
I used a pair of blue LEDs for the colon in the Totally Featureless Clock. Each one has a brass tube to define the dot and a white plastic diffuser to eliminate hotspots.
Some rummaging in the brass cutoff assortment produced a pair of tubes with a 0.300 inch ID that closely matched the width of the LED segment bars. The catch is that I don’t have a core drill that spits out 0.300 inch slugs…
Milling the dots
So I taped a chunk of translucent acrylic to some plywood scrap and milled the dots. Helix milling on the lesser of a 4% slope or 1/5 of the cutter diameter, 15 inches/min, no cooling, maybe 1500 rpm.
The resulting disks were snug slip fits into the tubes, although I added a dot of cyanoacrylate to ensure they didn’t get any ideas about perpetrating an escape.
It took two disks to remove all the hotspots, which reduced the light intensity to the point where I had to increase the LED current, which really heated up the linear regulator driving the dots. Fooey! In retrospect, I think frosting the LED lens would eliminate the need for a second diffuser without decreasing the intensity much at all.
The code is available as an OpenOffice file there, too.
(Post milling)
(Ed Nisley KE4ZNU - Feb 2010)
(Origin = center of post at surface)
(Double-stick tape holding acrylic sheet to sacrificial plate)
(-- Dimensions)
#<_PostDia> = 0.300 (post OD)
#<_PostRad> = [#<_PostDia> / 2]
#<_Thickness> = 0.120 (sheet thickness)
#<_MillDia> = 0.250 (cutter diameter)
#<_MillSpeed> = 15 (cutting speed)
#<_MaxCutDepth> = [#<_MillDia> / 5] (max cutting depth)
#<_MaxCutSlope> = 0.04 (max cutting slope)
#<_TraverseZ> = 0.300 (safe travel height)
#<_TraverseSpeed> = 25 (safe traverse speed)
G20 (inches!)
(-- Figure cut depth per helix pass)
#<_PassCut> = [#<_MaxCutSlope> * 3.142 * [#<_PostDia> + #<_MillDia>]] (limit max cut for each pass)
O9000 IF [#<_PassCut> GT #<_MaxCutDepth>]
#<_PassCut> = #<_MaxCutDepth> (limit max cut for each pass)
O9000 ENDIF
(-- Set up cutter comp)
G0 Z#<_TraverseZ>
G0 X[0 - 3 * #<_PostRad>] Y0 (get to entry point)
G42.1 D#<_MillDia>
G2 X[0 - #<_PostRad>] I#<_PostRad> F#<_TraverseSpeed>
(-- cut down through sheet)
#<CurrentZ> = 0.0
G0 Z#<CurrentZ>
F#<_MillSpeed>
O1000 DO
#<NextZ> = [#<CurrentZ> - #<_PassCut>] (figure ending level)
G3 I#<_PostRad> Z#<NextZ> (once around)
#<CurrentZ> = #<NextZ>
O1000 WHILE [#<CurrentZ> GT [0 - #<_Thickness>]]
G3 I#<_PostRad> (clear final ramp)
G40 (comp off)
G0 Z#<_TraverseZ>
G0 X0 Y0
M2
The latch closing my tea ball consists of a nice stainless steel dingus held on by a grotty rivet of unknown provenance that I’ve repeatedly staked over the years. It finally came undone this morning, so I had a few minutes of Quality Shop Time right after breakfast.
My tiny-screw box (left over from the long-gone Leichtung Workshops) has some stainless 0-80 screws that I found somewhere, but only brass nuts. Ah, well, we used to use brass water fixtures and lead pipe, so an 0-80 nut in hot water isn’t going to kill me.
The ball rim has a recess for the rivet head, but the screw head was slightly larger. I braced the rim of the ball across the vise jaws and give the recess a few shots with a fat punch to enlarge it.
Stainless screw and brass nut
Then…
A dot of Loctite on the threads
Assemble everything
Take it apart to put the latch on the correct side of the rim
Reassemble
Attempt to close
Gently bend the rim to flatten it out
Close
Attempt to latch
Brace closed rim on vise opening with screw head up
A few shots with a drift punch to settle recess around screw head
Success!
It seems I ain’t worth a damn in the morning without a hot cuppa. The rituals must be preserved.
I tossed the ball in the dishwasher and opted for a tea bag today…
Just for curiosity’s sake, I applied a slitting saw to the oldest defunct generic NP-FS11 battery pack, cutting carefully along the bonded joint between the two parts.
No coolant, 1000 rpm, 200 mm/min, the saw is 22 mm diameter. Much slower than you’d use if you were in production, but I’m not.
First cut all the way around at 0.5 mm inside the case, then another pass at 1.0 mm. The second cut went ting as it passed the tabs at the base of the cells, so I knew the halves were released.
Inside we find a pair of 14430 Li-Ion cells, wired in parallel, with a little protection circuit board just jam-packed with teeny parts. One may reasonably assume the circuit controls over-charge and over-discharge, as well as current limiting.
Pack opened
So a reasonable (or, perhaps, amusing) thing to do would be to buy raw cells from a nominally reputable supplier, do a heart transplant, and see if that improves the situation.
Protection Circuit – Outboard
Photos of the protection PCB, showing the cell connections. Positive end of the cells is toward the PCB. I think there’s enough clearance in the camera’s battery compartment to allow a wrap of tape around the case in lieu of re-bonding the plastic together.
The Smell of Molten Projects in the Morning 