The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Repairs

If it used to work, it can work again

  • Harbor Freight Bar Clamp Failure

    The squeeze handle that tightens the bar clamp cracked exactly where you’d expect: directly across the pivot hole where the miracle engineering plastic thins down to a precarious ridge. The end of the handle is still inside the clamp:

    Bar clamp with broken handle
    Bar clamp with broken handle

    Nothing bonds that plastic, so, in the nature of a quick fix, I cut a steel strap to wrap around the perimeter of the broken section and epoxied the whole mess together:

    Reinforced bar clamp handle
    Reinforced bar clamp handle

    That lasted for exactly 2.5 squeezes and then pulled apart; the epoxy doesn’t really have anything to grab.

    ABS isn’t a good substitute for engineering plastic, so this will require a bit of CNC work on the Sherline. I’ll probably carve the first one from polycarbonate, just because I have a sheet of the right thickness, but it really cries out for aluminum, doesn’t it?

    Why CNC? Well, I’m going to make a handful of handles and get proactive on the other clamps.

    My other bar clamps have much heavier sections in that area, so perhaps the folks supplying Harbor Freight could take a hint? Yeah, but the clamp was cheap, which always conflicts with good. On the other paw, I’ve seen exactly this same clamp priced at not cheap elsewhere.

  • Glass Chip Flat

    Having had trouble with tire liners eroding the rear tube, I went with just a tube and a Kevlar belted Marathon tire. Somewhat to my surprise, that lasted for most of the riding season, but a recent trip had a protracted rest stop:

    Glass chip in tire
    Glass chip in tire

    The puncture came from a knife-edged glass chip that avoided most of the Kevlar belt inside the tire:

    Glass chip - detail
    Glass chip – detail

    I think even a tire liner wouldn’t help with this one.

    Other than that, the tube was in fine shape, so I’ll probably patch it and toss it back in the bike pack. Tire liners prevent most flats from gashes along the midline of the tire, but …

  • Expedient Handlebar Mirror Repair

    We frequently host touring bicyclists who need a campsite in the Mid-Hudson Valley. The most recent couple has been riding for two years, starting eastward from Paris shortly after their wedding. Yeah, it’s a honeymoon trip.

    After riding through Western and Eastern Europe, the Middle East, and several of the ‘Stans, JeanMarc’s handlebar mirror broke in Kazakhstan. Marie toted the carcass out of the ‘Stans, across India, through China, and then from Montreal to here. They’re biking to Houston, where they’ll fly to Peru, ride south and across the Andes, and work their way across the Atlantic on a cargo ship that eventually docks in Germany. Then, a year from now, they’ll just bike back to Paris.

    Makes you feel like sludge, too, doesn’t it?

    With that as prologue, JeanMarc wondered if I could fix the mirror mount. It started as a 10 mm plastic ball on a molded plastic fitting with an integral worm screw and strap; of course, the ball stem snapped off during a hard landing or some such event that comes naturally during long-distance riding. We kicked around some ideas, rummaged through the heap, and came up with a workable, albeit hideous solution.

    I applied a Dremel slitting wheel to a pair of Zerk grease fittings, sliced off the inlet valve, extracted the valve spring, and cleaned up the residue to leave a somewhat misshapen 9.3 mm (really a scant 3/8 inch) ball-like end. A bit of lathe work converted a chunk of PVC pipe into a sleeve grooved for a metal hose clamp. I drilled two #3 holes, tapped them 1/4-28 (which, believe it or not, is the correct thread for a Zerk), bandsawed the pipe in half, introduced the pieces to Mr Belt Sander to round the edges, screwed Zerks into holes, and wound up with a pair of these:

    Handlebar Mirror Mount - detail
    Handlebar Mirror Mount – detail

    Which looks awful on the handlebars, but we’re pretty sure it won’t break and he has a spare if the mirror on Marie’s bike snaps off:

    Handlebar Mirror Mount - fixed
    Handlebar Mirror Mount – fixed

    The Zerk fitting could unscrew, but the threads aren’t exactly in pristine condition after all that fussing and seem to be jammed firmly in place. If we had more time, I’d have heated the PVC and molded it around the handlebars, but we decided that wasn’t really necessary.

    They rode off into the distance this morning… may you have smooth roads and a tailwind, JeanMarc and Marie!

    JeanMarc and Marie
    JeanMarc and Marie

  • External USB Case: DVD Overcurrent

    Well, it turns out that the DVD drive I stuffed into that case really does require a whole bunch of current. I tried playing a DVD and got erratic results, including weird keyboard (!) failures. Finally, I hitched a bench supply to the coaxial power jack on the case and caught it in the act:

    Laptop DVD - current display
    Laptop DVD – current display

    That jack normally connects to the power-only USB cable, which implies an upper limit of 100 mA. A bit of poking around inside shows that the coaxial power jack simply parallels the USB jack’s VCC line, so there’s no fancy negotiation or current sharing going on.

    When the keyboard went nuts it was sharing an unpowered USB hub with this thing, which means that the overcurrent dragged down the hub’s supply. I was permuting all the choices to see if the failures suggested anything; eventually it did.

    A bit of rummaging in the Basement Laboratory Warehouse Wing uncovered a 5.0 V 3.7 A wall wart switching power supply that is grossly in excess of the drive’s 1.5 A rating. Amazingly, it even had the correct coaxial power plug on the end of the cable, which never happens.

    Alas, because the external supply back-powers the USB data cable, it lights up the Q150’s power button when the PC is turned off. I think I can insert an isolation diode into the USB power trace to isolate it from the jack, somewhat along the lines of that hack. However, that seems to require removing the USB connector to uncover a very well protected top trace. For now, I’ll just unplug the drive.

  • Flex-fatigued Helmet Cable

    I cable-tied the mic/earphone cable on Mary’s bike helmet to a rib on the fancy air vents near the back end, hoping that would reduce the inevitable flexing. Alas, it didn’t work out that way and the cable lasted only two seasons. This cut-away view shows the pulverized shield braid inside the jacket:

    Fatigue-failed helmet cable
    Fatigue-failed helmet cable

    The symptoms were totally baffling: the mic worked perfectly, but the earphones cut out for at most a few syllables. Of course, I can’t wear her helmet and it only failed occasionally while riding. I barked up several wrong trees, until it got so bad that I could make it fail in the garage while listening to the local NWS weather radio station.

    I spliced in a new USB male-A connector and (re-)discovered that the braid seems to be aluminum, rather than tinned copper. In any event, the wire is completely unsolderable; I crimped the braid from the new connector to a clean section of the old braid. The braid serves only as an electrostatic shield, as it’s not connected to anything on the helmet end. That should suffice until I rebuild the headsets this winter.

  • NFS V4 Tweaks

    Come to find out that Ubuntu 11.10 uses NFS V4 by default, which means the various clients scattered around here, all of which use NFS V3 by default, report all files have user & group 232 – 2: an awkward and unforgettable unsigned 4294967294. That’s -2 in 2’s complement notation with 32 bit hex numbers, corresponding to the unsigned 16-bit 65534 = -2 for the nobody user & group.

    Fix that by editing /etc/default/nfs-common to set NEED_IDMAPD=yes. Unmount the NFS share, do sudo start idmapd, remount, and it’s all good. The next time the client boots, the idmapd daemon starts automagically, and that’s all good, too.

    Adding the -t nfs4 filetype in /etc/fstab seems to be not necssary.

    How I got into this mess: the Intel Atom D525 that had been driving the Thing-O-Matic has a bog-standard Intel graphics chip that, despite (or perhaps because of) having an open-source video driver, reports doing only OpenGL 1.4. OpenSCAD, however, requires OpenGL 2.0 and those hacks don’t allow it to run properly, which makes it awkward for demos. The AMD that’s currently the file server has, IIRC, better graphics that might improve the situation; I think it sports a somewhat peppier processor, too. The fact that it’s running Ubuntu 8.10 says that it’s time for an update.

    Soooo, I swapped in a new 1.5 TB SATA drive, installed hot-from-the-oven Ubuntu 11.10, replaced Unity with XFCE, inhaled all the current data from the file server’s external USB backup drive, configured ssh / nfs / etc, and I’m now doing some simpleminded tests before I swap the IP addresses.

    Now, if the AMD has craptastic graphics hardware, it’s unhappy dance time…

  • Sawed-off Sawhorse

    As part of sawing a kitchen countertop apart to fit it into the bathroom, this happened:

    Sawed-off sawhorse
    Sawed-off sawhorse

    I’d very carefully checked the clearance for the first two cuts, but …

    The sawhorse is polyethylene, which cannot be glued, so I drilled holes in the internal bulkheads, slobbered JB Industro-Weld epoxy through them, and filled the gaps with wood blocks:

    Wood-epoxy PE repair
    Wood-epoxy PE repair

    The goal being to not have metallic fasteners where the saw blade can find them.

    This should work for a while:

    Sawhorse cap repaired
    Sawhorse cap repaired

    If that’s never happened to you, I’d say you aren’t doing enough circular saw work…