Not the first time this has happened:
Confronted with a pair of perfectly fitting granular surfaces, a drop of thick cyanoacrylate adhesive seemed appropriate.
As before, we’ll see how long it survives …
Tag: Mini-lathe
Tweaking an LMS 5200 Mini-Lathe
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One-Watt LED Autopsy: No Trouble Found
Over the last several weeks the taillight on Mary’s Tour Easy became dim. I verified the LED had failed by soldering the taillight driver to a different 1 W LED stuck on a separate heatsink, whereupon the LED lit up as it should.
Testing the failed LED with a bench power supply clipped to its wires showed it passed only 15 mA, even with 6 V applied directly to the wires. Those 1 W LEDs normally drop 2 V at 400 mA, so something was definitely wrong in there.
Which meant I had to build another taillight, as described yesterday, and reuse the original electronics and PVC tube. After mounting the new taillight on Mary’s bike, I could autopsy the failed LED.
Because everything is glued into the heatsink, the first step is cutting it apart to free the LED:
1W red LED Autopsy – heatsink parting I stopped the first cut when it just kissed the two wire holes, moved over a little more than the width of the cutoff tool, and tried again. Second time was the charm and I now have a clean aluminum tube that ought to come in handy for something, sometime.
Concerted prying under the edge of the LED PCB popped it off the heatsink:
1W red LED Autopsy – heatsink epoxy bond The red wire sticking out on the right shows a little damage from the cutoff tool, which also chipped the epoxy while bending the aluminum LED base. The bare spot in the middle matches the screw hole in the heatsink, with the rest remaining firmly bonded, so the epoxy was doing its job.
Prying the LED off the lens holder:
1W red LED Autopsy – lens holder detached If I didn’t know better, I’d say the red silicone insulation was sun-faded, but for sure no sun gets inside the lens holder.
An ohmmeter showed both wires had good continuity to their LED pads, which were firmly soldered to the PCB pads; the pads don’t carry any current in this setup. I then hitched up the bench supply to the wires again:
1W red LED Autopsy – no trouble found Whereupon the LED glowed brightly and some quick testing (because it’s not on a heatsink) with the bench supply in constant-current mode showed it once again drew about 400 mA with 2 V applied and glowed brilliantly as it should.
I had previously removed the reflowed solder from the PCB thermal pad and added thermal paste before resoldering the LED:
1W LED – thermal grease So I have no idea what caused the original failure, how the LED could survive with 6 V applied to its terminals, or what would have caused it to recover. It now has a “?” scrawled on the PCB for future reference.
The world is full of mysteries …
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Window Latch Cam Rebuild
One of the living room window latches stopped working and, although the correct response would be to simply replace it, the window sash already had six holes surrounded by paint scars suggesting this wasn’t the first failure.
The latch as built:
Window latch cam – as built The stamped steel spring holder was loose on the handle arm’s square pot-metal post, due to obviously poor factory swaging during assembly. Unseen below the plate is a cam molded into the handle intended to slide the white latch plate with the stamped post (over on the left) guiding the plate around the curved track and into the recess.
I don’t have a “before” picture of the cam, but it had completely worn away against the various steel parts. The task boiled down to replacing it with something more durable, which turned out to be a reshaped M3 brass screw:
Window latch cam – test fit The Sherline setup to remove the worn cam, with the screw in place for a test fit:
Window latch cam – Sherline setup The vise loosely clamps the handle, mostly for alignment, with the step block clamp holding it firmly in place.
The lever arm looked like this after poking the endmill into it a few times to clear the rubble, then using a smaller endmill as a drill to get a flat-bottomed recess:
Window latch cam – milled hole Obviously, that was accomplished with eyeballometric alignment and manual jogging.
Reshaping and trimming the screw with Tiny Lathe produced a suitable cam-like object:
Window latch cam – screw installed I planned to epoxy it in place, but AFAICT there is no way for it to go anywhere, so I just reassembled everything in reverse order:
Window latch cam – reassembled I brutally swaged the square post with an automatic center punch cranked to maximum throttle while forcing the spring holder firmly atop the stack. The latch now moves smoothly and everything stays properly aligned.
While that was going on, the window sash had wood pins pounded into the errant screw holes with wood epoxy filling the gaps. Aligning the latch, drilling holes in the proper spots, and screwing the latch in place proceeded as expected.
That wasn’t easy, but now I can install plastic film over those windows for the winter.
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Countersunk Screw Recess Fillers
For reasons not relevant here, a friend must fill several pre-drilled countersunk flat-head screw holes with brass plugs suitable for M5 screws. These proof-of-concept samples give the general idea, with the red blotch on the left marking the first attempt:
Shelf flush screw fillers – samples He gets to make as many as needed …
The flat-head screws have an 82° included angle, so the lathe compound angle must be 41°. Tiny Lathe lacks sufficient reach to accomplish that on the front side, but cutting the back of the brass rod with the spindle running in reverse will work:
Shelf flush screw fillers – lathe setup The quick-change tool post is aligned parallel with the lathe bed to put the tools at the proper angle.
It turns out 41° is about as far as the compound will go:
Shelf flush screw fillers – compound angle setting This, readers of long memory may recall, is the mini-lathe with the cross-slide DRO interfering with the compound enough to prevent it from cutting ordinary 60° screw threads, which is why the angle tops out at 42° instead of 60° in both directions.
The filler needs a 5.1 mm hole for EZ clearance, which is straightforward:
Shelf flush screw fillers – drilling That was the first attempt after I got the compound angle worked out, which is why it eventually got the red mark. You want to drill on a flat end after countersinking with a center drill. It’s also good practice to drill only a few diameters deep, rather than trying to gun-drill sufficient hole for half a dozen fillers with one poke.
Run the spindle in reverse to cut the 41° angle on the back side:
Shelf flush screw fillers – backside cutting – detail Run the spindle forward to separate the finished filler with a cutoff tool:
Shelf flush screw fillers – parting off The length isn’t critical, so holding a millimeter scale against the right side of the tool and eyeballing the distance from the end of the taper should suffice.
Filing to polish, deburring to finger-frendliness, and similar activities are in the nature of fine tuning.
Now for some Quality Shop Time!
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Bike Helmet Mirror: Always Have A Spare
As fate would have it, the telescoping stalk on Mary’s helmet mirror broke off at the ball mount a few days after I assembled another spare mirror:
Helmet Mirror Ball Mount – broken shaft That’s the point where all the stress concentrates, but the stalk lasted almost exactly six years and didn’t owe me anything.
So I clamped the mirror+shaft+ball from a spare into the mount on her helmet, and she rode off as planned.
Once again being down to a single spare, I drilled a few more 10 mm balls:
Helmet Mirror Ball Mount – ball drilling Cleaning up the end of the broken shaft let me shove it into a drilled ball:
Helmet Mirror Ball Mount – repaired – drilled balls The insert and random screw came from the stub end of the broken shaft: ramming it into the cleaned-up end makes the job look Good Enough™.
Clamp the repaired stalk into the spare mount, drop the drilled balls & lathe fixture back in their bag, and maybe it’ll be another six years before they’re needed.
Life is good!
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Mini-Lathe 100 TPI Stacked Change Gear
Before turning the PVC conduit to the proper diameter for the Shopvac hose adapter, I set up a 20-50-32-80 change gear train for a 100 TPI finish. While the urethane adhesive cured in the hose, I fed the BC gear pair into my change gear generator:
Mini-lathe stacked change gears – 32-50T – solid model It’s ready for the next time I cut something down to size:
Mini-lathe 100 TPI change gears One reference suggests a 256 TPI finish for “general turning”, which works out to 20-80-20-80:
Mini-lathe stacked change gears – 20-80T – solid model That’s just crazy talk, because the BC washer overlaps the D gear teeth:
Mini-lathe 256 TPI change gears If all else fails and I really need a 256 TPI finish, lathes are pretty good at making washers.
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Shopvac Hose Adapter
Adapting a previous adapter to put a much longer hose on the Least Shopvac now lurking under the bandsaw / Sherline / lathe workbench:
Spiral Hose – 1.25in nozzle adapter – installed The tapered adapter drags the OpenSCAD code into the BOSL2 era:
Spiral Hose – 1.25in nozzle adapter – solid model The ID of the hose determined the OD of the lathe-turned PVC tube inside the 3D printed adapter, so a straight pipe would just slide right into both parts.
It would be possible to skip the 3D printing and make the adapter from a single piece of PVC:
- Turn one end of the conduit to fit the hose ID
- Maneuver the lathe compound to the required 1.05° half-angle
- Turn the taper to fit the crevice tool
- Clean up the original OD between the two sections
Just turning the whole pipe to a smaller OD and sliding the taper on was definitely easier, particularly given the mini-lathe’s cramped quarters with the compound nearly parallel to the bed.
A generous helping of JB PlasticBonder urethane adhesive bonds the PVC pipe inside the vacuum hose and the tapered adapter.
The as-printed taper perfectly fits the crevice tool shown in the picture and is one wrap of electrical tape smaller than another crevice tool of “the same size”. The
Finessevariable handles that situation, should it matter to you.The OpenSCAD source code:
// Shopvac spiral hose to 1.25 in nozzle // Ed Nisley - KE4ZNU // 2026-07-25 include <BOSL2/std.scad> Finesse = 0.2; // [-0.5:0.1:0.5] // PVC pipe liner final OD PipeOD = 28.5; /* [Hidden] */ NumSides = 4*3*4; $fn=NumSides; Protrusion = 0.1; // make holes end cleanly HoleWindage = 0.2; // make holes large enough to fit //---------------------- // Dimensions TAPER_MIN = 0; TAPER_MAX = 1; TAPER_LENGTH = 2; Tool = [30.0,31.1,30.0] + [Finesse,Finesse,0]; FlangeOD = 37.0; FlangeLength = 5.0; //render() difference() { union() { cyl(FlangeLength,d=FlangeOD,anchor=BOTTOM) position(TOP) cyl(Tool[TAPER_LENGTH],d1=Tool[TAPER_MAX],d2=Tool[TAPER_MIN],anchor=BOTTOM); } down(Protrusion) cyl(2*Tool[TAPER_LENGTH] + FlangeLength,d=PipeOD + HoleWindage,anchor=BOTTOM); }
