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.

Category: Machine Shop

Mechanical widgetry

Terracycle Idler Shaft Cleanup

Crusty Sliding Shaft

I installed a Terracycle Idler on Mary’s Tour Easy when the old chain tensioner wore out. It’s significantly quieter than a double-idler tensioner, but the rear derailleur can barely handle the 11-34 sprocket / 30-42-52 chainring combination.

She likes it, that’s what counts.

Anyhow, while poking around under the bike, I noticed that the idler no longer slid left-to-right on the shaft through the bearing. The bearing itself spun fine, but the shaft… ugh, they should have used stainless steel.

The sliding motion is important, as the idler should self-adjust to the chainline during shifting. I don’t know how long this one has been jammed, but it could contribute to the noises she’s been mentioning of late and that have prompted me to embark on a major maintenance project.

Cleaned Shaft Installed

It shined up nicely with a Scotchbrite wheel in the drill press and now looks merely horrible; you can see the copper plating (wrong: see Update below) showing through. I had to hit one end of it with a medium diamond file to knock off an invisible high spot.

I added a bit of lube and reinstalled it; the bearing slides back & forth like it used to, but I have my doubts as to how long this will last. Fairly obviously, the plating is shot.

The next time it fails, I’m sure I’ll wind up trying to turn an exact 0.3125-inch diameter stainless-steel shaft with a polished surface…

Oh, and the three orange retro-reflective strips? The idler turns backwards because it’s on the return side of the chain: it’s rather disconcerting and I figured it’d be fun to highlight it.

Update: The folks at Terracycle say it’s plated zinc over a brass bushing… which (Ah-ha!) explains the corrosion.

The zinc forms an anode against everything else on the bike; nothing is more anodic than zinc. Because the plating has no volume, it turns into a Fizzy at the merest sight of the usual road salt around here.

Unplated brass would be better: more volume, cathodic against steel, anodic but pretty close to stainless, just as slippery. Might tend to wear against the inner bearing race, but I’d expect it to be at least as durable as the plating.

Worn Terracycle Idler shaft

Here’s a pic of the shaft from another Terracycle Idler I had on my TE for a while. While it’s not corroded, it’s worn through to the brass underneath. So maybe the plating isn’t buying much, anyway.

I spent some quality one-on-one shop time with a random hunk o’ stainless hex rod, came up with a good-looking 0.304-inch OD (a nasty bit of overshoot, but I haven’t done any lathe filing in recent memory and forgot how fast it removes metal), and verified that the race will cock-and-jam rather than sliding nicely.

The Terracycle folks will send a replacement shaft; they’re good folks who build quality stuff and stand by their products. I’m obviously abusing the poor thing…

Update: The stainless shaft arrived and is sized for the 6 mm bolt they’re using in new production. When we discussed this, I said it’d be no big deal for me to adapt it to the existing 5 mm bolt. A length of heat-shrink tubing does the deed, as it’s rigidly held on both ends. A dab of Loctite, a dot of oil, and it’s back in service. We’ll see what happens after a few months of riding under my regime of benign neglect.

Old brass shaft, new stainless steel shaft, 5 mm bolt with heatshrink

A tip o’ the cycling helmet to Terracycle!

2009-06-17
Quieter Luggage

Muted zipper pull tabs

Luggage now comes with a pair of sliders on each zipper, which means that the two sliders come together when the zipper is closed. That allows you to lock the slider pulls together, which is a nice touch for those of you who think luggage locks actually improve security.

It also means that the metallic pull tabs jingle and jangle merrily together in the back of the van all the way to grandmother’s house as we go, we go.

Not to be tolerated, sez I.

Apply a length of heat shrink tubing to each tab. If you’re a locking kind of person, leave the holes on the end exposed. If you’re a real cheapskate, you could get away with shrinking just one tube per pair, but even I’m not that far gone.

2009-06-16
Where To Put Too Many Clamps

Clamp storage plates on floor joist

Not in a drawer, that’s for sure…

Whack a narrow rectangle from some random scrap of thin wood-like substance, squirt hot-melt glue along one edge, stick it to the floor joist over your tool chest, align it pretty much horizontally, take two deep breaths while the glue solidifies, then neatly affix your clamps.

Repeat as needed when you get more clamps: you can never have enough clamps!

The red-handled spring clamps on the far right hang from a row of nails where, this being directly in front of my tool cabinet, they don’t quite knock me on the head. I really wish the original owner of this house had sprung for one more course of concrete block; another nine inches of headroom would have been just ducky.

2009-06-13
Aligning to a Hole With a Defocused Laser Spot

Defocused Laser Spot on Hole

When you’re aligning to an edge or scribe mark, you want the laser spot as small as it can possibly be, so you tune for best focus.

To locate the center of a hole, you first find the edge, then move toward the center by one radius… so you must know the diameter, too. It’s tricky to find an edge exactly on the X or Y axis, which means you generally resort to successive approximation. I did something like that there with good results.

If you defocus your laser aligner to produce a spot slightly larger than the hole, you can simply position the hole under the beam to produce a nice bright ring. Adjust the focus to make the spot barely larger than the hole and you can get pretty close to the center without any messy arithmetic.

Now, should you happen to own a real laser aligner, you might actually have a nice-looking defocused spot. My homebrew Orc Engineering aligner, as shown there, starts with the beam from a chip laser in a hacked carpenter’s level, so the defocused spot is rather, mmm, ragged, even after passing through the not-very-restrictive aperture behind the lens.

With the lens in the spindle, though, I can spin it at a few hundred RPM and persistence of vision blurs the beam into a nice, symmetrical disk. Jog to center the disk around the hole, twiddle the Z-axis position to adjust the focus / size / blobbiness, jog more slowly, tune for best picture, and it’s all good.

This obviously doesn’t produce jig-boring quality alignment, but, then, I’m not doing that sort of work. In the picture, I’m enlarging a 4-40 hole molded in a Pactec case to fit a 6-32 screw. Normally I’d do that by hand on the drill press, but this time I also had to enlarge the counterbore at the top and figured I’d use a quick G2 with an end mill after I had it aligned for the drill.

Maybe everybody else knows this trick, but I was delighted to find that it actually works pretty well…

2009-06-06
Electronic Ballast Shoplights: So Much For Efficiency

Just picked up a batch of electronic-ballast shoplights from Lowe’s, motivated by a 10% off card they sent a while ago. Not a killer deal, but it evidently got plenty of folks into the store on a Sunday morning.

The new lights don’t claim much about their abilities, other than “Electronic Cold Weather Start (0° F)” and that the reflector sizing requires T8 (1″ dia) fluorescent tubes. One would expect an electronic ballast to have a decent power factor and improved efficiency.

Because I’m that sort of bear, I opened one up to see what was inside. Here’s the ballast:

Electronic Ballast Dataplate

Although the fixture is sized for T8 tubes, the ballast would be perfectly happy with T12s. Similarly, the box insists on F32 tubes, but the ballast is OK with F40s.

I thought a comparison with one of my old magnetic-ballast fixtures would be of interest, so I hitched up the Kill-A-Watt meter and ran some comparisons.

The results…

Amp Watt VoltAmp PF

Old magnetic ballast

F40T12 0.64 60 76 0.79

F32T8 1.11 80 126 0.62

New electronic ballast

F40T12 0.75 47 89 0.53

F32T8 0.77 49 91 0.54

The electronic ballast has a much lower power factor and thus much higher current. The box & ballast don’t say anything about power factor correction and, wow, there sure isn’t any. The power company hates gadgets like this…

I cannot compare the brightness because the F40 tubes are several years old, but it’s interesting that the electronic ballast runs both tube sizes at essentially the same power (just as the dataplate indicates, sorta-kinda). The magnetic ballast really cooks the piss out of the smaller tubes, though… or it’s dumping a lot of energy into the ballast. Hard to say.

The T12 tubes are rated for 3000 lumens & 20 k hours. The new box of T8 tubes I got a while back are 2800 lumens and 24 k hours. Frankly, I don’t believe any of those numbers, particularly given the actual power consumption: it looks like either ballast runs them at just 75% of their rated power.

Anyhow, these were the cheapest shoplights in stock; I bought eight of ’em, because I’ve been replacing one dead fixture every month or two for the last year. I’d like to think I’d get a better ballast if I spent twice as much, but to a good first approximation the additional cost seems to have gone into black plastic trim and a burnished-chrome exterior finish; not what I need in the Basement Laboratory.

I wish the boxes were more forthcoming so you didn’t need to perform exploratory surgery.

2009-06-05
Rattle-free Sherline Handwheels

Knobless Sherline handwheel

The standard Sherline mill comes with tapered plastic knobs on the handwheels, which is exactly what you want for a manual mill and what you don’t want on a CNC machine: they rattle like crazy during computer-controlled moves.

Some folks contend the knob unbalances the handwheel, but I’m not convinced that’s a real problem. Their advice is to remove the entire knob assembly, leaving a bare shaft sticking out of the motor. Seems a bit extreme to me.

In any event, shortly after I got the mill, I unscrewed the little retaining screw from the end of each knob, put all the parts in a ziplock bag, tucked it in my tool box, and have been rattle-free ever since.

The metal shaft is entirely adequate for those rare occasions when I turn the knob manually, the graduated settings let me detect when if I’ve screwed up the acceleration (on a new installation) to the point where the motor is losing steps, and all is right with the world.

Oh, that orange-barred white tape in front of the motor? That’s a reminder to keep the usual pile of crap away from the spinning knob. That little shaft can fling small objects a fair distance and makes a nasty tangle out of a misplaced red rag…

2009-06-04
Digital Caliper Roller Repair

Broken caliper thumb roller mount

The thumb roller fell off my digital caliper in the heat of a project, forcing me to deploy a hot backup from the upstairs desk.

This looks like a clear-cut case of underdesign, because it broke exactly where you’d expect: at the midpoint of the arch. Having my thumb right over the spot marked X, though, meant that I had all the pieces and could, at least in principle, glue everything back together.

Glued and clamped

As with all repairs involving adhesives, the real problem is clamping the parts together while the glue cures. I clamped a stack of random plastic sheets to the back of the case to establish a plane surface behind the mount, with a small steel shim to prevent the top sheet from becoming one with the repair.

The roller shaft was about the same size as a #33 drill and the opening was about 110 mils. Some 3/32″ (actually about 96 mils) rectangular telescoping brass tubing was about the right size & shape to hold the opening in alignment. Another length of tubing kept the broken part from sliding to the left.

A dab of solvent glue (I still use Plastruct, but it’s not like it used to be before it became less toxic) on both pieces, line ’em up, apply a clamp to hold it in place, and let it cure overnight.

I have no confidence that this will stay together for very long, so I’ll probably be forced to mill a little replacement mounting doodad.

Ought to be good for a few hours of quality shop time…

Memo to Self: Don’t run the slide off the end of the body, because that rubber boot is an absolute mumble to put back in place.

2009-05-31