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

Avid Rollamajig Repair
Avid Rollamajig with new ball socket

Mary’s shifter cable broke at the rear derailleur, causing the Avid Rollamajig to undergo spontaneous auto-disassembly. The only part we couldn’t find was the socket between the ball and the derailleur’s adjusting thimble.

Good news: my parts heap had the Rollamajig from my bike, which I’d replaced because the most recent derailleur has an integrated gadget that serves much the same purpose.

Bad news: the socket had a chunk broken out of it and I didn’t want to put a broken part on Mary’s bike.

Good news: at least I could measure the dimensions to build a new socket.

Bad news: it needs a spherical socket for what measures out to be a 6.8 mm (0.268 inch) plastic ball and that’s not one of the three ball-end mills I have in the tooling cabinet.

Good news: this isn’t a really critical high-speed / high-stress rotating joint. Pretty good will be close enough.

Sherline chuck in lathe chuck

Turning the part was a quick lathe job on a random hunk of what’s probably nylon.

Bad news: the nylon was a rectangular cutoff from a slab and the three-jaw chuck on my lathe has been firmly stuck for the last year. It’s resisted all the non-Armageddeon-scale techniques; I fear I must machine the damn thing off.

So I…
- mounted the nylon in the Sherline 4-jaw chuck
- grabbed that teeny little chuck in the lathe’s much bigger 3-jaw
- converted one end of the square hunk into a cylinder
- removed the small chuck
- mounted the cylinder end in the 3-jaw
- completed the mission
Offset roughing mill

Lacking the appropriate ball-end mill, I offset a ball-end roughing mill in the tailstock chuck so the near side was at the right radius from the lathe axis, then poked it into the end of the socket-to-be.

Which, of course, produced a not-quite-spherical dent that was a bit too shallow, so I chucked up a too-small ball mill (on the centerline) and carved out the bottom of the socket. The result was a more-or-less spherical socket of about the right depth, pretty much.

The right way to do this, and what I was going to do before I came to my senses, was turn the part on the lathe, drill the axial cable hole, then chuck it up on the Sherline CNC mill. Getting a spherical socket of exactly the right radius and depth using a too-small ball-end mill is then a simple matter of G-Code. Maybe I should write that up for my Digital Machinist column…

Yeah, you could use a ball-turning attachment, if you should happen to have one. Sue me.

Broken and new sockets

Anyhow, it all worked out OK. The new socket is slightly longer than the old one, as it’s made to fit the derailleur thimble at hand. The end around the socket is slightly thicker, too, as it seemed more meat would add more durability where it was most needed.

The Rollamajig seems to be discontinued, although some of the smaller online sources still offer it. Building one looks like a straightforward shop project to me.

Ball socket dimensions

The sketch has dimensions in inches, because I was doing this on the lathe. Our daughter measured it in metric and came out with much the same answers, so it’s all good.
2009-06-21
Bird Box Entrance Reducer

Wren-sized entrance reducer in place

We put out bird boxes to encourage more House Wrens, but House Sparrows often take over the boxes. This year we kept the boxes down until the sparrows had already started their nests in the bushes, hoping that the wrens would get a head start on their nests. Two days after we put the boxes up, we had a nesting pair of wrens… and two days later a pair of sparrows had evicted them and were installing their own nest.

Rechecking the box specs, it seems wrens prefer a hole somewhere between 7/8″ and 1-1/8″, but I’d drilled 1-1/2″ holes for bluebirds (a long time ago, before we knew bluebirds vastly preferred the edges of open fields). Making a hole larger is easy, making one smaller is more difficult.

Cutting off the barb

I thought of making a wood bushing, then came to my senses: a 3/4″ thick wood ring with 1/4″ walls just wasn’t going to work. Given that the wrens (or their ancestors or relatives) have already tried nesting in our gardening boots, bicycle helmets, and tool trays, I figured they wouldn’t be too fussy about the material around their entrance hole.

To the Basement Laboratory Machine Shop Wing!

The parts heap disgorged a box of huge hose barb fittings, one of which had a 1.1″ ID and a 1.4″ OD: close enough. I parted off 3/4″ from the end of the barb, using a bit not really suited for the purpose that gave a nearly perfect edge in the soft plastic. One swipe with a deburring tool and it’s done.

Bushing ready to install

A few wraps of duct tape provided a nice press fit and a springy retaining force without gluing the barb in place. This is pretty, mmmm, barbaric, but if it survives one nesting cycle I’ll do something much nicer.

Time is definitely of the essence here, as we fear the wrens have been driven away: we haven’t heard them since their eviction. I did three boxes in about half an hour; we’ll see what transpires.

The bottom pic shows the box from the front yard, where Downy Woodpeckers nested for a few years. They thought the hole needed a bit of renovation… and they have the tools for the job!

2009-06-18
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