Mailbox Door Rebuild
Posted by Ed in Home Ec, Machine Shop on 2019-09-18
The flanges around the door of our giant mailbox rusted through, leaving the door to bend along the embossed (debossed? Whatever) lines across the front. Eventually, the bend got bad enough to keep the door from latching closed, but reviews of the current crop of mailboxes suggest they’re even more prone to rusting after even fewer years.
Well, I can fix that:
Because the bottom third of the door, basically everything around and below that horizontal ridge, had corroded, the general idea was to stiffen it with an internal plate:
The array of small holes suggest the plate’s rich lived experience. Some are even tapped!
External angle brackets stiffen the sides along the corroded flanges and surround the equally corroded pivot holes:
The term “brick shithouse” springs unbidden to mind, doesn’t it? Those spare holes come from previous uses; I decided this application didn’t demand cosmetic perfection and, as a result, the remaining angle stock has no holes at all.
Also, the angle brackets are as long as they are because that’s the maximum throat depth for Tiny Bandsaw™. I splurged on a Proxxon 10-14 TPI blade (for future reference: PN 28172) that cuts aluminum like butter, much better than the stock 14 TPI blade.
The hinge pins used to be rivets. After careful consideration, I replaced them with 1/4-20 button-head cap screws:
Yes, the sheet metal now pivots on screw threads, rather than a nice smooth cylinder. The nyloc nut maintains the proper amount of looseness around the battered sheet metal.
While I had the door open, I slobbered hot melt glue over the flag anchor, which should keep it from spitting the ratchet pin into the roadside debris ever again:
A pleasant evening of Quality Shop Time, indeed!
The alert reader will note I’m securing aluminum plates with stainless steel hardware on a (nominally) galvanized steel box, thereby forming several batteries with a brine electrolyte from wintertime road salt. My engineering judgement determined this repair will last Long Enough™ and, most likely, succumb to somebody not quite making the curve while accelerating from the traffic signal.
Aaaaand those painted numbers still look pretty good after four years.
Hawk vs. Praying Mantis
A young Coopers Hawk swooped across the yard, landed on a branch, and proceeded to dismantle something yummy, scattering little bits on the driveway below. One piece fluttered down like a feather, but, after the hawk flew off, we found this:
It wasn’t a feather, it was an entire wing!
A few feet away, we found another:
Not that there was any doubt, but these parts clinched the identification:
Some days earlier, we admired eight Praying Mantises on the decorative grasses and bushes out front. Perhaps it was this one:
Or this one, a few feet away:
We don’t know what, if any, the difference between brown and green wing covers might indicate. Age? Gender? Attitude? Skill level?
It’s a food chain out there!
Walnut Husk Fly Damage
A recent Amazon purchase of three 3 lb bags of walnuts from a known-good seller arrived with many damaged nuts:
The damage matches what I read about Walnut Husk Fly infestations: shriveled kernels and terrible taste.
In round numbers, I found 8 oz of damaged nuts in each 3 lb bag, enough to ruin the entire batch. The seller immediately refunded the purchase price for all three bags, so there’s that.
It’s definitely not one of the counterfeit products plaguing Amazon, but I wonder why that lot didn’t fail incoming inspection.
I’m loathe to buy more walnuts for a while, though.
Memo to Self: Always inspect incoming purchases, even from reputable sellers!
Monthly Image: Praying Mantis vs. Monarch Butterfly
Posted by Ed in Oddities, Photography & Images, Science on 2019-09-15
The Butterfly Bush in front of the house attracts all kinds of insects, including Monarch Butterflies (shown here on the Goldenrod planted in the garden):
This year, the bush also attracted a Praying Mantis:
Then lunchtime happened:
A closer look:
Now, if that isn’t enough nightmare fuel for you, find some in your own neighborhood.
Schwalbe Marathon Plus and Michelin Protek vs. Glass Chip
Posted by Ed in Machine Shop, Recumbent Bicycling on 2019-09-14
The rear tire of my bike was flat before our morning ride and pumping it up produced a hissing sound with a spray of tube sealant:
We run Schwalbe Marathon Plus tires on the rear of our Tour Easy ‘bents, because otherwise I’d be spending far too many hours repairing flats by the side of the road. Searching the blog for the obvious keywords will produce many examples of what it’s like to ride a bike in Dutchess County NY.
Schwalbe says the tires have 5 mm of “highly elastic special rubber” and claims “Even thumbtacks can’t puncture it.” They use the term “Flat-Less” in the sense of “flat less often”, rather than “not flatting”, which seems disingenuous at best.
Flatting less often may be true, but they obviously haven’t tested against Dutchess County road debris:
It’s not quite 5 mm in the longest dimension, but it was embedded deep enough in the tire tread to cut through the armor belt and nick the Michelin Protek tube:
Of course, the hole is dead-center between the two bumps that are supposed to compress around the puncture while the goo fills and seals the void.
Before taking everything apart, I tried gently inflating the tire and putting the puncture at the bottom to let the sealant fill the hole overnight. In the morning, the tire was once again flat, although the floor wasn’t covered in goo. Pumping the tire up produced another spray of sealant.
It’s likely the Protek tube got me home with a slow leak on the previous day’s ride, but it definitely didn’t solve the problem and, frankly, I’ve had ordinary tubes do the same thing. Given the trivial size of the puncture and the complete lack of permanent self-repair, I don’t know what kind of damage it’s supposed to cure.
I’ve already discarded two Protek tubes with slow leaks through the valve stem and no punctures, so they’re definitely not worth the hassle. Michelin no longer lists the tubes on their bike tire site, so it seems they agree.
I made up a boot by punching a 5 mm polypropylene disk, sticking it to a small tire patch, then sticking the patch over the puncture on the tire. With a bit of luck, nothing will line up with the gash and punch through the boot.
I recently replaced all four tires on the Forester, slightly ahead of schedule for reasons not relevant here, and it’s worth noting that a Marathon Plus tire costs about a third of what I paid for a car tire; they’re not to be discarded lightly.
CNC 3018-Pro: Milling the CD Fixture
Posted by Ed in Machine Shop on 2019-09-13
It turns out that the outer diameter of CD platters isn’t quite as perfectly controlled as you (well, I) might imagine, although the differences between CDs from different sources amounts to perhaps ±0.1 mm. Of course, instantly after putting the tape-down fixture into use, the next few discs atop my stack of scrap CDs were just large enough to not quite fit.
The Sherline’s workspace can’t maneuver the holder’s perimeter around the spindle, so embiggening the OD calls for the rotary table. The general idea is to clamp the center of the fixture to the rotary table, run a small end mill about 0.1 mm into the fixture’s OD, spin the table one revolution, and be done with it.
Of course, the rotary table’s 3/8-16 threaded center hole doesn’t match the fixture’s 6 mm center hole: we need an adapter. Start with a 1 inch long 3/8-16 stainless steel hex bolt, center drill the end, peel off the hex head, then turn to 6 mm OD, going down far enough so the threads don’t stick up out of the table too much:
The Sherline uses 10-32 screws, so poke a #16 drill 15 mm into the bolt to get maybe 25% thread depth (because it’s a blind hole into stainless steel for an application requiring minimal strength and I hate breaking taps), tap 10-32, clean out the hole, and call it All Good:
Find the trim plate from an old faucet to reach around the central boss, stack up enough flat washers to meet the nut, snug a Sherline spherical nut + washer set (because it’s within reach), chuck up a 1/8 inch mill, and have at it:
The fixture sits atop an aluminum plate cut to fit a smaller version of the table riser, but this requires zero fancy alignment. The 6 mm adapter centers the fixture on the rotary table and the cutter sits at a fixed radius from the center wherever it contacts the fixture rim; just spin the table and it cuts a neatly centered circle.
A test fit showed the oversize discs fit perfectly:
Bonus: a nice new adapter for the rotary table!
CNC 3018-Pro: Tape-Down Platter Fixture
Posted by Ed in Machine Shop, Software on 2019-09-12
Diamond drag engraving doesn’t put much sideways force on the platters, so taping the CD in place suffices to hold it:
Wrapping a flange around the screw-down platter fixture provides plenty of surface area for tape:
Which looks exactly as you think it would in real life:
Admittedly, masking tape doesn’t look professional, but it’s low-profile, cheap and works perfectly. Blue painter’s tape for the “permanent” hold-down strips on the platform would be a colorful upgrade.
It’s centered on the platform at the XY=0 origin in the middle of the XY travel limits, with edges aligned parallel to the axes. Homing the 3018 and moving to XY=0 puts the tool point directly over the center of the CD without any fussy alignment.
The blue-and-red rings around the center hole assist probe camera alignment, whenever that’s necessary.
The OpenSCAD source code as a GitHub Gist:
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