Growf.

I mentioned setting up the lab for some power-electronics tests?

Feeling a fair bit better today (but stressed, what with my to-do-soon list getting more longer than shorter, and a nasty problem having cropped up with regard to a bog-standard switching voltage regulator), I took a bunch of clutter to electronics recycling, dug out the big honkin' lab power supply, and rounded up a pile of power resistors that, suitably connected, should present the requisite load while safely dissipating an Imperial smegload of waste heat (while I check the teeny-tiny unit under test for signs of overheating; the math says all should be cool).

Gotta organize the things, and 'tis best they should be bolted to a hefty slab of aluminum.  So: mark positions, and drill and tap twenty mounting holes.

Well... around the fifteenth hole, my #4-40 tap snapped.  And why did I have only one #4-40 taper tap in my toolbox, anyway?  There's a matching bottoming tap, but I don't really want to use that.

Ah, there's a spiral tap.  Or, as one might say, this is spiral tap.  Not really meant for handheld use... and it snaps on the second hole.  Foo.

Guess it's off to the hardware store.  And, later, I'll have to find the bottle of Tap-B-Gon.

Update: The dreadfully Searsified OSH no longer carries a nice selection of taps in little bags.  There's a rack of overpriced American Vermin threading products, but individual taps start at #8-32; for #4-40, the only option is an even more overpriced tap-and-drill set.

Oh, well.  It got the last few holes done, with much more effort than a proper Greenfield (or even generic industrial) tap would have taken.

Note for next time: do all tap breaking in the morning, and make an MSC run while (a) they're open and (b) it isn't rush hour.