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

  • Rehabilitating an Old Variac

    Variac Rotor Before Fixup
    Variac Rotor Before Fixup
    Variac Brush Holder and Staking
    Variac Brush Holder and Staking
    Variac Rotor After Fixup
    Variac Rotor After Fixup

    So I’ve had this ancient 5 A Variac on the heap for far too long, finally came up with an actual application, and discovered that not only was the line cord shot, it basically didn’t work.

    Of course, I had to replace the cord & outlet before I discovered that it didn’t work…

    The classic Variac failure happens when the carbon brush wears down to nothing, at which point the holder scrapes on the windings and the whole thing burns out. In this case, the brush still had 3/16″ left, but the sliding holder was firmly corroded in place.

    I soaked it in PB’laster, rapped it all over with a small drift punch, and managed to drive the holder out. In the process, the brass sleeve around the brush holder came out, putting the entire problem on the bench.

    The rotor had two brass rivets securing the brush contact bar (the part that’s connected to the actual brush holder by a length of copper braid) that would not come out, nohow. After I broke one off (the first picture), I found that they were swaged over on the bottom, so I broke the other one off and punched both stubs out.

    I spent a few hours wearing a headband magnifier and gently filing everything to a pair of slip fits: brush holder into sleeve, sleeve into rotor. The rotor is aluminum, so I applied a liberal dose of oxidation inhibitor, slipped the sleeve in place, and staked that sucker down.

    Which meant I spent another half hour filing the brush holder to restore the slip fit…

    Turned out that the rivets were 40 mils, the holes were 43, and 00-90 machine screws are 43.5. I don’t have a 00-90 tap (mostly because I know I’d break it by looking hard at it), so I just ran a screw into the hole and formed the threads. They must have 10% engagement, tops, but this isn’t a high-stress application.

    This is, I think, the first time I’ve ever used those 00-90 screws and nuts. The washers are 0-80 so they reach over the brush contact bar far enough to hold it in place. Dang, those things are small!

    The main conduction path seems to be through a brass slip contact, into the aluminum rotor, through the brass sleeve, and into the carbon brush. I’m not convinced the rivets / screws conduct any appreciable amount of current to the contact bar and through the braid, but I shined up the contact patches anyway.

    Put it all back together, fired it up, and it worked!

    Ought to be good for the next half-century, at least…

  • Door Chocks

    Radial Arm Saw Setup
    Radial Arm Saw Setup

    So I volunteered to make 40-odd door chocks for the Marching Band’s motel stay in Syracuse: by edict, all room doors must remain open until lights out. You’re probably not astonished to hear that the kids can think up all manner of reasons why their room doors just sort of drifted shut…

    I contributed two battered maple library bookshelves (which my father salvaged from a flooded library three decades ago)  to the cause, whacked ’em into 5-inch chunks, then ripped each chunk into two wedges. Being the sort of bear I am, I had those suckers immobilized every which way from zero, with a push stick to make sure nothing exciting happened near my knuckles.

    Worked like a champ; nothing exciting happened at all. It just looks like the blade should suck the wedges into itself and fling ’em across the shop; they’re actually held in position from the outside and wind up quietly zinging against the blade without being caught.

    I applied my cute little corner-rounding plane to one of the wedges, did some mental math, then came to my senses: Mr Chock, meet Mr Belt Sander. Ten minutes later, they’re all done!

    A pleasant hour of shop time that made the whole basement smell of cut wood… which means that I’m breathing all those fine particles, even with the shopvac catching nearly everything else. Ran the lah-dee-dah radon reducer for a few hours, which helped a bit, and played with my upstairs toys for the rest of the afternoon.

  • Safety Principles, Deliberately Ignoring

    http://www.public.navy.mil/navsafecen/Pages/photo/Photo-of-the-Week.aspx

    Bet you can’t stop until you see the entire archive. Talk about a target-rich environment…

    Their poster-size print of a “degloved” finger hangs over my drill press. Our daughter says she hates it. I say that’s why it’s there. Word.

    [Update: their site structure has changed enough that deep-linking probably doesn’t work. Go to archive, look down the left column until you find the Photo Of The Week, and proceed accordingly.] The archives are now PDF “posters” that you can’t browse online, which is probably why they did it.

  • Stainless Steel Band Clamps, Endurance Thereof

    cimg1422-stainless-steel-hose-clamps
    Corroded Band Clamps

    As part of clearing the area for our fence project out back, I sawed off a few more lengths of ol’ Gene’s irrigation line and hauled them out of the battle zone. The line ran from the pump house (about 200 feet from the creek), up the hill, and about 400 feet along the property line to our house.

    Presumably the plants really liked creek water…

    Anyhow, he used a variety of hose clamps to hold the PVC pipe to the barbed fittings. They’ve been out in the weather, under the leaves, and generally left to rot for about two decades.

    I salvaged the few clamps that were all-stainless steel, because they were in great shape.

    The others have beautiful shiny bands with rotted worm screws and housings. Some are little more than rusty lumps that, if you didn’t know they were a screw, you’d never guess.

    Moral of the story: make sure the clamps are all stainless steel.

    I have no clue how you’d do that, though, because none of the clamps I’ve ever bought came with labels and I’d never trust the box on the LowePot shelf to match its contents.

    Maybe I should add a magnet to my chandelier o’ gear, right next to the credit cards in my wallet?

    Grrr…

  • Home Shops

    Found this while I was looking for something else…

    http://www.cnn.com/2007/WORLD/meast/02/22/iraq.main/index.html

    CNN being pretty much ahistorical, that’s a dead link by now. Here’s another copy:

    http://www.powermediaplus.com/news/archive.aspx?newsTypeID=1&newsID=2653

    The money quote:

    We also found the various components of a metal shop,
    including welders, burner stoves, circular saws, sanders
    and other items needed to build explosive devices.

    Remember:

    When guns are outlawed, only machinists will have guns.

    Memo to self: The Man knows that, too.

  • Blender repair

    Blender blade bearing repair
    Blender blade bearing repair

    So a while back I replaced the blade bearings in our cheap-after-rebate Farberware blender: a $20 pack of ten bearings (5 repairs!) from eBay for a $15 mixer.

    [Update: They’re 6 mm ID x 13 mm OD x 5 mm thick.]

    Of course, it turned into a shop project. I added spacers that held the shaft in the right position by eliminating some vertical play, dripped Loctite around the housing to fasten the outer races in place, silicone-lubed the seals, and generally did the last few dollars of engineering & manufacturing they couldn’t afford in a cheap blender.

    The blender now works better than it ever did before. It used to emit a horrible whining rattle and didn’t have much go-power. Now, while it’s not silent, it whirs solidly and engages the pancake batter with a vengeance.

    Blood no longer runs out of our ears…

    I think the original bearings were crap quality, badly sealed, poorly mounted, and failed so fast we never knew how the mixer should behave. Grumble, etc.

    Now that I know what to do, the next four repairs should go much quicker. If, indeed, the new bearings ever fail. The old ones were, IIRC, “dishwasher safe”, but I think that is a cruel hoax from the Planned Obsolescence & Early Failure Department. We’re rinsing the blade assembly by hand now.

    If I thought spending more on a blender would get better bearings, I’d probably still buy cheap-after-rebate ones just for the quality shop time…

    Memos to self: left-hand shaft thread, slightly shorter bottom extension, make stainless hardware.