Not All Fiberglass Is The Same?

  A few posts ago, I sang the praises of fiberglass scratch brushes. Since using the new one a bit, I noticed the brush end had developed 'split ends' and is now very soft and more-importantly, non-abrasive.

 In other words, it's fucking useless now.  WTH?

 So now I will go buy an Excelta*, which is what I had my original positive experiences with, and I will throw this PoS in the trash.

 I assume the original has a more brittle glass in the bristles, I dunno.  These have gone soft on the ends, and under a loupe, they look like human hair with split ends.  The opposite breakdown behavior from what we want. We want the tips to chip, crack, or break off (eventually) but not to split, ever.

 ~≈{👁}≈~ 

 "There is hardly anything in the world that the Chinese cannot make a little worse and sell a little cheaper, and people who consider price only are China's lawful prey." - J.A. Richards, updated
(it was never John Ruskin)
___________________
* yup, the Swiss wait, California?  Wow.  Anyway the $60 tweezer & $150 pliers people.

Which Wavy? How Much Gravy?

  I am looking at buying a set of wavy parallels; mostly these exist so you can put thin parts in the mill vise which are thinner than a single (1/8 or so) conventional parallel, while still enjoying the benefit of a parallel, ie; aligning the part with the vise ways, and thus (presumably) with the mill's table surface.
Like standard parallels, they come in sets containing various heights.

these are sane curves for wavy parallels

 They are not terribly expensive, depending on whose word you are willing to trust, and how much you want to spend.  They _should_ be easy to make.  Cut out with laser or waterjet, stamp shape with simple tool, heat-treat, stack a bunch of them together in a vise or on a magplate, and surface grind to dimension.  Do a hundred (of each size) at a time.

 So when shopping, I immediately noticed something: most of the less expensive sets have an "accuracy" stated as ±.0002 (over the length of the tool) which is a typical accuracy for both kinds of parallel... BUT most of the cheap sets aren't six inches long.  They are ±.0002 over FOUR inches, not six.  I've even seen a few sets that were three inches long.  I hope it's obvious that they are less accurate than parallels with the same spec over six inches because I'm still in a lot of pain and I don't feel like typing out the explanation. 

 Caveat Emptor. Buying name brand does not necessarily gain you anything; the ones I've looked at are expensive because name brand, but the promised accuracy is the same.

Aside: the acid test for these things - that is, to see if they are any damn good - is all about their spring temper, testing that they can be compressed and will spring back to their original full width.  It goes like this:

1. pick one out, lay it flat on something reasonably flattish
2. measure the wave height - a scale is sufficient, no need to bust out the surface plate and height gauge :) - and write it down
3. stick it in the mill vise and smash it flat.  Ignore it until the next day
4. take it out and measure the wave height again
5. if there is no difference, or only a very tiny (< 1/16) difference, they have good temper and will probably hold up.  If it loses a bunch of wave height, its temper is too soft - if it cracks, its temper is too hard - in either case, return the set to the vendor as defective.

 The other critical feature - how parallel are they really, requires a surface plate, height gauge, and a tenths indicator.

 By the by, the sideways wave shape of these things should be quite shallow, like a shallow sine wave.  Yet I've seen some wild (deep) curves in a few of the cheap ones, even in the Grizzly set, which I suspect will become problematic some day.

Have a look at how deep the curves are
vs. the ones in the photo up top

  It just seems to me that if wild curves were good and workable, all the name brands would have them, since it lets them support wider parts, even parts you would normally need two standard parallels for.  But they don't, which makes me suspicious of the few Chinese-made versions that are deeply curved.  I would avoid those, without real evidence, on general principles and the above reasoning. :)
(and I'll be happy to be proven wrong in this case)

 And another thing: they give you pairs of wavy parallels, but unlike regular parallels, you should never need two wavy parallels.  I asume it's because there are two parallels in regular kits - where you actually need two.  If I ever find a use case that is handily solved with two wavy parallels, you can bet I will brag, I mean blog, about it here.  Otherwise, they're just spairs.

 ~≈{👁}≈~

Craftsman/Diehard "quality"

 Because I've never owned anything but used vehicles, I've had an automotive battery charger since about 1985.  Recently the timer stopped working, which is sorta bad, but I never trust mechanical timers so I was monitoring it and nothing bad happened.

 But I needed to replace that timer. 

(it was readily available on Amazon, probably turns up in a hundred different products including bathroom light timers)

Aside from a heaping helping of spider webs, this is what I found inside...

 The small (about 1in x 1in) circuit board hanging loose from the wires it is soldered to - that's the regulator board for the fan.  There is no regulation or filter provided for the battery being charged.  The fan exhausts the cabinet from the bottom, and thus also fails to blow on the rectifier "heat sink".   Boy was I young and stupid when I bought this thing.

 Changing out the timer was trivially easy, even tho it was held into the panel by some low-profile, tiny-head hex-head screws.  The case was held together by about twenty tek screws.  I wonder where it was made, they sure hadn't heard of Fastener Reduction!

 I was disappointed to find no inductor inside.  Professional grade battery chargers have a big fat inductor (AKA "choke" because it chokes current flow) in series with the output as a filter.

Note that Google's AI knows abso-fucking-lutely NOTHING about this topic.  It will lie to you instead of saying "I don't know".  AI will NEVER say, "I don't know" and that's a huge problem.  Stop trying to use AI!

 I am making an effort, but since Google made AI responses the default behavior, my choices are A) an engine with no depth, like DDG, or B) an engine that wastes tremendous quantities of electricity and water only to lie to me.  I dislike this choice.

 ANYWAY, the battery acts like a capacitive load - you don't filter voltage peaks when your load is capacitive, you filter the current peaks.  Passing current peaks to the battery shortens the plate life!

 Now that I've seen the inside, and that it has a mounting place for an inductor, I may track down said inductor and install it.  Sears sold three versions of this charger; Silver, Gold, and Platinum.

 This was the mid-grade "Gold" unit.  Presumably the pro-grade unit had the choke.  And based on what I'm seeing here, presumably the "Silver" unit just connected your battery directly to the power line. ;)

 edit: So far, I can't find the OEM inductor - if there was one - nor a suitable alternative that I can afford.  There are some perfectly serviceable units for welding supplies, but they cost more than a new, much fancier charger.

 This charger line is so old, there aren't even videos on YouTube about people servicing theirs - it's as if this product line never existed.

 In cheap units like this one, there is only a step-down transformer and a full-wave rectifier.  The so-called charging rates on the selector switch simply change taps to different maximum voltages.  There is no temperature sensor either.  Charge tapering is not managed, it is only the product of the battery's charge coming up to meet the charger's fixed output voltage.  In fact, it doesn't even monitor state-of-charge (battery voltage on an expanded scale).

 It has no trickle-charge or "battery maintainer" circuitry.  It is strictly a brute force machine, and it assumes a more-or-less healthy battery that just needs its charge brought back up.  It will not limit its rate-of-charge if the state of charge is low.

 High charging currents should only be used to equalize a fully charged battery with unequal cell voltages.  This typically happens when the battery has been severely depleted (you left the lights on, would not start the car) and then recharged.  After that, the battery (total series) voltage may be 13V or so, but individual cells can be quite a lot lower or higher.  Charging an unequalized battery slowly kills the plates of the under-charged cells, and of course the total amount of energy it stores is much less than if all cells are working and charged properly.

 So my typical process is to use the 2A rate until it stops charging, then switch to 15A rate until it seems fully charged, then give it a very short equalization charge at 50A for only a few minutes.

 Did I mention you should always disconnect the battery from the vehicle before using an outboard charger?  Yeah, that's a thing. If you go to a high current setting while the vehicle is connected, resulting in an excessively high voltage (16V or more) across the battery and vehicle power bus, you can zorch your Engine Control Module, bricking your car.  So don't do that.

 And the charging current meter is useless due to low readability; I need to replace it with something equally cheap but with a digital display.  Accuracy isn't all that important in this case, it's only used to tell when charging rate is dropping (meaning battery voltage is coming up).

Battery University's excellent page for lead-acid batteries: https://www.batteryuniversity.com/article/bu-403-charging-lead-acid/

 ~≈{👁}≈~

Hot Reels, pt.2

1. As I mentioned in my last post, I got a well-regarded filament drier and have been trying it out on a roll of flex-PLA.
   As of late this morning, the humidity reading is a resolute 25% and will not go lower.
   
   

   

   
   Now, I trust the cheap plastic-film hygrometer sensor not at all. If you do those right you can get them into the ±15% range. The metrology field says the claims from the sensor makers are bushwa. A hand-calibrated aneroid hygrometer gets you down to 5%, and a laboratory instrument (not for field use) called a chilled-mirror hygrometer gets you down to 1%. When compared to things we can measure down to one-gazillionth, such as voltage, or length, or time, that is absolute canine feces.
   
   RH is the worst measurement in the field of PMEL/metrology- we are terrible at it.

    

   Anyway, we shall see. I've got one of my "silica gel hamsters" in there with the reel but it's not clear to me that it's helping. It is now nearing the end of its 2nd 12 hour run so things aren't looking good for this reel. Need to bag it up with silica gel and run the unit with nothing in it, and then with a bag of silica gel, for a sanity check.
   
   I wonder if this reel is just a lost cause or if the ambient humidity is just too damn high. When I open the lid and "burp" the air, it feels humid, and then the humidity reading drops to 25% for a minute, then begins climbing again.
   
   I don't have a hygrometer, but I suspect the latter.

    

   I need to make more hamsters. That sounds weird.
   
   

   1. On the plus side, the dryer turns out to be very quiet, quieter than the printer running a print with the tent closed up, which is pretty quiet.

       

      If the issue is the ambient humidity being too high, I might get an aquarium pump and build a desiccant cartridge and just pump dried air into the drier via its vent port. If the issue is this reel of filament is wet AF, then I will just keep cooking it.
      
      Also, this morning the unit overheated on me. Which means it stops running until it has cooled off enough, then it starts up again. There is a noticeable, not ear-splitting alarm for all alarms. It will alarm on all kinds of things like the heater is too cold, too hot, the fan isn't running, etc. These are all soft limits, apparently, rather than a TCB, because the control panel stays lit.
      
      This heat issue was something several reviewers observed. It is not the interior air temp that is too high, it's the PTC heater housing in the base. When I put my hand on the bottom, it was too hot to hold it there. This has also been observed. The unit comes with no feet to speak of, so no air gets to the bottom panel at all. Good thing it's sitting on a steel-cased UPS which provides a partial heat sink.

       

      

       So I'll add some stick-on rubber feet (I like 3M Bump-On™ bumper-feets because they use everlasting TPU and good adhesive) on the bottom, as soon as new ones arrive; I ran out. 0.4in height tho - I hope that's enough. If not, I'll either swap 'em for higher feet or...
      
      If I get really ambitious, I may fab a new bottom panel out of aluminum instead of plastic. If I get really crazy (like it becomes a problem when drying PETG at 70ºC or whatever) I will consider adding a real heat sink.
      
      I'm not too bent out of shape; everybody gets thermal design wrong, and I knew about this issue going in, and most units from different vendors have similar issues.
      
       And so it goes...
      
      

       ~≈{👁}≈~

Hot Reels, pt.1

  Herewith, the current Three Dee Pee Cave:

oh, look at all those displays
very dark, very dramatic

 Ever since I received my 3D printer courtesy of a good friend and bro, I have been unable to print in the summer time because of high humidity caused by our evaporative cooler.  And, well, I spent last winter doing upgrades, breaking things, then fixing the things I broke... now I want to try again, but... it's summer again.

I finally broke down and bought the filament drier I have been eyeballing (Sovol SH02) for over a year.

 Materials and construction-wise, it is as flimsy as I had feared.  Will need to be handled gently throughout its life.  The filament ports didn't receive much thought and are not at a good angle nor location to permit smooth feeding from the periphery of a reel.  I'll worry about that when I've got the extra long bourdon tubes to run between drier and printer tent.  I haven't decided where it will live - either on the filament storage shelf above the printer bench, or on the printer bench to the side of the printer.  There is currently no room for it in either location.

 As I write this, it is drying a spool which has been out of its bag for months, because I forgot about it.  Recommended time for very wet PLA is 12 hours.  Set it and forget it.  It shuts off when the selected time runs out.  Has surprisingly slick touchscreen interface, although the display on mine was out of position slightly; on the bottom-right corner, part of the virtual button is below the housing opening.

 Not enough to bother me.  The dryer is visible in the top photo as the blue display with icons, halfway up the right side of the image.  It can dry two small reels or one big (wide) reel.

 I will probably attempt to print with the filament stored in the drier, it has rollers and ports for that purpose, so I'll run a long bowden tube between drier and tent.  The heat source is a PTC element so minimum fire worries, and it's only 120W 150W.

 The tent temp can be elevated only a little; it's main purpose is providing a sane "room temperature" environment for the printer in the winter.  I have several little hamster-sized beanbags of nylon stocking material filled with silica gel which live in the tent, and I can make more.  Can't hurt.

 More as it happens.

 ~≈{👁}≈~

Crapsman tools and A Secret Technician's Tool

 You know, back in the day*, Craftsman tools weren't terrible, they weren't terrific, but they were serviceable, and they came with a lifetime guarantee which I have only rarely needed.

 But after Sears folded and the brand was sold off to a tool holding company†, their quality become more variable.  The tools are still made in the same factories, but there is no QC.

 Case in point, I managed to do this while tightening a screw... with one hand:

 Have you seen my arms?

  I am not a beast.

 Hardened too little or tempered too much, or both, I dunno, but I know it should not do that unless I put a wrench on it, and ya can't on this one, the shaft is round.

 So I am shopping for a new brand of screwdriver.  I like Wiha, but they're expensive.  Klein doesn't make large sets, just small sets intended more for field techs and the trades most-often-used sizes.  Too bad, as Klein are made here in the Oosa. 

Grace USA has been making tools in Michegan since 1941, but their prices too reflect American labor.  I own a small brass/delrin hammer from them which seems nice.  I'll be getting the next larger one some day.  Because you can never have too many hammers.

 I am actively soliciting suggestions.  I balk at the cost of buying a full set at a time, I want to tell myself I won't be bothered by mismatched (in both quality and appearance) screwdrivers, and I can just replace the old ones as they break... but I hardly ever break tools.  Feh. 

 Maybe I'll find a charity recipient, some kid who is just getting started collecting tools, who won't mind if they aren't top-drawer.  Give them the old set, then I'll be without any and will have to buy a new set. ;)

 ~≈{👁}≈~ 

 Now then, Subject Number B:
 Like most specialty tools or instruments, I learned about these from a job, early in my technician career.  They are familiar to many electronics techs, yet I've run into experienced folks who have never heard of them.  The scratch brush pen, voila:

L-R: fiberglass, brass, nylon, steel

 These things have "brushes" of various materials which are about 4mm across.  The length, and therefore the stiffness and aggressiveness of each brush, can be adjusted with a knob.  They are typically most useful with the brush mostly retracted / maximum stiffness.  Nearly retracted, either the steel or fiberglass brush is mean enough to take the shine off of a new love.  On the other hand, the nylon brush, fully extended, is very gentle indeed.  The kit of four (not name brand) is <$10 and worth every peso.

 These tools are mighty fine for cleaning corrosion off of primary consumer (AA, AAA, C, D, 18650, 9V, etc) battery terminals, and for cleaning varnish or copper oxide off of PCB edge connectors, getting various kinds of annoying cruft out of nooks and crannies of instruments or gadgets or whatever, for exfoliating your nose... (j/k).

 My first one I'd forgot about because it was in my fancy tool kit which got stolen.  There was only one brand offering them back then - Excelta - the Swiss precision pliers people, and there was only the fiberglass one available.  Even so, I think it was only $9 - $10 back then.

If you work on "stuff", have a set of these in your toolkit.  You can thank me later.

___________________
* 70s, 80s, even 90s

† The Craftsman tool brand is now owned by Stanley Black & Decker, which bought the trademark and global rights from Sears Holdings in March 2017 for $900 million.

Making Big Holes

 

  This was supposed to have been posted ages ago.  I thought I had posted it.  But I've searched the blog for various key phrases, and it seems I never posted it.  If I did, and you're reading it twice, my apologies.

 ~≈{👁}≈~ 

When one wishes to poke a hole in something, of arbitrary size, and especially when it's bigger than any drill bit you have... there are ~~several~~ well, two, machining options and one sloppy option.

The tool shown offers one thou adjustment per screw graduation. 
Some will even do a tenth. (Bring money)

Ze Boring Head

• Chinese units are expensive.  Good ones are breathtakingly expensive.

• Large; the smallest I've seen (some rare beast Mr. Pete found), is about 1.5" in diameter (minimum hole size)

• Capable of very precise cut adjustment

• Convenient to use- once the tool is set up, increasing the depth of cut by a thou is a matter of turning a screw

• Lots of off-center mass, tries to shake/sway/bend your machine's column, so best used in a full sized knee mill or a VERY stiff, square-column bench mill.  You will typically have to run at lower speeds than the SFM would normally allow

• Uses boring bars which usually have carbide inserts, some are just brazed - maybe you can sharpen it, but probably not.

• Best for deep holes like engine cylinders

Ze Fly Cutter

• So cheap they're nearly free.  Seriously, HF practically gives them away as door prizes (nearly - a set of five might be on sale for $10), and because it's basically a hunk of funny-shaped steel which has no built-in need of precision, there's no need to shop for anything better.  This is a tool fetishist saying this.  Cheap ones work fine, it's the cutter you'll want to spend your time and money on.  (cutters are almost never included)

• cutters can be made from inexpensive HSS square tool stock, which you grind to a cutting tip yourself - this is less convenient than carbide, but ever so much cheaper cost of ownership, and a very useful (some would say mandatory) metal shop skill to acquire. Use both ends of the tool stock.
You can also use cheap Chinese insert holders in these.

• "tool setting" - that is, setting a fly cutter's tool to a specific, precise diameter - is fiddly but you get used to it.

• readjusting depth of cut once you've set it is a simple matter of doing the tool-setting job all over again - wait, what?  Yeah, that's a fiddly disadvantage.  Did I mention they are cheap?

 AFAIK, that's it for precise and semi-precise holes.  The other large hole cutting options I can think of are not adjustable, and they make relatively imprecise holes.


 If your hole is a nice common dimension and not say, "pi inches", you might find a shell mill cutter that will do the trick, provided the material is less than an inch or so thick.  These are expensive.  The cost of re-sharpening shell mills is nearly as much as buying a new one.  Used ones on eBay tend to be dull.  These are non-trivial to sharpen, it requires a "universal tool grinder" and knowledge/skill.


 A third option, for making approximate holes - not cut to any tolerance at all, is ordinary hole saws. 
They are cheap.
  Good (AKA “bi-metal”) hole saws are quite capable of cutting steel, aluminum, brass, whatever, provided one:


• uses copious amounts of a good-quality cutting fluid*

• backs off the cutter frequently; lets fluid back into the hole, allowing teeth tips to cool a bit

• uses low cutting force - if you tend to burn up drill bits, this method is not for you


 
 I have a few garden-variety, hardware-store hole saws that have seen _extensive_ use, including cutting lots of circles out of .25 and .5in steel plate,
 and they are still sharp.  Done right, this method is _messy_.  It can be less messy if you’re willing to burn up your hole saw halfway through cutting a hole, but I recommend letting it be messy.

 On numerous occasions I have rough cut a hole with a hole saw, then cleaned it up and dimensioned it with a carefully-set fly cutter.  i should probably do an entry about how to do that, although there is probably one on YouTube already.  I'll look and maybe link it.

 ~≈{👁}≈~ 

_____


* ie; preferably _not_ the stuff sold in the hardware dept for threading pipe - that’s the Lowest Common Denominator of cutting fluids; it works for carbon steel only, its high sulfur content stains copper and brass, it does you no good with copper, soft aluminum or stainless… 
personally I'm not a fan.


 I prefer Tap Magic™(standard grade).  It is expensive but I brush it on by hand so I only use a quart every year or two.  There are plenty of other good productss.
  Just use _something_.  The thing about the high performance fluids like Tap Magic is that they make difficult-to-machine materials like copper, 300 series stainless, and (gods-help-you) titanium, much easier to machine, with a cooler running
 tool, better chip breaking, and better surface finishes because little or no Built-Up Edge.  High-sulfur cutting oil from the
 plumbing department does nothing for these materials. And plumbers don’t much care about the surface finish of 
their pipe threads either - you might. ;)

A New Angle On An Old Problem

    

When I grow up (hahahaha!)
I want to be just like Inheritance Machining. 
So if he chamfers all the things, then I must also.

 More honestly, I've always broken the corners of machined things to some degree - you can't hardly help it since even a clean 90º angle can cut flesh.  The amount of effort I've put into this depends a lot on the part or tool I am working on.  Sometimes a few strokes of a file suffices, sometimes just running some nasty burrs under the deburring wheel.

 When I make a thing, I like to break all the corners.  I've faked it with things like countersinks, which never have the right angle of 45º because they are countersinks.  But the results don't look as good or feel as good to the hand.

 Watching real craftsmen at work has has left me very dissatisfied with my deburring / chamfering game.  I began watching out for chamfering tools of various sorts, especially something with inserts, because although there are plenty of solid carbide cutters around, I can't sharpen one if it gets dull, and I do plan to use this hypothetical tool extensively.

 Right then, I may have just made a tooling purchase error, but I will remain optimistic until I've actually played with the thing. (it should be here in a few days)

 Part of the issue with making my own is I still don't have a way to do decent heat treating. I can barely manage to heat things with a propane torch (oxyfuel tanks are nearly empy so they can't be used) and dunk them in water, observing the nitride color bands.  I've had mixed results.

 So I've kept my eyes open for a long time for a milling insert holder with a 45º cut.  Finally found one, cheap because it was missing the insert hold-down clamp.  One could make one if one had to (again with the heat treating problem) but fortunately, this one is still available - I haven't called for the price yet - from the maker. 

I was at first concerned that their catalog has this to say:

"This cutter was developed in 1982 for spot drilling and chamfer milling small slots
in non-ferrous part materials. If used prior to drilling in non-ferrous
materials it performs well. If used as a countersink after the hole is drilled it is
chatter prone."

(my note: AFAICT this is a consequence of their insert choice)

"It is not for use as a rotating cutter in ferrous materials since the (25 ) relief
angle is too weak."

Again, this refers to the inserts they provide.  Other inserts exist, as this size and shape is extremely commonplace, and many, many geometries and coatings are available, different relief angles, different chip breakers, flat with no chip breaker, etc.  Also, chattering is unlikely in my interrupted cut chamfering operations on the outsides of parts.  Even so, I bet with the right insert geometry I can do holes without chattering too.

"However, in the more rigid lathe environment
it can be used successfully to spot drill holes in ferrous materials.
We spot drill our Accu-Holds (4340) in CNC lathes at 900 RPM and
.0005 IPR, with tool life of 200 holes per insert corner.
It should never be used in a drill press."

 Well yes, and duh. :P  One does not use an indexible single-edged carbide cutter in a floppy drill press, ever.  I am imagining the stupid customer service calls which resulted in these warnings.  My mill is reasonably rigid as turret / knee mills go.

 Anyway, they are talking about drilled holes.  I can imagine the inserts they sell would chatter in drill holes, even tho that's what they sell their damned tool for.  But they are very focused on firearms, too, so they have weird viewpoints on tooling, they are not a generic tool supplier.  Anyway, my mill is more rigid (I think, can I prove that? hmm!) than my lathe and much more rigid than the drill press, so I might squeak by, heh.

 Hopefully the maker does not want too much for the insert clamp.  $10 seems reasonable to me.  $20 seems more likely.  It's a tiny piece of curved steel the size of your thumb nail.  OTOH, if they want $40 or more just because it's a $200 - $300 tool and they know it's useless without the clamp, then I'll tell them to fuck themselves and I will make my own clamp.  Business office opens tomorrow, we'll see.

 ~≈{👁}≈~

Relegated To The Safety Shelf

  A few weeks ago, I was watching a video of a steam calliope fire, and one of the things a friend of mine and I both observed was A) a lot of running around at first indicating a lack of any practiced plan, B) insufficient fire extinguisher size, type, and quantity, and also C) the fellow who eventually gets the gas turned off seems to have been unsure where his hot gloves were.

 It got me to thinking about the (rather nastier than propane) welding tanks I have in my shop, and the one inert gas bottle of shielding gas which is nevertheless pressurized to around 1,000 PSI until it is nearly empty...

 I have an A-B-C extinguisher in the shop now, and I really should also have a CO2 extinguisher.  But the latter are expensive!

 It occurred to me that I have a pair of too-heavy high heat gloves I never use.  I think I received them with my cutting rig, not sure.  All I needed was a shelf mounted above the fire extinguisher at the entrance of the shop...

I tinted the "airship" braces with a torch,
clearcoated with acrylic, then masked that
and painted the remainder gloss black.

The fancy finish isn't obvious on the
finished article, but I know it's there.

 I may have overdone the shelf a little too - a lot of filling and sanding before paint, so it wouldn't look like the scrap of plywood that it is.

 ~≈{👁}≈~

Stabistor And The Bipolar Power Supply

 "The stabistor was the crucial invention which first
made possible the stabbing of others over the internet..."

  This morning I was watching a fellow repair a vintage Hewlett-Packard instrument and the word "stabistor" came up.  Now, I got into electronics in the 1970s, I'm retired now, and I've never heard of a stabistor.

  A quick search turned up this Stack Exchange post from someone else who had never heard of one:

 https://electronics.stackexchange.com/questions/636786/what-is-exactly-a-stabistor-how-does-it-work-and-how-is-it-constructed

What is a stabistor?

 And that's pretty much it, in case you ever find yourself troubleshooting an HP 6826A, which by the way, is a fascinating instrument.  For more on that, here's the video I was watching:

This HP 6826A Can Output MUSIC?! Bipolar Power Supply Repair & Test

 ~≈{👁}≈~