A23 Panel Mount Battery Holder

If you decide to use an A23 battery (small cylindrical 12V) in a project you will discover that there are no A23 panel mount holders available.  If you don’t want to open your enclosure to change batteries, here’s a suggestion.  The A23 fits in a Bussmann HPF fuse holder but is slightly too short.  You can use a 3/8″ (or 100 mm) diameter brass disk,  0.280″ (or 7.1mm) long, dropped into the panel side of the holder to extend the back contact.    Insert the negative end of the battery into the cap where it is held by friction and screw in the cap with the battery positive end against the brass spacer.  The internal spring will compress about 0.035″ as the cap is screwed in to maintain battery contact.  The Bussmann terminal labeled “LINE” will then be the +12 terminal.

Bussmann makes variants of the HPF holder for non-standard fuses that still require a (shorter) brass spacer but the plain HPF is the most common and easiest to find.  allfuses.com had by far the best price for these I could locate.

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Reinstalling screws into plastic

We live in a world of plastic consumer goods held together with screws.  These are thread-forming screws with sharp threads that cut threads into unthreaded holes in the molded plastic parts with the intention of never being removed.  Unfortunately sometimes removal is necessary for repair or, increasingly, simply to replace batteries in inexpensive goods.  The problem is that simply screwing the fasteners back in cuts new threads each time, destroying the integrity of the plastic threads and the strength of the joint.  All is not lost, however:

There is a technique to reinstall thread-forming screws without damage.  Place the screw at the start of the hole on the end of your screwdriver.  Using the tips of your fingers loosely on the shaft of the screwdriver, turn it backwards, i.e. counterclockwise, with only the weight of the screwdriver pushing on the screw.  Since the screw is turning backwards the sharp threads will not cut into the plastic.  Turn until you feel or hear a light click – immediately stop.  This means that the screw thread has dropped into the start of the original plastic thread channel.  Now turn the shaft gently forwards, clockwise, to make sure the screw threads slide in smoothly.  If so,  run the screw in.  Do not over torque it.  When you feel it bottom out, stop turning.  That will be firm enough for most plastic assemblies.  If it does not turn easily or feel smooth,  back off and turn backwards feeling for the click and try again.  Some screws are called double lead or hi-lo and have two thread heights.  In that case you will get two clicks, one lighter and one harder.  The harder click is the proper thread channel.  In general it is a good idea to turn backwards at least a full to turn to find the most definite click.  This can also make the best of an already compromised hole.

This works as well for reinstalling wood screws without damaging the threads in the wood.

While I’ve done this for decades, I was reminded that it is not a universally known technique while working on my Dyson vacuum.  These are pricey vacuums with the subassemblies held together internally with screws that you really want to be careful with.  The subassemblies themselves snap to each other.  Dyson only sells subassemblies on their web site that can be replaced without removing and replacing screws.   As all I needed were beater bars and not the entire floor head I kept looking.  I found the smaller parts I needed at evacuum.com for much less than the assembly cost.  After carefully removing the old parts and installing the new screwed on parts without damage I realized why Dyson only sold snap-on parts to consumers but sold smaller parts to dealers.  They did not want consumers to inadvertently  damage their units trying to repair them, but assumed repair shops would know how to do this safely.

Hence this post.  I hope it helps you with future plastic and wood repairs.

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Small Arms Resistant Spotlight

The United States has not fought a symmetric war of front lines and maneuver since Korea.  From then on our actual opponents have not had artillery, tanks, or attack aircraft for more than a few days.  Symmetric warfare has been replaced by asymmetric warfare with the enemy using small arms, IEDs, and infiltration in Southeast Asia, Africa, the Balkans, and the Middle East.  The current response involves fortified bases with cleared fields of fire and targeted operations launched from those bases.  While night vision technology gives US tactical forces a big advantage at night, illumination of the base surroundings makes infiltration harder and aids target identification by troops without NVDs.  The main problem is that conventional spotlights and searchlights are both fire magnets and extremely vulnerable to ordnance.  While economical and very useful for general surveillance, conventional lights can be taken out by snipers at the start of an attack and need to be backed up by something more resistant to small arms that can reasonably survive a short firefight.  Small arms resistance should be sufficient as heavy weapons like artillery, tanks, and attack aircraft will have already been taken care of by the Air Force.  Also it should be possible to keep RPG teams beyond effective range with an adequate field of fire and enough light.  Conventional spotlight weaknesses fall into two categories.  Reflector surfaces are often silvered glass which shatters at the first hit.  A tougher reflector directs ricochets toward the light source, be it a light bulb, arc electrodes, or LED’s which are all easily destroyed by small arms projectiles or shrapnel.  “Bulletproof” glass is not very effective here as high velocity hits will craze it, reducing illumination, and ultimately break through, especially 12.7mm rounds.

The only light source which is truly bulletproof is an illuminating gas flame.  Properly armored reflectors and burners could provide a robust back-up to conventional lighting.  A typical illuminating gas would be acetylene burned in air which produces a bright white light.  Acetylene is readily available and is a normal part of the military supply chain.   Alternately, acetylene could be produced by generators at the light by reacting calcium carbide with a controllable water source.  Other illuminating gas mixtures could be optimized for the application.  Acetylene has been used for some lighthouse lamps from 1896 to the present.

The illustration is for an acetylene tank version with a 3 foot diameter dish.  A carbide version could mount the generators on the back of the dish and eliminate the gas controls except for water shut-offs.

Since any light will be a fire magnet, it is critical that this be remotely operated with perhaps a covered manual override.  The tank is installed below grade or certainly under RPG proof cover.   The idea is to provide four redundant gas channels with separate nozzles, fed through unions in the pitch pivot.  The control modules consisting of the flame arrestor, regulators, and control valves for each channel would reasonably be mounted in the turret and move with it.   Each channel and the main tank would have a zero back pressure shut-off valve so that if a line is severed, flow to that line automatically shuts off.  A possible reflector would be 3/8″ of 17-7 PH stainless steel formed to the desired profile, hardened, and polished to a mirror finish.  This would be bolted to a curved backing plate giving full support made out of armor plate.  The plate would be bolted to the pitch/yaw mechanism.   The burner head would bolt to the mount and contain four separate o-ring sealed passages running between receivers in the mount and the burner nozzles.  Like all parts this would be a plug-in, bolted assembly to facilitate field repairs.  Flame ignition would be electrical or possibly catalytic depending upon gas choice.  A rear mounted chimney of a refractory material would direct the gas exhaust up and away from the mechanism.  This would avoid darkening the reflector with soot and spilling light onto the defenders.  The top of the burner assembly would have a sufficient thickness to resist small arms and have a conical top to deflect ricochets away from the dish surface.  Ricochets from the main part of the dish would pass though the flame without effect.  Near the center, a glacis would deflect shots safely that would otherwise ricochet into the gas nozzles.  The redundant gas channels and auto shutoffs would allow the spotlight to continue operating after losing nozzles.  The illustration is scaled for 7.62×39 but could easily be adapted for heavier weapon resistance.

Body Mass Index

After losing 40 pounds over several years my BMI is now the same as it was when I was in the Army … 50 years ago.  BMI is a formula* used to classify people as underweight, normal, overweight, or obese.  These classes are used as predictors of health, originally intended as guidance for physicians.  When I was in the Army I was in the best shape of my life.  Since I now have the same BMI I should be perfectly healthy and (after 50 years of a sedentary career) should fit into the same clothes.  Of course I do not.  My waist size is still 3 or 4 inches larger and I no longer have the same muscle mass.  While reasonably accurate for mass sedentary populations, BMI treats fat just like muscle and is biased against taller, younger, and athletic people.  Many champion athletes and action movie stars rate as overweight or even obese under the BMI.

*   BMI  =  kg / m²   =  10,000 x kg / cm²  = 703 x lb / in²     Note that this formula requires access to a weight scale, more math than some people are comfortable with, and needs a correction factor depending upon the units used.  Proposed new formulas suggest a 1.3 multiplier and raising height to the 2.5 power, not the kind of thing everyone understands.  Other tweaks include things like multiplying your BMI by your serum albumin level in grams per liter.

BMI is a crock.   It is also an inferior predictor of health outcomes.  This is not news.   The main social problem is that it has evolved from guidance for physicians into a absolute mandate for the bureaucrats who run our children’s lives and is used to bully athletic school children who have more muscle and less fat than their compatriots.

A much better metric is the waist-height ratio.  Measure your waist and divide by your height.  Simple.  All you need is a tape measure.  It doesn’t matter if it’s in inches, centimeters, or old Russian vershoks.  WHtR does a far superior job of accounting for muscle versus fat.  A 2010 study that followed 11,000 subjects for up to eight years concluded that WHtR is a much better measure of the risk of heart attack, stroke or death than the more widely used body mass index.

In any case, unlike BMI, waist-height ratio sorts people into a reasonable order:

0.3359   Marilyn Monroe

0.4240   Female college swimmer

0.4280   Male college swimmer

0.4580   Bodybuilder

0.4920   Female at increased risk

0.5000   General healthy cutoff

0.5100   Risk equivalent to BMI of 25

0.5360   Males at increased risk

0.5700   Risk equivalent to BMI of 30

0.5770   Obese

0.5820   Substantial risk increase

As for me, my WHtR tells me I have a ways to go yet.

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