On Jun 5, 3:29*pm, (Dave Platt) wrote:
In article ,

john royce wrote:
I have one of those small LED pocket torches (flashlight). *To turn it on
and off, I have to screw the end up towards the bulb end to compress the
contacts against the battery.

The thread in the screw end is an extremely 'loose' *fit and tends to
'unscrew or scew up' *when it sits in the car glove compartment for a while.

Is there a way to *stiffen* this 'loosness' in the thread, without *reducing
the electrical conductivity?

It needs to make good electrical contact for the torch to work, so I guess
that rules out putting a dab of wood glue on the thread? * * Thanks for any
advice.

From your wording "thread in the screw end" and "a dab of wood glue on
the thread", I infer that the loose thread is down at the bottom of
the light - that is, the junction you want to tighten up is *not* the
one that you rotate to turn the light on and off?

If so, you can probably use a *small* amount of Loctite to secure it
in place. *Unscrew the bottom a few turns, place one drop of Loctite
"removable" threadlocker on the threads, and tighten the bottom back
into place. *Let it sit for a few hours.

This ought not to affect the conductivity adversely, for two reasons.
For one, you won't be putting enough on to coat all of the threads.
For another, when you tighten the bottom securely, the threads will be
forced into proximity (cap to body) and will squeeze the excess
threadlocker out of the way - you'll still get a good metal-to-metal
junction. *This will remain after the threadlocker "sets" into its
final (elastic-solid) state. *In fact, the presence of the
threadlocker in that area will probably act to preserve good
metal-to-metal contact, as it'll prevent oxygen from diffusing into
the junction. *The "removable" (low-strength) Loctite is strong enough
to secure the threads against vibration and thermal-expansion
loosening, but can be "broken free" with a firm twist with hand tools.
Loctite is intended for use on metals (wood glue isn't).

Now, if the problem is a loose thread up at the *top* of the light...
this is a somewhat more difficult problem. *You'd need to tighten the
threading (or at least make it less prone to vibration) without
eliminating your ability to move it, and without compromising the
electrical connectivity.

The best I can suggest here is to use a bit of electrically-conductive
grease... viscous enough to damp out vibration, but not enough to
stiffen or lock the threads permanently. *There are a number of
possibly-suitable antioxidant/conductive greases - they're loaded up
with carbon particles, zinc, or copper.

One I would suggest is sold as "Butter-it's-not" by the company which
makes Butternut amateur-radio antennas... it's an orange-colored
copper-loaded grease, quite viscous. *I believe that its original
purpose is as a treatment for vehicle brake drums/discs/shoes!

Be careful how you use it - a little goes a long way - and it's more
than a little messy. *One down-side of using any such grease is that
it's likely to end up working its way out of the threads, and staining
things in your glove box / pockets.

--
Dave Platt * * * * * * * * * * * * * * * * * AE6EO
Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior
* I do _not_ wish to receive unsolicited commercial email, and I will
* * *boycott any company which has the gall to send me such ads!

Dave's suggestions sound right on track