[R-390] R390 knob set screw - JB Weld

[John KA1XC]

Barry,
I didn't know there was a quick set version, all I've used so far is the
regular stuff  which is dark grey after mixing. The next time I'm out
shopping I'll look for the quickie stuff out of curiosity.

Check out  http://jbweld.net/index.php especially the FAQ and technical
section, it has some of the info you seek.

Yes, I've also noticed that it is a pretty good match for the front panel
and its shade can also be altered depending on the resin/hardener mix ratio.
It also can be thinned with the usual paint solvents.

They call it a "steel" epoxy. The MSDS info didn't say anything about steel
but the two components do contain calcium carbonate, iron powder, and barium
sulfate in large parts which probably account for it's hardness and
machinability.

They also said in the FAQ section that the quick set version is only half
the strength of the original JB, which agrees with my thinking that the
longer set time epoxies are inherently stronger. I'll use quick set epoxy on
tiny parts and things that don't require a lot of strength  but use the
longer cure time stuff  elsewhere.

I just epoxied part of  a hair dryer power switch back together where the
switch contactor broke away from the finger slide part of the switch. It was
an easy fix but I couldn't believe how freakin' weakly they designed the
broken joint; for lack of a bean sized amount of additional plastic they
created a very weak link. So besides gluing the original break I also filled
in the entire hollow end of the joint and now it's strong as a rock.

73,
John


> Hi John
>
> Coincidentally, I have a question about JB Weld.  I just used it to repair
a
> small folding table which was inadequately glued to start with.
>
> I'm more accustomed to regular and quick-cure epoxy which is clear.
>
> Had some small tube sets of JB weld somewhere, but lost track of it.  I
> picked up some at Pep
> Boys -- big box "J-B Industro Weld, Cold Weld Shop Size"
>
> This stuff when mixed is medium to light gray.  Are all of the J-B Welds
> that color?  I also picked up the small tubes of the quick set version.
>
> That grey looks very similar in shade to the "right" shade for R-390 front
> panels.  Anyone try it to detail out a chip?  Might not even need
touch-up.
>
> I used to assume J-B was the same basically as regular epoxy glue, but
> possibly better quality.  Must be something very different as it doesn't
> have that characteristic annoying aroma.  It also cleans up a heck of a
lot
> easier.
>
> Barry
>
> ----- Original Message ----- 
> From: "John KA1XC" <tetrode at comcast.net>
> To: "R-390 reflector" <r-390 at mailman.qth.net>
> Sent: Thursday, April 14, 2005 12:21 PM
> Subject: Re: [R-390] R390 knob set screw
>
>
> > Dan,
> > my notes say it's 8-36 UNF thread, yet another oddity of the 39x's. If
you
> > had the tap you could epoxy the hole and drill and retap it but a
> > replacement knob can be gotten cheaper.
> >
> > Sometimes you can smear some JB Weld across just the damaged area, let
it
> > firm up a bit, and then use the setscrew itself as a tap, then remove it
> > and
> > let the JB cure. If your lucky it can give the setscrew the little extra
> > bite it needs to do the job.
> >
> > That phenolic insulating shaft on the 390 is pretty tough, I wouldn't
> > worry
> > too much about hurting it.
> >
> > John
> >
> >
> > ----- Original Message ----- 
> > From: "Dan Merz" <djmerz at 3-cities.com>
> > To: <r-390 at mailman.qth.net>
> > Sent: Thursday, April 14, 2005 12:22 AM
> > Subject: [R-390] R390 knob set screw
> >
> >
> >> Hi,  I ran into a minor problem.  The set screw in one of the larger
> >> knobs
> >> (on the ant trim on R390) doesn't want to tighten against the shaft and
I
> >> see that the threads in the knob are damaged in the area near the shaft
> > and
> >> the screw likes to just ratchet back at the critical point of
tightening.
> >> It's the knob not the set screw that's the problem.  I think a longer
set
> >> screw of 3/8 length would solve the problem.  What is the thread
> > size/pitch
> >> on these set screws? I make it to be 8-36, an unusual size these days.
> > Are
> >> there some screws longer than the standard 1/4 inch length in
somebody's
> >> pile?  The other alternative is to drill and tap it for the next larger
> > size
> >> set screw but who wants one knob to have a different size wrench, hi?
I
> >> guess I could shove a piece of solder or piece of plastic in front of
the
> >> short one and hope for the best.  The trimmer shaft looks like phenolic
> >> so
> >> I'd like to treat it nicely.  Any advice on fix appreciated,  more
later,
> >> Dan.
> >>
>