stuck knobs... the plot continues

[Fred Olsen]

To clarify just a bit; Kroil DOES contain petroleum distillates.  I
didn't mean to imply that it was different in that regard from other
products.  I've never encountered deterioration of plastics using it,
but can't say that it won't happen.

I rather suspected that the screws in question were slotted, not socket,
head.  The usual failure mode when those have been horsed by a
ham-fisted (not "Ham") geek is that one of the halves, not both, will be
broken off.  The only 'good' way to fix that problem is to set the whole
mess up in a milling machine and take the other half of the screw head
off with a small end mill, then proceed to remove the body with means
as-available.  Right, and everybody has a machine shop, I know.

The only halfway reasonable alternative I've found is to take out the
remaining head half with a small carbide cutter in a Dremel tool.  This
takes lots of patience and a steady hand, but will work.  Then one
carefully center punches the remainder and proceeds to drill it out with
a LEFT-HAND drill bit.  Keep the bit size below the thread root
diameter, keep it in the center, be very careful; and the CCW rotation
will often break the screw loose and wind it out as one is drilling.
And the success of all of that depends upon using Kroil, for a good long
while, before the drilling process.

Doesn't that sound like tons of fun?  And it even works, some of the
time.

One other suggestion Mike, if the radio really is a parts rig, and the
knobs aren't worth salvage.  Break off the plastic portion with the
customary brute force methods, then use a mechanic's "nut cracker" to
get the bushing off the shaft.  That's the thing which looks like a
weapons-grade C clamp, with a chisel anvil.  Normally that won't damage
the shaft.

BEST of luck,
Fred

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