[Elecraft] [K3} Help, hex key for split knob

[drewko]

Out of curiosity reading this thread I just removed the knobs on my K3
for the first time since they were installed nearly two years ago. The
screws came out easily after the initial stiction was overcome;
Twirling the wrench between thumb and index finger is all that is
required to drive the screws through the knob. I doubt that even the
ceapest 0.05 allen wrench would have a problem loosening them, yet the
knobs have remained firmly in place for all this time.

The "loose" threads on mine make it easy to adjust the screw tightness
by feel. I suppose this would not be the case if the threads were very
tight. In that case I would adjust the screws by sight initially then
cinch them up a bit against the shafts.

If someone is having a problem with the knobs coming loose or
cracking, I'd suggest inserting a small "dot" of neoprene-cork gasket
material into the threaded hole between the shaft and the screw. The
friction will keep the knob on the shaft while the soft seat will
perhaps reduce the chance of overtightening and cracking. (I do this
for the speed weight on my bug to avoid having to apply a lot of
torque to the setscrew; it is very easy to adjust by feel yet holds
the weight snugly in place on the pendulum shaft.)

73,
Drew
AF2Z




On Wed, 12 May 2010 10:29:03 -0500, you wrote:

>Don,
>
>Wrong answer, guess again.
>
>The kit supplied allen wrench strips because it is a cheap, low quality tool
>that can not support the required torque.  The required torque is higher
>than necessary because of the overly tight, tapered, and/or incomplete
>threading of the set screw hole in the knobs.
>
>The concentric knobs are undoubtedly splitting because they are plastic
>knobs that have the set screw threaded directly into the plastic.  That
>design is a non-starter from a quality perspective and is bound to fail in
>one way or another, sooner or later. 
>  
>The engineering dilemma with an all plastic knob is that if the set screw
>threading isn't tight the set screw will strip out the plastic threads
>before achieving enough force to secure the knob to the shaft.  On the flip
>side if the threading is tight enough to allow securing the knob, it is also
>tight enough to tend to split the plastic around the set screw hole via
>radial pressure when torqued.  
>
>This is why quality knobs are either all metal or have metal inserts for the
>set screws.
>
>Being an old gunsmith, I'm not intimidated by slotted screws and wouldn't
>hesitate to swap out the allen drive set screws with slotted ones, and
>probably will if these knobs ever need to be removed.  I realize that this
>is a good solution only if one actually knows how to properly fit and
>operate a slotted screw driver.
>
>The "pinky" tight approach is OK if you are working with a "D" shaft that
>provides positive indexing.  Otherwise, as in the round shaft K3 concentric
>pots, the set screw has to be very tight to maintain the knob indexing.  
>
>
>73 Jack KZ5A
>
>