RE: CX 12 problems

["MLeFree" <mlefree@xxxxxxxxxxxxxxxxxxxxxx>]

First Siegfried clarified the nomenclature for the CX parts:
8<clip>...
> Can we agree that the spring is that piece of wire which moves the slide
back?
> There´s a coiled spring at the CX 12 and an "open" spring at all other
chroms.
>
> That thing which presses the CX comb against the mpc is called in Hohner´s
> English catalogues "tension band" which I found to be an appropriate term.
> It consists of elastic hardened steel. So, I name this thing also "spring
> band". But Michelle names it simply "spring", however, I think that this
> is reserved for the slide spring...<clip>8

Thank you for clarifying and standardizing CX terminology, Siegfried.  I
admit to being a bit "loose" with my use of the term "spring".  I will say
that I was using the term in the context of the thread that had already
started.  From now on, it will be the tension band to me!  :)

Siegfried then moved on to my comments about his recommendation to modify
the CX tension band:
> Michelle writes:
>
> > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > The reasoning you suggest for filing the edges sharp makes sense, but I
think
> > that doing so creates a new problem. .....I'm sure that machining the
culprit
> > sharp corners in the production of the instrument to a shape that would
conform
> > to the inside surface of the combat the key points of contact would cost
several times
> > ..............  This is a typical management decision made to cut
manufacturer's cost...
> > .... filing the sharp corners round as you (and G) suggest is not
> > the answer to this manufacturing shortcoming.  The reason I say this is
that once
> > the stock spring is properly installed the sharp corners, though the
> > wrong shape, ~are~ spaced the appropriate distance apart so that the
slide
> > is prevented from moving along its length.  That's the whole idea behind
> > making the comb slots half the full thickness of the spring in the first
> > place.  The "field modification" that you suggest makes the tabs more
the
> > correct shape, but it narrows the distance between the points at either
end
> > of the spring where they would otherwise contact the comb and prevent
the
> > spring from moving longitudinally.  Filing the edges back even further
> > compounds this problem, in my view.  The result?  The modified CX
becomes a
> > veritable hand grenade.  If ever there is a significant shock or the
> > instrument is dropped, the spring can be bumped or even move due to its
own
> > interia.  Because there is nothing stopping the spring from moving in
either
> > direction along its length, the spring can easily pop out, causing the
> > harmonica to explode!  (Please don't ask me how I discovered this.  :)
...
> I understand what you fear when the edges are filed back. However,
unfortunately,
> you didn´t tell us how you have discovered that the CX can explode like a
hand
> grenade.

Darn it, Siegfried, I asked you not to ask me that question!  ;^)

But, since you did, I'll tell you.  I did it in the interest of science!  :)

I embarked on my tension band modification process with zeal.  But my
momentum began to dissipate as I worked on rounding the corners on the first
side of the tension band.  I noticed two things.  The most obvious was that
the result was ugly as sin, which was not unexpected.  Less obvious was the
new degree of freedom I had introduced in the tension band's ability to move
with repect to the cover.  I realized that without the sharp corners in
question resting against the inside surface of the cover (or very close to
it), there was no longer any mechanical object stopping the tension band
from moving along its axis in the direction of the modified end.  The static
friction of the band against the comb assembly and the narrow strips of
plastic in the slots of the cover was the only thing holding the assembly
together.  Being the engineer I am this worried me so I decide to see what
sort of force it would take to overcome the static friction now holding the
instrument together.  In an admittedly loosely controlled experiment, I
began tapping the harmonica's cover at the modified end with the heel of my
hand with ever increasing force.  I was able to confirm my fears and get the
tension bar to move enough to have it pop out of the cover completely and
fall to the floor halfway across across the room.  Fortunately, I was
holding the instrument tension bar-side up, so the rest of the parts
remained in my other hand.  Needless to say, the other end of my CX tension
bar remains unmodified.  And, I didn't proceed with the gravity impact
testing phase of my experiment.  ;)

> I suppose that it is a theoretical explosion only because I assume that
you don´t
> have a CX 12 with filed band edges. But I assure you that it can´t happen
because
> the pressure of the tension band is simply too high to move the band
longitudinally
> quite alone. Believe me, you always have to press down one end to get the
band free.
> I just checked that again at all my CX 12.

Perhaps I banged my assembled CX a tad too hard?

> Of course, when a CX 12 drops to the ground, you have a grenade,
> not surely but likely.

This has not happened to me personally, but I ~have~ heard of it either here
or on Slidemeister.  I don't know whether the instrument(s) involved had
modified tension bars.

> Your advice to assemble or take apart a CX 12 always very carefully I can
only underline
> fullheartedly. Before I engage the tension band I check whether
> the slide moves properly.

Thank you!

> At my CB chroms (B stands for brass) I provided a tolerance of 1 mm for
shifting the
> comb there and back in its mpc guide to make it absolutely sure that the
comb AND
> the slide are correctly placed.
>
> Finally, to mention also this. In case, the pressure of the tension band
is too high,
> it´s possible and allowed to file back the band at its curved (convex)
point or to
> rebend it a little.

Siegfried, you are a fearless CX modifier and a true pioneer!  I think that
I will remain content to limit my CX modifications to adjusting reeds and
replacing valves.  I'll leave the gutsy stuff to you and Brendan!  8^)

Thank you for your considered reply to my taking exception to this one small
piece of advice amongst the many you've so freely offered over the years.

And thanks once again for coming back to harp-l!!!

Michelle