In a previous post about the mandocello, I mentioned pin
point capos. This is a custom feature that Jonathan specified; the idea being
that individual “capos” can be screwed directly into the fretboard, stopping
the pairs of strings at the required fret to allow for a variety of open
It appears that there are very few instruments around with
these devices, so as far as I 'm concerned there is no right, wrong or should I
say established way!
So, from first principles…..
The fretboard has to have a threaded hole, in order to take
the screws, but even ebony would not be resilient enough, so a nut has to be
inserted into the ‘board. In order to get the nut in the correct position, it
can only be fitted once the mandocello has been set-up.
The nut also needs to be as large as possible, so that
there is the maximum possible depth to the thread. This, however, is governed
by the space between the strings- it so happens that on this instrument, a M2.5
screw fits with minimal disturbance to the alignment of the strings.
So after a trial............
...................... the fretboard had to be drilled, a nut
inserted and then filled over.
After looking at many different types of
fixings, I decided to use button head socket screws. They do not have any sharp
edges and sit quite low, so they should have minimal interference with Jonathan's playing
and as importantly not inflict any injury, if accidentally caught by a stray
finger! They’re also made from stainless steel (as are the nuts) so that they will
not corrode in contact with sweaty fingers.
The next choice was for the material which comes into
contact with the strings and presses them down on to the frets; essentially large, soft
washers. Either felt or rubber seemed to be appropriate choices but after
testing, the rubber was far superior, the felt just fell apart.
Also I had to perfect a method of making the washers. I made
up a mild steel punch which worked very well on thin rubber.
However, it soon became clear that a thicker rubber washer was
required, so again a bit more testing.
3mm thickness worked the best but using
the punch distorted the rubber, so I improvised this “press” and then made a
simple jig to drill a hole in the washer’s centre. Rubber, being flexible,
isn’t easy to work accurately and to get 10 good ones, I made 27!
And at last a pin point capo!
One other advantage of the rubber is that, once
the capo is tightened down (so that the string is firmly pressed onto the fret) you
can still tune the strings and you may need to, because if you overtighten the capo,
the pitch of the string will sharpen.Now of course it took many hours to get to this stage, not only
experimenting in the workshop, but also on the internet trying to source components,
buying them and later rejecting them!
The next question is where do you keep those tiny capos when
not in use?
Both Jonathan and I wanted
them kept on the instrument and the most unobtrusive position, I feel, is the
back of the head. So I designed and made this Swiss army knife inspired gismo.
The Allen key slips into a slot and is held in place by two tiny rare earth
magnets and there are embedded nuts to take the capos. Being fixed between the
tuners, also helps to protect the capos from accidently getting knocked.
And there we are; you would not believe how long all that took! Now I'm ready to strip down the 'cello and start polishing.
Labels: 10-string mandocello, Gary Nava luthier, Pin point capos