Glide bolts

[antares]

> From: Richard Brekne <Richard.Brekne@grieg.uib.no>
> Reply-To: Pianotech <pianotech@ptg.org>
> Date: Sun, 27 Oct 2002 23:31:11 +0100
> To: Pianotech <pianotech@ptg.org>
> Subject: Re: SV: OT - Treating Centers with Alchohol
> 
 > What about those glide bolts ?? :)

Awright bud,

Key frames tend to move, due to changes in humidity. I have seen this often
with especially larger instruments. One season key dip is too deep and then
the next time it is too shallow. It also happens many times that the left
and right ends of 'certain instruments' curl up, which is very annoying, the
more so, because it still happens and they still have not changed their
design.
The invention of glide bolts did not end these complaints but made the key
frame more stable and gave the technicians the possibility to quickly alter
key dip and key height which was not possible before in such a short amount
of time.

As older key frames tend to curl up and thereby cause instability and noice,
the idea was to create an arch in the new frames. An arch from North to
South and in the case of Steinway also from West to East to accommodate the
arch of the soundboard.
When we put a modern key frame on a straight table/bench without keys and
action, we will notice that the arch is higher and that the glide bolts are
not in contact with the surface of the bench/table.
As soon as we put the keys and the action back on the key frame, the arch
has flattened and the glide bolts may touch the surface underneath.
Because the glide bolts are screwed in the balance rail, we can screw them
up or down, according to what is necessary.
All factories have specific measures for their key height and this means
that every instrument will have about a standard amount of paper punching
under balance rail punching and front rail punching, to get the desired key
height and key dip.
With the glide bolts we can alter key dip and key height, but there is more
to it.
A glide bolt has two other options :
With the glide bolt we can also control the pressure, put onto the key bed
by the glide bolt in combination with the weight of action and keyboard.
If too much pressure is applied, the key frame is probably pushed up too
high, causing all kinds of regulation problems, but at the same time the
quality of the tone will change.
That is option number 2 : the glide bolts have more or less the same
capacities as a tuning fork.
We can not hear the vibes of a tuning fork if we don't put it down on an
amplifying object. By pressing down a key and making a tone we create a
vibration transmission between our finger and the generated energy of string
and sound body which is the sound board and actually the whole instrument.
The less deviation in the energy transmission, the more energy is being
transmitted and the more power we literally feel in our finger. With less
deviation I mean : a well regulated action, a well tuned unison and, very
important, a firm front rail punching.
A less firm front rail punching sucks energy, creates a very  'soft landing'
of the key and thereby causes an unclear and diffuse after touch.

By regulating the key frame and the glide bolts, which is the beginning of
the regulation process - with the cheek blocks fastened please -,  we can do
a few very important things at the same time (in Holland we say "kill two
flies in one stroke') :
We check the key dip first and measure the key height (from the key bed to
the underside of the key top covering).
If the key height should be 64 mm but is (on average) 63.5 mm we should turn
the glide bolts just a little to the right to bring the balance rail up a
bit, but before we do so, we measure the key dip.
As the key height is too low, the key dip 'should' be too shallow too.
If that is the case, key dip is for instance 9.3 mm, we can be assured that
we do the right thing and we start by turning the middle glide bolt just a
tiny bit to the right while at the same time feeling with our left hand (if
we are right handed) the movement in the key dip measuring block.
A quick short turn is usually enough.
We repeat this process with every glide bolt, but with the one most on the
left we have to depress the left pedal as the action will be obstructed by
friction between action and the left side of the rim.
When we 'think' that on every place of the keyboard the key height and the
key dip are corrected we tap with protruded fingers (or the side of the
hand, or a fist) on the balance rail near every glide bolt to make sure that
every glide bolt makes a firm contact with the key bed.
This is not as easy as typing in these words. It needs a lot of practice
before we do it right at once and actually a seminar on this subject should
at least take a few hours.

OK...after we have made sure that every glide bolt hits the key bed and key
height and key dip are still what they should be, we should take care of
eventual glide bolts on the under side of the key frame, which is the case
with Yamaha grand pianos.
On the left side we will see two glide bolts in two sections, which we were
not able to service from above as there is no place to stick them through
the keys. Yamaha sells a special tool for glide bolts with a possibility to
grip and screw the bolts underneath. By pulling out and lifting up the
keyboard and action, be careful not to damage the piano with the drop
screws!
Again we tap for rattling and when we are sure the work has been done, we do
a 'weighing test'. If it is an instrument with a hammer rail which is easy
to lift by hand, like a Yamaha, we lift the hammer rail with our left hand
and knock on the balance rail at the same time to find out how easy or
difficult it is to create a knocking sound. between the lifted balance rail
and the key bed. It should not be too easy, and it should not be too
heavy.(this is something I can only demonstrate during a seminar)
The weight should be the same overall but we can can choose for a difference
in pressure/weight in regard to 'tone'. We will notice that when a lot of
pressure is applied the tone will have a sort of 'grounding' quality. We can
hear the same if we pit a tuning fork - lightly - on a wooden surface or
press it down very hard. If we press it down very hard the tone will change
to what I call this 'grounding' quality. (I am sure  a native speaking
American or other English speaker will find a better word)

When all this work has been done, there is a final test :

We bang on the piano (on the wooden beam that is situated against the iron
frame and directly over the keyboard, what is the name? please) and listen
for a rattle.....
If we hear a rattle we put one finger lightly on each bolt, ubtil we have
found the one that causes the rattle.
Tighten bolt, end of story.



friendly greetings
from

Antares,

Amsterdam, Holland

"where music is, no harm can be"

visit my website at :  http://www.concertpianoservice.nl/