Glide bolts

[Richard Brekne]

Thanks very much Andre' for taking the time to write this out.. This one goes
into my cyber notebook for sure !  After reading this my mind seems to recall
some class that showed a way of finding correct key height useing glide bolts
and a key dip of 10mm.... this ring a bell in anyone... or am I mixing my Q's
and L's ?

Thanks again..

Cheers

RicB



antares wrote:

> >
>
> 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/
>
> _______________________________________________
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--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html