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MMD > Archives > January 1998 > 1998.01.13 > 07Prev  Next


Function and Replacement of Bridal Straps
By Bernt Damm

Lots of conversations going on about bridal straps, the function and
the replacement thereof.  Let me add some comments to this, in the hope
that they will help someone out there.  As to the function of bridal
straps, they are very necessary for the repetition in upright pianos.
It works as follows:

When the key is released after a stroke, the wippen falls back to rest
on the capstan screw and the hammer tilts backward around its centre
pin to its rest position.  The wippen falls straight down while the
hammer has to rotate backwards.  This means that the wippen is much
faster than the hammer in returning to the rest position.  The function
of the bridal strap is to jerk the hammer back when the wippen falls
so that it will return quickly to its rest position (if adjusted
properly).

What about the return springs then?  Well, they are by far not
strong enough to accelerate  the hammer back quickly on its own.  If
you don't believe this, unhook some of the bridal straps and see if
the piano repeats properly compared to the notes with the bridal straps
installed.  Some older German pianos don't have a return spring at all
and they still repeat quite well.

The next function of the bridal strap is to prevent the hammer from
hitting the string if a key is pressed partially.  Keys get pressed
partially quite often when a piano is played manually because of
thick or misplaced fingers not exactly fitting on the correct keys
all the time.  Ask any pianist.

If the bridal strap is missing, the force exerted on the hammer by the
upward movement of the wippen is enough to make the hammer fly forward
towards the string.  The hammer could then be still on its way back
when the key is really pressed to play the note.  This will result in
an un-controlled striking force and the key will press in a 'strange
fashion', without the proper touch or even skip altogether, depending
where the hammer is at the time the wippen comes up.

Therefore, the wippen must be 'married' to the hammer-butt with the
bridal strap to ensure proper repetition and to control the striking
force and touch at all times.  Try it!

From the above, it becomes evident that a grand piano does not need
bridal straps because the hammer also falls straight down with the
wippen, not backwards.  It has the full gravity advantage.

Last comment on this, yes, they do keep the whippens up when the
action is removed, but if this was their prime function, it would
surely be an expensive way to do it as a thin horizontal rail
under all the whippens would do this much easier.

Now, with all that knowledge, we do of course want to replace and
adjust the bridal straps of our piano.  This is can be done in
several different ways.  For instance the clip on straps, the cork
straps and the plain ended original straps.  All these will work if
the replacement straps are of the correct length.

I will describe here how to replace the old straps with plain ended
proper straps as originally used.

Let us assume that some original straps are still intact.  Unhook them
and use a sharp knife to cut them off the Catcher shank.  Use a good
one as a measurement for the new ones.  One can painstakingly measure
and cut each of the new ones or use a simple jig to cut them all
perfectly.  Remember, if they are not all exactly the same length,
the piano action will look very untidy and unprofessional afterwards.

For a once off job, a jig can be made as follows:

Use a piece of wood longer than the bridal straps required.  Screw a
razor blade onto the side end of the block so that the cutting edge is
about 2 mm higher and parallel to the top of the block.  Now put the
original strap onto the block so that the plain end lines up exactly
with the cutting edge.  Straighten it and hammer  a nail (without head)
into the wood through the hole in the hook end of the strap.

To cut the new straps, simply  hook them into the nail, and pull them
over the blade.  This will cut them exactly equal.  For professional
use, the jig can be made with a little adjustable slide into which the
nail is hammered, to cater for the different lengths in different
pianos.

The new straps are then glued in place with a suitable glue, observing
that they are all glued in equally with the rear edge lining up to
whatever point the original ones did and the glue 'seam' being of the
same length as the original.

The adjustment of the bridal straps is part of a proper piano
regulation and is done in the following way after the capstan screws
have been adjusted:

The bridle wires are bent towards or away from the action to take or
give slack so that the straps will be taught but the whippens will just
not move when the soft pedal is pressed fully down.

If the straps are far off the correct length, it will not be possible
to achieve this without the wire either hitting some other action or
player parts.  The wires will only look exactly even, like 'factory
installed', if all the straps were cut exactly the same length.

One last hint, to avoid lots of broken wires,  bend them in the middle
with a bending tool, not where they enter the wippen.  When old and
corroded, they often break right there and are very difficult to
repair.

Bernt W. Damm
Restorer of Automatic Musical Instruments,
Cape Town, South Africa
Tel/Fax:  +27 21 592 5124  (Member of AMICA & GSM)


(Message sent Tue 13 Jan 1998, 21:45:24 GMT, from time zone GMT.)

Key Words in Subject:  Bridal, Function, Replacement, Straps

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