Hammers

[Tony Caught]

Hi Del,

Thank you for the input. Makes sense to me.

Great post

Regards

Tony Caught ICPTG
Australia
caute@optusnet.com.au

----- Original Message -----
From: Delwin D Fandrich <pianobuilders@olynet.com>
To: <pianotech@ptg.org>
Sent: Sunday, December 31, 2000 8:16 AM
Subject: Re: Hammers


>
> ----- Original Message -----
> From: "Tony Caught" <caute@optusnet.com.au>
> To: <pianotech@ptg.org>
> Sent: December 29, 2000 9:19 PM
> Subject: Re: Hammers
>
>
> > I don't know what type of glue they use but in this day of cost cutting
I
> > would not be surprised if this glue also failed. Be it water penetration
> > into the glue or the extra tension put on by swollen felts or a
> combination
> > of both.
> >
> -----------------------------------------------------
>
> Tony, et al,
>
> There are many excellent adhesives available at relatively nominal cost
and
> there is very little difference in the cost of a given adhesive type from
> one vendor to the next. There are so many much more creative and
interesting
> ways to have problems gluing hammer felt to wood moldings--I doubt it's
> necessary for the company to try saving money by using an inferior
product.
>
> To start with, these are all two-part adhesives--one part can be
water--and
> there can be problems if this mixing in not done properly. They are also
age
> and temperature sensitive. As process-conscious as Yamaha is, though, I
> would quite surprised if Yamaha was having problems with either mixing
these
> adhesives or with using out of date materials.
>
> Moving on, moisture content (MC) of both the wood and the felt--especially
> the felt--is critically important during the actual hammer press process.
> Especially that of the felt. The felt strip must have some minimum level
of
> moisture before it is pressed. If there is not enough, and the felt is
some
> on the dense side--as is most felt used in 'modern' hammer
construction--it
> will break and tear as it is pressed into the caul. If there is too much
> moisture in the felt, the excess moisture will tend to block the glue
liquor
> and not enough adhesive will penetrate the felt surface to form an
adequate
> bond.
>
> A much more common problem is having the felt MC excessively low--i.e.,
just
> barely enough to keep the felt from breaking. In this case excessive
> solvent--most commonly water--will be drawn out of the adhesive mixture
into
> the felt and there will not be enough solvent left in the felt
> inter-penetrating layer (the transition layer of felt and adhesive which
> should be thoroughly penetrated by glue liquor of the proper chemical mix)
> to insure proper chemical cure of the adhesive mix. The adhesive will
still
> dry--it will be quite hard and brittle--but it will not have reached full
> adhesive bonding strength due to improper chemical cure.
>
> This same problem is evident even if the felt started out at the right MC
> but the temperatures of the heated side cauls is excessively high. The
felt
> layer between the side caul and the wood molding is relatively
> thin--especially toward the treble end of the hammer set--and the heated
> cauls force moisture out of the felt very rapidly. If the heat is
> excessively high too much moisture is forced out too rapidly. It will be
> replaced by moisture drawn rapidly from the adhesive with the end result
> being a 'starved' glue joint.
>
> Most of the heat-cured adhesives of the type used in modern piano hammer
> production cure to a relatively rigid glue line. This is always a problem
> when bonding substrates that are not moisture-stable. Obviously, neither
> wood nor felt are moisture stable. As they both expand ad contract during
> the various seasonal cycles quite a strain is put on the adhesive joint.
If
> there is any weakness in any part of this bond, the joint will fail.
>
> This problem, incidentally, was also common with so-called 'cold-pressed'
> hammers made using animal hide glue. The adhesive worked best when it was
> fairly hot and quite thin. When too much water leached into the felt too
> quickly the resulting adhesive bond was often not strong enough to hold
the
> felt to the wood molding over a long period of time. Especially when
> confronted with more extreme climate swings of non-air conditioned homes.
> Various techniques were developed to solve the problem, the most effective
> being the addition of various pre-hardening solutions being added to that
> portion of the felt that was actually being glued to the wood molding--the
> shoulder of the hammer. This so-called 'reinforcing' had nothing to do
with
> the voice of the hammer and was only an aid to gluing the felt to the
hammer
> molding.
>
> Insurance was then provided by inserting a staple into, or through, the
> shoulder felt and molding. This staple also had/has nothing to do with the
> 'voice' of the hammer. It is there only to hold the shoulder felt to the
> molding and help prevent glue failure.
>
> Del
>
>
>