Felt quality

[John Delacour]

At 16:48 -0700 13/10/07, David Love wrote:

>Can anyone comment about different grades of felt generally, Wurzen felt
>specifically.  Does a higher grade mean more processing necessarily?  If so,
>does it also mean less lanolin left in the felt, less elasticity for in the
>fibers or anything else that might be considered a detriment?  It seems to
>me that higher grade may not necessarily produce a more resilient hammer
>(felt), or better tone.  Any comments?

This is a vast topic, and I'm always amazed at the great variety of 
different hammers on the pianos I deal with (mainly 100 years old or 
so) that produce good results.  Some are apparently very dense and 
firmly felted and others (eg. Bechstein) are superficially quite soft 
and fluffy.  Both produce good results and last well.

All that really matters in a hammer is the characteristics of the 
felt between the apex of the moulding and the nose of the hammer, but 
to achieve the proper characteristics of this part requires special 
skill on the part of the hammer-maker and a good choice of felt.

Owing to the way the rhomboid felt strip is forced wound the 
moulding, the outer surface of the hammer is under great tension and 
as the felt approaches the moulding the tension graduates to great 
compression, so that there is a cylindrical area round the apex of 
the moulding that is under greater and greater compression towards 
the centre.

The reason, so I understand, for impregnating the "wings" of the felt 
strip, as on the old Steinways etc. was to lock the fibres so that 
when the felt is forced round the moulding greater tension is 
produced at the nose of the hammer, since the fibres cannot pull 
round.  If the quality and length of the fibres is wrong, then the 
felt can pull apart and release the necessary tension, relieving the 
compression further in.  Most hammers, of course, are not impregnated 
and the gradual transition from felt under tension to felt under 
compression is achieved nevertheless, and the shape to which the 
"rhomb" is cut is probably most important.  It's also important that 
a good cement be used and a lot of modern hammers are greatly 
inferior to the old ones owing to the use of inferior glue.

I wish that Dolge had expanded the section on piano hammers his book 
When he recounts that at his factory two expert gluers could cover 
240 sets of hammers in a ten hour shift on one machine, one gets some 
idea of the scale of things in those days, compared to which 
piano-making today is a cottage industry!

I read a lot on this list about doping hammers.  Why should it be 
necessary to dope any hammer that is properly made from the proper 
felt in the first place?

JD