[pianotech] WNG Parts Question(s)

[David Love]

My concern is that since the shanks become so malleable when heated does
that present a problem for removing hammer heads with heat.  Or, if they are
somewhat brittle, does using an extractor run the risk of simply shattering
them.  

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Tuesday, July 06, 2010 11:16 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] WNG Parts Question(s)

At 06:37 -0700 6/7/10, David Love wrote:

>I am curious what is required to remove the hammers from these shanks and
>what the problems are.

I raised this question with Bruce a couple of weeks ago when I was 
asking about the glue to use, since they have admitted problems with 
the white glue previously used.

I was not happy with the idea of using the CA Gel they now supply and 
recommend, and asked if it might not be better to use a thickened 
epoxy, for example West System.

His answer made sense, and is this:  when sufficient heat (using hot 
air) is applied to remove the heads, the CA Gel turns pasty (or 
something like that) and is easy to remove; it can be rubbed off. 
While it might be easy enough to remove the heads if they were stuck 
on with epoxy, it would not be so easy to remove the residual glue.

It has to be remembered that the heads are bored to a fine tolerance 
so that they fit freely on the shank.  The 'gap' such as it is is 
filled with the glue, so that the head is only firmly fixed once the 
glue has set.

This is very different from the way the head is glued to a wooden 
shank, where an interference fit is quickly achieved that does not 
rely on the glue.  In fact the way I do things the hammers hardly 
need any glue at all - the head can only be fitted to the unknurled 
shank by force if at all.  The shank is compressed by knurling to get 
just the required amount of freedom for the half minute allowed to 
fit and align the head and after that the shank expands, with the 
moisture in the animal glue, to its natural diameter and it is 
impossible to adjust the head any more.  This way there will never be 
any loose hammer heads even when the humidity drops low.  I know some 
people don't knurl their shanks, and I know the same people get 
clicking heads.

JD