[CAUT] center pinning changes/ long pin method

[John Delacour]

At 10:31 -0600 11/9/07, Fred Sturm wrote:

>In burnishing center felt, it seems to me that the burnisher is 
>going to be pressing against the felt hard enough that fibers 
>wouldn't be able to move around, at least significantly. At this 
>point in my own work I mostly do a rapid back and forth action, fast 
>enough and enough of them to create a good bit of heat. (You can get 
>heat pulling the burnisher through all the way rapidly, but  I think 
>I get more heat faster by doing back and forth, as the metal of the 
>burnisher heats up). That seems to set the felt quite nicely. And it 
>seems to be possible to move up a half size to a full size just 
>using burnishing action without removing any felt, just the ironing 
>action. I haven't been doing it this way long enough to have a good 
>sense for longevity and whatnot, but it seems to be good so far. 
>Certainly makes sense, as long as the felt in the bushings doesn't 
>swell later, maybe due to humidity rise, and make the centers 
>sluggish, and I haven't found that in university pianos, which get 
>quite a bit of use. Of course I am dealing with my own humidity 
>environment, which is typically 10% to 60% range.

For a short while a long time ago I did burnish with a smooth broach, 
creating more or less heat, but I quickly gave that up and now never 
burnish or do anything that will "iron" the bushing cloth (it is not 
felt!).  Any heating or pressing of the cloth produces very 
unpredictable results.  I strongly deprecate such a practice.  If it 
has been done, it would be best to leave the bushings unpinned for a 
day or two before commencing centring.

Before I start a centring job I make sure that the parts have 
acclimatised to normal room environment by keeping them there for a 
day or two.  I use a broach about 5" long roughly the same size as 
the new pin and roughen it so that I will achieve the desired degree 
of friction with about five passes.  If the broach is too slow I 
roughen it more and if it's too fast I dull it with a few strokes of 
sandpaper.  To use a broach that is too dull and requires ten or 
twelve passes is simply a waste of time and energy, and too sharp a 
broach does not allow the fine final adjustments unless very special 
care is taken.

When I started out in the trade I used to use talc for lubrication as 
well as the trace of oil from dragging the pin through my hair, but I 
now use no magic powders and have no plans to use teflon or anything 
else.  As Ted and I have mentioned before, it is common to find a 
well-used piano a hundred years old whose centres are still very 
good, and yet here I read of someone recentring every few years, 
presumably using some modern method.  At that rate the action will 
not reach 20 years, let alone a hundred!  If I needed to re-centre 
after ten years I would severely question my methods and materials.

JD