[CAUT] center pinning changes/ long pin method

[Fred Sturm]

Hi John,
	I think we will probably agree to disagree on a number of these things.

On Sep 11, 2007, at 1:21 PM, John Delacour wrote:
>
> 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!).

In fact, it is felted cloth. The process of making center and  
keybushing cloth involves a great deal of felting, including  
agitation, pounding, heat, pressing, etc. It's woven, then felted.

> 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.

I don't know that I agree with the notion that it produces  
unpredictable results. If you use a standard, carefully controlled  
process, you will get very predictable results in my experience. For  
me, in this case, it means precisely the same number of back and  
forth polishing moves at the same speed for each bushing (a kind of  
norm is maybe ten back and forths within 2 seconds). Assuming we are  
starting out at a reasonably consistent point to begin with. And it  
would seem to me that leaving bushings unpinned would be  
counterproductive in the process of getting them to a stable state.
>
> 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.

My experience with the method you describe is that my results will  
last very little time at all in a heavy use environment (which is  
where I do almost all my pinning). A degree of friction achieved only  
by passing a roughened broach through the cloth will, in my  
experience, drop from, say, 5 grams to 1 or zero in very short order.  
Some degree of burnishing is utterly essential, in my experience.  
Otherwise you end up with a center that has not enough firmness, and  
whose friction is very unstable. I have come to the conclusion that  
more burnishing is better than removing material, the heat and  
friction providing the modest packing and reduction of dimension I  
desire, ending with a firmer condition of the felt.
>
> 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.

I use Protek as a standard treatment in all re-pinning jobs. Firm and  
lubricated is my general watchword. Heavy use pianos whose actions  
last even 30 years are exceptional, in my experience. It's not the  
centers that go first. Keeping a piano at performance level involves  
new parts at regular intervals, and I don't find any problem with  
that whatsoever. Sure, it's lovely to see a piano 100 or more years  
old in wonderful condition. I see a few myself. But not at the  
university.
>
> JD
>
>

Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu


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