Tining pin bushing purpose, was Xylol for tuning pin bushings

[John Delacour]

At 8:00 am -0400 31/3/07, Frank Emerson wrote:

>Given the angle of the drill (approx. 7 degrees) if the drill is centered
>at the top of the bushing, it is considerably off-center at the bottom of
>the bushing.


>...Look at any piano with bushings, and you will likely see a gap 
>between the tuning pin and its bushing on the side opposite the 
>string tension, and the bushing compressed on the opposite side.

Well here is a picture of the top of the wrestplank plate on an 1899 
Lipp grand.  I have this and another slightly later (1907) and 
smaller grand in the shop at the moment and neither of them has the 
slightest ovality at any point

<http://pianomaker.co.uk/openplank/lipp_200_top01.jpg>

As to the angle of the pin and the eccentricity of the hole at the 
underside of the plate, the following two pictures show what you mean:

<http://pianomaker.co.uk/openplank/lipp_200_underside01.jpg>
<http://pianomaker.co.uk/openplank/lipp_200_underside02.jpg>

Both Lipp grands came in with the original wrestpins (6.75 mm) good 
and tight and were fine to tune.  In the second picture I have 
inserted a 6.60 pin from underneath to show the angle of the pin. 
Inserting the pin from the top requires some degree of force from the 
outset and there is no gap at all between the pin and the plank at 
any point on its perimeter.

>...I have no experience with open-face pinblocks in a production piano, but I
>suspect that there is a measureable gap between the tuning pin and its hole
>in the pinblock on the side opposite the pull of its string tension.

It is always better to hold off suspicions until you do have the 
experience, as any European technician has.  At present I have two 
uprights and a grand with open planks, all from excellent makers. All 
of them were "end-of-life" pianos when I got them and had been badly 
abused but the pins were tight in all of them and there is none of 
the ovality you guess at.  They are a 1905 Lipp overstrung, a 1904 
Brinsmead vertical-underdamped and a 1905 Grotrian-Steinweg grand. 
As you will see from the pictures all have the plank veneered, the 
Lipp in birds-eye maple, the Brinsmead in boxwood and the Grotrian in 
mahogany, with the veneer countersunk.

The pictures are listed at <http://pianomaker.co.uk/openplank/>

>   While it is clear that an open-face pinblock provides optimal 
>support to the pin higher on the pin, a tuning pin bushing provides 
>similar support, when the drilling optimizes the bushing material on 
>the effective side of the hole.

What is the "effective side" of the hole?  More damage can be done in 
one visit from a pin-bending tuner or a tuner that holds the lever 
wrong than in 40 years of steady tension from the strings.  Provided 
the piano is well made and the tension is not excessive, no 
ovalization will occur until a bad tuner turns up -- and there is 
plenty of choice! How much resistance to crushing the plate bushing 
provides in comparison with the top layer of a beech plank will 
depend on the quality of the wood (or other material) used for the 
dowelling.

>So, what is the purpose of the tuning pin bush?  I would say:
>
>1. To prevent direct metal-to-metal contact between the tuning pin and plate.
>2. To center the pinblock drilling in production, or in some cases, 
>to deliberately off-center drilling, on the side opposite the pull 
>of the string.
>3. To provide support to the tuning pin as high as possible, if not 
>as well as with an open-face pinblock, the next-best thing to it,

It is simple enough, in the case of an unbushed plate, to provide 
pilot holes in the right place and get the wrest-pin holes right.  In 
fact I don't see your point at all.  If there are no plate bushings, 
as on a Steinway, the plank can be far more easily and accurately 
drilled detached from the plate once it is marked up.

JD