Open face vs. closed face pin blocks

[larudee@pacbell.net]

Great response, Phil, and perhaps that really is the thinking behind it.  If so,
however, do you really think it works as intended?  In the first place, the front flange
is a sort of I beam itself, with the serif portions of the I being the plate struts on
either side, which strengthen it.  Second, the sans serif portion of the I runs parallel
to string tension, giving it added strength and stiffness in that direction.  Cast iron
has very little tensile strength, anyway, and if it were capable of giving at all, it
might be more likely to break.

Another point to consider is that only a small proportion of the string energy is going
to reach the front flange and pin block area of the plate.  If everything is working
right, most of it will be absorbed through the bridge, and the next largest portion
partly reflected and partly absorbed by the capo bar.  Only a small remainder will get
through to flange and pin block.

Even if it does work as intended, we need to remember that the tuning pins are 3 or 4
times farther above the pin block in a closed design and that string tension is
therefore exerting that much more leverage upon them.  To the extent that string energy
might be absorbed by the pinblock/plate in an open face design, wouldn't it be at least
as likely to be absorbed by the flex of the tuning pins in a closed design?

I am to some extent playing devil's advocate here, because I'm sort of half convinced of
your argument, but would like someone to remove my remaining doubts.

Paul Larudee

Phillip L Ford wrote:

>      As I see it, with a closed face pinblock, the plate in the pinblock area
> is acting as a beam - a Z section beam if you will (like an I beam with
> a couple of pieces of flange missing).  The plate flange against which
> the pinblock bears is one flange (or cap) of the Z and the upstanding
> flange at the front end of the plate (along the stretcher) is the other
> flange (or cap) of the Z with the portion of the plate over the pinblock
> acting as the web of the Z beam.  The presence of this web allows
> the entire section to work as one beam.  If this web is not there (as
> in an open face pinblock) the two flanges work independently as separate
> beams.  The bending stiffness of these two independent beams is
> substantially less than the bending stiffness of the entire section
> working as one beam.  In practice, on an open face pinblock, the
> flange against which the pinblock bears will be the only flange
> working (resisting bending) with the front flange in effect doing nothing.
> So, there should be less deflection of the pinblock in the direction of
> the string load with a closed face pinblock than with an open face
> pinblock.  What effect this has on the tone and on tuning stability
> would probably depend on just how massive the pinblock and plate
> structure of the open face pinblock in question are.  I can imagine
> it could have an affect on power, as some of the string energy
> would be used in flexing the pinblock and plate.
>
> Phil
>
> ---
> Phillip Ford
> Piano Service & Restoration
> 1777 Yosemite Ave
> San Francisco, CA  94124
>
> On Mon, 13 Aug 2001 07:28:29
>  larudee wrote:
> >List,
> >
> >Does anyone have any ideas about why so few manufacturers use open face pin
> >blocks?  Cost is a major factor, of course.  Leo Duricic of Bechstein says that it
> >takes a master craftsman 11 hours to fit a block in an open face plate vs. 3 for
> >the closed face.  However, precision robotic manufacturing techniques such as those
> >used by Yamaha and others should be capable of greatly narrowing that difference.
> >
> >Leo also says that the closed type produces more power, which is why their concert
> >size instruments recently switched to that design.  I don't buy that.  Bechstein
> >invariably uses agraffes in the entire scale with open face blocks but is now using
> >a capo bar with the closed blocks in their concert instruments.  I think that this
> >a more likely factor in power production.  Bosendorfer, which pairs open face
> >blocks with a capo bar, agrees.
> >
> >Are there any other performance or design considerations that might lead
> >manufacturers away from open face blocks?
> >
> >Paul Larudee
> >
> >
>
> Get 250 color business cards for FREE!
> http://businesscards.lycos.com/vp/fastpath/