Bridge pin angles

[Phillip Ford]

>Phil, Ron, and the rest of you -
>
>Phil, are you discounting, or unaware of the Wapin system of bridge pinning?

I am aware of it but hadn't really thought about it until last night when I 
got a private e-mail mentioning it (BTW, to the person that sent that 
e-mail, I got it and tried to reply privately, but one of our servers 
wouldn't let me).  It did make me wonder if the notch crushing is less on 
the Wapin termination.  I've never done one and never serviced 
one.  Perhaps some of  you who do Wapin installations could weigh in on 
this, if you're allowed to (if not you may e-mail me privately - I won't 
tell anyone).  I also haven't paid attention to Wapin for a long enough 
time (and my memory is fading fast enough) that I'm no longer sure how the 
installation looks.  I went to the web site, but there was no diagram or 
picture of the installation that I could find - I did, however, find 
several encomiums to the system.  As I recall there is a vertical pin for 
the front bridge termination, with an angled pin somewhat behind it.  The 
things I don't remember are how far back is the angled pin, and is there 
any side bearing on the front vertical pin.

>I know Ron is aware of it...
>
>As I see it, you need to decide, from the beginning, whether your inquiry 
>is directed towards understanding the mechanical processes at work, or the 
>more practical aspect of building something that will continue to function 
>for a reasonable length of time.

Actually, I thought I was interested in both, and that they were 
related.  What I'm ultimately interested in is a better design that will 
give a cleaner termination and give it longer term.  But I believe that I 
need to understand (or at least have a bit better understanding) of what is 
causing falseness at the termination, and contributing factors to that.

>For the most part, questions of loosening bridge pins and crushing notches 
>and caps are of the latter direction.

I agree.

>That an angled bridge pin might be more prone to causing cap damage than a 
>vertical one is helpful to understanding piano forensics, but it doesn't, 
>by itself, explain the possible differences in acoustic properties of 
>between each.

I hadn't really intended to explore acoustic properties or differences in 
acoustic properties in angled vs vertical pins, at least in the context of 
this discussion.


>Phil, you said:
>>If there was no side offset at all and the pin was straight up and down 
>>then it could easily slide as the bridge moved and the downbearing would 
>>be enough to keep it seated on the bridge at all times.  Of course, it 
>>wouldn't sound too good.
>
>First, to round out the model,......
>With sufficient angle (downbearing), the string would not lift off the 
>bridge, but, depending upon the frictional coefficient between string and 
>bridge surface, there would be some sliding side to side.  That whole part 
>of the strings wave form requires a vertical termination.  A bridge pin 
>(vertical).  How much force is required to prevent wave energy from 
>slipping around terminating pin?

Yes.  Or once you've stuck a pin in there, to prevent the string from 
buzzing on the pin.


>How much, if any less than the 8 degrees at the lower end of Ron's tolerance?

I would be interested in knowing.


>So, assuming you had adequate down and side bearing, what's changed by 
>slanting the bridge pin?  I don't know.  If you assume that the "clamping" 
>mechanism spoken of is an actual part of the interaction of the energy 
>wave and the bridge, i.e, that the string "lifts" the bridge, than that 
>slant would seem essential.  Or if you thought that, even with positive 
>front bearing, the string would tend to lift off the bridge (slide up the 
>pin), the slant would be critical.  If, on the other hand, the behavior at 
>the termination is more pull (pulse) than lift, the slant seems to become 
>less critical than the side bearing, without which some of the energy of 
>the longitudinal (I'm sure I'm misusing this term) wave would escape.

I also don't know the reason for the angled bridge pin.  I think that with 
adequate down and side bearing that the string is not going to lose contact 
with the bridge cap or the bridge pin and that there would be no falseness 
or buzzing.  I don't believe that the string needs to be 'clamped' to the 
bridge.  But I may be wrong.  This should be easy enough to demonstrate one 
way or the other.  It just requires a subject piano and some playing around 
with side and downbearing angles and bridge pin angles.  I'll put it on the 
list of things to do.  Now I'm back up to 998 things on the list.


>If there is any accuracy to the preceding, then the other issues are our 
>attempts to deal with real world imperfection.  Is there any difference 
>between a properly terminated string (side and down bearing) and one where 
>the role of down bearing is fulfilled by the clamping of the front pin?  I 
>don't know, but it seems like a reasonable question, and one which, with 
>the right equipment, can be measured.

If the string does in fact not need to be clamped to the bridge if there is 
adequate side and downbearing, then the angled pin may in fact be there to 
deal with real world situations or with situations where there is not 
'adequate' downbearing.  One of these situations could be a bass bridge, 
where you don't really want a lot of downbearing, and where you have large 
string excursions.  Here the downbearing may not be 'adequate' to keep the 
string from buzzing on the bridge if it is not clamped down.  Another might 
be the bridge that has overall positive downbearing, but gets it by having 
positive bearing on the front side of the bridge and negative bearing on 
the back side of the bridge.  If the angled pin wasn't there the backscale 
would probably buzz.  I suppose another situation is that in which the 
piano (either new or with some age) no longer has any downbearing.  The 
angled pins may be saving the factory from having to take the piano back.


>As has been previously raised, we use downbearing for two disparate 
>purposes, termination and board loading.  Is it possible for the 
>requirements for each to conflict?

I'm not sure.  I've never really thought of downbearing serving to 
terminate the string.  But now that you bring it up I don't really have any 
evidence to back up that thought.  I believe that the current explanation 
on offer for downbearing is that it increases board stiffness without 
increasing mass.  If downbearing needs to do both of these things, then 
differing amounts of it may be needed for each function, so in that sense 
they could be in conflict.  If it only needs to do one of these, then there 
is a conflict in requirements, but the question may be - is there any 
detrimental effect on the other function that the downbearing is 
causing?  To say this in another way, if downbearing is needed to raise 
board stiffness but is not needed for string termination, is the 
downbearing in some way adversely affecting the string termination.  If 
not, then it's probably not hurting anything.


>Now, as to how them waves git into the bridge, and beyond...
>
>
>David Skolnik
>"Honey?  Where's my super [flame] suit?
>Family's favorite quote (modified) from The Incredibles

I await your explanation.  I think this is where Robin Hufford chimes in <G>.

Phil Ford
"No brains, no headaches".
A friend's favorite quote.