Bridge pin angles

[Phillip Ford]

>.......
>Pictures are much easier to fake than math and logic, and so are 
>going to be of no use. Something this supposedly common and obvious 
>should be reproducible. If strings get up and stay up pins against 
>positive downbearing, offset angle, and pin angle while people are 
>playing the piano continually until the tuner can come and tap them 
>back down, it ought to be dead easy to pull them up the pin and make 
>them stay there any time you like. I don't see how they could be 
>kept down. The feeler gage can prove it happened, and playing the 
>thing for a while and trying the gage again will prove that strings 
>stay up pins. I'll most definitely attend the convention class where 
>that is demonstrated.

I had had the same thought about lifting the strings up the pins and 
seeing if they would stay there.  It was a matter of making time for 
this experiment.  So,  today I tried lifting up strings on a couple 
of subject pianos at the shop.

I tried this on two pianos (hardly an extensive sample, but a start). 
A little background info -  I checked bearing with  a Lowell gage. 
The feeler gage that I used was the thinnest that I had available, 
which was 0.004 inch.  To begin I checked all strings at the bridge 
cap to see if I could insert the feeler gage under any string, 
anywhere along the string to bridge contact area.  I then tried to 
select two or three sample strings in different sections of the piano 
to attempt to lift up.  I checked around randomly with the 
downbearing gage trying to find strings that seemed to represent the 
lower end of the downbearing range for their particular section of 
the piano, thinking that if a string were to stay above the bridge 
when lifted up, then a string having a lower amount of downbearing 
might be less likely to seat itself on the bridge due to playing 
(string vibration).  But I also insured that the subject strings had 
positive downbearing.  I then lifted up the chosen strings at the 
front and rear bridge pins with a stringing hook.  I checked with the 
feeler gage to see if there was a gap between string and bridge cap 
anywhere along the bridge cap - string contact area.  For the subject 
strings, I then measured as accurately as I could with strings and 
bridge pins in place, the sidebearing angle and the bridge pin angle. 
Note that measuring bridge pin angle from a little stub of bridge pin 
sticking up from the bridge is not easy, so bridge pin angles should 
be taken with a grain of salt.

First subject piano:  A 1958 Baldwin SD-6.  Original strings as far 
as I know.  Bridge and pins in very good shape.  Strings showing a 
little bit of oxidation.

Initial check with the feeler gage indicated no gaps anywhere.  I 
then selected three strings in different sections of the piano to 
lift:

String 1.  Sidebearing angle 8.5 degrees.  Bridge pin angle 15 
degrees.  Tried lifting this string but the feeler gage showed no gap 
after attempted lift.

String 2.  Sidebearing angle 8.5 degrees.  Bridge pin angle 9 
degrees.  When I lifted this string it stayed above the bridge.  I 
could insert the feeler gage beneath it.  So, this seemed to indicate 
that my calcs back in the early days of this thread, about a string 
being able to stay above the bridge in a static situation, were not 
completely fictitious, which was reassuring.  After general banging 
on the piano and pounding on this note a couple of dozen times there 
was no longer any measurable gap.  I tried tapping down the string 
but didn't notice any substantial down movement.

String 3.  Sidebearing 13.5 degrees.  Bridge pin angle 11 degres. 
When I lifted this string it stayed above the bridge.  I could insert 
the feeler gage beneath it.  After general banging on the piano and 
pounding on this note a couple of dozen times there was no longer any 
measurable gap.  Tapping down the string showed no substantial down 
movement.

Second subject piano:  A Steinway B.  New bridge cap and fairly 
recently restrung, so everything was in pretty good shape.

Initial check with a feeler gage indicated no gaps except on the back 
side of the bass bridge in certain spots.  The strings were visually 
above the bridge at the rear pin on some notes on the bass bridge.  A 
check with the downbearing gage indicated small overall positive 
downbearing, but slight negative bearing on the back side of the 
bridge.

I tried tapping down a couple of strings in this area of the bass 
bridge, so that they were against the bridge at the rear pin.  I then 
did the general pounding and observed that they were still against 
the bridge.

String 1.  Sidebearing 8 degrees.  Bring pin angle 8 degrees.  When I 
lifted this string it stayed above the bridge.  I could insert the 
feeler gage beneath it.  After general banging on the piano and 
pounding on this note a couple of dozen times the string was still 
above the bridge and I could insert the feeler gage beneath it.

String 2.  Sidebearing 11 degrees.  Bridge pin angle 14 degrees. 
When I lifted this string it stayed above the bridge  I could insert 
he feeler gage beneath it.  After general banging on the piano and 
pounding on this note a couple of dozen times there was no longer any 
measurable gap.

The conclusion from the limited sample was that it was possible for 
the string to be above the bridge, but it seemed to be for situations 
where the bridge pin angle was low enough.

>
>
>>>One final note.
>>>
>>>The whole line of reasoning Ron N lays out lives and dies upon the 
>>>existance of
>>>negative bearing when the string is off the cap.  Alls one has to 
>>>do is find a
>>>case of strings off the surface of the bridge while at the same 
>>>time finding plenty
>>>of positive bearing.
>>
>>
>>I believe he did say that he doesn't believe any piano that has 
>>positive bearing could have strings off the bridge.  He also seemed 
>>receptive to being proved wrong.  Anyone with a feeler gage (and a 
>>downbearing gage, I might add) can do so.  No one has spoken up yet.
>
>As I continue to point out, even under positive bearing, the notch 
>edge will still be below the string after it is sufficiently crushed 
>by cyclic bridge movement.

Right.  I think I was agreeing with that.

>
>
>>I also don't think he said that string seating was useless.  I 
>>think he said that it was temporary.
>
>I said it was temporary, and I said it didn't fix the problem, 
>because the resulting tonal problems are almost entirely from loose 
>bridge pins..
>
>>3.  To investigate the effects of string vibration alone is a 
>>little trickier.  Perhaps the setup in number 2 but with no 
>>downbearing.  Subject this to string vibration.  One potential 
>>problem here - is the arrangement of two bridge pins having typical 
>>angles, but no side to side offset, clamping the string down in a 
>>realistic enough way for this test to be meaningful.  Thoughts on 
>>this?
>>
>>Phil Ford
>
>It isn't conclusive, since I can't know the piano's entire service 
>history, but de-stringing a bridge, I typically see more pin and 
>notch damage on the speaking side. I have no way to determine 
>whether this is from play, front bearing angles, or seating of 
>strings.
>
>Ron N

I've noticed the same thing.  If we want to try to establish which of 
these factors is contributing to bridge or pin damage then I think we 
need to come up with some experiments which attempt to isolate the 
various factors.

Phil F