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Why are bridge pins so short? #2923152 12/15/19 01:22 PM
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Ralphiano Offline OP
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I just watched a video tour of the Steinway factory in New York, and, was surprised at the miniscule length of the bridge pins that were being installed. My initial guess was that they were only about 3/4" in length. I looked at the Vanda King website and saw thay they sell them in lengths of 3/4" and 1".

Given the tendency of piano bridge caps to develop cracks due to the bridge pins' inability to resist the side bearing force of the strings, it seems that a simple improvement would be to make the bridge pins substantially longer. It seems that bridges are generally tall enough to house a 2" deep hole to accommodate a 2" long bridge pin. Doubling the length of the bridge pins would seemingly greatly strengthen the bridge/cap/pin assembly by improving its ability to resist the side bearing of the strings, and give much greater life to bridge caps than is currently provided.

I know a lot of you have spent years of serious study, testing, and consideration of ways to improve the piano. What are the reasons for not using a much longer bridge pin?


Ralph

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Re: Why are bridge pins so short? [Re: Ralphiano] #2923157 12/15/19 01:43 PM
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Gene Nelson Offline
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Iv never given it much thought, except that I don't want a pin that is excessively tall.
Why do you think that the string side bearing on the bridge pins develops cracks in the bridge cap?
Why do you think that a longer pin would prevent this?
Im not seeing how a longer pin would strengthen the bridge/cap/pin assembly.
One thought on this is: Longer pins equal more mass on the soundboard assembly and less wood in the bridge. (Maybe minor but your making me think about it)

I have always thought that splits in the cap happen because of excessive moisture swings and defects in the wood - then the bridge pins follow the crack.
The string side bearing will make the pin flex slightly (if its going to flex) near the contact point regardless of how long the pin is. Drilling the bridge pin holes and getting the correct fit is more important.
In regard to minimizing the possibility of a bridge cap splitting, I use laminated maple as opposed to solid maple.
Other things that contribute to bridge cap issues is the practice of flattening the tops of the bridge pins as an expedient to getting a uniform pin height. Its usually done mechanically and if not done carefully it can heat the pin and contribute to elongation of the hole its fitted in as well as possibly even benging the pin.
I leave my pins rounded at the top and take the time to tap them in to a uniform height.
Then there is inserting the pin into the hole - it needs to be done carefully and in line with the hole.
So much technique done right is much more beneficial than the length of the pin IMHO.

Last edited by Gene Nelson; 12/15/19 01:44 PM.

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Re: Why are bridge pins so short? [Re: Ralphiano] #2923182 12/15/19 02:50 PM
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P W Grey Offline
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Actually, a longer pin will do nothing to affect the forces being exerted at the bridge surface/pin base juncture. The pin itself is not strong enough to resist the side pressure. Resistance is primarily due to wood choice, seasoning, and grain orientation relative to the force.

Another reason is that the design intent is not to make a system that lasts 100 years. The design intent is 30-40 years...then rebuild, or preferably replace. This has been true since the 1700's...and the technology is essentially the same today as it was then.

Pwg


Peter W. Grey, RPT
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Re: Why are bridge pins so short? [Re: Ralphiano] #2923215 12/15/19 04:28 PM
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Ed McMorrow, RPT Offline
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I do think longer bridge pins help reduce cracking. If the bridge pins are tight in the hole they will act as reinforcement against wood movement. As Gene mentioned they would add mass and my testing shows that more mass in the bridge makes the tone thinner.

I do know that the hardness of the pin has a profound effect on tone. Harder pins damp the Longitudinal mode, (L-mode), less and this can cause L-modes to interfere with the Transverse mode.

I also have found that I must use one size smaller drill bit than Steinway does to insure proper pin tightness. It does make driving the pins in more challenging, but it is worth it in my opinion.

I do drive them to the bottom of the hole and file flat. If carefully done there are no ill effects.

Many of the German styled pianos, (which includes all the Japanese, Korean, China and other nations), have pin lengths reduced as the diameter is reduced. I don't like this at all. I always use copper plated 1" long pins of the smallest diameter possible for the scale so as to reduce mass and less weakening of the wood.


In a seemingly infinite universe-infinite human creativity is-seemingly possible.
According to NASA, 93% of the earth like planets possible in the known universe have yet to be formed.
Contact: Ed@LightHammerpiano.com
Re: Why are bridge pins so short? [Re: Ralphiano] #2923255 12/15/19 05:52 PM
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P W Grey Offline
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Ed,

How many .xxx" difference do you like to have in general for bridge pins...003"...004"...?

Pwg


Peter W. Grey, RPT
New Hampshire Seacoast
www.seacoastpianodoctor.com
pianodoctor57@gmail.com
https://www.youtube.com/watch?v=PK0T7_I_nV8
Re: Why are bridge pins so short? [Re: Gene Nelson] #2923315 12/15/19 09:16 PM
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Ralphiano Offline OP
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Thanks to everyone for your thoughtful replies.

Originally Posted by Gene Nelson

Why do you think that the string side bearing on the bridge pins develops cracks in the bridge cap?



I got that idea from seeing so many pianos with cracks running exactly through the bridge pin hole, while, not having cracks in other parts of the bridge or bridgecap. The proximity of the pin to the crack gave rise to my possibly simple notion that the side bearing of the string was pushing the top of the pin sideways within its hole, with the resulting pressure on the wood of the bridgecap causing it to split and relieve that pressure by allowing a slight sideways repositioning of the pin in the direction of the sidebearing force.


Originally Posted by Gene Nelson


I have always thought that splits in the cap happen because of excessive moisture swings and defects in the wood - then the bridge pins follow the crack.



This comment has me wondering whether the cracks I have seen are also present on the non sidebearing side of the pin holes. If the cracks also extend in the non sidebearing direction, then that would support your thesis about humidity being the culprit, and, side bearing being inconsequential to the cracks. It is possible that I have not been as keen an observer as I needed to be to come to an accurate conclusion. My memory of the cracked bridges I have seen does not include cracks running from the non bearing side, and, does not include cracks in other regions of the bridge cap that does not have pin holes, thus pointing me away from the humidity possibility. But, that memory may be biased in favor of my original, quickly drawn conclusion that the pins and side bearing are the cause. I am going to look again.


Originally Posted by Gene Nelson

Why do you think that a longer pin would prevent this?
Im not seeing how a longer pin would strengthen the bridge/cap/pin assembly.



My idea on this is that since the side bearing is applied to the top 3/16" of the pin, the corner formed by the side bearing side of the hole and the top of the bridgecap would act as a fulcrum around which the pin would attempt to rotate. As the top of the pin pushed in the direction of the side bearing force, the bottom of the pin, down within the pin hole, would attempt to move and exert some of that side bearing force in the opposite direction, against the nonbearing side of the pin hole. A longer pin, set in a deeper hole, would be better able to resist the sidebearing force as it would distribute the side bearing force over a greater surface area of wood (the deeper hole providing greater surface area).

Originally Posted by Gene Nelson

The string side bearing will make the pin flex slightly (if its going to flex) near the contact point regardless of how long the pin is.


I had not considered the possibility of the pins actually bending to comply with the side bearing until you mentioned it. It raises the question of just how much do the pins flex or bend within that last 3/16" or so. My initial instinct is to think that the bending would be so slight as to not be sufficient to cause bridgecap cracking. But, my idea is not backed by any special knowledge, research, or experience.

I would be very interested to hear if you, or any of the others, have detected bends in that exposed top part of the pin among any of the bridge pins you have removed.

Thanks again for sharing you knowledge and ideas.

Last edited by Ralphiano; 12/15/19 09:20 PM.

Ralph

Kawai VPC1
Garritan CFX Lite
Pianist since April, 2015
Re: Why are bridge pins so short? [Re: P W Grey] #2923321 12/15/19 09:39 PM
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Ralphiano Offline OP
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Originally Posted by P W Grey
Actually, a longer pin will do nothing to affect the forces being exerted at the bridge surface/pin base juncture. The pin itself is not strong enough to resist the side pressure. Resistance is primarily due to wood choice, seasoning, and grain orientation relative to the force.



What are your thoughts on the idea I expressed in my reply to Gene Nelson above about the greater surface area of a deeper hole allowing much of the sidebearing force to be diffused over the greater surface contact area of the deeper hole and longer pin?


Originally Posted by P W Grey


Another reason is that the design intent is not to make a system that lasts 100 years. The design intent is 30-40 years...then rebuild, or preferably replace.


There seems to be ample evidence of this. The movement toward composite materials will be very interesting to follow. I have a nice stable of carbon fiber bicycles, and I like the material very much.


Ralph

Kawai VPC1
Garritan CFX Lite
Pianist since April, 2015
Re: Why are bridge pins so short? [Re: Ralphiano] #2923323 12/15/19 10:04 PM
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Ralphiano Offline OP
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Originally Posted by Ed McMorrow, RPT




I do know that the hardness of the pin has a profound effect on tone. Harder pins damp the Longitudinal mode, (L-mode), less and this can cause L-modes to interfere with the Transverse mode.........

I always use copper plated 1" long pins of the smallest diameter possible for the scale so as to reduce mass and less weakening of the wood.




Does the copper plating, in your opinion, also do a better job of damping the Longitudinal mode than does the harder surfaced pins, such as nickel plated? Or, is that effect negligible?


Ralph

Kawai VPC1
Garritan CFX Lite
Pianist since April, 2015
Re: Why are bridge pins so short? [Re: Ralphiano] #2923331 12/15/19 10:57 PM
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Ed McMorrow, RPT Offline
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Ralphiano,
I am still trying to answer that question. I did just switch out a the nickel plated mild steel bridge pins for copper plated mild steel ones on a piano. And am able to compare that piano to one that I did not do the switch on since both are in my shop right now. The switched one is just starting to hold a tune well enough to reveal how clear the unisons can be tuned. I think the copper plated is better, certainly not worse, but I need a little more time with them to feel able to claim a confirmation.


In a seemingly infinite universe-infinite human creativity is-seemingly possible.
According to NASA, 93% of the earth like planets possible in the known universe have yet to be formed.
Contact: Ed@LightHammerpiano.com
Re: Why are bridge pins so short? [Re: Ralphiano] #2923333 12/15/19 11:42 PM
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Gene Nelson Offline
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Originally Posted by Ralphiano
Thanks to everyone for your thoughtful replies.

Originally Posted by Gene Nelson

Why do you think that the string side bearing on the bridge pins develops cracks in the bridge cap?



I got that idea from seeing so many pianos with cracks running exactly through the bridge pin hole, while, not having cracks in other parts of the bridge or bridgecap. The proximity of the pin to the crack gave rise to my possibly simple notion that the side bearing of the string was pushing the top of the pin sideways within its hole, with the resulting pressure on the wood of the bridgecap causing it to split and relieve that pressure by allowing a slight sideways repositioning of the pin in the direction of the sidebearing force.


Originally Posted by Gene Nelson


I have always thought that splits in the cap happen because of excessive moisture swings and defects in the wood - then the bridge pins follow the crack.



This comment has me wondering whether the cracks I have seen are also present on the non sidebearing side of the pin holes. If the cracks also extend in the non sidebearing direction, then that would support your thesis about humidity being the culprit, and, side bearing being inconsequential to the cracks. It is possible that I have not been as keen an observer as I needed to be to come to an accurate conclusion. My memory of the cracked bridges I have seen does not include cracks running from the non bearing side, and, does not include cracks in other regions of the bridge cap that does not have pin holes, thus pointing me away from the humidity possibility. But, that memory may be biased in favor of my original, quickly drawn conclusion that the pins and side bearing are the cause. I am going to look again.


Originally Posted by Gene Nelson

Why do you think that a longer pin would prevent this?
Im not seeing how a longer pin would strengthen the bridge/cap/pin assembly.



My idea on this is that since the side bearing is applied to the top 3/16" of the pin, the corner formed by the side bearing side of the hole and the top of the bridgecap would act as a fulcrum around which the pin would attempt to rotate. As the top of the pin pushed in the direction of the side bearing force, the bottom of the pin, down within the pin hole, would attempt to move and exert some of that side bearing force in the opposite direction, against the nonbearing side of the pin hole. A longer pin, set in a deeper hole, would be better able to resist the sidebearing force as it would distribute the side bearing force over a greater surface area of wood (the deeper hole providing greater surface area).

Originally Posted by Gene Nelson

The string side bearing will make the pin flex slightly (if its going to flex) near the contact point regardless of how long the pin is.


I had not considered the possibility of the pins actually bending to comply with the side bearing until you mentioned it. It raises the question of just how much do the pins flex or bend within that last 3/16" or so. My initial instinct is to think that the bending would be so slight as to not be sufficient to cause bridgecap cracking. But, my idea is not backed by any special knowledge, research, or experience.

I would be very interested to hear if you, or any of the others, have detected bends in that exposed top part of the pin among any of the bridge pins you have removed.

Thanks again for sharing you knowledge and ideas.


Obviously more than one cause for bridge cap splits. Sometimes the bridge root will split. I’ll stick with flaws in the wood and large humidity fluctuations. But next on my list is poor quality work. A root split is likely a glue joint failure.

I only mentioned flex for context - if the bridge pins do Flex it’s not enough to bend the pin, at least I dont recall seeing any.

The string engages the pin at its base (interface with bridge cap) and the lean angle plus the radius of the pin provide string offset as well as hold the string firm against the bridge cap. with string tension and offset angle you can calc the side bearing force on the pins. Then if you know the physics of the pin you can plot flex or bending if you want.
If the string offset is not excessive and the pin fit is tight with no elongation of the hole, it’s a very solid termination weather the cap is laminated or quartered rock maple.



Last edited by Gene Nelson; 12/15/19 11:44 PM.

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Re: Why are bridge pins so short? [Re: Ralphiano] #2933274 01/13/20 11:09 AM
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Goof Offline
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There is a new design where pins are replaced by a set of rollers !
A member might have a picture of said advance ?

Re: Why are bridge pins so short? [Re: Ralphiano] #2934418 01/15/20 08:18 PM
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Chernobieff Piano Offline
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Bridge pin hole tolerance must be proprietary info Peter. As It seems to be consistently dodged when asked.


Chernobieff Piano Restorations
Lenoir City, Tennessee U.S.A
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grandpianoman@protonmail.com

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