Taking an iron rod and rubbing it with pressure on the bridge top before notching is a pretty common practice to compress the top layer and minimize string indentations somewhat. Prestressing, or precompressing the fibers (however you want to call it) does make sense and I do it routinely.
There is both soft maple and hard maple (sometimes called rock maple). It has to do with the density and weight. For example, Ronsen uses a soft maple for some of their moldings. It's quite light in weight and machines well (which is why Ray uses it) as compared to harder maple that you might see in use, typically, on bridge caps or some other hammer moldings (Hamburg Steinway hammers, I believe, use hard maple). Hard maple was sometimes used for key buttons or key shoes (a bad idea in my opinion) as well as for key frame inserts for new key pins (not a bad idea). The low density of soft maple makes it inappropriate for use on bridge caps.
On this thread there was also discussion of shimming. I'm not so bullish on shimming anymore (and haven't been for some time). I prefer to use a two-part epoxy (West System) and a medium density filler or wood flour mixed in. I'll open the crack just slightly to allow ease of application and use a mix that remains somewhat runny (Goldilocks viscosity--not to thin not too thick). Tape off the bottom of the board and run tape as close to the edges of each side of the crack as possible on the top. The tape also serves to raise the level at which the epoxy will level off just slightly above the plane of the SB. Then inject the epoxy into the cracks working it in with a thin blade to penetrate the entire depth of all the areas in crack. When cured you can sand it flush and finish as you would. I find this method to be more efficient and stable. I do dry the board with Dampp-Chasers first so that the board is at the equilibrium point where I intend to leave it.
------------------------------
David Love RPT
www.davidlovepianos.comdavidlovepianos@comcast.net415 407 8320
------------------------------
Original Message:
Sent: 11-07-2019 20:45
From: Chris Chernobieff
Subject: First Soundboard and Bridge Recapping!
Farretl said,
Hard rock maple? Are you suggesting that is different from "hard maple"? I've not ever heard of prestressing maple fibers. What exactly is that? How would "running" an iron rod back and forth over the wood prestress fibers?
I'm surprised a veteran woodworker would ask these questions.
"Steinways like to vibrate in the 50-60 hz range when under compression."
That sure seems unfortunate. Most music I'm familiar with has a much wider range than that....
There is a difference between a boards fundamental tapping frequency and the frequency of the notes.
-chris
------------------------------
Troubles are Bubbles, and they just float away.
chernobieffpiano.com
grandpianoman@protonmail.com
Knoxville, TN
865-986-7720
Original Message:
Sent: 11-02-2019 10:58
From: Terrence Farrell
Subject: First Soundboard and Bridge Recapping!
Chris C. wrote: "If you didn't use hard rock, you probably should start over. You can pre-stress the fibers by running an iron rod back and forth over the caps."
Hard rock maple? Are you suggesting that is different from "hard maple"? I've not ever heard of prestressing maple fibers. What exactly is that? How would "running" an iron rod back and forth over the wood prestress fibers?
"Steinways like to vibrate in the 50-60 hz range when under compression."
That sure seems unfortunate. Most music I'm familiar with has a much wider range than that....
------------------------------
Terry Farrell
Farrell Piano Service, Inc.
Brandon, Florida
terry@farrellpiano.com
813-684-3505
Original Message:
Sent: 11-02-2019 00:57
From: Chris Chernobieff
Subject: First Soundboard and Bridge Recapping!
I sure hope you dried the board and the shims pretty good to take advantage of any hygroscopic movement you could get, and to hopefully add compression back into it. Steinways like to vibrate in the 50-60 hz range when under compression. If it is lower than that it could be an indicator of no compression. If you didn't dry the board and shims then the crack will open up again in due time. Also, I recommend pre-stressing the maple fibers in the cap to further strengthen the hard rock maple. If you didn't use hard rock, you probably should start over. You can pre-stress the fibers by running an iron rod back and forth over the caps.
-chris
------------------------------
Troubles are Bubbles, and they just float away.
chernobieffpiano.com
grandpianoman@protonmail.com
Knoxville, TN
865-986-7720
Original Message:
Sent: 10-31-2019 10:29
From: Alden Jack
Subject: First Soundboard and Bridge Recapping!
PTG Family, I just finished my first round of soundboard shims and bridge capping! I was excited and felt like I wanted and needed to celebrate with someone (my wife doesn't quite understand the significance :) I picked up an old Steinway upright to practice removing a plate, shimmed soundboard cracks, and recapped the top section of the treble and bass bridges. Wow, I learned a lot!
------------------------------
Alden Jack
Smithfield UT
435-760-3974
------------------------------