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When recrowing and bridge recaping, How much downing should I set the bridge for? Is there a rule of thumb and should it vary from bass to treble?
Dan

OK,

New board or old board?

If the old board, how are you re crowning it?

Also, moisture content at the time matters.

LArry

Old board, About a year ago I got a free baby grand that the soundboard lost it's crown and actually was concave. The bass strings sounded like a banjo so I thought it wood be a fun project to start learning piano rebuilding on. Well I took the strings off and the plate out and when I hit the sound board it sounded like the bottom of an old drawer. After reading some techniques on recrowning I braced up the soundboard routered and shimmed the cracks and after removing the braces it has a low ring when I hit it and the crown is about 3/16"

That crown may be left over summer humidity.

Adding crown using a shim is not giving you the supporting crown you need to do much loading on the board.

I would recommend drying the board to 6%EMC, 2mm at 88, 1.5mm across the high tenor, 1mm at the low tenor and 1mm on the bass bridge.

Depending on how you you take deflection measurments.

We are having a Boston PTG meeting at George Crawfords place in Hyde Park, Nov 21st. Doors open at 6pm. Technical presentation by Tom Malone, Head of technical services at Baldwin. You are welcome to come. No oblogation or cost. There is a whole lot of rebuilding going on there. Lots of good ideas.

I am happy to help you find your way there.

Larry

I got the shop down to 20% and let it sit for 3 months.
PTG Sounds good , I would love to go. I will be there.
Thanks
Dan

Just a bit more,

Lets say for a moment thst you did acheive crown with a shim. It would be what is called "edge crown" All of the bearing is on the new wood shim and the wood surface it contacts. Bearing by the way against the woods least strong surface. If the edge crown was bearing against the end grain, it would be more resistant to crushing.

Crown on a board is held along the enire glue joint of the rib to sound board. There is conpression crowning, dish crowning and rib crowning. Most pianos have used a combination of compression and dish crowning. Today there are many more boards being crowned additionally with rib crowning.

Do you know where George Crawford's shop is?

I'm not familiar with George Crawford's shop,
With your experience do you think the crown will diminish, say within a year making it a waste of money to put $250 in bass strings. Or should I restring it and see what happens.
Thanks for your advice,

Dan

Well, if you are not changing the bridge cap, then how would you adjust bearing?

Truth is many pianos are restrung with the kind of work in place you have done. Also, a great many people find it satisifying to play.

The margin for error in tolerances, well, I'd have to see it before I make an educatated recommendation.

oming to Georges on 11/21 could help give you more information to make a decision.

Plus, you will meet a lot of really great people who enjoy pianos with experience they will share.

Larry

Hi Larry,
I was under the impression that the end grain of the soundboard holds nothing. Most board aren't cut tight to the outer rim. The glue joint holds it all. The proof is in the boards that are installed with a mm of clearance betweem the rim and the end of the board, if the glue joint didn't hold and the board moved out to the rim upon stringing, there would sure be a lot of buzzes. The glue joint adds strength to the structure as when the board is glued in a dished position.
In reality, you have propt the ribs up into a crowned position, then supported them with more material added to the diaphram part of the board. It is similar to a compresion crowned board. This will give you a board that has more impedance but structurely will not support the downbearing pressure needed at the bridge when you string it. With the right hammers it will be a pleasant sounding instrument and a piano tensioner from Pianotech like the M&H ones might help even more. It's a lot of work to find out the old board still doesn't have it. On the other hand, you might have the knack to make an old board work decently. Not many people do.

Hi Keith,

I am not supporting the idea of edge crowning, just clarifying the termilogy.

Personally, I have not found edge crowning in the fashion woodfab is describing, to be a supportive crown.

Hey Larry,
When I read your post over a few more times I felt we really were saying the same thing. Didn't mean to sound accusing or contrary.

Thanks Kieth,

Hey, I think CA is a bit warmer than here in Mass....

I've always been skeptical of any real benefit from this sort of recrowning. It seems to me that the board has lost crown through crushing of the wood fibers over the years. Adding material in the form of shims may push it back up and restore crown for a while, but you still have the same tired soundboard just in another position.

Niles Duncan
Piano technician/rebuilder, Pasadena, CA
www.pianosource.com

It really depends on what use the piano is going to get. Even a tired board can have much expression and tonal quality so in a living room it is a wonderful thing to play and you don't have to use the una corda all the time. Put it on a stage and the listeners won't be thrilled, it's noy a powerhouse.
A compression/dish crowned board can only exert so much pressure into the bridge/string coupling anyway and most pianos don't have much more sound than the old shimmed/reconditioned board does. The biggest difference between a new piano and the old is the strings and the hammer, reg, etc...

If you use Del's epoxy treament method the impedence of the board improves and the sound brightens and becomes more definitive. At least it has in these old uprights I did it to. The boom as you hit the board is tighter. You still can't get the boom you hear in a new rib crowned board. Think of the board as a drum head that has different spots or pools of resonance. An old drum head can be tighten and tuned but a new drum head has a livelier spark to it. A rib crowned board has a greater bridge/string coupling force that is more stable in humidity swings and aging.

Really, if you are going to spend much time reconing a board, it would be worth it to put a new one in.

Have seen good results but the work is a bit more tedious.
It involves carefully removing ribs in critical but accessable areas - may only get 3 or so - and replacing using epoxy rather than glue. The rib is braced up against supprot beam while epoxy cures - similar to the way you would brace up in prep for shims.
New crown if any is supported by the epoxy bond.

Just out of curiousity, did you measure the downbearing before you took the piano apart, Dan?

I did measure it and there was none at all.
And after I pulled the strings and plate the board was slightly concave.