[pianotech] Measuring Crown Radius

[Ron Nossaman]

On 7/12/2011 1:04 PM, David Love wrote:
> I think you need both (crown with load and without load) along with the
> bearing measurements before and after as well.  An analysis of the rib scale
> is also helpful even with pure compression crowned boards and certainly with
> hybrids.  The ribs still do a fair amount of work even in compression
> crowned boards once glued into the rim.

I've never found rib scale analysis of a compression crowned board to be 
of any use whatsoever, since it's an entirely different system than a 
rib supported board. Rib crowned and panel supported, sure. You can 
learn what the panel will have to support.


> Measuring the crown under load doesn't tell you much.  You could have
> negative crown on a board that's way overloaded that might respond ok once
> the load is adjusted to the proper level--damage aside.  The crown with
> bearing measurement tells you more, but still not enough.

I don't know about you, but I've said probably a thousand times that 
either crown or bearing alone is useless. That's why both of these 
measurements are taken with the piano at pitch.


> Measuring the
> crown with tension and without tension and the bearing change with and
> without load tells you quite a bit about how the board is responding and
> whether it can withstand any significant load or not.

I disagree. It can confirm the initial diagnosis if the crown doesn't 
come up, but you learned what it would hold with the crown and bearing 
measurements under load.

And the question you asked was about unloaded crown alone, which I 
answered.
Ron N