[pianotech] Belly talk

[Jim Ialeggio]

David L said:

<Maybe Jim should clarify which crown he is referring to. I didn't think 
he was referring to removing crown in the rim such that the bass end 
would not have to be forced down once the treble end was clamped.

My interest is:

1st and foremost- a good glue joint surface. This is hard, to achieve in 
such an inaccessible location, but possible.

2- a simple plane is easier to machine accurately than a serpentine 
plane(if you can call a serpentine thingee a plane)

3- Not adding unneccessary stress to the board @ glue-down. Having said 
that, by definition, in a small belly at least, the back is going to 
have to be forced down, sometimes considerably. So there's not getting 
out of this one without adding some stress. And thinking about it, maybe 
just not that important at all...still considering this one.

Thinking out loud regarding the glue-down stress in # 3 above, the way 
this original rim is shaped, had to greatly accentuate the amount of 
tail force down required. This because along the curved side of the rim, 
the high treble and low bass are the low points of the crown. It seems 
clear to me that they were trying to add stress to the board in shaping 
it in the way they shaped it. I don't think the accentuated long bridge 
crown actually adds anything in the way of stress induced stiffness to 
the system anyway, but it seems clear that that is what they thought 
they wanted to achieve.  Just to be clear, I don't buy the stress 
induced stiffness scenario.

Some stress is getting added...no way around it. But do I want to add 
the amount of stress they had in mind. I don't think so, but as always, 
I remain open to reasonable explanations to the contrary.

HOwever, 1st and foremost, I want a good glue joint surface, and a good 
glue surface on this difficult to access ledge, is a challenge. The 
stress of glue-down while probably being ineffective at adding 
stiffness, is quite effective at challenging the glue joint. Hence my 
skepticism of making this joint more complex than it needs to be.

I'm not sure where I come down on the beveled face of the inner rim glue 
ledge. The existing was a full 5 deg, and had plastic resin filling and 
leveling the joint in some spots, undoing some of the beveling.

Jim Ialeggio

-- 
Jim Ialeggio	
jim at grandpianosolutions.com
978 425-9026
Shirley Center, MA