laminated ribs

[Erwinspiano@aol.com]

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Ron
  By the way you sent this thru last week & I didn't have time to  say it was 
very well described & if one takes time to really anaylisze the  dynamics of 
this rib design the vibrational effiecncy of this  shape  rib seems ... 
transparent.  
   The way you described it made it crystal clear in my  thought process  & I 
hope others.  I catch on quick after a long  time!
  What about using the same approach with a solid rib.   The only difference 
in our procedure as to shape  has been not  using as much of a straight taper 
at the rib end. 
    Vibrational waves emanating at the bridge &  radiating outward is all 
s.o.p. thought and this rib design whether it be  laminated or not seems to aid 
the idea of the soundboards center as the starting  point for vibration & also 
showing the most movement. 
 
  Dale


>   Are we say the same thing in a different  language?  i.e..  A one inch 
> square rib until  the  taper begins?.  Then it becomes ...tapered?
>    Dale

Almost. Crowned top, flat bottom, taper feathering. I cut 'em  
to depth on a table saw, so the thickest part is in the 
middle. I make  no attempt to keep the section depth constant 
through the center, and  would prefer not to even if I could 
easily do it. They're a taper of one  sort or another from the 
center point to just inside where they meet the  rim. I want 
them to bend as uniformly as possible, like a bow, so stress  
is evenly distributed and vibration response is from the whole 
rib  (and membrane) at once. At least, that's the intent.

Make a 1/3-1/3-1/3  taper-straight-taper test rib, and another 
of the same dimensions with  conventional tapering. Support the 
ends and load the center. The taper  feathered rib forms a nice 
smooth continuous arc, or if it was constant  radius crowned to 
begin with, it deflects to a nearly straight line under  the 
right load. The conventionally feathered rib shows a tight 
bend in  the feathered sections, a relatively straight run, and 
a relatively tight  bend in the center where the load is. The 
tight bends are the high stress  areas. while the relatively 
straight sections aren't responding like they  could. The 
conventional rib shape just wasn't very well designed as a  
load bearing member, which is why I use the shape I do. It 
does what I  think I want it to do.

If I had an easy way to do it, I'd probably  crown the bottom 
of the rib too, but the taper is easy and quick with a  router 
jig, even though it buries me in chips, and works pretty  well.

Ron  N
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