Rib dimensions

[Sarah Fox]

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Ack!  I thought that was off list!  Sorry....

BTW, Just another thought about measurements:

It would probably be best to do these measurements without the influence =
of gravity.  To do this, turn the rib on its side and clamp it to a =
straight board.  I really have no idea, from a practical perspective, =
how stiff these ribs are, but I would think the "height" measurement on =
a long rib could be skewed quite measurably by gravity.

Peace,
Sarah


  ----- Original Message -----=20
  From: Sarah Fox=20
  To: Pianotech=20
  Sent: Thursday, December 11, 2003 2:33 PM
  Subject: Re: Rib dimensions


  Hi Ric,

  You're right!  You came up with the same thing!  (duh)  8-P  Of course =
I did make it more user friendly.  ;-)  I think you have too much faith =
that people know how to use mathematical formulae without being given =
detailed instructions.

  I also think...  that you enjoy mathematics far more than you let on!  =
I always enjoyed things mathematical -- very satisfying to solve a =
difficult problem.  My dissertation was very mathematical as well.  I do =
recognize others who have caught this bug!  ;-)

  Peace,
  Sarah

    ----- Original Message -----=20
    From: Richard Brekne=20
    To: Pianotech=20
    Sent: Thursday, December 11, 2003 1:50 PM
    Subject: Re: Rib dimensions


     =20
    Sarah Fox wrote:=20

      Hi Terry, OK, here's a more user-friendly method for you that will =
give you the correct position of the rib anywhere along its length.  =
(You can also use this method to plot out points on a template.  Compute =
numerous points and connect the dots.  :-) Clamp any part of the rib =
against a flat surface, concave side up (soundboard side down).  With =
this arrangement, let: h =3D the height of the rib above the flat =
surface r =3D radius of the rib d =3D the distance along the rib you are =
measuring, with respect to the clamp point.  For instance, if you clamp =
in at the middle of a 4 ft rib and measure at the end, d would be 2.  Of =
course this is approximate.  More accurately, d would be the distance =
from the clamp point to the position on the flat surface, directly =
underlying the measurement point.  (Think right triangles.) Then: h =3D =
r - Sqrt ( r^2 - d^2)=20
    Which is exactly what I wrote in my last post, exept I didnt specify =
that you could measure anywhere along the rib... figuring that was kind =
of self explanitory.. :)=20

    ""You could also do this simply by   r - Sqrt( r ^2 - (0.5L)^2)   L =
being the length of the rib. ""=20
     =20

    What I thought was neat about all the replies... is that we came out =
with two basic approaches... solving for crownheight, and solving for =
radius. So you can check either way you set up your rib jig. If you want =
a 60 foot radius.. then use the above... if you want to use a certain =
crownheight and want to be sure what radius you are imposing.. then use =
the formula Ron N put out.=20

    Cheers=20
    RicB=20
     =20

    --=20
    Richard Brekne=20
    RPT, N.P.T.F.=20
    UiB, Bergen, Norway=20
    mailto:rbrekne@broadpark.no=20
    http://home.broadpark.no/~rbrekne/ricmain.html=20
    http://www.hf.uib.no/grieg/personer/cv_RB.html=20
     =20

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