Rib dimensions

[Don A. Gilmore]

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Hey Jude:

The area moment of inertia is only dependent on the crossectional shape =
and size and not on the material.  So if you can find a standard set of =
formulas, they are good for any material.  Most common crossections are =
here:

http://www.efunda.com/math/areas/Common_Geometric_Shapes_Index.cfm?search=
_string=3Dmoment%20of%20inertia

You can also easily calculate compound crossections made up of any =
combination of these fundamental ones.  I can show you how to do that =
too, if you're interested.  The units should come out in "length to the =
fourth power", like inches^4, or m^4.  Be careful not to use the "mass" =
moment of inertia as that is used for dynamic calculations and is in =
units like lbm-ft^2, slug-ft^2, or N-m^2.

One psi =3D .0703 kg/sq.cm
One kg/sq.cm =3D 14.23 psi.

I don't think I understand your angle question.  60' should mean "sixty =
arc-minutes", which is one degree.  What does your jig look like?

Don A. Gilmore
Mechanical Engineer

----- Original Message -----=20
  From: Absolute Piano=20
  To: pianotech@ptg.org=20
  Sent: Wednesday, December 10, 2003 3:40 PM
  Subject: Rib dimensions


  Hello,

  I'm trying to apply some science to my soundboard rib making and I am
  looking for "tables of static values for  the Resisting Moment (W) and =
the
  Moment of Inertia (I) for all the possible cross sections of sugarpine =
and
  spruce (DIN 1052 Class I will suffice).

  What is the formula for converting pounds/inch squared to kg/cm =
squared?

  Given a right angle connected to the outside of an arc of a circle, =
how do
  you prove the circle is 60'? (I made a jig for crowning ribs that is
  adjustable and I want to calibrate it.

  Thanks,

  Jude Reveley, RPT

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