Could not send message to USER: jennfee Reason for Mail Failure below: ******************************************************** Message not Delivered. Recipient's Mailbox Over Quota. ******************************************************** ---------------------- multipart/alternative attachment Frank: I have not participated in this discussion simply because it is over my head. I'm learning, not teaching. However, if you think if compression as the state where something is smaller than it wants to be, and tension as something being larger than it wants to be, that can simplify the engineering definitions. If a traditionally crowned board is held smaller than it wants to be, it is under compression. On this board that is constrained by the rib, the bottom is smaller than it wants to be because of the rib. The top is smaller than it wants to be because of the bottom - and the fact that it is one piece, this panel. If the top, although it is larger than the bottom, it's smaller than it wants to be, so it is under compression. Does this make sense??? dave *********** REPLY SEPARATOR *********** On 9/27/99 at 12:01 PM Frank Weston wrote: Richard, Forget humidity. Forget made up numbers. Do this. Tape a flexible steel rule onto the end of one side of a spruce stick (a wooden yard stick will do for demo purposes). Mark the opposite end of the steel rule on the spruce stick. Bend the spruce stick. Notice that as you bend it, the mark on the spruce changes position relative to the steel rule. If the rule is on the outside of the bend, the spruce gets longer. If it is on the inside of the bend, the spruce gets shorter. If the spruce is elongated it is in tension, if shortened, in compression. Now, bend the spruce stick and glue another piece on the bottom. Nothing has changed. When the glue dries, the assembly will hold a curve. The outside curve of the spruce is still longer than it was originally, and it is still in tension. I hope this is simple enough for you. Frank Weston Lets say we have a panel exactly 1 meter across grain, and a rib that is 998 cm long in a room with 50% relative humidity. The panel is put into the oven and dried to the point that it is also 998 mm long. Now if we take the panel out and simply let it re-adjust to the room humidity it will "grow" back to 1 meter in length. The top and the bottom of the panel will both shrink the same, and grow back the same amounts... ok so far ?? But if we quickly attach the ribs while the panel is at 998 and then allow it to re-grow to what ever length the room humidity and this constraint from the rib allows for, its length will be less the 1 meter. (This following what I think I got from Dels description.) Ok.. assuming this is a correct picture so far, stretching a measuring line across the top of this ribbed panel after its re-adjusted to room humidity shows that it measures less then 1 meter. If, (Frank) you accept that this is correct so far, I would appreciate it very much to know the reasoning behind why this top half of the panel is not (if it is not) to be considered in compression. As initially stated, please follow Dels kind "laymans language" approach to demonstrating the reasoning. Richard Brekne I.C.P.T.G. N.P.T.F. Bergen, Norway _____________________________ David M. Porritt dporritt@swbell.net Meadows School of the Arts Southern Methodist University Dallas, TX 75275 _____________________________ ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/59/2f/af/c5/attachment.htm ---------------------- multipart/alternative attachment--
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