Originally Posted by SLAC_Engineer
You make a lot of assumptions in your statement some of which are insulting. I'm an ME and a good one.
If you read through the post you will see that I intend to use glue. I also intend to draw bore the frame. the only 1x2's are on the side.
I am concerned with flex in the lid which is a 3 dimensional deflection and by no means a sophomoric level problem. I could solve it with complex equations from roarks formulas or I could do an FEA analysis on the lid or I could just shoot from the hip and glue a ridge back/rib.
And last time I checked, sophomore engineering classes don't discuss wood movement as a function of ambient humidity levels. Which is what I am con concerned with so as to not over-constrain the lid.
Not intended to insult. If you were a Database Engineer you probably wouldn't understand the equations. My Intent is to get you thinking through the problem to a real solution. using your full skill set.
I was quite serious in my recommendation that you get and read the USDA wood manual. A lot of folks don't have the background knowledge to fully understand the contents. You apparently do, and it will change the way you design. The base knowledge is taught in Mechanics of Materials, a sophomore level class.
Wood is a pretty straight forward material. The USDA manual has all the design values for it, including the shrink/swell rates for varying humidity.
The problem is complicated only by the frame and panel front, and back if you used it there. The panels are free floating, and don't contribute until there is already deflection enough to bind them up. So you have in essence two stringers held apart by the verticals. Assume a point load at mid span and see how much it deflects. If that is more than you are comfortable with add more wood at the top, the bottom or both.
Now analyze the top, it is long and narrow, and supported continuously on the sides by the front and back, which since you now know will carry your design load without excess deflection, you can concern yourself only with the deflection mid span front to back. The glue joint, if done right, is at least half again as strong as the wood. So you don't need to consider it.
My guess based on training and experience is: the front and back need to be beefed up a bit, and the top is fine as is.
But take the twenty minutes or less to download the book. Then look up the engineering properties of your wood and do the calcs, so you know the answer, and aren't just guessing.
This is obviously a piece you care about. Use your full set of skills to make it the best you can produce.
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