Saturday, April 16, 2011

Back on March 6th...

A little over a month ago (check the post of March 6th) I started a little experiment and posted the picture shown below.

Well the results are in! I can answer the puzzler that was posted with it. Maybe some of you figured out that these two boards crossed at right angles and pined together with 5/8" diameter pegs was to simulate the full sized joinery that will be used on the 32' South Wayne bridge. The boards were "green" at over 30% moisture content. The test was to confirm that when the wood dried and shrunk the area around the pegs would split in both pieces and severely reduce the strength of the lattice in bridge truss.

As a rule wood shrinks the most across the annual rings and little to none, grain wise, from end to end (arrow direction in picture above). In the picture,  you can see that the bottom piece grain would hold the pegs in place while the top piece would shrink causing the pegs to split the wood. The same results would happen to the bottom piece because the wood grain is at right angles to each other. Two drywall screws were placed in the "green" wood across the width grain in each piece and using a dial caliper a careful measurement made and recorded. This piece was then placed behind the wood stove for the next month to dry out the wood. What happened? Not much!

 I thought they would pop like a chess nut roasting in the fire. After a month of drying the moisture meter showed the boards now had less than 10% moisture content. 
  Re-measuring the screw distance it is clear that the wood did shrink by almost 1/8" and I did notice some cupping of the wood but no splitting at the pegs.

  I still agree with Milton Graton's  take on potential problem shrinking wood could have on the lattice structure strength and we will still have the bridge truss material Kiln dried down to 17%. I may try this again with full sized 2" x 10" material and 1.5" diameter trunnels to see what happens.

Puzzler - Just how much "fun" will it be to change the South Wayne bridge roof design to go with cedar shakes instead of a metal roof? This will be some "serious fun" new learning!

Tech Vocab - square - 12 by 12 bundle - 9 by 9 bundle - hand split - resawn - shake - shingle - premium - No. 1 - heavies - mediums - 18" - 24" - 3/4" butt -  1/2" butt - exposure - 6d box stainless nail - interlayment - underlayment

1 comment:

  1. Thanks for the ideas. There's always something new to learn and improve on in this mad internet world. Uptiming is surely something to keep an eye on. moisture meter

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