## Friday, May 20, 2011

### Jigsaw puzzles anyone...

The time and energy spent assembling the 3/8 scale model several times for practice will prove its value later when we are working with the real 20 foot long 2 x 12 chord pieces that make up the lattice trusses for the South Wayne bridge project.

Here Alex and Lynnan are pinning together chord layers 1 and 2 using two inch long trunnels. After figuring out the numbering and playing card identification system they carefully layed these two layers and will place one shortened trunnel into each group of three holes.

At the top of the picture, behind Alex you can see layers 3 and 4 in their bundles. Very important not to mix them up.

With the layers 1 and 2 secured the first web layer, layer 3 was put in place and secured with a single trunnel in each end. This trunnel was three layers long.

After a little head scratching and hunting the process was in full swing. Layer 4 in the truss goes on.
The "pile of parts" in the picture above is something I hope we learn to avoid when we do this with pieces that are three times this size. The web pieces they are holding in the picture above will actually be 15 foot long 2 x 10's!). This would be a good time to use those math skills and calculate the board footage ( ( T" x W" x l ' ) / 12)= bd. ft. . Then knowing that KD Pine weighs in at about 2 pounds per bd. ft. find the weight for each web piece. Or you could just guess - 10 - 20 - 30 - 40 - 50  pounds each?  The goal is gain the understanding that packing the layer pieces will be as important as putting them together. It will be another teachable moment.  Oh, did I mention the actual trusses are going to be assembled in place over the waterway at South Wayne! There will be no nice blacktop like this to walk around on.

These guys are good! After just 1.5 hours there progress and what they now understand about the assembly has come a long way. Mention the word Camber to Alex or Lynnan or the process of using shortened trunnels as "drift pins" to assemble the truss layers and they get it!

They ran out of time for the day but I assured them that I would dis-assemble their work, re-bundle the pieces and they would have another opportunity to have some more "serious fun" and try it again. This time finishing the full assembly without any help. They said they were up for the challenge!

Puzzler - What is the difference between the two clamps in the picture below and how are they used in truss assembly?
Tech Vocab - Drifts - Camber - Chord - Web - Trunnels - Vaseline