Friday, June 29, 2012

Knoty Problems

Could designing, planning and building a 32' Town Lattice covered bridge be a valuable learning experience for high school students? I believe so. I would happy to show and explain it to anyone interested in 21st Century education. The first time was a great experience and the learning continues.

For today's work some of the things to consider are:
- Sawing up the kerf in each butt joint for a tight fit.
- Laying out the lattice spacing on the bottom chord.
- Laying out the lattice spacing on the top chord, perpendicular to bottom chord.
- Orienting annual rings in first lattice layer (frown, this time).
- Layout of first lattice pattern piece.
- Cut first layer of lattice to length.

Sawing up the kerf and then driving the pieces together elminates the gap that is caused by the camber put into the chords (shown in the bottom picture). The fit is tested with a playing card used as a feeler gauge. This joint passes inspection and loads will be transfered  through the butt joint like it was a solid piece.

This way or that way? What do you think? These words strike fear in many a high school students today. However I find it refreshing to apply this to tasks in search of new learning and improvement.
On the South Wayne bridge using the lattice pattern piece I cut each as you would if you were cutting rafters for a roof. I could use the pattern to a degree to make the end cuts and avoid knots in the area where the trunnel holes would be drilled. However with the 45 degree angle and 6 inch tail piece on each end this wasn't as straight forward as it would seem.

This time I placed each lattice piece in place on the chords and then shifted them doing my best to keep any knots out of the area where holes would be drilled. I will lay on the pattern and then cut them to length in place.

This will be close. I'll let you know in the next post how "this way" goes.

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