## Sunday, February 27, 2011

### Welcome to the clamp factory...

I thought they must be kidding when in Milton's book, he said that they used three hundred clamps in building the 140 foot long Union Street bridge (Woodstock, Vermont 1969-1970) ! Each clamp was made of two pieces of 2" x 3" hardwood, and two 5/8" rods.  Do the math on that. How many board feet of materials just to make the clamps? How many linear feet of 5/8" threaded rod? A lot!

In the making of this 3/8 scale model I had to just about set up a clamp factory! No kidding. If you have been following along you know that 3 clamps are need to hold and align each joint in the chord lamination assembly. There are 14 of those. Then there are the chord ends, 8 of those. Then another 18 or so used to align and hold the second layer, web members and first chord layer together. Whew!

For the 3/8 scale model, the clamp material came from the "scrap" pieces ripped from the 1 x 6 boards used to make the chords (3/4 x 4.5"). Using a simple stop block on the miter saw the 3/4" x 7/8" strips were cut to length. Making a simple fixture (shown in the picture above) on the drill press each piece was located so the holes could be drilled. Not rocket science, but a good exercise in problem solving. We'll see how the students tackle this for the real bridge project. For the 3/8 scale model the long clamp pieces needed to be 6.5" long and the short ones 3.5" long. The lengths for the full size bridge clamps are pretty important and will need to be carefully calculated if they are to do their job and not get in the way during the assembly process. Something I appreciate so much more from the experience of building the 3/8 scale model.

Puzzler - So just how many feet of material will be needed for the bridge clamps? How many 3' long 1/4" threaded rods will be needed? 1/4" flat washers and nuts?

Tech Vocab -       1/2 -13  NC Thread