Monday, March 29, 2010

#003 07 Clear Creek Timber Howe Truss Bridge - The Drawings Part 3

Howdy!  A quick correction before we start.  I realized later when looking at my timber stock that I had incorrectly drawn the bridge base timbers at 12" deep, when they should be 18" deep.  This has been corrected.  This is what I don't like about making drawings.  One little mistake will cost you lots of time and material.  Be careful!

F.  Draw the bridge base.  The bridge base is the surrounding frame that joins the two truss assemblies.  These require strength and squareness.  I first started with the long beams and then the cross members.  While looking at Wolfgang's model I noticed a gap in several spots.  This is when I started getting concerned that nothing was holding the bridge together from side to side.  Going back to Harry's drawings I realized that he left out the cross members.  This is something a judge would catch easily.  The reason it happened is probably because the timber size for these pieces is not listed on the drawings.  When making drawings step back a second and ask "would this really work?" or "if I'm building this how would the engineer actually build it?"  Little thinks like cross beams stick out like a sore thumb.  He left the tie rods on the bottom out, too.  Never build from someone else's model, but learn from what they did.

G. Draw in the details.  Same as the previous section we need to put in the tie rods and the nbw's.  We've put a section of the truss upright in the drawing so that we can match the nbw's to the tie rods.  This points out that I drew the nbw's in the wrong size, so those will have to be corrected.  Are you starting to learn that I'm not a draftsman or engineer?

H. Make a list of materials needed.  This time we have to keep in mind that the truss sides are already built.  We only need the new materials.

That's all for now.  Next time we'll start on the upper deck and put in the outriggers.  If you know the proper name for these things, please let me know.  Is it a queen post?

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