How do you draw a full-size plan for a balsa bridge?
Step by step: mark the span and height, draw the chord centerlines, place the joints, draw each member at its real width and measure the cut lengths and angles.
Updated · 1 min read
Short answer: draw the centerlines of every member at full size on paper, then add the real stick widths around them. The plan then gives you every length and angle to cut, and a pattern to build on.
Steps
- Tape down a large sheet of paper, or several sheets joined, with a straight edge along one side. Graph paper helps.
- Mark the span and the support points, and draw the height limit as a line above.
- Draw the top and bottom chord centerlines at the depth you've chosen.
- Mark the joints (the points where members meet) along the chords, evenly spaced to give triangles with good angles. See diagonal angles.
- Draw the diagonals and any verticals as lines between joints.
- Add the real stick widths by drawing each member as a strip, centered on its line. Joints are where strips overlap.
- Draw the load point, the opening and the clear space at full size. See designing around the loading block.
- Measure each member for its length and its end angles, and write them on a cutting list.
Use it
Cover the plan with wax paper and build on it. See step-by-step building and cutting accurate angles.
Check the plan against the rules once it's drawn. See reading your rulebook.