Building it right the first time:
The cutting template is used to cut and join your wood with precision and ensures that the amount of wood received is used optimally to only a small amount of wood left after the completion of the bridge. Pupils normally get the cut and build template right after their second or third attempt.
Pupils who want to have their design approved first time round must be prepared to put in the required effort to combine the competition specifications, their CAD shape, basic structural theory of force transference and member reinforcement as well as the measurement of the trusses total length in mm to not exceed 6500mm - 6900mm.
Step by step:
1) Paste the 8 typing sheets together with Cello tape in two rows of four sheets by slightly overlapping each sheet with the other and taping the overlapped section on the back. Pritt can also be used.
2) Draw a horizontal line 210mm from the bottom edge of the template. This line will be known as the "level plane" and will indicate the imaginary line between the desktops.
3) Find the middle of the level plane line and mark it with a small cross. This will be the exact middle of your bridge.
4) Draw two vertical dotted lines 375mm left and right from the cross in the middle of the line on the level plane to indicate the actual total length of the bridge that needs to be built.(750mm long and resting on the desks.)
5) Indicate the area of where your bridge legs will sit on each desk with light cross hatching at the point of contact between desk and bridge. (This is done to know where to reinforce the 50mm area on each side of the bridge where the top compression member transfers the load into the desk "abutment")
6) Draw two vertical dotted lines to indicate the "gap" of 650mm of clear space that needs to be crossed between the desks. (This is to show the designer the area that may be used to reinforce the bottom section from the level plane downward as the loading harness exerts a bending force on the level plane and is similar to what a ravine would be for a real bridge.)
7) Draw a dotted line 80mm below the level plane. (To indicate the maximum depth that you may build below the level plane.)
8) Draw a dotted line 250mm above the level plane. (To indicate the maximum height you may build above the level plane.)
9) Draw in the two Drums (turned down D shapes) of the loading harness as indicated on the loading harness diagram. The two drums are 50mm wide, 50mm apart and 30mm high. The drums are drawn in to ensure that diagonal members do not obstruct the drums of the loading harness when crossing over the harness and that the harness will physically fit through the sidewall of the bridge.
10) Draw your bridge exactly as you plan to build it after Mr. Buys has discussed its shape with you. (Draw each member to its actual size i.e. 4mm) (Double or strengthened members must be drawn as double members separated by 10mm spacers every 50mm apart in between the double members. See the specification diagrams.)
11) Measure the length of the members in mm, it should not exceed 6500mm - 6900mm as you still need to leave wood to use as spacers for the double / reinforced members as well as wood for cross bracing and diagonal cross bracing between the trusses.
12) Check that you have reinforced the top compression members; the level plane and the area directly below where the loading harness fits.
13) Ask Mr Buys to check your cutting template for obvious and key mistakes with regards to shape and design. He will approve your design to in terms of some basic things such as the length of the structure (750mm), that the structure will sit flat on the testing desks, that the height above the level plane does not exceed 250mm, that you have drawn the members to their actual with of 4mm, that the distance below the level plane does not exceed 85mm, that the top compression member is reinforced all the way to the desk abutment, that you have physically measured the total length of wood used for one truss and that it does not exceed 6500mm - 6900mm.
14) After your template has been approved you may use your approved template to receive your wood for the competition from Mr. Buys who will sign it off on your template.
