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People have been talking about a "jig" to connect the two sides of the bridge, what exactly is this? My main problem is having the two sides of the bridge at the same height, which doesn't happen. Therefore, the load is applied more to one side, causing a horizontal force to be present. The bridge (obviously) isn't designed to withstand horizontal force, so it breaks. How could I fix this? Thanks.

stickyglue wrote:People have been talking about a "jig" to connect the two sides of the bridge, what exactly is this? My main problem is having the two sides of the bridge at the same height, which doesn't happen. Therefore, the load is applied more to one side, causing a horizontal force to be present. The bridge (obviously) isn't designed to withstand horizontal force, so it breaks. How could I fix this? Thanks.

A jig can be any of a variety of tools you use during construction of the bridge to temporarily hold pieces in place while you glue them together. At it's very basic concept it can just be a block of wood a certain size that you lightly clamp the 2 bridge sides to so you can glue the cross members to the sides.

stickyglue wrote:People have been talking about a "jig" to connect the two sides of the bridge, what exactly is this? My main problem is having the two sides of the bridge at the same height, which doesn't happen. Therefore, the load is applied more to one side, causing a horizontal force to be present. The bridge (obviously) isn't designed to withstand horizontal force, so it breaks. How could I fix this? Thanks.

It's not exactly a "jig", but we use this fixture to help hold things in place while being fitted & glued.

See page 221 of https://c10645061.ssl.cf2.rackcdn.com/p ... obigbk.pdf

Thanks, would this also be used to fix the other problem?

stickyglue wrote:Thanks, would this also be used to fix the other problem?

Yes, a jig or fixture would ensure the sides are even when you glue them together.

stickyglue wrote:People have been talking about a "jig" to connect the two sides of the bridge, what exactly is this? My main problem is having the two sides of the bridge at the same height, which doesn't happen. Therefore, the load is applied more to one side, causing a horizontal force to be present. The bridge (obviously) isn't designed to withstand horizontal force, so it breaks. How could I fix this? Thanks.

One thing I have used as a VERY effective jig are LEGOS. When stacked and pushed together sufficiently, the create a near vertical face to build off of and can also be used to create "right-angle" jigs as well. Another thing I have noted is that 1/8" balsa and bass wood fit tightly between the studs. Those can be used to hold pieces in place. The only downside i find is that you cant touch it at all until the glue has dried.

I'll second the Lego idea... By building square "Columns" stuck to the boards provided, they hold the 2 sides of the bridge perfectly vertical while applying the lateral bracing. If you have a big enough base plate, or you get creative and figure out a way of attaching a couple of baseplates together, you can even stick end gates at both ends to align the two sides in the Y axis as well. At this level of competition, it is critical that both sides of the bridge are symmetrical. If you are going to lean one side in toward the center, the other side must lean in at the same angle. Depending on your Lego assortment left over from your childhood, there are pieces available to help set up a form to lean the sides in symmetrically as well.

We are lucky to have our own 3D printers and we use jigs for literally everything related to bridge building. In its essence, we build each individual beam of the bridge using a jig to hold them together, place two of those into another jig for cross bracing, use a third jig to cut the top pieces at a precise angle, and use a fourth jig to hold all three components together when we glue them.