West Point Bridge Project
In this project me and my partner worked on creating the West Point Truss Bridge in the Designing and Building File-Folder Bridges text book. To create the bridge we used CorelDraw for the laser cutting files, we cut the files on the Epilog Fusion pro with chip board, we then super glue to combine all the pieces, testing machines that were already made, and more to help create and test this project.
Project files
Links
These are the two links me and my partner used. The first link is to the creation of the West Point Truss Bridge with a step by step process and has more from the text book, the bridge activity starts on page 29. The second link is to the testing of each component and how to calculate tension and compression.
Link one - https://drive.google.com/file/d/1U-qYN7UlromiVJHNW5YgojewDLzHpwhw/view
Link two - https://drive.google.com/file/d/1LMC12pQCbDvp1IINIDdDsdBUThj_z2NZ/view
Files
In this photo you can see the file we created on Corel Draw to cut out each support beam for the bridge. The red lines are scored so we could fold them, and the black cut all the way through. From the top down: 6mm x 6mm x 9cm, 6mm x 15mm x 10cm, 6mm x 10mm x 12cm, 10mm x 10mm x 17cm, 10mm x 10mm x 21cm. The first two values are of the rectangle they create top down, and the last value is the length.
In this photo you can see what the gusset plate file looked like. The file did not include the numbers or any of the text on the bottom.
Workflows
Epilog Fusion Pro - https://docs.google.com/document/d/1qD0LRhzoDkfVyfnCCNbM-DmZQnyk_Nr_hm7WTA6FlrM/edit
Epilog Fusion M2 - https://docs.google.com/document/d/1GOyWMEj3ViTaLE_5XUlAyPPT1OH4zOMdRdKFBexndLw/edit
Using the laser cutters
For the gusset plates we cut on the Fusion Pro and imported the cardstock cut and vectored the whole file and at this point we were able to us auto focus on the laser cutter but eventually we had to manually focus it by drooping a plunger on the laser and raising the bed to touch the plunger. For the support beams we used the Fusion Pro and we set the file to vector by color and we imported cardstock cut for the black and cardstock score for the red. From Fab Academy I tested the kerf on the Fusion Pro and determined that the value is so small that in this case there would be no real affect from it.
Part Processing
Blueprint
To help plan out the bridge we created a blue print on a sheet of card board. From the West Point textbook included above (page 32), we split the page into 8 pieces of paper and taped them to the card board sheet and then taped a layer of wax paper over so that we could glue and assemble the bridge on the blueprint.
Here you can see how we used the cardboard blueprint in created the bridge. You can see tape in the image which we used to help keep the Gusset Plates in Place.
For creating the support beams we used super glue to hold them together. The process was first making sure to crease the score lines and to create the beam without glue. Then lift the glue tab and apply the super glue and hold the tab down with our fingers that we covered in tape so we didn't get glue stuck to our fingers. In some cases we had to trim the beams to fit, and to do that we layered the piece over the blueprint marked in sharpie where to cut then cut with either scissors or an exacto-knife.
Constructing the Bridge
The construction was pretty easy but time consuming. To start we laid out all of the gusset plates and glued them all together with the beams.
Then one side of the gusset plates we added support beams and flipped the other side of gusset plates on it to comple one side of the bridge and we did that twice. We then laid out the middle part of the blueprint which is the top if the bridge. We glued that together and then we had to side pieces and the top. To connect them all we laid the side pieces on top of the top piece and glued one by one. Then we added beams to connect the sides of the bottom of the bridge.
Bridge fully constructed
Testing Bridge Components
To test the bridge we followed the instructions in this West Point Guide. Using the Testing machine and sand as the weight we were able to calculate the mount of force each member could withstand. The members of the bridge under tension apear to break around the middle of the member, while the members under compresion will break almost anywhere. The West Point doc linked above showes how to turn the weight of the sand into Newtons of force for compression and tension and the doc also shows and explains graphs of bridge force distrobutions.
Testing the bridge
To test our bridge we placed the bridge over a gap between two tables. To make sure our calculations were accurate we placed Legos on each of the load bearing members to make sure the load was only on those members.
The first weight we tested was 2 books that weighed 3500grams. Our bridge was able to handle that weight.
The next weight we tried was 4 books that weighed 5003 grams. Our bridge was able to handle that weight.
IMG_0370.MOVThis is a video I took of testing Griffin's bridge, the only diffrence between the way Griffin and I tested our bridges was he put all the weight on at first when I put the weight on two at a time.
Conclusion
In this project we created laser cutting files in Corel Draw, a vector based program, cut the files on chipboard. The using the pages we printed and a cardboard back we created a blueprint that we placed our cut chipboard and used super glue and West Point instructions to create the bridge. Then using the West Point guide, we used the testing machine and sand as the weight to test compression and tension forces on members of the bridge. I learned how to test members of a bridge and how to calculate the newtons of force. I learned how to calculate the load on each member if the bridge is experiencing dynamic load.