A wooden laser-cut scale replica of the iconic F40PH four axle passenger locomotive.
Skills: CAD, Laser Cutting, Parametric Design, Design for Manufacturing
For the first project in Mechanical Prototyping, we were tasked with creating some form of box for laser cutting. The requirements included using five different types of joints as well as four different types of fasteners. We were given one 24'' x 18'' sheet of 6mm plywood. In addition to the requirements, my two personal goals for this project were to use only joints that could be fabricated using a laser cutter (2D cuts only), as well as keeping my model to scale (I set this goal after deciding on the design of my box).
I'm a long time train enthusiast and fan of the F40PH, an American four axle diesel-electric passenger locomotive. I decided to make a replica of the front end of the locomotive for my project, complete with undercarriage and plow area. After creating an initial CAD model I laser cut a sketch model out of cardboard. This was my first time making finger joints connect two pieces rotated across two different planes, so the sketch model confirmed they worked as I hoped.
I tried my best to make the model to scale, and used reference diagrams in my CAD to confirm my geometry. By the time my CAD model was complete, I had integrated a number of types of joints, including finger, mortise and tenon, butt, mitered butt, and half-lap. I used primarily wood glue to join components but I also integrated a bolt with pronged tee nut, a nail, and a dowel to attach the wheels. After laser cutting I assembled the undercarriage and body separately and then joined the two together.
During the development of this project I anticipated and encountered a number of challenges. The primary initial challenge I was concerned about encountering was the fit of the angled finger joints around the nose of the locomotive. I approached this by laser-cutting a model out of cardboard. Another challenge that I anticipated was that not all the provided material would match the nominal thickness of 6mm. To account for this, I parameterized my thickness in CAD to make it easy to switch between materials and thicknesses while maintaining a proper fit. Another challenge that I had was trying to use only laser-cuttable joints. I was mostly successful except around the windows, which required some post-processing. I solved this by using one of the joints introduced in the course, by mitering the inner edges to form a mitered butt joint.
I'm extremely satisfied with the end result of this project. I was able to exceed the course requirements for the number of joints and met the requirement for hardware variety. Additionally, the model is mostly to scale (within the limitations of 6mm plywood thickness) and is almost entirely laser-cuttable. The one exception is the inside faces of the window frames which need to be slightly mitered to fit together. This compromise was made to keep the window frames in scale, as putting a laser joint would have forced the geometry to change.
