Now my designs are finished, it is time to move onto the manufacturing stage. I have decided (with some advice from John) that I will use Fused Deposition Modelling (FDM) for the lid and CNC the casing. In order to do this I had to convert my Creo 3D drawings into STL (stereolithography) files. I also had to add a flange to the casing. This is to allow the underside of the 3D model to be machined out first and provide a flat surface for me to flip it over to machine the top. This is basically a 3mm thick base. I added a flange to the top and bottom parts of the casing.
Converting to an .stl file is relatively straightforward. I first had to save my flange file with a new name, then re-save and change the file type to a .stl. This brings up a dialogue box to allow me to export it as a .stl. After it has been saved, the shape of the 3D model has triangles covering the surface. These provide the geometric reference points that the CAM machines use to create the 3D model. The picture below shows this.
My lid has now been manufactured on the FDM machine. This involves very fine strands of melted nylon built up in layers. This process has created a few problems with my finished piece. The surface of the circle detail has ridges and I think that might have something to do with the rounded corners I'd put on. There are also some slight holes on the insole detail. I'm not sure what has caused this. Under normal circumstances I would have left these minor faults as I am short on time. But I'm concerned that I haven't made the slot big enough for the USB metal part to fit into. I seem to remember John Stanley telling me to check the dimensions after he helped me, but I'm pretty sure I forgot. I can only put this down to rushing and stressing to get it on to the FDM machine. I am usually so meticulous with things like that. I've changed the depth and think I shall try to get it redone on Monday. It didn't take long to manufacture the first time so hopefully I should still be OK for time.
I ended up creating the whole thing on the FDM machine. I was worried about using the CNC machine and the technicians were concerned that my material wasn't square enough. I didn't really have time to prepare some more material so they suggested I did it all on the FDM machine. I had to resave my casing as a .stl file without a flange as it is not needed.
The above video shows the process on the FDM machine. The brown base is support material made from starch and is dissolved in a bath of alkaline when the model is complete.
After an hour or so the support material had dissolved and I was ready to prepare it for spraying. Lots of sanding is required to get a good finish as the nylon strands cause ridges.
