After being in a programming rut for a while, I put the 3D printer project on hold, and decided to put more concentration on producing my stepper driven linear actuators. Although my current endeavors do not particularly pertain to robots, lost foam casting can be used to make parts for robots, so hopefully Parallax won't mind me being a little off subject, because I am more or less writing about this for the robot builders benefit.
Over the last several years, I have only dabbled with aluminum casting here and there, meanwhile studying the subject of casting quite intensely, and for the first time, I will be attempting lost foam casting. The part that I will be casting, is really quite labor intensive to produce with my limited amount of machinery, requiring a lot of machining and drilling. So instead of machining several components and screwing all the parts together, I have decide to cast it as a single part. Let me just say that the part is fairly small and quite complex (1-1/2 X 1-1/2 X 3).
Since I am considering production, I want to be able to create my molds and cast them as quickly as possible, by any means necessary. In my case, I will have to improvise and create new tools. In many instances, molds are made by cutting large sheets of foam with a hot wire foam cutter, but I will not be using a hot wire foam cutter. As mentioned, the part has a rough dimension of 1-1/2 X 1-1/2 X 3, so instead of buying a huge sheet of foam, I am using small foam blocks used for floral arrangements. These foam blocks will be cut to rough size, with the aid of a band saw, and lightly sanded with a back and forth motion against a sheet of sandpaper glued to a piece of laminated flooring. For further cuts and dissection, I have created custom sawing jigs. These jigs are simply coping saw blades glued to accurately machined spacers, glued to laminated flooring, and may or may not have a back stop. In total, I had to create seven of these particular types of jigs, for the various cutting operations. However, I cannot accurately perform all cutting operations with these jigs, so I am currently in the process of creating a small router table from a Dremel rotary tool and a broken drill press, and instead of using a router bit, for routing, I will be using a carbide PCB drill bit(0.025 Dia.). This router table will be used to cut various rectangular holes and perform various trimming operations, with the aid of router templates.
When the molds are completely machined, all the surfaces will be lightly sanded with an emery board, commonly used on finger nails. After sanding, a sprue, riser, and vents will be added to each mold, although this will require a little experimentation to achieve the best results. Upon adding the previously mentioned items, the mold will be coated with two coats of thinned down lightweight drywall compound. To facilitate faster drying drying times of the drywall compound, I will be creating a makeshift drying chamber from several concrete blocks and a space heater, with a maintained temperature of 100 degrees. When the mold is completely dry, the mold will be placed in a bucket of fine grain sand and then the bucket will be vibrated, so that the sand tightly encapsulates the mold, to prevent mold blow outs. To maintain proper pressure when pouring the molten aluminum, an open ended soup can will be placed over the sprue.
Since I lack the proper facilities to efficiently do my casting, I will be creating several makeshift furnaces. These furnaces will be made by digging several six inch holes in the earth, with a post hole digger, with each one having a diagonally run three inch hole intersecting with the bottom of the six inch hole, to accommodate forced air for a hotter burn. The entire furnace assembly will be constructed from HVAC duct work and surrounded by dirt, with the exception that approximately three inches of the six inch duct will extended above the earths surface. The bottom side of the six inch duct will have a duct cap to facilitate easier cleanup and the top side of the duct will have a duct cap with a two inch hole in the center to help retain heat, but still allow it to burn. For fuel, I will be using charcoal.
I will add more to this thread as I progress.
Any comments? :)