Pewter trinket cast in ABS

thingiverse

Just as much an exercise in mold design as anything else.. Instructions This post is a continuation of my original attempts to cast metal in ABS molds. http://www.thingiverse.com/thing:286521 The design began life as a torus (in Blender), twisted around with the Simple Deform modifier. It looked nice but how could I possibly design and print a mold for this thing? Luckily, a basic sphere shape fit the requirements for a core. After printing the parts all the cavity areas in the core and in the box sides are accessible. This allows all support structures to be removed before assembly. Either no-support, or accessible-support in the cavity is absolutely required in a mold of this type. Otherwise, not only would there then be plastic embedded in your finished casting, but any support in the metal flow path will slow it down or stop it, as well as inhibit gas escaping.. The core (that ball thing) and the box sides will need to be cleaned up before they can be assembled into a tight mold. There is no clearance built into the design. The slightest printing defects will prevent the mold from closing all the way. Use sandpaper, a Dremel, or whatever to take down any high spots until there is a good fit. There is an opportunity to clean up the cavity itself. 3D prints always show layers and unless this torus thing had a snake's head the scaly texture is probably undesirable. But ABS is certainly not wax, and it's really tough (for me) to shape or smooth things out at this stage... Assembly: The ball-core is aligned by way of an off-center hole and pin through all 3 parts. I had some 4.5mm (0.18") aluminum rod handy so that is the size of this hole. No hot metal contacts this alignment pin so the rod can be substituted with a drill bit, a printed plastic rod, or anything else that fits... (included an STL to print a pin) Print took 150 minutes at 0.20 layers, 35grams ABS. Also pictured on the build plate is a "sacrificial" pin so the extruder doesn't hover over the ball shape, and allows it some time to cool between layers. Despite that, I did see a little softness and used forced air cooling on the last several layers of the print. Pewter (mp 466F) was poured a little on the warm side at ~540F because I felt the thin sections, tortuous metal pathway, and lack of venting might cause a short pour (aka an unfilled mold). ABS prints have almost no porosity (for gas escape) so I cut an additional vent at the top and routed out that chain-hole / vent with a tiny round Dremel burr. I recommend you do it too. I'm not gonna mess with the STLs now because Blender can be very finicky about remodeling things. After the pour, I sliced off the sides of the mold with a band saw and then clipped away as much plastic as I could without endangering the casting. Then it was put in a small jar of acetone and the ABS dissolved. With mild agitation it didn't take too long.. maybe 90 minutes with one change of acetone.. ,,,,,,,,,,,,,,,,, This was just a quick write up and I know I forgot to mention a few things so feel free to ask questions if something is less than clear..