On Wed, Dec 19, 2018 at 3:31 PM Fred Cisin via cctalk <cctalk at classiccmp.org> wrote: PLA (polylactic acid) will easily evaporate/burn if you pour molten metal into a sand mold packed tightly around a 3-D printed positive (pattern) made of that material. Be aware that you need to allow for the pattern's dimensions being about 4% larger than those of the final part's, for aluminum after it cools, due to its high thermal expansion coefficient (or contraction, in this case). The coefficients for other metals/alloys have to be looked up, but will generally be less than aluminum's, which also has one of the higher melting points. There's a YouBoob video from a few years ago somewhere that I can't find any more, made by a crazy guy in Idaho. He shows the whole process for making a large CNC lead screw bearing mounting part, from a 3-D printed pattern, including mixing plaster with sand using an electric hand mixer in a stainless steel bowl in his kitchen (obviously a confirmed bachelor, or he has the most awesome wife _ever_!). He also shows how to use small pieces of cut-up rigid insulating foam to form channels (where molten metal enters) and chimneys (where gases from pattern/channel/chimney materials evaporating/burning escape). Best of all, he's in his fuzzy slippers outside on snow with an aluminum high-temperature firefighters pants, jacket, and hood on, pouring molten aluminum (with pieces of copper pipe melted in to improve pourability) into a sand mold from a crucible heated in a homemade furnace. The latter was made from a 20-gallon steel barrel found in the dump ... I mean, "recycling center", into which he had poured a cylinder of firebrick mortar formed by a smaller steel barrel placed in the center of the larger one as a form, which was removed from the inside after the mortar had hardened. He referenced a website that shows how to make awesome propane burners from cut and drilled iron pipe, then showed how he cut tangential holes through the barrels and had inserted a pipe through the holes before pouring the mortar, the same diameter as the burner. The combustion gases would then swirl up around the crucible inside the mortar cylinder for the fastest melting of the metal, when the burner was inserted through the tangential holes and where the placeholder pipe had been. The money shot is when his Husky/Malamut keeps walking back and forth, in and out of frame behind him during the video, restrained by a chain attached to an elevated wire line, and then at the end the dog sits down. The dog is looking at him with this priceless, straight-man expression with narrowed eyes and appears to be thinking something akin to, "Are you done with this foolishness yet, so we can go inside to get some chow and warm up?" BTW, he cited his source for all of his knowledge as the WW-II era U.S. Navy manual for casting metal, from back when sailors just made whatever parts were needed. They had well-equipped and stocked shops on larger ships and tenders, with furnaces for casting all the way through lathes, milling machines, and drill presses for final machining. Those manuals are on-line and contain a wealth of industrial technical information about every facet of metalworking, electricity and electronics, radio, steam and diesel engineering, etc., but in language that boys off the farm could understand quickly and comprehensively. I sure hope that there are copies stashed in that critical human history document vault, that the Long Now Foundation (LongNow.org) is building, with a mechanical clock that will be able to run for 10,000 years with no maintenance, to be installed underground in a remote part of West Texas (kinda redundant, I know!).

Another nice resource for casting, especially for aluminum and for amateurs, is the famous series by Dave Gingery on how to build machinery (lathe, mill, shaper) from cast aluminum (recycled aluminum scrap). I have a couple of his books; the full series starts with how to make a foundry using charcoal for fuel, and goes on to making a lathe, then a shaper, then a mill, and more. Neat stuff. Lindsay Publications used to print these, but Lindsay retired and that company closed down. I did see Gingery's books still in print via some other path more recently, though. paul

There?s a lot to be said for the Navy manuals because we (22 years in my case), as all of the branches of the military and, increasingly, industry, have had to educate our enlisted people in STEM principles, concepts, practices, and skills. That?s because the K-12 ?education? system has largely punted on doing this because it?s largely run by people with humanities degrees and teaching experience. Kids are more likely to be asked how something feels about being oppressed by gravity and jackbooted thugs that walk on them, rather than calculating the force of gravitational attraction, per g*M1*M2/(r^2). I know this because, following my Navy and SillyCon Valley careers, I?ve been teaching 6 - 12 grade STEM and Computing in multiple districts in four states and have been continually battling to get equitable funding and administrator/board support everywhere, all the time. One school district thought nothing about spending three million dollars for an AstroTurf football field with a state-of-the-art scoreboard and stadium bleachers, but my annual budget was a whole $200 for equipment, materials, books, software, etc. STEM textbooks were upwards of 12 years old - the periodic tables in chemistry books didn?t contain the 10 most recently fabricated elements (atomic numbers 109 - 118). The Earth and Space Science books had nothing more recent about planetary probes/landers/rovers since the Voyagers were launched in 1977 (which I witnessed). On-line/optical-digital companion material didn?t exist for any of the STEM textbooks at any price. I could have taught at universities and colleges, but I discovered that none of the students were from the local region because they just didn?t have strong enough STEM academic performance to be able to succeed at the post-secondary level. I suspect that the administrators of these institutions were also swayed by foreign students whose authoritarian governments are more than happy to pay full freight in tuition, etc., because it?s not their money, anyway. The result is that tuitions, fees, etc., are rising even faster than they had been due to loan guarantees, grants, and scholarships. I?m doing as much as I can as a lone voice in the wilderness. The humanities types are complaining that my incessant howling is oppressing the snail darters, though ...