OT RE: 3D printer $179.99 (today ONLY) (Was: 8-Update

[Jim Manley]

On Wed, Dec 19, 2018 at 3:31 PM Fred Cisin via cctalk <cctalk at classiccmp.org>
wrote:

> On Wed, 19 Dec 2018, Jay West wrote:
> > Some are casting metal parts by 3d printing molds.
>
> Besides printing molds, I have heard that there is now a filament
> available that can be melted out/away, for a variant of lost-wax
> [sandbox?] casting.


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!).