<VV> Looking for a small casting operation

[Tony Underwood]

At 02:23 PM 4/5/2011, Grant Young wrote:
>Hi. I am searching for a casting company (or someone will to try it) 
>that will do
>small batches of metal carburetor parts, using an original part for the mold.
>The metal type is not critical.I need a few 1953 Corvette Carter YH 
>carb choke cable
>mounting brackets. For those not aware of what goes on the Corvette 
>parts market,
>it is strange (and often grossly inflated) to say the least. I can 
>buy a complete core for
>less that the parts on it (but that still leaves me short of the 
>parts). Thanks for any leads.
>The Carbmeister



Back When, while in the military, I spent a lot of spare time at the 
craft shop next door to the photo lab (spent more time in the lab but 
that's another story).  I watched a few of the guys in the craft shop 
make castings from plaster molds.   Belt buckles, amulets, rings, 
that sorta thing.


Some of it was done from silver (mostly melted down silver coins, of 
all things) although some things like amulets and belt buckles were 
made from pot metal scrap picked out of the trash bins at the motor 
pool.   When twiddled a bit with some other metals, pot metal looks a 
lot like pewter.  And stained with certain types of oils when still 
very hot, it can take on darker hues.   Same thing with shellcase 
brass, which can look rather dynamic when stained in such a 
manner.    But I digress...

The mold form was made from plain wax.   Paraffin wax (candle wax) 
bought off the local economy worked just fine for making mold 
forms.   Once the mold form was satisfactory, a plaster mold was made 
from the form.   The metal of choice was heated in a small crucible 
until melted (using a small torch) and poured into the plaster mold 
which for one shot castings was later simply broken off the 
casting.  It worked out very nicely.

Ron, the shop manager, showed us how to make a 2-part mold that could 
be reused several times.   This worked out reasonably well with 
silver... pot metal may do equally well.   This did nicely for making 
belt buckles...


If you only needed a few brackets, like 4 or 5 or thereabouts... and 
depending on how complicated the bracket actually is, you may want to 
consider casting your own from pot metal or aluminum.  A mapp gas 
torch works out nicely to melt aluminum or pot metal scraps.


I've made wax mold forms by making a wax mold out of modeling clay 
packed around the part in question, then carefully removed (with some 
help from a misting of light spray oil like WD40).   Melted wax is 
poured into the clay mold, which is pulled apart to reveal the wax 
form that of course is used to make the plaster cast mold.   This was 
to duplicate a badge, and I used plain ordinary silver solder to cast 
the dupe after using the wax form to make the plaster cast, from 
which I cooked out the wax since it was a one-shot deal and didn't 
care about the wax form once the mold was made.   Two-part plaster 
molds need some sort of alignment pins or dowels... in one small mold 
I made, I simply used toothpicks snipped to length in one half of the 
plaster mold which was then "greased up" and the other half of the 
mold was poured on top, to allow the halves to come apart 
easily.  Afterwards, the tooth pick guide pins (this was a pretty 
small mold) kept the mold halves lined up nicely.

Now, all that being said:

I have also used GE RTV-11 silicone to make casting molds, although I 
used epoxy resin to form the product (after oiling the inside of the 
mold).   RTV-11 uses a catalyst to cure quickly.  Uncured, it pours 
like pancake syrup and when cured, it's like plain silicone 
rubber.   It will stand up to temps of around 700 degrees easily 
enough, which will allow silver solder casting.   It will, however, 
start to break down if it's exposed to temps much above 800 or so, 
which is around the melting point of pot metal... so, not sure how 
many times you could use an RTV-11 cast with melted pot metal.   I 
did this sorta thing with epoxy (JB-Weld) to reproduce control knobs 
for survey laser products which got broken often and were rather 
difficult to obtain, worked out nicely.   Made one from molten 60-40 
solder once just for the heluvit and it came out well.

...your own personal mileage could well vary.



This might sound labor-intensive, but if you need a small batch of 
parts, it could well be cheaper to make them yourself than have to 
deal with a foundry somewhere who might only do the job if several 
hundred of the product were ordered etc.



tony..