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Vacuum casting spruing


I have been using my Neycraft Centrifuge for casting but as it is
hard for me to wInd, am considering using my Rio vacuum—the one
which uses the same table for investing and casting.

I know that I must not fill the flasks all the way to the top for
vacuum investing, but have a question about spruing. One of my books
on casting states that for vacuum casting, the sprues should be much
thicker than for centrifuge casting. Currently when I use the rubber
base with the doughnut center, I have been using 8 gauge for the
sprues. When I tree the models I have been using trees 3/8", for
several models, and 1/4" for about 2 models. Is my current spruing
method sufficient for vacuum casting?

Another related question. When I cast with the centrifuge, I always
tilt my models slightly. However, the author of one of the booksI
have on casting states that for vacuum casting the sprued models
should not be tilted, but should be horizontal --no tilt. Another
books states that the models should be prepared exactly the same as
for casting with the centrifuge, the only exception is the filling
of the flasks with the investment.

Thanks for all you help


Casting advice is always all over the place, that just goes to show
that there’s more than one way to get good results. Personally I
think that it’s easy to over-think casting. Really you just need to
find a routine that works and stick with it. To respond to your
questions. I always fill the flasks all the way to the top whether
spinning or vacuum casting. The only difference is when vacuum
casting, before I put them in the kiln I just take my metal spatula
and scrape off any excess investment, leaving the edge of the flask
exposed and cutting the investment so it’s slightly concave to
insure a good seal. I sprue the same either way, both with sprue
diameter and model positioning in the flask. When I can I do like to
sprue directly to the button rather than building a big tree, but
either way works. I think you should just try it and you’ll probably
get good results. If you don’t then your can pick apart your routine
with your online co-casters and get plenty of contradictory and
confusing advice. :wink:



Hi Alma, The spruing strategy you use for centrifugal casting should
work fine. I tilt my models about 45-60 degrees away from the sprue
andI usually get good fill. Lining the flask with wax web helps a
lot. there should be around 1/4 inch space between the top of the
investment and the top of the flask so that the vacuum is pulling
from the sides of the flask and not just the center. Good luck…