Here is my Two Pence;
I have been casting 3 x 5 inch flasks with average of 80 pieces in
them, pieces that weigh on the average of 1.3 Grams each.
My sprue main sprue weight is 90 Grams, then my feeder sprues, (from
the tree to the part) weighs average of .6 Gram the pieces are
rectangular frames with lettering (Greek) in them and are open.
Some of the sprues weigh more than the charm (finished weight) most
have as many as 3 sprues some only two, and the pieces are
approximately 16 Ga. thick and are sprued with 14 Ga. wire, tapered
right at the connection point to the piece., some which are difficult
patterns are done with 12 Ga.
I have been using the Neutec Sprue from Rio, and have noticed a
SLIGHT improvement in casting rejects, which I attribute to less
turbulence. I still work in the stone age, and on these particular
items I’ve been using my old standby Centrifugal casting machine,
(too poor to buy long 3 inch perforated flasks) ;^)
With the Neutec flasks, it is extremely easy to get an accurate
metal weight, just unscrew the tree from the base, and weigh it, As
for the button what purpose could it possibly serve. I am using 14
Ga or 12 Ga. they are sprued to a tapered sprue that goes from just
guessing but the sprue section starts at about 3/8ts of an inch and
tapers to about 1/4 inch. So adding a button of lets say 100 grams
is going to help me HOW?
Now were I using lets say a 6 Ga sprue from the part to the tree,
and the part weighed 40 grams, the main sprue / tree was still the
same size. (which would be silly anyway) and I had 10 or 12 pieces
like that so that my total weight was 4 or 5 times that of the
sprue, then I might consider adding an extra bit of button. But
setting up a flask like that would be looking for disaster any way,
the main sprue should have been larger any way.
Now having been a Gear Head in a former life (around 40 or so years
ago) or BFI Before Fuel Injection) we used to go to great lengths to
minimize turbulence when flowing a combustible fuel/air mix from the
Carburetors to the combustion chamber. Things like eliminating rough
surfaces in the flow areas, (smoother sprues) eliminating as many
sharp angles as possible (filet the area where the part comes off the
tree) putting larger valves in the cylinder heads (make your feeder
sprues at least as big or larger than the thickest place on the part
Now I hear there is this thing called Fluid Dynamics, heck I guess
we weren’t as dumb and stupid as the old people thought we were ;^o
. Also I think flask temperature has a lot more to do with complete
fills and surface quality than adding extra metal weight to a piece,
unless you are casting in a flat base, Then we are in a hole other
game and the weight of the button or base does become relevant.
This would be when casting Conchos or large belt buckles, several at
a time which also can be done on a ball base but you can’t cast as
many at a time, so having a 200 gram button/base is a good thing,