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Weighing models for casting


#1

Finally, after a lot of procrastination, and dealing with the
unfounded fear of my vacuum, I am finally ready to do the vacuum
casting. I still have a question, before I attach all the sprued
models to the flask bottoms, and get ready to invest.

I have weighed each model and its sprues. multiplied the weight by
10.4 grams, then multiplied that weight by 1.33 to allow for the
button. So far so good.

Now to my question. I will be casting 3 rings in each flask. For the
button, do I add the full amount of the extra (1.33) figured foreach
model This seems to me to be too much silver as I only have the one
botton. Nothing has changed except that instead of attaching one
sprued ring to it, I will be attaching 3. The wax button Is the same
size and weight as for one ring. I was wondering ifthere is some
formula or rule when casting more than one item in the flask.

Thanks for all your wonderful help. Alma.


#2

I have great success just using the first calulation of 10.4 and no
additional. IF I have weight my wax model correctly I always get a
good button. Great Luck!


#3

FWIW, I write the weight (in gm & dwt) on the bottom of all my bases
using a grease pencil, then sprue my base, weight it, do the
specific gravity math and subtract the weight of the base.

Then I add 1/2 a troy ounce for a button.

Paf Dvorak


#4

Too much is better than not enough. Adjust accordingly next time if
you have too much. Vacuum is so easy you will think you’re doing it
wrong.

Just remember to turn on the machine. With the hiss of the torch
it’s hard to tell sometimes. Look at your guage for good vacuum.


#5

Hi Alma,

With vacuum, you don’t have to worry about the ‘oh-oh’ factor of
things going wrong with whirling metal the way you do with a
centrifuge, so it’s always easier to go heavy on a vac pour. Worst
comes to worst, you just pour any extra off into an ingot mold. So
when in doubt on a vac, round up.

That said, the way I figure (sterling) pours is this: Total weight of
wax. (model, sprues, tree, everything) All in one go. Times 11.
(Yes, sterling’s 10.4, but 11 makes the math easy, and gives me a
safety margin.) So nevermind what each ring weighs individually.
Sprue them all up, then tree them, then weigh the tree. Then
multiply that by 11.

Then multiply that final figure by 1.2. (for a 20% margin for the
button.) Then melt and pour. (after burnout, of course.)

So a 1gm ring wax ends up calling for 11gm of silver, plus another
2.2gm for the button. (Total pour=13.2gm, ss) Personally, I normally
use a centrifuge, and normally don’t throw anything less than 1/2
ozt, (15gm) so for me, I’d be throwing 15gm of sterling. (especially
on a vac. They don’t hit as hard as a centrifuge, so smaller pours
have less power behind them. So make them a bit bigger.)

I get more persnickety about it with gold, because it matters a
lot more. Sterling isn’t so expensive that the extra few dollars
are worth cutting into my insurance margin. Recutting one wax, even
once, is much more expensive than a little bit of extra button that
I reclaim on the next casting.

FWIW,
Brian


#6

Alma- Only one button weight is ness. If it’s your first time I’d do
an experiment on one wax that was something you already have a mold
of before you cast 3 rings. Especially if they are something you’ve
spent hours carving. Good luck and let me know how it comes out.

Jo Haemer


#7

you only have one button but you have three spruse need to include
them also

don


#8

I can see the logic in figuring the extra 1.33 for each model when
doing tree spruing, as each time a model is attached to the tree,
the tree is growing and needs additional wax.

However, if one is spruing directly to the button, the amount of wax
neededfor the button remains the same, therefore it seems to me that
figuring anextra 1.33 for each model attached to the button would be
overkill.

I may be totally incorrect in my thinking, which is s whyI will
appreciate your help and advice.

Alma


#9

Alma,

Let’s think about what you are trying to do and then decide how to
do it consistently.

What will always work, for all models and for every sprueing
configuration: If you weigh the models and sprues and multiply by
10.4 you will just fill the models and the sprue but there will be no
button. The purpose of the button is to supply molten metal as the
models and sprues harden and shrink. If the button doesn’t stay fluid
you will get shrinkage porosity.

So pick out an old button or measure enough casting grain to cover
the bottom of the pouring cup and will produce an adequate button.
Weigh that button or grain and simply ADD that amount of casting
grain to the calculated weight of the sprue and models.

This approach always gives the correct results while multiplying the
weight of the wax model and sprue times 1.2 or some other fraction
sometimes gives the wrong result. For example, if you were to cast a
single dainty ladies ring and sprue you might want a button that is
1.5 or more times the calculated silver weight to produce a button of
size sufficient to cover the bottom of the pouring cup.

This isn’t rocket science. Just add enough grain or an old button
that will create the size button needed to stay fluid to supply metal
to the shrinking casting. I also usually multiply the wax weight by
11 so that also gives an additional safety margin as pointed out by
someone else. The only silver button that is too large is one that
overflows the pouring cup and wastes silver. I am more precise with
gold.

I hope this helps.
Fred Sias


#10

Shannon- " Too much is better than not enough." A good idea, but not
always true.

If I am casting something really small like say a crown and the
button is really large, the molten metal will want to pull up towards
the button. So I go a little lighter on the button weight then.

Jo Haemer
timothywgreen.com


#11

I weight the sprue and multiply by 11.

I use a central sprue, I put about 20-35 waxes, looks like a tree. I
use centrifugal casting. With centrifugal I have to be careful to
not put too much metal in crucible, too much Results in the crucible
becoming fused to the flask, and the end of the crucible breaks off.

I would be curious if someone using vacuum casting do an experiment
sometime, weight wax times 11, pour and see how much button you have.
That is for sterling.

Gold is 13.6 and I add 20-30% more for gold.

I used to do 27 3x7 flasks a week with 50-75 pieces per flask.


#12

Hi Alma,

I only usually add 20% (1.2x) instead of 33% (1.33x) but the
important thing is that it isn’t calculated based on each wax.
You’re pouring the whole tree, so you calculate all your weights
based on the full weight of the whole tree. Everything that gets
cast needs to count.

I could have 50 rings in there, but what I’d weigh would be the
whole, completed tree, nevermind the weights of the parts. (Frankly,
nevermind the existence of the parts. They’re just branches on the
tree, and your goal is a completed tree. Therefore.) (If you’re only
doing one ring, that’s your tree. Weigh that one ring (With sprues),
add 20%, and away you go.)

By that logic, therefore, it doesn’t matter how many items you’re
doing. You add 20% (or 33%) of your total weight for the button,
regardless.

When I get up in to hundreds of grams, I scale back a bit, but if
you’vegot a heavy tree, you probably need a heavy button too.
Besides, you get it back, so there’s no reason not to make sure it
comes out well. With a Vac, you can always just stop pouring if you
look like you’re going to overfill. Keep an ingot mold next to the
caster, ready to roll, and you don’t need to worry about anything.
(basic ingot molds can be made out of angle iron quite cheaply.)

Regards,
Brian.


#13
I write the weight (in gm & dwt) on the bottom of all my bases
using a grease pencil, then sprue my base, weight it 

This is what the tare function on a scale is for - put the sprue
base on, zero the scale, make your tree and weigh it and that is
precisely your wax weight. Triple beam you weigh the base, move the
tare weight so it balances, and then weigh your tree. John…

donivanandmaggiora.com


#14

I have always been told. weight of wax times KT and 20 percent for
button…

Andy “The Tool Guy” Kroungold


#15

I do it more like Fred. I know how big I like my buttons, depending
on the flask size and what’s in it. So I calculate the metal needed
for the models and sprues and then add enough grain for the button I
want.

Mark


#16
I have always been told. weight of wax times KT and 20 percent for
button... 

Kt being karat?


#17

I have always been told. weight of wax times KT and 20 percent for
button…

Kt being karat? 

yes

Andy “The Tool Guy” Kroungold


#18

I have always been told. weight of wax times KT and 20 percent for
button…

Kt being karat? 
yes 

um. not really, though most of the times you won’t be far off.

Correct would be weight of wax times the density or Specific gravity
(same thing here) of the alloy, plus for the sprue, which might be 20
percent, or more, or less, depending on needs of the sprueing setup.
Easy ways to estimate for the button are to use a chunk of wax about
the size of the button you want and weigh it along with the sprued
models, or to use actual sprue weights that you’ve kept track of from
prior castings that were about the size you want, or to just eyeball
it with a bit of extra casting grain or metal thats about the amount
you think should be there. Once you’ve got the right amount for the
models and sprues, the exact amount for the button is usually not
critical so long as there’s something there.

Peter

For 14 K gold, who’s density is around 13.5, using karat instead
would be fine.

But 18K gold generally is around 15 in S.G., so you’d be
overestimating the amount of gold. That won’t cause it to fail, but
means using more metal than you need. And that formula doesn’t tell
you how to estimate for silver or platinum or bronze, etc.


#19

Having taught for over 30 years, I’ve learned that the less math
involved in a casting, the more consistant the result. We use a
removable sticker for each flask showing the student’s name, day of
week to be cast, a space for the weight of the wax, then a list of
multipliers for each type of metal being cast. Another box shows the
casting weight.

The factor for brass is times 14, Silver X 16, 14K X 18, 18K X 20.
If the wax weight (including sprue) is 1.0 gr., for instance, and you
want to cast it in sterling, you just multiply that amount by 16,
which is 16 gr. of silver to be cast. This formula for each metal
allows for a sprue button along with the item(s) being cast. No need
to add percentages to specific gravity computations. Much easier for
students to accomplish, less chance to goof up added percentages, and
easy to check their math.

Thanks to the San Diego Casting Company (many years out of business)
for this handy and useful formula!

Jay Whaley


#20

Interesting, does that result in a pretty big button? Is that how
Stuller casts?