I am trying to make a sword hilt out of sterling, and this requires
casting a 1" diameter spherical ball for the pommel. I am a complete
novice at this. One source said that the sprue should be as thick as
the thickest section of the piece, in order to avoid shrinkage
porosity. But if I connect a 1" sprue to a 1" sphere, the sprue
removal will be quite difficult Is there some way around this? Is
investment casting the wrong process for this object?
Forgive me if this question is too āfoundryā, but silver hilted
smallswords were the menās jewelry of the 18th century!
If I were to do what you have mentioned, I would be inclined to take
the wax sphere and split in two, hollow out the inside, and cast it
in 2 pieces. You donāt have to have a huge sprue for the wax, but you
might want to put on a couple of return sprues from the top of the
spheres back to near the base of the flask base. After you cast the
pieces, finish them, lap the sides that match up, and solder them
together. Just a thought.
In principle your advice is right , you will risk shrinkage cracking
in the centre of your ball. I have a similar thing to do with a12mm
ball on the end of an 8mm bangle, I am going to make an 8mm recess
half way into the ball , this then reduces the overall thickness of
the ball . I assume you have to fix this onto the hilt, so a deep
hole (perhaps going all the way through) will allow the inevitable
shrinkage to happen inside the hole. Whatever you will have to cast
really cold maybe at about 960deg C.
A good way to make round wax balls on a lathe is to turn them with a
wadding punch, just sharpen the end and use the whole circular end .
You will have to roughly round the wax first and use a punch a bit
smaller than the ball but it is remarkably effective.
Iād recommend casting this massive of an article in a sand mold,
such as Delft Clay. Many jewelry suppliers sell a ācope and dragā
design casting āflaskā, really a cast iron 2 part frame, a miniature
version of the old style used in industry before ceramic shell and
catalytic resin sand technologies. The jewelerās version is large
enough for something like a sword hilt, but Delftās largest flask is
only 100 millimeters, maybe large enough, maybe not. As for sprue
thickness, I would, if casting a 1" diameter sphere, sprue this with
a 1/4 sprue, but consider, with sand casting, you need some pretty
significant vent sprues too, at least 1/8" in this case. That all
said, youāre biggest problem is going to be shrinkage, and the
attendant porosity problems, as well as gas porosity, which is less a
problem in sand molds. Think about casting these parts a little on
the thick side and doing a bit of forging towards the final shape,
which should compact the metal and reduce the porosity problems.
Another option would be to fabricate in heavy gauge sheet and weight
the parts by filling with lead.
A sphere is probably the hardest item to cast without large amounts
of shrinkage porosity. your best bet may be to cast two hemispheres
spruing to the flat side then trim the sprue and solder together.
Otherwise you should look at a 1/4-3/8 in. gate (sprue) keep your
temperatures low for the flask (900F). I would also use a tree type
arrangement for the spruing in a tall flask with the sphere gated to
the top of the tree (farthest away from the pouring cup). This will
give you the greatest pressure to help fill the sphere as it cools.
But in all likelihood you will have to try this a couple of times to
make the casting work well enough to use.
Have you thought about making a pair of hemispheres from sheet and
soldering them together? Much easier and even in heavy sheet much
lighter.
Jim
James Binnion @James_Binnion
James Binnion Metal Arts
A long time ago I had very good results casting 15mm thick sterling
pieces on a 6mm sprue when I finally lowered the flask temperature
around 500 degree F. The basic idea is to have your piece solidify
before the sprue or button. As long as there is NO moisture in the
investment you can probably cast at room temperature. A big reservoir
on the sprue could also help.
Successful casting is a mix of scientific theory, consistency, and
black arts. Think about what you want to happen, observe (and
document !!!) what does happen and break any of the āconventional
rulesā til the two match.
Have you thought about making a pair of hemispheres from sheet and
soldering them together? Much easier and even in heavy sheet much
lighter.
Hi Jim;
Iām not a sword maker, but I believe the hilt and pommel were
traditionally made pretty massive for the purpose of acting as a
counterweight to the blade. Somebody feel free to correct me if Iām
misinformed.
Casting a solid piece of that size will present many problems of
shrinkage, porosity and firescale.
Rather than one massive sprue you might make a tree with many
smaller branches attached to the sphere. You will want to use the
lowest temperature on the mold and metal as you can.
Can the sphere be hollow? If so I suggest you mount the wax block on
a large spindle then mount the spindle in a cable driven handpiece.
Mount the handpiece in a vice and turn the sphere. You can hollow
the sphere by turning. That is how I make all my pieces of pottery.
If you cast a hollow sphere be sure to place a silver rod into the
center of the hollow sphere or the investment core will break and
you will get holes in the casting.
Its a very simple process.
I have an illustrated paper on how to turn wax which I would be glad
to send you if you are interested. It also shows how to place
reinforcing bars into the center of the sphere. I might be able to
e-mail it.
If I were to do what you have mentioned, I would be inclined to
take the wax sphere and split in two, hollow out the inside, and
cast it in 2 pieces. You don't have to have a huge sprue for the
wax, but you might want to put on a couple of return sprues from
the top of the spheres back to near the base of the flask base.
After you cast the pieces, finish them, lap the sides that match
up, and solder them together. Just a thought.
That pommel ball/nut isnāt just a decoration, itās partially a
counterweight for the blade, so a hollow probably would not serve
Peters purpose. Even for a dress blade, it would need to pass muster
for handling.
I'm not a sword maker, but I believe the hilt and pommel were
traditionally made pretty massive for the purpose of acting as a
counterweight to the blade. Somebody feel free to correct me if
I'm misinformed.
You are exactly right David but I have never come across one with a
solid silver pommel. I think it was normal for these to be made of
sheet and then filled with lead or made to surround an iron ball.
Many of the silver pommels were decorated with repousse work or given
other decoration such as mounted stones or applied decorations of
twisted silver wire. The only solid silver pommels I have seen have
been the āmedallionā (flat sided) or āsculptural typeā and used
mainly on Italian ādecorativeā swords and daggers.
Whenever we have cast extremely heavy sterling silver handles and
large pieces of hardware in Bronze and in Silver, We have done so by
using a single sprueā¦ 1/2 inch in diameterā¦ it is best to flare
the round sprue into the ball that is being cast.The sprue length
should be about 1 + inches long.
Flask temperature and metal temperature become very important as well
as casting method. Normally, I would recommend Vaccuum casting at a
flask temp around 450 to 500 oF. If you find some porosity in a
particular area, put a riser in that area to get rid of the porosity
/ gas problem.
Is there some way around this? Is