Hi, Since many years, I am in front of the same problem when I
start the teach the 20th lesson (bijou articul=E9) articulated
bracelet. By the past, I was using (leads for pencils…I don’t
know this word in english and hope you will understand) inside
the hinges of the wax links to keep them hollow during casting.
For about ten years the leads melt in the furnace and results in
full hinges that have to be drill. So, I stopped to demonstrate
this technique and only explain it, hoping someone will find the
good leads. I bought a lot of different brands and I have made
tests over tests without result. Does anyone knows a brand of
lead who will not melt or the alternative to my problem.
salut again… by the way , what you might be looking for is Not
a lead pencil , but more to the point… a Graphite rod. graphite
has the temperature resistance that lead does not have. try
art supply stores . Dan Grandi racecarjewelry.com
The problem is that few pencils contain Graphite now. It is
mostly synthetic. Perhaps the more expensive brands of pencil
use Graphite. If you can find a brand of pencil that uses
genuine Graphite that will probably solve your problem.
Aloha Guy, You could use graphite leads(as opposed to the
lead (graphite in wax,they make now.). I have used nylon hinges
used on model RC cars. I know some people will cringe at this,
but the wall thickness is excellent and the spacing of the tubes
is consistant (yes, I can and have done handmade (for years) and
I own every size of broach). I always equated, accuracy is speed.
My humble 2 cents.
Regards,
Christian Grunewald
Precision Modelmaking
Hawaii
Hello Guy , I have found this method to work. If you are
injecting a wax from from a rubber mold, when you vulcanize the
rubber, include a stainless wire thru the tubing of the hinge of
the model.It may take some practice in cutting the mold but
after the model is removed, just replace the stainless wire back
in the rubber mold.Now inject the wax, pull the wire out with a
twist, and remove the wax. If you are working from direct wax, I
don’t understand a need for lead inserts (graphite) at all since
the plaster will fill in the hole of the wax tube. Hope that
helps, Don Wollwage in perfect CA. weather
G’day Guy; the softer the pencil lead (yes, correct English
though it is really graphite) the less clay is used in
manufacture. B6 pencil leads are the softest, though they do
have wax to keep the graphite particles together, for it is very
fragile. Whereas, the hard 6B leads contain the most clay as a
binder. Try both? They are cheap enough. Actually graphite
doesn’t melt until it reaches extremely high temperatures, though
it oxidises to carbon dioxide and monoxide gases at quite low
temperatures, like for instance in a redly glowing charcoal fire.
It is either the wax or clay binders that melt , but pure
graphite won’t melt at those temperatures. It only fades away!
However, you could try titanium wire - nothing adheres to it at
soldering or casting temperatures. Cheers,
Bonjour Vincent. What i do instead of lead pencils is this.When
i make a mold of the particular item, I insert a stainless steel
rod in the model to be molded. afterwards , when the mold is
cured, i remove the model and reinsert the stainless steel pins
back into the mold. After shooting the wax into the mold, remove
the pins and put them back into the molds to be used again. The
result is a perfect hole in the wax. If you use a good investment
plaster such as Kerr satin cast or Ransom and Randolph
investment, the investment will not break inside the hole so the
hole will only have plaster in it and can easily be removed with
a small drill or if it is left in an ultrasonic cleaner with a
good investment remover for a long enough period,it will come out
on its own. often when making rubber molds of this type,i have
managed to design the mold in such a way that the metal pins are
locked permanently into the mold and when you flex the mold, the
wax pattern stands up out of the moldon the pins. occasionally
spray the pins with a silicone mold release. i hope this helps.
Dan grandi racecarjewelry.com
... I don't understand a need for lead inserts (graphite) at
all since the plaster will fill in the hole of the wax tube.
Yes, but with fine guages of hole, the resulting plug of
investment is quite thin, and if the tube is more than a very
short section, that suspended plug is quite prone to break off
when the molten metal hits it. Then, not only does the tube cast
solid, but the little plug is floating around in the motlen
metal, and will cause a nasty defect in the casting.
by the way, if you cannot find a suitable graphite that will
withstand burnout, you can always use plain iron wire (like
binding wire, or even broken drill bits) in the same way. Don’t
use stainless, it’s harder to remove later. After casting, which
it withstands just fine, you treat the casting in the same way
you’d treat an item in which you’d broken off a drill bit: Let
it soak in some hot sparex for a while (kept seperate from the
pickle you normally use, of course), and the iron will dissolve
out. Depending on the depth of the tube, it can take a couple
hours or more, but it’s still easy enough.
Salut Dan, Yes but, with an inside tube diameter of 0.5 to 1.0 mm
(thing I forgot to specify to Don) the plaster do not flow in the
center of the tube without a special attention to each one. Nice
to speak to you in French if want to practice. @gaudette
Vincent - You can use anything to fill the wax links in your
casting process that has a higher temperature than the burn-out
cycle and melting temperature of the metal used in the casting.
Like platinium or stainless steel wire. However there’s also the
’shrinkage-factor’ to consider, to quote Sinefeldt’s George. So
to remove the metal from the casting will take some doing.
Experiment with the alternatives. Bon chance! Kim Eric Lilot
I don’t know the leads by brand, but be sure the lead is not a
polymer (plastic) binder lead. You can test easily, a polymer
lead is rather flexible, a clay bonded lead (old fashion, but
usable) will break rather easily, and will take ~2000+ degree
rather that only 350 to 400 degrees of the polymers. Also, I
know that solder won’t stick to titanium or niobium, in casting,
the cast metal might stick tight (depending on expansion rates,
but worth looking into or experimenting with)? Please, let us
know what works!
Hi Brian, I have always used the same casting temperature during
these 25 years. To resume, I bring the furnace slowly at 1250
-1300 F, then let it cool to (all depend of the type of casting)
900 -1000 F, then wait to be sure that the center of the flask is
realy at 900 -1000 then I cast.
Hello again. what exactly are you trying to cast ? are the
hinges long or very short? you mention that they are .05 to 1mm
in diameter,but what is the length. The reason for my question is
that there are many ways to eliminate the use of graphite rods.
if you can create a thin slit in part of the tubing (not all the
way down)…where the slit is not visible or obtrusive …in
this maner, the plaster will stick through to the inner section
of plaster… reinforcing it just enough so that a graphite rod
is not neccessary. Use the metal pins in the rubber mold as i had
mentioned previously to guarantee that the hole stays round in
the wax.Also an important factor is to make sure that the metal
flow from the Gate is in the same direction as the pin hole…
that way the plaster is pin is nevr damaged. When i cast fine
hinges, i have never had a problem so long as the metal flow was
in the same direction as the pinhole. I hope this helps a
bit…good luck vincent. Daniel Grandi Racecarjewelry.com