I’m about to begin casting after recieving a Neycraft Centrifugal
Casting Machine Mod # jcc4X4 for Christmas . The one with the winding
and locking knob . anyway my question is , do I need to do any thing
to prep the Silica crucible before doing the first casting ?. It came
with no manual or any info with it so I want start out right .Thanks
in advance . Timothy
Timothy: YES, you need to coat it. Get some boric acid or borax and
heat the crucible good an hot with alot of the powder in it. It takes
awhile but get it all real hot and use the tongs to swish the liquid
flux around inside to coat all the surfaces then pour out the excess.
You can even put an empty flask in the cradle and wind it and let it
fly with the hot flux to force out the excess. The excess won’t stick
to anything and will flush completely out. One thing you’ll probably
end up doing is overestimating the amount of metal and the nose on the
crucible will stick to the button after you cast and if you wait til
the caster stops spinning it will be too late and when you remove the
flask you’ll break the nose off the crucible. This is on the Neycraft
with the spinning shell around the whole deal. Do your first cast then
weigh the button and figure a future button weight that won’t contact
the crucible. On your first cast have a screw driver ready and BEFORE
it stops spinning near the end try to pull the flask out, if it
resists use the screw driver to pry it away from the crucible. You
need to do this while the flux is still liquid. Or, like me you can
get use to casting with broken nosed crucibles 
Dave
Hi Timothy, 20 other people will tell you, but I’ll say it anyway!
Heat your crucible to a nice red glow and throw pinches of "Boraxo"
in. Use the tongs to keep changing the the angle and give the entire
inside a very light glaze. Don’t use too much, it can carry through
with the metal to your casting. J.A.
Hi Timothy, Being a dental tech specializing in crown and bridge (in
essence gold work), I have prepared many crucibles for casting. I
used to use the old Wesgo Brand quartz crucibles but I now have
switched my Kerr Centrifico casting machine to use Ney crucibles
because of the increased capacity of their crucibles. When I prepare
a crucible, I put it into my burnout and run it up to 1500 deg F.
When it is glowing red, I take it out and put it on a soldering
platform (mine is an old very hard asbestos one [I know, I know] but
fire brick will do as well). I put on my welders glasses and fire up
my oxy/propane torch and I literally melt the inside of the crucible
turning it white hot and fuseing it into glass. Pay special
attention to the throat and the spout. I have never ever used borax
or anything else to prep the crucibles. My crucibles only last for 8
to 10 years though.;o) (honest) Nothing sticks to it except flux
if you use too much casting flux but it is gone after the next melt.
When I first started and was using the old fireclay crucibles we used
to cut a piece of asbestos casting ring liner for each time that we
would cast and taper the end towards the throat. We would soak it
and press it firmly against the bottom of the crucible and melt on
this.
Regards,
Skip
Timmy flux and heat to casting temp; reflux to glaze over.
Don in I F
Dear Skip, I am really intrigued by your method of "burning in"
crucibles. You stated that you heat them to 1500 degrees F. and then
heat them further with the torch.You then state that you have never
coated them before using and yet you also say that you flux your
melt. If you flux your melt you are then coating the crucible by
default, especially if you are using a stirring rod. Furthermore, it
is my understanding that crucibles are made using extremely high
heat; if this is the case it would seem to me that re-heating would
be redundant. I am not quibbling over the matter…just trying to
pursue the logic. I have many friends who are dental lab tech.s as
well as a number of dentist friends. I owe them all a great deal for
what I have learned…they are wonderful sources of technical
insight inasmuch as their endeavours are not that much different from
ours. The main difference, however, is that these people do what we
do only they do it a hell of a lot more frequently and often have had
a better opportunity to finesse techniques. My favorite tool is an
old Torit vertical casting machine…a legacy from an old retired
dentist. There is no better tool for a small shop doing regular ring
and other smaller castings. Thanks for your input…I hope there
others out there in your industry who will come forth with their
experience. Ron at Mills Gem, Los Osos, CA.