I made a ring using PMC (precious metal clay) and was so excited with
the design, I forgot to use ceramic tape on the mandrel.
The ring turned out beautifully…but is STUCK to the mandrel. Argh!
I tried reheating it to a low temperature in the kiln, figuring I
could maneuver it away from the mandrel. I also tried refiring
upside down, but it started to become misshapen.
Would it be possible to break the mandrel and use a flexible shaft to
burr away the rest without damaging the ring?
The ring has sentimental value to me; it’s a “layered” ring with
patterns taken from articles of clothing, hats, canes, and an army
boot belonging to my deceased father.
PS I wrote to the PMC Guild approximately 3 weeks ago…no answer
yet…
I don’t see why not. I almost got myself into that same situation
and was considering that alternative. If the ring means more to you
than the mandrel by all means break it out!
You don’t say what kind of mandrel, but I assume it is the type Rio
sells for firing PMC on. The problem is, of course, that the ring
shrinks until it is as tight as it can get. I would first try
lubricants–oil, soap, vaseline, whatever comes to hand (which will
probably require gentle heat removal afterwards, as PMC remains
porous). If that doesnt work, I would try to think of ways to enlarge
the ring a little. Is there a plain part you can hammer, streching the
ring a tiny bit so it can come loose? Then, maybe, lube again. As a
last resort, I would saw the ring open and solder it back, though
soldering PMC is difficult, and different from soldering other forms
of silver, because of its porosity. You use lots of solder, burnish
the surfaces first–a flex shaft hammer handpiece is great for
this–and then heat only until the solder melts. If you heat it to the
flow point, it will soak in and disappear.
If all else fails, if you still have the textures, you should be able
to duplicate the piece. It is even possible to use sculpey or fimo to
take an impression, perhaps cut it and flatten gently before curing,
and use it as a press-mould. I often textures in this way. If you are
not used to PMC, it can be hard to get used to the more clay-oriented
mindset that it requires.
Try drilling a tiny hole in either the ring or mandrel (actually in
the space between them), so that you can slip a saw blade through the
area where they make contact. Then careful saw around the mandrel to
separate the two.
My husband, the techie, suggests putting the whole thing in the
freezer, and if that doesn’t make it cold enough, try dry ice. Use
gloves when handling the dry ice. Alana Clearlake
Have you tried rolling the ring/mandrel on an anvil or bench block
while tapping with a leather mallet? It may stretch enough to slip it
off. If you wrote or e-mailed the PMC guild, you may not have heard
anything because most of the staff was at the SNAG conference and CeCe
Wire probably has a ton of e-mail to wade through! Good luck!
G’day folk Perhaps it might help to put ring and mandrel in the
coldest part of the deep freezer, then when properly cold try a little
concentrated heat on just the ring? The difference in expansion might
free the ring. I would hold the mandrel in a bench vice at it’s very
end, and quickly go round the ring with a small hot flame, tapping all
the while to move the ring on the mandrel.
Or perhaps a long tube with an inside diameter just a little larger
than the mandrels would knock off the hot ring from the cold mandrel
if placed over the mandrel and tapped downwards.
I was responsible at one time for lab use production of liquid oxygen
and nitrogen, and I several times managed to help our engineers free
jammed bearings and fittings by dunking them in liquid nitrogen then
we would put a oxy-torch on the bearing and tap it off the shaft using
a bit of tube. With this method there was never any damage.
Of course, being wise after the event, a gently tapered mandrel might
avoid the problem! Cheers, –
My instructor was able to get the ring off the mandrel by tapping it
off with a leather/rawhide hammer (I forgot to tell everyone that it
was a ceramic mandrel from Rio Grande).
I didn’t have the heart to tell him I have another ring at home
…stuck to another mandrel…
:: laughing :: I fired them at the same time. Think I’ll check to
make sure the ceramic tape is on securely next firing? You betcha!