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Strength / toughness of PMC?


#1

How strong is PMC? Could it be used for low-load gears? A friend got
a 3-D printer and it started me thinking. --RC


#2
How strong is PMC? Could it be used for low-load gears? 

In a word, no.

It is fine silver, with all the bendy softness that inspired the
creation of sterling-- with millions of micro-pores. It has its uses,
but mainly to create either pieces that will not get much abrasion or
rough treatment, or metal models for casting. Working with it has
some advantages over wax work (though many here will say otherwise),
for some kinds of pieces. I enjoy using it, myself, upon occasion.
But the shrinkage is a huge problem if you need precision; it is
REALLY worthless if not fired to 1650 for at least 1 1/2 hours; and
even at maximum density, it is no match for milled material.

Noel


#3

Hello,

This would certainly depend on how “low load” you mean. PMC or
Precious Metal Clay, a brand of metal clay made by Mitsubishi, is
either fine silver, 22k gold, or sterling. Of the three, the sterling
would be the best choice for gears, but it is still not as dense as
milled sheet would be. There are a number of brands of bronze metal
clays available and perhaps they would be the better choice. They are
not made by Mitsubishi (I’m guessing you were using “PMC” as a
generic term, which it is not). As I said, it all depends on how you
intend to use the gears, and how much stress there would be on them.

And, would you describe your take on the application of the the 3-D
printer to the use of metal clay, please. Just curious, as, although
I am familiar with the use of metal clay, I have a very limited
understanding of the use of a 3-D printer, and would not have thought
of to apply that process to metal clay procedures.

Thanks,
Linda Kaye-Moses


#4

well i too originally (in the long ago, pre “certification” PMC guild
scheme/ Mitsubishi testing period around "97) thought metal clay
(when it was only .999 silver) could potentially be used for all
sorts of short cuts and repairs that were too hard to do without
fabricating the entire X altogether. i tried all sorts of
experiments, with all forms, later, all brands, even making my own
in both golds and silver and ultimately it’s up to the sintering
process. Using a kiln or furnace is absolutely the best way to go -
and using, in the case of a gear- provided it’s what i’m envisioning
(a flat-ish disc with a hole in the centre and teeth on the
perimeter) if it has to be silver then a sterling alloy metal clay
clay should be chosen for the added strength of the copper provided
it will be installed in a closed mechanism (like a watch or clock
case, under glass, etc. where tarnish or no sulphurous gasses will
attack it readily - alternatively, a coating of micro-crystalline
wax could help if it has to be exposed to the air)

But I would recommend a stronger alloy if silver isn’t necessary and
you want to give it the appearance of say, a finely engraved piece
like you would see on a period A. L Breguet movement, then the
bronze clays would stand up to almost any load far better!
(particularly those motorized in the 2.5mA - 10mA range with low
speed high torque or the powerful but small Mabuichi 12 vDC
sprocketed motor that draws only 8mA and spins up to an amazing 700
RPM [ no load] and costs about $1.89 !! ) …the pro type metal clay
silver is I believe only 900 silver and may repack the silver
particles best for a silver clay, better than the sterling. again,
the bronze if gold colour is desired or you want to experiment as the
cost is far more reasonable than silver or gold clays no matter what
the brand, and I personally like the Art Clay silvers better than PMC
brand. though there isn’t a lot of cost difference between the two
major competitors. there is a maker of a green and rose gold 14K
alloy if you want to go with a strong gold at a reasonable price once
you have refined /finalised a printed model and don’t want to alloy
your own yellow gold using gold clay and a .925, silver clay- that
way the carbon sintering could be eliminated while adding the
strength of the copper already contained in the silver clay, but a
kiln would be necessary to prevent any internal fissures, breakage or
fractures. that you couldn’t see particularly if the gear has a
raised edge and maybe rays in the design leading to the centre hole.
.(I suppose I am conceptualizing an engraved looking piece so keep
referencing a stylised design in my mind). So considering the
shrinkage you will get with a metal clay remember to add that into
your 3D Printing original drawing and then maybe buy some powdered
non-precious metal clay to work out any details with (it can always
be used later for something! and I must admit that bronze stuff looks
pretty good if you crush the carbon to eliminate the rainbow effect
bigger chunks can give it as well as providing as flat a bed as
possible to prevent any torquing of the disc in the firing process-
where forging it or planishing after the fact won’t be practical). I
am very into 3D printers at the moment and also experimenting with
coloured gold alloys in metal clay so I would be very interested to
know what you come up with- Bottom line is any precious metal clay
(gold, silver or alloy) is about 3 times the cost of the real raw
material but I have found a world of uses for precious metal clay
alloys in my restoration work, so more things are possible with them
than I originally found when clays were limited to.999 clay and 23 kt
yellow only.,…rer


#5
It is fine silver, with all the bendy softness that inspired the
creation of sterling-- with millions of micro-pores. It has its
uses, but mainly to create either pieces that will not get much
abrasion or rough treatment, or metal models for casting. 

Remember that Sterling PMC is out now. Probably still not
appropriate for gears, as the OP asked, but stronger.

Elaine
CreativeTextureTools.com


#6
It is fine silver, with all the bendy softness that inspired the
creation of sterling-- with millions of micro-pores. It has its
uses, but mainly to create either pieces that will not get much
abrasion or rough treatment, or metal models for casting. 

Remember that Sterling PMC is out now. Probably still not
appropriate for gears, as the OP asked, but stronger.

Elaine
CreativeTextureTools.com


#7

Linda, I don’t have a specific application in mind. In fact I don’t
know of any 3D printer today that can handle something like metal
clay (and I was thinking more bronze or copper clay than silver).
What I’m wondering about is if the sintered clay has enough strength
for simple machine parts. The only way you could use clay with a
current printer is to form the part out of thermoplastic, use that
to make a mold and use the mold to form the part in clay before
firing it.

–RC


#8

Not knowing what your exact application for these gears are I will
venture to advise that your simplest solution is to buy one set of
brass or steel gears of the proper types, sizes and pitch for the
mechanism you want to build and have molds made so that sterling
gears can be cast. Gearing is a precise engineering problem and it’s
best left to firms that specialize in making gears to make the
originals.

If you’re good at machining and have a mill and the requisite
hobbing tools then you can make your own directly in silver, but I
think it’d save time to mold commercially made gears and then clean
the castings.

Elliot Nesterman


#9

Check out Hadar Jacobson - a few years ago I visited her studio in
Berkley and she had developed a steel clay that seemed super tough -
In clay form it was smooth as silk and then became a little gritty
it seemed, as it dried out - not sure how it stands up after firing
or if she is still selling it -but she is a great resource for all
metal clay structural issues. (She sold her clay in powder form so
you can mix up just what you need.)

Robyn


#10

Hello,

It seems to me that the process you describe (printing a mold of a
gear from thermoplastic) is an inefficient way to make that mold,
when, in fact, you can take a hardware store gear, press it into the
thermoplastic (or other mold making material), and be ready to press
metal clay into the resulting mold. Of course, if your gear is of
unique dimensions, then the method you describe might be the way to
go.

There is also the most direct method, which would be to simply cut
the gear from metal clay or milled metal sheet.

And again, I would suggest that bronze clay will give you the
strongest gear. If the gear has to be precious metal, then, for
strength, I would choose to use milled sheet.

Keep us all posted on your project,
Linda Kaye-Moses