3d mold making

In article , Michael
writes:

Charlie Gary wrote:


snip prior post


Hey Michael,
any experience with slip casting? I have a need for ceramic
letters of a
certain size, and availability dictates doing it myself. My
current idea
is
to make a pattern I can pull a latex mold off of, but the little
bit of
information I've found talks about using a pourous mold material to
absorb
the water from the slip. The parts I want are small, so a mold
made of
rigid materials that comes apart all around the sides would be a
huge PITA
for the quantities I want. Especially if there are twenty six of
them.
Any thoughts? Maybe I just need to pour into a mold and let it
evaporate
naturally.



Charlie,
My wife has been pouring ceramics for years. Here is a link to pouring
molds off silicone rubber. For ceramics you use slip, the standard
ceramic molds are not flexible although you can pour the same slip
into
a silicone or latex mold and do the same thing. You will need a kiln
to
fire the resulting casting. My wife has a few kilns, how large are
the
letters you want to cast? I'd be glad to get them fired for you.
Here is a link to Freeman Supply's video section on silicone casting.
http://www.freemansupply.com/video.htm


In article , Michael
writes:

Charlie,
You can machine the mold you want and send it to me, I'll get my wife
to pour it and fire the objects, a freebie if you like.
Here is a snippet about the slip she uses.
Michael

My wife uses Excel
ASTM D-4236
Cone 04 Premium Quality White Ceramic Casting Slip
She usually buys a couple of dozen of the 2 gallon sizes for
freshness.

The Excel Company is in Hickory KY
1-800-242-6885

This guy is amusing G.
--
Cliff

Cliff Huprich wrote:
In article , Michael
writes:
Snip

This guy is amusing G.

But the entertainment value of the two of you together can be too much,
sometimes, and I have to make myself go back to work. :-)

On Wed, 14 Jul 2004 11:34:45 -0700, "Charlie Gary"
wrote:

Cliff Huprich wrote:
In article , Michael
writes:
Snip

This guy is amusing G.

But the entertainment value of the two of you together can be too much,
sometimes, and I have to make myself go back to work. :-)


I seem to have missed the beginning of this thread, but I gather
that someone wants to slip-cast letters. Assuming these are
letters on a tile or the like, you may find it easier to just press
mold them. Make a plaster mold of the tile by sticking it down
in a box, face up, and pouring plaster over it. (Use a release
compound like soap unless the original is smooth plastic or
similar.) Remove the master, let the mold dry thoroughly, and
then press a slab of clay into it. You might want to dust the
mold with a little talc first. Let it sit for a while (5-30 minutes
depending on how wet the slab was) and then the piece
will pop out. (Same effect as slip-casting: The clay shrinks
as water is drwan into the plaster.)

HOWEVER, if you want letters with a lot of relief, or even
free-standing, this may be more of a problem no matter
which way you do it, simply due to shrinkage of the clay.
Most letters have some enclosed portion, such as A, B, D
and such, and when the clay starts to shrink in the mold, it will
tend to crack around that "island" for the enclosed part.
Even C and E will have this problem.

If this is what you want to do, use a lot of draft angle on the master
to help squirt the part out as it shrinks. Then (assuming
you press-mold these), invert the mold and suspend it a
fraction of an inch over a flat surface (or whatever) to catch the
part as shrinkage squirts it out of the mold.

Good luck!






Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

"Bob Masta" wrote in message
...

I seem to have missed the beginning of this thread, but I gather
that someone wants to slip-cast letters. Assuming these are
letters on a tile or the like, you may find it easier to just press
mold them.

After carefully avoiding this thread, I'll chime in that this definitely
sounds like a press-mold job, and that's how such things are made in
commercial quantities.

Before somebody demands bona fides, no, I don't know ceramics. I do know
gypsum tooling. And U.S. Gypsum has some information on the grades of
plasters to use for press molding, slip casting, and related work. You may
have to call to get your hands on it. There's one guy in the entire company,
based somewhere in the upper Midwest, who maintains the old tooling data for
USG. I have copies of most of it, having done a lot of research on it in the
mid-'80s (I wrote a series of articles on gypsum sweep-molds). If you need
some USG data, there's a good chance I have it.

BTW, you can't do reliable slip-casting with just any old grade of Plaster
of Paris. It's pretty touchy. It has to have just the right absorbance or it
will either stick, or it will let too much slip run to the bottom of the
mold. And that's also a function of the percentage of water mixed with the
slip-casting plaster. You can learn it by fiddling around, but you will
waste enormous amounts of time that way. USG can save a lot of time for you,
if you can reach the right people there.

Ed Huntress

In article , "Ed
Huntress" writes:

"Bob Masta" wrote in message
...

I seem to have missed the beginning of this thread, but I gather
that someone wants to slip-cast letters. Assuming these are
letters on a tile or the like, you may find it easier to just press
mold them.

After carefully avoiding this thread, I'll chime in that this
definitely
sounds like a press-mold job, and that's how such things are made in
commercial quantities.

So you don't recommend, as Michael did, slip casting clay in
Silicone or Latex molds? Like he says his wife does?

I don't think that Michael foresees any problems .... even after
all the posts ... after all, he has a (claimed) wife in the basement
and the daughter "paints" ceramics too ..
--
Cliff

Cliff Huprich wrote:

So you don't recommend, as Michael did, slip casting clay in
Silicone or Latex molds? Like he says his wife does?

Gee Cliff, you have selectively begged for help in ceramic groups now.
Why did you pick out ONLY snippets that changed the point of my
statement? You are a crooked lying *******, and that is actually being
nice about it. I see why you like Michael Moore, he does the same thing.


Why did you go to these two ceramic groups to try to find support for
what you selectively create as a statement by me? You trying to drag in
support for your earlier lack of knowledge?
And why you started this cross post of your personal problems into
their newsgroup?

Cliff, explain to these two newsgroups how you don't know a cone from
a witness cone arrangement.
Please tell them the truth that you have never poured a single ceramic
piece.



I don't think that Michael foresees any problems .... even after
all the posts ... after all, he has a (claimed) wife in the basement
and the daughter "paints" ceramics too ..

Back in the looney bin for you Cliff, you are a complet TROLL. Your "in
the basement" comment is pure fiction, why must you lie to try to win an
argument? Because you are an idiot TROLL.
Michael


--



Michael Gailey
Artistic CNC Mill, Router and Engraver Programming
3D modeling for Product Design and Development
http://www.microsystemsgeorgia.com/toc.htm

On 15 Jul 2004 12:08:56 -0700, (Cliff Huprich)
wrote:

In article , "Ed
Huntress" writes:

"Bob Masta" wrote in message
...

I seem to have missed the beginning of this thread, but I gather
that someone wants to slip-cast letters. Assuming these are
letters on a tile or the like, you may find it easier to just press
mold them.

After carefully avoiding this thread, I'll chime in that this
definitely
sounds like a press-mold job, and that's how such things are made in
commercial quantities.

So you don't recommend, as Michael did, slip casting clay in
Silicone or Latex molds? Like he says his wife does?

I don't think that Michael foresees any problems .... even after
all the posts ... after all, he has a (claimed) wife in the basement
and the daughter "paints" ceramics too ..
--

Apparently this thread started on another NG and only the
tail was posted to rec.crafts.pottery and sci.materials.ceramics.
So I'm not sure about the exact nature of the letters to be made.
I have never heard of anyone slip-casting clay into flexible molds.
The reason they are not used is that such molds are pretty much
waterproof, so the clay never dries out enough to set up. Flexible
molds are typically used to cast plaster, which sets up due to an
internal chemical reaction with water and doesn't depend on
drying to set. Then the plaster molds are used (after drying!) to
cast clay slip. But you still have to worry about relief angles and
shrinkage issues to prevent sticking or cracking.



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

"Bob Masta" wrote in message
...

Apparently this thread started on another NG and only the
tail was posted to rec.crafts.pottery and sci.materials.ceramics.

It started on alt.machines.cnc and was cross-posted in midstream, Bob. I
don't think there was any indication that the letters were to be undercut.
Actually, they're to be 3/4"-square tiles, 1/8"+ thick, with recessed
letters on top. The original poster wants to make sets of all 26 letters.

As you suggested, it's a press-mold job. But the molds don't have to be
plaster. He has an offer by someone else to machine them out of another
material.

So I'm not sure about the exact nature of the letters to be made.
I have never heard of anyone slip-casting clay into flexible molds.

I think somebody got confused about ceramic casting processes, and used the
wrong terms.

The reason they are not used is that such molds are pretty much
waterproof, so the clay never dries out enough to set up. Flexible
molds are typically used to cast plaster, which sets up due to an
internal chemical reaction with water and doesn't depend on
drying to set. Then the plaster molds are used (after drying!) to
cast clay slip. But you still have to worry about relief angles and
shrinkage issues to prevent sticking or cracking.

Ed Huntress

On Sat, 17 Jul 2004 02:57:47 GMT, "Ed Huntress"
wrote:

"Bob Masta" wrote in message
...

Apparently this thread started on another NG and only the
tail was posted to rec.crafts.pottery and sci.materials.ceramics.

It started on alt.machines.cnc and was cross-posted in midstream, Bob. I
don't think there was any indication that the letters were to be undercut.
Actually, they're to be 3/4"-square tiles, 1/8"+ thick, with recessed
letters on top. The original poster wants to make sets of all 26 letters.

As you suggested, it's a press-mold job. But the molds don't have to be
plaster. He has an offer by someone else to machine them out of another
material.


The problem with any sort of machined mold will likely be that wet
clay is pretty sticky, and you will be using pressure to drive it into
the mold details. If the mold doesn't absorb any moisture, the
piece may not release. Some production press-molds use porous
molds that release the piece with air pressure, so in theory you
could machine a non-porous mold and then drill a bunch of
teeny holes in it. But plaster is a lot easier and cheaper!
You can make your originals in plasticine modelling clay
(the kind that never dries out) and just pour plaster over
them to make the molds. You don't even need a parting
compound. Or, have the machinst make models and
cast the molds from them.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

"Bob Masta" wrote in message
...
On Sat, 17 Jul 2004 02:57:47 GMT, "Ed Huntress"
wrote:

"Bob Masta" wrote in message
...

Apparently this thread started on another NG and only the
tail was posted to rec.crafts.pottery and sci.materials.ceramics.

It started on alt.machines.cnc and was cross-posted in midstream, Bob. I
don't think there was any indication that the letters were to be
undercut.
Actually, they're to be 3/4"-square tiles, 1/8"+ thick, with recessed
letters on top. The original poster wants to make sets of all 26 letters.

As you suggested, it's a press-mold job. But the molds don't have to be
plaster. He has an offer by someone else to machine them out of another
material.


The problem with any sort of machined mold will likely be that wet
clay is pretty sticky, and you will be using pressure to drive it into
the mold details. If the mold doesn't absorb any moisture, the
piece may not release. Some production press-molds use porous
molds that release the piece with air pressure, so in theory you
could machine a non-porous mold and then drill a bunch of
teeny holes in it. But plaster is a lot easier and cheaper!

A good point, and the reason that USG's main tooling application for its
materials is press-molds. Considering that many press-mold jobs are long
runs and that a metal mold certainly is a lot less labor-intensive than
making many copies of press molds, it seems that the industry has settled on
plaster as the best mold material for that work. The really big power mixers
are used mostly for making press-molds, for example.

You can make your originals in plasticine modelling clay
(the kind that never dries out) and just pour plaster over
them to make the molds. You don't even need a parting
compound. Or, have the machinst make models and
cast the molds from them.


Bob Masta
dqatechATdaqartaDOTcom


Ed Huntress