Mold cutting ponderings

[Norah_Kerr]

So I have a piece (two actually same shape different size) that I’m
going to vulcanize, I’m already a little worried about cutting it
though.

I’m not the most elegant cutter when it comes to rubber, but if it
works it works, right? Anyway I’m thinking this piece might end up
being a pain.

It is functionally similar to a cube with a hole drilled through all
the way one way and halfway through another meeting in the middle
forming a T of space inside the piece (the long hole isn’t actually
round and the overall piece isn’t actually a cube, but as I said
functionally similar). I’m worried about mould lines or even the
inner tab(s?) of rubber wandering totally during wax injection.

Any suggestions? So far my most practical idea is to take it
downtown and cross my fingers, but I don’t think that would be as
much fun. grins

Cheers,
Norah Kerr
www.besmithian.com

[richard_hart2]

It is functionally similar to a cube with a hole drilled through
all the way one way and halfway through another meeting in the
middle forming a T of space inside the piece 

I have made molds with pieces that had holes, even tubing, they were
beads, and I used a piece of wire the size of the hole. Make the
mold, put the wire in shoot the wax. Remove the wire, reinsert the
wire, shoot another wax If you use vulcanized rubber molds, after you
make the mold, cut off a little of the wire for it to fit right
because of shrinkage. Make the wire long enough to easily hold onto
so
you can pull it out of the wax.

Richard Hart

[John_Donivan]

Make the mold, put the wire in shoot the wax. Remove the wire,
reinsert the wire, shoot another wax

Was going to reply to this yesterday and forgot. Richard is right for
one way to do what you want, except for the “T” part. Some people use
teflon wire for it, and it’s not as easy as he says - the wire is
molded in place and has to be cut carfull so it always goes back. Not
so hard, but he makes it sound easy ;}. But that’s not going to get
you a “T” hole or an “X”. My real suggestion is to mold the piece,
cut it normally, cut the rubber off that goes into the holes so they
leave a depression, and then drill it after. Otherwise you have to
cut all 3 or 4 pieces so they meet neatly in the center - you can
pull each one out, but you just can’t pull a “T” shape, obviously.
The problem with that is that a formation like that is hard to get in
place when shooting, and the thinner and longer it is the more the
rubber will float out of place when shooting waxes. You can use
Richard’s wire idea, but again you’ll have to have 3 or 4 wires
meeting in the center, and you can get the same issues of blowing out
of place in shooting waxes, but much less than rubber. I would leave
dimples of rubber for the holes and drill it after - making it in one
(2x1 part) or two halves (1x2 parts) and assembling after is the
truly proper way to do it, but that’s much more complicated.

http://www.donivanandmaggiora.com

[Norah_Kerr]

The main section that I’m most worried about is half round and much
wider then anything I have kicking about short of a file, but in
size compared to the piece still might be an issue if there is a seam
across it.

hrmmmmm maybe it’s time I try my first 3 piece mould, unless there
are any other suggestions. I’ll be sure to count my fingers carefully
before and after. grins

Cheers,
Norah.

[stride]

I have a suggestion that might work. It is not tested, so other
members of this forum need to provide more detail or approve the
whole consept. Also… I’m assuming that water soluble wax can be
injected into a mold just like ordinary injection waxes. If that is
not possible this idea won’t work grin

I’m assuming you have already made your pieces?

If so… Fill up the “hollow” area of your piece with wax that won’t
melt when making a mold. Where the wax-core extends all the way out
to the surface of the piece, insert some “guidance rods” that extends
a few millimeters. When done make a mold of the whole thing.

Finalize mold and make a wax model of this shape. When done carve it
down so that you end up with the “hollow” space inside your piece.
Make a new mold of this shape. This shape is the “hollow core”. The
material you have just removed represents the metal in you piece.

“Big mold shape minus hollow core shape equals final piece.” Right?

The approach is to inject water soluble wax into the smaller/“hollow
core” mold. Once the mold is filled take out the wax shape and insert
into the bigger mold. The “guidance rods” makes sure it is positioned
correctly. Fill up with ordinary injection wax. The final wax piece
should now consist of a water soluble core with a layer of ordinary
injection wax on the outside.

Dump in water and you end up with the final master pattern.

Another approach might be to make the “hollow core” shape in a
material of your choosing. Make a mold. Then add on to the “hollow
core” shape some material that will represent the outer or bigger
shape. The material added represents the final piece.

Now… this is theory only - and feedback or more elegant approaches
will be appreciated

Best regards,
Morten Karlsen

[richard_hart2]

but you just can't pull a "T" shape, obviously. 

Two pieces of wire, one all the way through, and one meeting center
of the through wire. Thought it would be obvious. Bet I can.

Richard Hart

[John_Donivan]

Two pieces of wire, one all the way through, and one meeting
center of the through wire. Thought it would be obvious. Bet I can. 

I would just let it pass, but you never know what readers are
thinking - of course you can. That’s not a “T”.