Casting and rubber molds

[Michael Koblic]

I was gong to try casting some small objects using epoxy (of which I have a
bucketful). I was thinking possibly knife handles etc. in future.

I thought I would try a rubber mould. Being cheap, I bought a couple of
tubes of silicone caulking from Home Depot (rather than 2 lb minimum of the
proper stuff that sculptors use). I read somewhere that silicone does not
need any release compound. I had a couple of small flat objects with various
patterns made of steel; I thought I would try those. I slathered both
liberally with silicone caulking, one kind on each and let it cure for 24
hours.

I actually picked the silicone which was meant to have "inferior adhesive
properties". Not true! I could not get the silicone off the two objects.
Even cutting it with a knife and trying to scrape it would not remove the
silicone coating off them or from the plastic tray I had the whole
experiment in. I had to scrap all three.

I made another model this time with clay, sealed it with shellac after
drying, used dishwashing liquid with water as a release compound and this
time it worked - sort of. The mould was kind of uneven with some holes. I
did not bother with trying to make a "mother" mould of plaster as I did not
think it would be great for casting.

So here are the questions:
1) Has anyone here tried making knife handles (or other things for that
matter) from epoxy?
2) Has anyone got experience with making rubber moulds of things? What did
you use?

And one comment"
1) The silicone caulking adherence to metal was rather surprising. I filed
it away for future reference - a bi-metal joint of considerable strength
which might require some "give" could be achieved this way.

--
Michael Koblic,
Campbell River, BC

[Greg Wormald]

As far as I know silicone molds will not stick to fibreglass or other
casting material **once cured**. They are usually quite flexible and can
be 'peeled' off the casting.
Of course if the silicone is applied wet it is a good bonding agent (as
you have discovered).
I would try some spray silicon on the object before coating with
silicone.
Good luck next time.
Greg

[Ford]

Michael,

Epoxy resin by itself is not all that strong, it's brittle and usually
not very hard. It needs a filler such as fiberglass, milled fibers,
wood flour, powdered limestone, graphite powder, carbon fibers, or
kevlar to make a strong composite material. Check out the System
Three (www.systemthree.com) and West System, Inc. (www.westsystem.com)
web sites for various fillers and additives.

Have fun experimenting,
Ford

[Michael Koblic]

"Ford" <ford....@embarqmail.com> wrote in message
news:8e907e12-285b-4efa...@m73g2000hsh.googlegroups.com...

> Michael,
>
> Epoxy resin by itself is not all that strong, it's brittle and usually
> not very hard. It needs a filler such as fiberglass, milled fibers,
> wood flour, powdered limestone, graphite powder, carbon fibers, or
> kevlar to make a strong composite material. Check out the System
> Three (www.systemthree.com) and West System, Inc. (www.westsystem.com)
> web sites for various fillers and additives.

I use the West System epoxy and am always impressed how hard the unused
residue is in the mixing cup. I do use the silica filler when I do not want
the epoxy to flow too freely.

I am collecting steel filings in the workshop and was going to clean them
and try them as a filler. Once I get the mould production right I thought
experimenting with various fillers would be half the fun.

I will look at System Three, thanks. I have never heard of them.

BTW I was looking at Devcon products, trying to compare the bonding strength
with West, but the companies seem to use different way of quantifying it
(even on their own products)