Re: [ATM] start...tool....

[Mark Holm <mdholm@telerama.com>]

Vladimir Galogaza wrote:

> There is no doubt that tool made this way will work. But amount of epoxy
> required will probably match the price difference between the plaster of
> Paris
> and dental stone while dental stone tool will take much less time and effort
> to be fabricated.

Also some people develop severe allergic reaction to epoxies.  The
Probability is said to increase with exposure, so best to save them for
when you really need them.  Wear rubber gloves too.

I have done the dental stone method, and I was almost giggling with
surprise when done at how easy and quick it was.  I used Richard
Schwartz's instructions, and they worked like a charm.  I think dental
stone is worth the extra bother to obtain.  As an alternative, look for
a business that casts outdoor statuary.  They might be using something
very similar to dental stone.  I suppose in a Muslim country, outdoor
statuary might be less common.  The same techniques and materials are
used to cast architectural details that look like chiseled stone, but
are less expensive.

> 
> Second remarque is about using twice as much hardener as recommended. There
> are
> some very good chemists on the list capable of rectifying me if I am wrong.
> Epoxy and hardener work together in chemical reaction. The reaction is
> complete and
> final product is best if interacting parts are used in stoihometric amounts
> which is
> given by manufacturers recommendation. Surplus of epoxy or hardener remains
> in the
> final  staff unused (unpolimerized) and weakens the whole thing. Surplus
> hardener does not
> make final product harder or stronger.

Just so!

Probably a confusion with polyester resins, where the hardener is a
catalyst, and using more can result in somewhat harder, though more
brittle, result.  It will also cure faster and get hotter.  With
epoxy-amine systems, the "hardener" is not a catalyst, but is the other
half, or third, or whatever the correct ratio is, of the final
molecules. The ratio given is determined by molecular structure and
going off-ratio does not usually give useful improvement in any
property.  Mix it like the instructions say.

Mark Holm
mdholm@telerama.com

_______________________________________________
ATM mailing list http://www.atmlist.net/