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

["Richard Ozer" <rozer@pacbell.net>]

Good comments... but here's what I've found..

1.  You are right about the cost.  The epoxy is expensive; but we have it 
around in large quantities.  Also, plaster of paris is sooo cheap that it 
still comes out ok in the end.

2.  Doubling the hardener makes the epoxy set faster; using the proper 
amount slows the hardening process and also has the desirable effect of 
maximizing the resin's transparency.  By doubling the hardener, the 
resulting color of the epoxy is pretty ugly; but for what I'm using it for, 
aesthetics are irrelevent.

3. When I pour the epoxy over then tiles, the channels are not actually 
filled up.  Enough channel remains to be useful in the grinding process but 
the bottoms of the channels close up, preventing the formation of grit 
traps.

4.  Dental stone is probably better.  But I hate going to the dentist ;-)

RO

----- Original Message ----- 
From: "Vladimir Galogaza" <vladimir.galogaza@zg.htnet.hr>
To: "ATM List" <atm@atmlist.net>
Sent: Monday, April 10, 2006 12:16 AM
Subject: Re: [ATM] start...tool....


>I would like to comment Richards recipes,
>
>>The general approach is to make a plaster of Paris disk, let it completely
>>dry for a week out in the sun, coat the entire thing in fast drying (5:1)
>>epoxy.. use twice as much hardener as recommended.  After the epoxy has
>>dried, pour more epoxy on one side of the tool, lay the tiles on top,
>>pour/brush more epoxy on top of the tiles thereby filling in the gaps and
>>creating a solid bond between the tiles and tool.
>
> 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.
>
> 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.
>
> Third, filling channels up with epoxy dispenses with advantage of having
> channels.
> More uniform distribution of grit and temporary storage for  glass already
> ground.
>
> Regards
> Vladimir.
>
>
>
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