Re: ATM wedge removal/dental stone

[Aplanatic@aol.com]

The subject of making dental stone tools has been covered many times.  I'm 
sure the archives are full of it.  Nonetheless, I feel like expounding on 
this difficult and fascinating adventure in pure creativity tonight....

Figure out how much stone to use and then add 20% more for good measure.  
When mixed with water, the powder will decrease in volume by about 50%.  Pour 
the powder into a vessel with nice high sides.  Note the time on your watch.  
Start pouring in the water, not too much at first.  Mix the powder and water 
with your hand.  Not that hand!, the hand without the watch!  You have to 
slowly get the feel of how much water this stuff will take.  On the other 
hand, you have only about 6 minutes to get the stuff mixed and poured into 
the mold.  You've prepared the mold, haven't you??  

Keep adding water, stir, and break up the lumps with your fingers -- good 
exercise if you're doing a large tool -- until the texture is just like light 
sour cream.  You've played with sour cream, haven't you??  If not, it would 
make good practice.  Check your watch from time to time.  Don't panic, but 
move as fast as possible.

Pour the creamy mixture into the mold.  Immediately clean out the mixing 
bucket, otherwise you'll have a nice flower pot.  At a certain point the 
stone will start to heat and set up.  You'll know the moment.  Carefully 
remove the warm tool from the mold and finish off the edges and flatten the 
back with a scraper or sureform.  In this state the tool will be very soft 
and easy to work with.  Once hard it takes dynamite to make a dent in the 
stuff.  Don't drop it!  It's very soft and easily damaged.  Do as I say, not 
what I do.

Bake the tool for a few hours -- overnight is better -- in a warm oven (150F 
to 175F) to drive out the moisture and to finish the curing process.  Some 
like to seal the tool in a full epoxy jacket, but I use it right out of the 
oven (after cooling).

Richard will recommend that tiles (for a grinding tool) be cast right into 
the tool, but I don't do it that way.  I prefer to do it the hard and messy 
way, by attaching the tiles with epoxy.

Best of luck,
Dave Rowe