From: "Bill T." 
To: atm{at}shore.net
Cc: rflrs{at}rcn.com
Reply-To: "Bill T." 



>Using lbs/in^3:
>
>Assuming that whatever water in it goes away with drying, that would
>make a cubic foot of it weigh 1728*0.05 lbs or about 86 lbs.  If
>water is 62 lbs per cubic foot, that would make the specific gravity
>of it about 1.39.  This seems suspiciously low to me.  Am I missing
>something here?

The units are "lbs. of dry plaster," and "inches of tool
thickness."

I plead empiricism.  The formula has often been observed to produce tools
near the desired thickness.  Strange are the ways of plaster chemistry -
about 1/2 of the water stays behind.  One test for tool dryness is to plot
the reduction in weight over time, until the curve flattens out.

Simplified formula:

   pounds_of_dry_hyrdrostone = inches_of_tool_thickness * diameter *
diameter * 0.04

First time around, try a factor of 0.05, then for subsequent use scale the
factor by the ratio of:

   thickness_you_wanted / thickness_you_got

Bill T.

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