To The Group,
 An entirely new question. When making a male plug for mold
 casting, what is the mixture and ratio. I have already tried a mix
 of Plaster of Paris and Baking Soda as well as a mix of Plaster
 of Paris and Corn Starch, each a mixture of 50/50. Neither of
 these has worked. Any suggestions!
 Frank Clementi

 What material are you casting?

 Paul Lamar


 Frank,   Plaster of parris needs to be porous to let trapped gasses  escape
 or they will be trapped in the casting  and make a terrible surface finish.
 A high speed agitator on a drill motor can be used to entrain air in the
 plaster which will let the hot gasses pass through.   Also the plaster must
 be
 very dry (baked for several hours)  otherwise the moisture will make steam,
 spall off into the casting and possibly explode. It seems to help to
 lightly
 sand the plaster surface after baking.
       A simpler medium for a mould is green sand with an oil binder. To
 get a fine surface finish  you would dust some fine grained sand on the
 pattern with a kitchen flour sifter then tamp the rest of the coarser sand
 over that.
    Aluminum generally will pour with a 4 inch tall pouring sprue with the
 metal entering from channels under the part with vent holes out the top
 and a riser near the thickest area to add metal as the casting
 solidifies/shrinks.  Magnesium needs a much taller pouring sprue to get
 enough pressure head to fill the mould quickly.

 george grimes



 To All,
 A little more detail. I am making a carbon fiber intake system.
 It will include the dynamic chamber, runners, and the port-
 connectors, all one piece. I remember reading somewhere
 you could make a male plug out of this matrix, lay-up your
 part, and after curing, you dropped the item in a tub of water.
 The next day you remove the item from the tub of milky
 water and you have your finished piece. As I recall, there is
 a commercial version of this matrix, but I don't recall the
 name. However, someone gave the components of this
 matrix, but I don't remember exactly what they were. Seems
 like it was Plaster of Paris and something else. If anyone
 recalls this issue and can let me know I would be extremely
 thankful.
 Frank Clementi


 I remember that conversation but I can't find it. It has been several years.
 I searched for "corn starch".

 Another way of doing it is use Styrofoam and cover it with plastic packing tape.
 After the epoxy cure melt the Styrofoam with acetone.

 Paul Lamar

Frank,

You may be thinking of "Aquacore"…see link…

http://www.acmtucson.com/files/Download/ProductLine.pdf

Gene Kahn


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