Volume is a 3 dimensional building block made from cast concrete. The identical modules form a regular structure which can be interlaced within itself to provide additional bracing. Large batches of modules can be made from a grid mold.
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Step 1: The Module
Each module is shaped like a + sign made from a separate mold comprised of 8 identical pieces. Although less convenient than a simple 2 part mold, the 8 part mold allows each cast piece to be easily released from the frame.
Step 2: The System
Step 3: The Mold - First Cut
The pieces of the mold are made from 3/4" x 3/4" x 1/4" beveled squares of MDF. We will cut approximately 500 of these pieces by hand in order to be able to cast 60 modules at a time. The process can be streamlined by table sawing 1/4" sheets of MDF into 3/4" wide strips. Make sure to keep your hand away from the blade and use a push stick to send the strips through the table saw. I recommend using 4' 3/4" wide strips, of which you will need 12 to make the 500 pieces.
Send the strips through the table saw a second time with the blade of the table saw at a 45 degree angle facing towards the guard to give each strip a bevel.
Step 4: The Mold - Second Cut
Using the same 45 degree bevel setting on the table saw, remove the guard and set up the mider fence perpendicular to the saw. Set up a stop block an inch away from the outside of the blade. Use this set up to cut the 3/4" strips of MDF into 1" lengths. Repeat the process until all 12 strips of 1/4" x 3/4" x 4' are cut.
Step 5: The Mold - Third Cut
The resulting pieces will have three out of four sides beveled. However we only want two sides angled, so we will have to trim the back edges of all the 500 modules. Since the pieces are now too small to cut with the table saw, we will have use another method to accurately cut them to size.
First locate a long narrow board of scrap wood no more than 1/2" thick. Cover the edge with double sided tape and place the MDF pieces with the shorter beveled end and the way to the edge of the board along its entire length. Sandwich the pieces under another board of scrap wood. Set the guide on the table saw 3/4" away from the blade and trim off the edge. Remove the taped pieces from the board.
Step 6: The Frame
Now that you have 500 pieces for the 60 molds, we will need a frame to hold them together while you cast. We will make a 6 x 10 grid of 1 1/2" x 1 1/2" squares. For this we will use 3/4" x 3/4" lengths which can be cut out of a 3/4" thick pine board. From these lengths we will cut 11 pieces at 22 1/2" and 7 pieces at 13 1/2" pieces.
These pieces will form a grid that will be half lapped together. To make this we will use a 3/4" dado blade set at a depth of 3/8" with the mider fence.
The most efficient way to produce these accurately will be to set up a standard box joint jig. First, run the dado blade through the wood that will be attached to the mider fence. Then, detach the mider fence and move the groove in the wood 2 1/4" over from the blade reattaching the wood to the fence. Insert a 3/4" x 3/8" peg into the empty groove. This will allow you to align the dado cuts at regular intervals along the 3/4" x 3/4" strips. Make sure to begin with the dado cuts on the ends of the wood lengths.
Once the pieces are all notched, they should fit into one another perpendicularly. Squirt some wood glue into the overlapping segments and clamp the grid to a table.
Step 7: The Mold in the Frame
Once the glue has dried, clamp the frame to a flat piece of plywood on a workbench. Arrange the square pieces of the mold 8 per empty square with the bevels facing inwards. The bottom layer of 4 will be facing up while the top layer of 4 will be facing down.
For the casting process, you should use a fine aggregate concrete or a plain mortar mix. I prefer to use expanding concrete filler such as Rockite as it produced strong results with a smooth surface texture. Mix 5 to 6 cups of the concrete and pour through the each of the top holes of the 60 molds. Make sure to fill up cavities all the way and don't worry too much about over pouring.
Depending on the type of concrete you are using, you may wait 1 - 6 hour for the cast to dry. Once it is ready, un clamp the frame from the plywood. You will likely find that most if not all of the molds and concrete pieces are stuck. Not to worry. Using a small mallet you can knock out the pieces from the frame. Be sure to do this in a clean area so as not to lose either the casts or the pieces of the mold.
Since you now have the mold and the pieces, repeat the process as many times as you would like in order to achieve the quantity of modules you desire.
Step 8: The Pieces
Depending on the accuracy of the cuts made for the mold and frame, the pieces are likely to have a few deformities caused by the over pouring. These can usually be chipped off or lightly sanded smooth.
Step 9: 6" X 6" X 6" Cube
The gridded structure is a combination of horizontal and vertically staggered pieces. The gaps between the structure allow another structure to interlaced within the dominant grid.