Monday, 28 February 2011

Making a wooden Soap Cutter

Adjustable-wire Soap bar cutter
Taken from “Making Transparent Soap” By Catherine Failor

The light, portable cutter shown here will cost very little for materials and will take just a couple of hours to construct.

It's designed to cut a 12" X 12" X 2" (30.48x30.48x5.08 cm) block of soap into any conceivable square or rectangular shape you wish to create. Professional soap- makers have more elaborate cutters with stationary wires,
but for the home hobbyist, nothing could be more simple and versatile than this adjustable cutter. You take the basic concept and create your own variation.

Two 2" X 4" X 28" boards
Two 2"
X 4" X 8" boards
Two 2"
X 4" x 3" boards
One 1"
x 2" x 28" board
Two 1"
x 2" x 20" boards
Two 14"
x 17" x 1/2" pieces
of plywood
Two 14" x 17" pieces of Formica or smooth linoleum (you should be able to find inexpensive scraps in the seconds bin of a flooring supply store)


Twenty-four 11/2" and 24 21/2" wood screws
One 3/8" wide x 2" long hex-head carriage bolt
Contact cement/glue
Medium-gauge guitar wire or 20- to 22-gauge music wire (sometimes called piano wire)
Utility knife
Hand or circular saw
Socket wrench or crescent wrench

Assembling the Cutter
Step 1: Apply the two sheets of Formica or linoleum to the two pieces of plywood with contact cement. (Note: You don't need a special cutter for the formica - a utility knife will do. Hold a ruler or T-square on the line you want to cut, and gently but firmly score it several times with a utility knife. It will then snap along the line with gentle pressure.) Allow the adhesive 15 to 20 minutes of setting time before proceeding to the next step.

Step 2: With a few 1 ½ " screws, attach the two pieces of plywood (Formica side up) to the
two 28" two-by-fours.
Leave a small gap between the two sheets - this will be the channel through which your
adjustable cutting wire can slide. Countersink the screws so their heads aren't sticking up above the Formica surface. Otherwise, the heads can slightly gouge the soap as it slides across the top.

Step 3: Using a few 1 ½ " screws, attach the strip of 1" x 2" X 28" wood to the Formica top.
This is the guide edge for the block of  soap as it is pushed through. Leave a ¾ " margin between the guide and the edge of the Formica.

 Step 4: Prepare the carriage bolt. Drill a hole through the shaft of the bolt, about ½ " down from the top. Mount the bolt in a vice, and use a 1/8" or 3/32 " drill bit; it takes just a few minutes to bore through the shaft. If you know someone who has a drill press or works in a machine shop, you might have him or her do it.This bolt will function exactly like a tuner on a guitar or piano. Later, the cutting wife will be threaded through the hole in the bolt, and the bolt will then be tightened into a wooden block.
 Step 5: Take one of the 3" two-by-fours and drill a %" hole through the entire depth of the block. This is the channel for the carriage bolt, but since it's a bit smaller than the bolt, you might need to tap the bolt with a hammer to get it started in the hole. A snug fit is important, because pressure from the soap as it's pressed against the wire can unwind the bolt. The wire then loses its tension. The best way to achieve a snug fit is to follow this procedure:
~ Using a crescent wrench or socket wrench, tighten the bolt 1" into the wood.
~ With a smaller bit – 1/16” or so – drill another hole completely through the block ½” from the bolt.
~ Now take the other 3" two-by-four and drill a 1/16" hole through that too, about l/4" from the edge of the block. Partially sink a 1" wood screw into the middle of the block.
A medium-gauge guitar wire works well- you want to avoid a wire that's too fine, as it might snap as the soap is being pushed through. An overly thick wire will offer too much resistance to the soap.  Buy one or two extra backup wires in case of breakage.  Or you can get what's called music wire. This comes in a quarter- pound or half-pound roll and is much more economical than guitar wire. It's also more difficult to find. Try calling a piano tuner or re-builder in your town - they might special order it or sell you some of their own. If not, contact the suppliers listed in Resources. A 20- or 22-gauge music wire is ideal for cutting.

Step 6: Screw or nail the two 8" two-by-fours onto the sides of the cutter. Make certain that
the middle of each block is aligned with the groove between the two sheets of plywood.

Step 7: To the tops of these 8" two-by-fours, screw down the two 20" one-by-twos side by side, leaving a slight gap between them. This gap should line up with the groove between the sheets of plywood below.

Carriage bolt. (The bolt should be tightened into the 3" block). Loop the end of the music wire once around the bolt, and tie a knot. You might have to use pliers to do this. Clip off the excess wire. If you're using guitar wire, run the length of the wire through the bolt until the metallic knob at the wire's other end hits the bolt. The knob is enough to secure the guitar wire - you don't need any knots.


Step 9: Feed the free end of the wire through the 1/16”hole next to the bolt. Now set this block of wood on top of the two one-by-twos that form  the "bridge" across the cutter. Pass the wire through the gap in the bridge, then on down into the narrow channel running the width of the Formica top. The wire should now be sticking out through the bottom of the cutter.

Step 10: Flip the cutter over. Thread the wire through the other 3" block, starting on the side without the wood screw. Pull the wire taut, wind it a few times around the screw head, and tie a knot. Sink the
rest of the screw into the wood. This will secure the wire to the bottom block. Clip off the excess wire. Now, flip the cutter right side up.

Step 11: Tighten the wire by turning the carriage bolt with a socket wrench or crescent wrench. (Make sure you twist clockwise so the bolt sinks deeper into the wood. You don't want to be tightening the wire at the same time you're unscrewing the bolt from the block). The hex-head bolt functions in the same manner as a tuner on a stringed instrument. Don't tighten it too much - wire with too much tension tends to snap under the pressure of the soap. Make it tight, but not too tight. Attaining the right tension is a matter of a little experimentation. The tightened wire should hold the 3" block of wood underneath the cutter snug against the plywood.
Your cutter is done!
Soap Cutter-001   Soap Cutter-002

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  2. Hi Odette,
    Thank you so much for providing instructions for building this soap cutter! I've been eye-balling those long cuts for years and ending up with badly cut bars... I've mostly finished building it (just have to wait for hubby to drill the hole in the carriage bolt) and wondering what that piece is in the block to the right of your bolt in the last 2 pics? Obviously a guide for the wire but what is it and where did you find it?
    Best regards,


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