Foam Cutter Frame

12 November 2018

Here I go again, another thought written out with no sight of when I might actually do it.

A dual usage adjustable bow construction frame for foam cutting; as a regular bow or as a gantry slicer. Adjustable collets allow easy securing, adjustment and replacement of the heating element. The heating element may be placed right on the tip of the cutting bow; allows thinner foam to be used and in the case where the airfoil has a flat bottom, eliminating the need to cut the bottom of the airfoil. Also, it can be a thin foam slicer.

Components:

1. A length of nichrome wire or stainless steel guitar wire for the heating element. Length = length of foam to be cut + 1 inch clearance to both sides of foam + 1 inch pulling grip to both ends of heating element = length of foam to be cut + 4 inches. Obviously, the power supply is a limiting factor of the length of the frame. 
2. Two 4" to 6" lengths of 1.5mm to 3mm springy wire prongs/legs. The lengths and diameters depends on how large the frame is to be and how thick is the foam.
3. Two wheel collets. More may be used and be useful, but two will be used to crimp on the wire legs and nichrome wire. The internal diameter of the collet hole should just clear the wire prongs/legs and the heating element as described above and securely hold the heating element against the wire prongs/legs.
4. Two pieces of wooden slats. Their lengths can be identical to the heating element. Drill holes that matches the chosen wire prongs/legs. The furthest holes are at 1 inch from the ends of the slats. The top piece will have reinforcement cross grain since it will be under tension. The top piece may be substituted with strong cord, then only one piece of wooden slat is needed. The bottom slat may be thicker since it will be under compression and it should not be bowed due to the eccentric compressive force. If using a strong cord for the top piece, the bottom piece become the sole spreader and needs to be thicker to prevent slippage.

Assembly:

1. Thread an end of the heating element from one end of a collet, insert a wire prong/leg from the other end of the collet.
2. Tighten the collet screw. Ensure the heating element and collet do not slip.  
3. Slide the free end of the prong/leg through the bottom wooden slat first and then through the upper slat. Maintain a slight gap between the two slats.
4. Slide the second prong/leg through the two slats.
5. Insert the second collet to the second prong/leg.
6. Thread the free end of the heating element through the second collet.
7. Pull the heating element taut and tighten the collet screw. Ensure the heating element and collet do not slip.

Uses:

1. As a loose bow. E.g. cutting airfoil over templates. 
2. As a gantry. E.g. cutting even thickness foam sheets. Making tapered foam sheets is possible through the adjustment of collets and additional runner.

Further adaptation:

With the frame secured against another surface, it can be used when  

1. Held vertically. E.g. squaring off or cutting multiple identical components from as many sheets.
2. Held at an inclined angle. E,g. cutting tapered pieces especially with additional runner.