Free Foam Cutter Plans
Here is a simple, inexpensive, safe foam cutter you can make and use that really works. By Lee Aston
THE SPAR SLOT CUTTER MADE OUT OF A SOLDERING IRON
1. To cut a slot in a foam wing or fuselage for a carbon spar.
2. Take a 25-40 watt soldering iron and grind the tip flat.
3. Slide a wheel collar up the shaft of the tip to the depth you want the cut.
4. Use a metal straight edge and trace the edge the length of the spar.
5. Use low temperature hot glue to glue in the spar.
AUTOMATIC SWING ARM CUTTER DESCRIPTION
If you want to cut constant cords or slightly tapered wings you need to cut in the more traditional way with jigs on each end of the foam and a mechanical device to pull the wire through the foam.The power supply and bow remain the same.
I started cutting foam in an apartment and needed something that not only cut well but would store well. This is the method I have used to cut most of my wings over the years.
The swing arm works by transferring gravitational force of a weight dropping to strings connected to each end of the bow that pull the cutting wire through the foam. Tapers are cut when you connect the strings to two different points along the swing arm that have different ratios of movement transferred to the cutting wire.
In other words, one end of the cutting wire moves farther than the other end because one end of the swing arm moves farther than the other. You design your jigs, calculate the ratios you want to cut, set them up on the swing arm and you get a wing.
Each wing is made by passing the wire twice over the foam to be cut, once to cut the bottom of the airfoil and once for the top. The jigs have to be changed between the two cuts. This requires the cutting of four jigs for each wing cut because there are top and bottom jigs for each end of the wing.
Your cuts will be faster and better if you use a wood platform with a jig mounted on each end of the wood with a wood weight on top of the foam.
I have had to invent some of the vocabulary used in describing the system. The "platform" is the main board to which everything is attached. The "swing arm" is the moving piece of wood that also acts as the weight to pull the cutting wire through the foam that is on the front of the platform. "Strings" are any type of string, fishing line or other non stretching line that transfers energy from the swing arm to the cutting wire. The "cutting board" is the piece of wood the foam sits on during the cut
HOW TO MAKE TWO PIECE JIGS
The cutting wire will always cut on the top side of the jigs.
Two different jigs will be used. One to cut the bottom of the airfoil and then it will be replaced with one that will be used to cut the top of the airfoil.
Both jigs have screw holes in the base that screw into the cutting board to align the foam and the two jigs.
The jig is made with 1" of Formica that is cut on the center line of the airfoil ahead of the airfoil and 1.5" behind the trailing edge of the jig to help with wire positioning and starting the cut and also with finishing the cut and getting a good trailing edge.
1. Determine which airfoil will best meet your needs for your design
2. Cut a Formica jig of the exact airfoil you want to make. Cut two different jigs if your root and tip are going to be different sizes or airfoils. You can cut washout with an automatic cutter by tipping the tip airfoil down when making the jig.
3. Cut a 2 pieces of Formica that are 2.5" longer than the jig and tall enough to give the needed clearance above the cutting board for the jig.
4. I like to lightly glue the two pieces of Formica together for the first steps of cutting. They will be separated later so do not use too much glue.
5. Square the bottom edge.
6. Draw a line at the level of the top of the cutting board.
7. Lay the Formica pattern on the jig to be cut and line it up so it is parallel with the cutting board line.
8. Leave at least and extra ΒΌ" of foam for the cutting wire below the jig.
9. Draw a parallel line to the cutting board line that goes through the center of the jig and is at least 1' ahead and 1.5" behind the airfoil.
10. Trace the jig pattern onto the Formica with the extension lines out the front and the back.
11. Drill the holes that will mount the jig to the cutting board. I recommend that you carefully center the holes and make them so that you can flip the cutting board for making both right and left wings.
12. Using a band saw cut the top of the airfoil.
13. Separate the two pieces of Formica and only on the one half with the pattern cut the bottom of the airfoil.
14. Your pattern and the bottom jig should be a perfect fit on the top jig.They do not have to be cut larger like the single jig is, because you will cut the bottom first the foam will drop and no gap will have to be accounted for.
I hope this information will be helpful. I am a hobbyist not an electrician or an engineer. What I am going to tell you is the way I have made my foam cutter work for me. There are many other good ideas out there and I encourage you to seek out other ideas and methods to make your foam cuts as safe and precise as you can.
