Free Foam Cutter Plans
Here is a simple, inexpensive, safe foam cutter you can make and use that really works. By Lee Aston
FOAM CUTTING ACCESSORIES MAKE CUTS LOOK PROFESSIONAL
In order to help you understand the different tools and techniques we use, I am going to tell you how to set up the tools to cut a "Wild Wing," which is our club contest and combat flying wing. It is a technical cut and uses many different tools and methods that we have refined. These techniques can be applied to any wing you want to cut.
THE ANCHOR
The anchor is the device that anchors one end of the cutting wire so that it will not move. It is a simple device with no moving parts. One end of the wire is anchored; the other end traces a single jig. Because one end of the cutting wire is connected to a fixed point, every movement of the other end of the bow will cut a perfect taper its entire length of any airfoil you choose to cut.
The "Wild Wing" is cut with an anchored bow set up. The foam cut is a 9" to 3" taper. We have cut over 104 Wild Wings, or 208 halves, of this plane to date with only 4 halves wasted (due to operator error, not mechanical error).
Be advised that because the cutting wire at the tip of the wing is moving 1/3 of the speed as the root of the wing, there will be some extra foam melting at the tip of the wing. At first I worried about this, but the plane looks and flies great without any tip stall characteristics, so I stopped worrying.
ANCHOR CONSTRUCTION
1. Purchase a 4 inch flat "L" corner bracket at your local hardware store. It will usually have two holes on each angle.
2. On one side of the "L" corner bracket drill ¼" holes every 1/2" of an inch. The two holes from the manufacturer are two of the holes you can use.
3. Screw the other side with two holes to the 4" end of a 1" x 4" x 10" piece of wood so the side of the "L" bracket with the holes stands upright in the air.
4. This wood will be "C" clamped or screwed to the table and then connected to the chain link that has the rubber bands through it with a bolt, two washers, and a wing nut.
5. The hole you choose to put the bolt through will decide the dihedral of your cut. The higher the hole on the "L" bracket, the greater the dihedral in the finished wing.
6. The two chain links act as a hinge and allow some movement and take some of the pressure off of the cutting wire.
THE CUTTING BOARD.
If you want to have the ability to mass produce a specific cut, you have to control all of the variables. I have a few wing shapes I cut on a regular basis. For these shapes I make cutting boards.
The EPP foam is expensive, so I try to determine the best layout of the plane in the foam to have minimal waste. The "Wild Wing" is designed to cut both halves out of a 2" x 12" x 24" block of foam. I cut this block diagonally on a 9" to 3" cut giving me two similar pieces out of the one piece of foam. The Wild Wing is swept to 37 degrees and I cut that angle into both the root and tip. After I have decided what wing I want and how to fit it in the foam with minimum waste, I cut 2 pieces of ¾" particle board the exact shape of the foam to be cut.
I write with permanent markers on the foam to help prevent mistakes. (I make sure the longest edge of the foam is the front of each wing core. This is the edge that was cut on the diagonal, otherwise the wing comes out short.)
One piece of the particle board goes under the foam to lift it high enough for the bow to cut the bottom of the airfoil without hitting the table on the switch end of the cutter. This piece of wood also has the airfoil jig attached to the root end of the board.
The other board sits on top of the foam to hold it flat and secure. I put a weight on it during the cut. I have found that weights set on top of the foam without the board can cause variations in the cut because there are variations in the pressures the wire has to pass through. I have had some foam that wasn't flat when I got it and other foam flex during cutting. The top board with weights helps to eliminate these variables.
The alignment with the wire anchor is easier because these boards are the same shape as the foam. When I am cutting 53 of the same core, I screw the anchor and the bottom board to the workbench, (or at least a board that sits on the workbench). When I align the back edge of the foam to the wing shaped board, it automatically aligns the anchor, jig, and the dihedral. We have reduced our cutting time by about 75% and drastically reduced mechanical and operator errors.
When we cut large numbers of wings I set up power supplies, bows, anchors, jigs and boards for both right and left wings. This way we get more people cutting and do not have to make changes in the set up during the cut.
ONE PIECE JIG AND ANCHORED CUTTING WIRE DESCRIPTION
A one piece jig is an airfoil shaped hole in a piece of wood. You trace the airfoil on the inside of the jig rather than the outside of the jig. This makes it so you do the entire wing with one cut and one jig.
If you are cutting tapered wings the one piece jig is more accurate. It does not have to be changed halfway through a wing core eliminating accidental repositioning of the foam and it does not require an automatic cutter for smooth cuts. It is probably 5 times faster than an automatic two-jig system. It only works on an anchored bow.
You will need an airfoil to cut. Here is an airfoil library. There is a great deal of discussion about which airfoils to use. There always will be. Look closely at the airfoils on this list. Notice how different they are. Some of the best flying airfoils I have ever seen were something that someone just drew. The airfoil is important, but your building skill and the weight and balance of your plane and your attention to detail have as much to do with how your plane will fly as the airfoil.
http://www.aae.uiuc.edu/m-selig/ads/coord_database.html
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.
