Making and Using A One Piece Jig
Here is a simple, inexpensive, safe foam cutter you can make and use that really works. By Lee Aston
HOW TO MAKE A ONE PIECE JIG
1. Find the airfoil you want and enlarge it to the size you want. The Wild Wing uses the top half of the SD7032 and the bottom half of the SD6060 which are both on the list.
2. Enlarge the airfoil to the size you want. The Wild Wing is a 9" root core.
3. With a spray adhesive, glue this pattern to a piece of flat Formica.
4. Cut the Formica carefully and accurately and sand to an exact shape. This piece will be used to create the cutting jig.
5. Glue a piece of Formica, slick side out, on each side of a piece of Masonite or ¼" plywood.
6. The single jig has to be strong. It has to be big enough to not flex when the cutting wire is tracing it. I leave ½" behind the jig and have 2" of solid jig ahead of the wing core and 1.5" of jig above the thickest part of the airfoil and enough jig below the airfoil to screw it into the side of the cutting board and still leave a ¼" space for the cutting wire.
7. My Wild Wing airfoil is cut into a 12" x 3.5" laminated jig as described.
8. Square the piece just glued.
9. Stand it next to the cutting board and draw a line that will mark the thickness of the cutting board down the length of the jig.
10. Place the Formica pattern you have already made on the jig and align its center line to 0 degrees with the cutting board line.
11. Leave ¼" to 3/8" for cutter wire clearance between the airfoil and the cutting board. Make sure your foam is thick enough that you will not cut through the top of the foam with the jig design.
12. Position the pattern jig leaving ½" behind the jig for the wire to enter the trailing edge of the airfoil. Trace the Formica pattern you have already made with a thicker pen or thin felt tip
13. You have to cut the airfoil in the jig bigger than the airfoil you want because the cutting wire will leave a small space, as it cuts almost the same as a saw blade. The thick line will give you that extra little space you will want as you cut your jig.
14. Cut an access slot following the airfoil to the trailing edge of the wing. This is needed for your band saw to cut the jig and for the cutting wire to cut the core.
15. Carefully cut the jig making sure it is smooth and as close to the desired airfoil as you can make it. I spend time hand sanding and using a fine file to the final line rather than using power tools. Make sure both sides of the Formica jig are the same because one side will be cutting the right wing and the other side will be cutting the left and they need to be the same. Your core will be no better than the jig. The test will come on your first cut as you put your pattern against the core you cut and see how close you came. I have had to re-cut a jig before because it just was not close enough.
HOW TO CUT WITH A ONE PIECE JIG
View the Foam Cutting Video- Before you try to cut EPP foam learn on some EPS. Test your cutter. Learn how fast to cut and how hot to set the temperature.
- Screw the jig to the root end of the cutting board making sure the front of the jig is to the front of the wing core.
- Wax the jig with a candle or ski wax where the cutting wire will touch.
- Attach the chain link on the bow with the rubber bands through it to the anchor with a bolt and washers. It needs to be a solid connection. Make sure you have adequate movement for the bow.
- Attach the anchor to the table with screws or 2 "C" clamps.
- Align the foam with the trailing edge of the cutting board.
- Put the top board and weights on the foam.
- Move the cutting wire around to the front of the cutting board to make sure that you have the proper distance and angle from the wire anchor.
- To make the tip of the wing bigger to fit the foam, move the core away from the anchor. To make the tip smaller move it closer to the anchor.
- Align the wire with the back edge or trailing edge of the foam.
- Place the cutting wire in the slot of the jig.
- Turn on your ventilation system to protect you from the smoke and fumes.
- Turn on the power. Hopefully you have already done some test cuts and know the cutter is working well and how hot the wire has to be to cut your foam. I recommend you practice on EPS or common cheaper bead foam before cutting the EPP.
- Cut the bottom first. Trace the airfoil. Your cutting speed will depend on the temperature of the wire and the type of foam you are using. You will get the feel for it quickly.
- Do not let the wire come off the jig or the cut will be ruined. This is where most errors occur.
- Slow down slightly for the leading edge so that you are sure the wire is not lagging behind the bow. If the cutting wire is lagging, the leading edge will not be straight. If you cut too slow, the wire will over cut on the leading edge and the tip of the wig will be too small.
- Turn off the power after the wire has totally exited the jig.
- Remove the foam from the cutting board.
- Split the foam cut open from the trailing edge. EPS foam core come out fairly easy but EPP will stick. Because there is only one cut made you will have to be careful as you pull the core out of its bed. The place that sticks the most is the thin trailing edge where the wire exits the foam. Use an exacto knife or razor blade to free the core from the bed. If you try to tear the core free it can tear the trailing edge of the wing.
- If you get a tear, use a low-temperature hot glue gun and glue the piece back in.
- Look closely at the core and learn from what you see. If there are cutting lines on your core, your cutting speed may not be right, your jig may not be smooth, your wire temperature may not be right, or your wire may be too loose in the bow. Experiment on scraps as you learn to cut. You will get the hang of it.
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.
