HOW TO MAKE A SWING ARM STYLE FOAM CUTTER
1. You need two pieces of wood a 1x4x48 for the platform and a 1x2x44 for the swing arm. Both need to be cut of straight smooth wood.
2. You will need four 2.5-inch shelf brackets. These are the brackets that are not flat. They look more like a bent ruler.
3. You will need pulleys. I found some 1.25" patio door replacement rollers at the local hardware store that can be bolted down easily. These rollers make good pulleys to guide the cutting wire forward. It takes four to six of the pulleys to route the string from the end of the core, over the edge of the table to the vertical swing arm that pulls the wire with gravity.
4. The strings have to be strong enough to not stretch at all. I have used fly line leader, Spider Wire fishing line and coated wire fishing leader. Be careful if you are using any type of wire for the strings. Wire carries electricity and can shock you by bringing the power to you from the cutting wire. If you use any type of wire you have to electrically isolate the cutting wire by putting a non conductive string in the loop. I use a regular fishing snap swivel to connect to the cutting wire. Snap swivels can handle the heat and are easy to use.
5. Center and mount 2 of the shelf brackets 36" apart on the top back edge of the platform. They catch the wire when it exits the foam so it doesn't pull into the pulleys.
6. Center and mount the other two shelf brackets 40" apart on the bottom front of the platform. I set them back 3/4" so there is room for the swing arm under the edge of the platform. They are to keep the platform from pulling into the core being cut and to mount the swing arm so it can rotate freely.
7. I mount the swing arm with a screw through one of the existing holes in the left shelf brackets that is under the platform with a short flathead screw. I connect it to the left end of the swing arm 1" from the end. The screw needs to be loose enough to allow free movement of the bow but tight enough to be secure.
8. I put a short, small-head nail in the other end of the swing arm that easily goes through a hole on the other shelf bracket to hold the swing arm in place when not in use. When you lift the swing arm free this end of the bow will drop.
9. The pulley positions depend on the length of core you are cutting. I position one pulley in 2" from the left side of the platform. It works best if you position the edge of the pulley over the back edge of the platform.
10. I then drill pilot holes that allow me to position pulleys along the top back edge of the platform that are the length of core being cut plus 2" away from the main pulley to leave room for the strings. Most of my cores are cut 18", 24" or 30" so I drill holes respectively and continue out to the end of the platform.
11. The top and back pulleys should be off-set with the instructions given so they do not touch each other.
12. I have been cutting foam long enough that I have put pulleys in all of the different holes and leave them there so I do not have to re-position them if I cut different lengths of cores.
13. You now need to draw alignment lines on both the platform and on the swing arm to represent the different ratios you may want to cut. The best way I have found is to put the first line on the swing arm over the screw that the arm rotates on. This is 0 %.
14. Proceed down the swing arm putting a line every 4" until you have made 11 lines. The first line mentioned is 0% the second is 10% the third is 20% and so on until you get to 100% or the 11th line.
15. Use a felt tip marker and make these dark lines. Label these lines appropriately as 0%, 10%, 20% and so forth for quick reference.
16. Using a framing square transfer a line up on to the back edge of the platform accurately marking all of the same lines on the back edge of the platform.
17. Drill pilot holes for pulleys in the middle of each of these lines on the back edge of the platform. These pulleys will route the strings from a horizontal pull to a vertical pull when used in combination with the pulleys previously installed.
18. Put a large head nail in the middle of each of the lines on the swing arm to help secure the string at a precise point so it will not slide while in use.
HOW TO USE THE AUTOMATIC FOAM CUTTER
1. Clamp the platform to the table in a place where it aligns with the bow hanging from the hook in the ceiling.
2. Set up the wood cutting board that the foam will sit on.
3. You will cut the bottom of the airfoil first cutting front to back on the airfoil. The back of the airfoil will be against the wood platform with the pulleys.
4. Mount the jigs for the cut of the bottom of the airfoil on the ends of the wood cutting board with both airfoils pointing away form the platform.
5. Put the foam on the cutting board and align the front edge of the foam with the start of the leading edge of the airfoil on the jig.
6. Put the weights on the foam.
7. If your wing is tapered you need to calculate the ratio between the two airfoils so you know how to route the string. If you are cutting a 9" to 7" core, you can hook to the 90% and the 70% marks on the swing arm to get the right ratio.
8. Make sure you cut both a right wing and a left wing.
9. Make sure you have the pulleys positioned so that the top pulleys are slightly wider than the foam to be cut and the back pulleys are mounted over the percentage that corallites with the cutting ration you want to cut. Which, in this case, is the 90% and the 70%
10. Snap the swivels with the string around each end of the cutting wire and position the cutting wire at the leading edge of the wing to be cut.
11. Route the string first through the pulleys on the top of the platform then over the pulleys on the back of the platform. Take the string from the 9" jig to the 90% point on the bow. If you reverse the strings the airfoil will be ruined. Do the same for the 70% airfoil.
12. Make sure that the angle of the string exit from the jig is as straight as possible towards the pulleys. If it is not straight one side of the bow may drop as the wire exits the foam. This is a problem if the cutting ratio on the swing arm is not exact.
13. Use a hand clamp to secure the string to the swing bar after wrapping it around the proper nail.
14. Lift the swing arm off of the catch so it is free hanging.
15. Make sure both strings have the same amount of tension.
16. Prepare to assist the cutting wire to follow the jig for the first of the airfoil. It will tend to hesitate.
17. Make sure you have cleared your work area so the bow is free to move. Make sure the bow isn't dragging on the table. Make sure there is enough slack in the rubber band suspension system to the ceiling, so that the bow can make the entire cut without meeting resistance. I have also had my swing arm hit an open drawer on the desk that is my cutting station. Make sure the system is working.
18. Turn on the power and watch for problems.
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.
