How to make a low-cost, lightweight foam cutting bow!
Hand cutting foam wings is not difficult but requires some tools that are expensive if purchased commercially. Fortunately, most of those tools are not difficult to make yourself.
The key to cutting foam wings is a bow that allows the cutting wire to stay tight as the wire heats up. For years I have used a very simple, lightweight bow that allows accurate cuts to be made with only one person. The cutting wire is simply .012 7 strand stainless steel control line flying wire. Similar wire can be found in large sporting goods stores that stock supplies for making your own fishing tackle and is sold as beading wire at craft stores but is plastic covered and will not work for cutting foam wings.
Single strand steel wire will work but you will need to go to a larger diameter and forming the ends is more difficult. The correct .012 wire is available from several companies including Sig Manufacturing, Brodak, and Sullivan. If your local hobby shop does not carry this item it can be ordered directly from the Brodak or Sig web sites. Stainless steel is made from steel and nickel. Hobby shops sometimes carry nichrome wire which is steel wire with nickel and chrome in the mix. Nichrome works well but is much more expensive and breaks more easily.
My bow is made from a 36″ long 1/4″ diameter dowel and XX inches of .012 wire with loops formed on each end. The dowel is notched at the ends to hold the wire and bent to make a bow shape. Because the wood dowel wants to straighten itself out it provides the tension needed to keep the wire tight as it heats. The only real issue is that the dowel quality needs to be high enough that it bends without breaking. If you have it available, you can use 1/4″ square stock found at some hardware stores for a bit more strength without gaining too much weight.
This is a very lightweight bow that is the key to easily cutting a wing without a helper. I have used heavier bows and they quickly become clumsy and accurate cuts are harder to make without help.
Forming the ends on the wire uses techniques that are common to control line modelers. The AMA website shows how to make strong loops in their rulebook. There are a number of options on how to make up wire ends shown. For a bow, the simplest technique is to use crimped tubing to make your loops. If you are a control line modeler who has ever made up a set of flying lines it is okay to use the technique that you are familiar with. Although it may be possible to simply tie the wire it will not be as secure and will probably fail while you are trying to cut the foam. Instead of using the brass thimbles shown below leave the loops large enough to go around the dowel and into the notch you cut at the ends of the dowel.
For .012 wire you will need two 3/4” long pieces of 1/16” diameter copper or brass tubing. Using too large a diameter of tubing makes it impossible to get a good crimp. Copper tubing is easier to work with as brass is a harder metal. Hobby shops used to carry line crimping kits and you can still order them from Sig and Brodak. Large sporting goods stores also carry tubing that you can use to make crimped lines in the fishing tackle section. Fishermen make up steel leaders for fishing for trout and salmon.
If your local shop does not have them you can also cut the short pieces of tubing yourself from a longer piece of 1/16 tubing. The easy way to do that is to run a piece of 1/16 wire through the tubing to keep it from collapsing. Next roll the wire under a hobby knife at the 3/4” mark to score the tubing. You will not be able to cut the copper tubing with a hobby knife. Once it is scored pull the wire partially out of the tube so that slightly less than 3/4” of wire is left in the tubing. Holding the wire in one hand and the tubing in the other flex the tubing. If you have the wire ending at the score mark the tubing will break easily at the score.
Once you’ve created loops at both ends of your wire, put one loop into the notch you’ve cut at one end of the dowel rod. Bend the dowel rod gently, until you are able to hook the other loop into the notch at the other end of the dowel. That’s all it takes, and you have a low-cost, lightweight foam cutting bow for cutting your own foam wings.
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