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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Thanks a lot for the interesting information. I thought of a way you could make a deeper “bow” using two dowel sticks held at an angle with a couple of wood disks. Think of two “tinkertoy” ( remember those? ) sticks stuck into two of the wood wheels, and the two wood wheels held together so the sticks were at a slight angle ( maybe 120 degrees ) to each other. Then you would not have to bend the dowel so much, and the depth of the cut could be greater ! Just a thought.
Again, thanks for your informative page.
Jim S
Jim,
I think that would work well. As long as it holds enough tension in the cutting wire, you’d be good. Bob’s method originally came about as a result of some experimentation, so you have the right idea. Feel free to try it out — then come back and let me know here how it worked!
Roy Furr
Editor
FoamWingCutting.com
Thanks, Iwill try it
Roy could you also use a child’s fiberglass archery bow for the frame of the foam cutter ? that would surely have tension on the wire at all times..Just another thought..
Thanks Don for the recommendation. That’s actually something Bob mentions in the video — that if he ever came across the right archery bow he’d use that. Although it’s hard to beat the dowel rod for weight, affordability, and for the fact that it just plain works. Of course, you’re free to experiment! Roy
Thanks for the first lesson
George, you’re welcome! Roy
Thanks for the first lesson!!!
nice!!
Thank you For The First Lesson.
thanks for the info,interesting and inexspensive,simple is always the best
This is a huge point, I wish I would have thought of this earlier.
Great and easy way to foam cutting..will try it out and make several sizes for diff types of cuts..
Thanx
Thanks for this lesson. I was ready to go out and build the traditional type bow with turnbuckles etc. This is inspired.
I did have trouble reading the text in figure 4.
thanks, again.
In the drawing it appears that there are circular rings at the end that the wire loops around. Is this correct? The drawing does not explicitly state what they are and it was a bit confusing to me. Please advise and thanks in advance.
Regarding the loops — we re-purposed that drawing, which is to show you how to put ends on your lead-outs for C/L planes. That loop is a grommet, and is unnecessary here. You just need a loop that’s big enough to go around the ends of the dowel and rest in the notches you cut for the wire. Roy
Roy: your process sure is a lot easier than what I have come up with. And, to use the wire you do is so much better than nichrome, which I have used for years.. Thanks for the lesson. Roger
I really like this first lesson it helped to answer some questions and point me in a direction taht works and is cost effective.
thanks
Hi Roy,good advice thanks.
set up the bow great, simple works!
but i use styrofoam, very dense! and the wire seems to lag no matter what,
how do you stop it lagging?
i also used fishing steel trace wire ! is this ok,
regards, John (UK)
Hey John, usually the reason a wire would lag is that it is not hot enough. The solution here is to get thinner wire, or more power. I know Bob prefers the .012 braided steel wire he also uses for C/L flying. If your wire is thicker than this, that may be the problem. Also, Bob uses an auto battery charger as a power supply. Depending on what you use, if there’s less power it may not work. One other alternative may be a lack of patience. Hot wire foam cutting is S-L-O-W and trying to rush it can cause problems. I know I personally have trouble with the patience required!
But if your wire thickness is okay, and you have sufficient power, then your solution might be to exercise a little extra patience to ensure optimum results. I hope this helps. Good building, and great flying! Roy
Appears it is fairly lively around here
Hi Roy,
Thanks for this first lesson. I am a pensioner and money is always tight and I am unsure as to whether I would go down this path, so I look forward to these lessons to give me some ideas and guidance to make up my mind.
Ian Hughes. (Australia)
thanks for first lesson
Thank you for the first lesson.I would have to cut my glider wings in stages,as one wing is 1.8m long.
the first try for me was using 0.8 steel mig welding wire, which seemed to be adequate for the job, but patience is the answer if you feel the other variants are right!
another try out was the electrical wire from a heater, which after rolling out the coil was very effective.
the more resistive the wire, the more heat per unit input you should get up to a point.
nichrome wire does wot it says on the tin, and thats where i have rested my case! good luck, and always leave a little extra for remedial sanding!
Thanks for the excellent information. I’ll get that NLA wing by cutting my own!
Thank you Roy for a treasure trove of good information. Cannot wait to get started on my first bow.