|Bow Cutter:||24" to 48" Adjustable|
|Hot Knife:||8 inch|
|Bow Cutter MSRP:||$179.95|
|Hot Knife MSRP:||$129.90|
|Available From:||Hot Wire Foam Factory|
Two good people you need to get to know in this hobby are Dave Natal at Hot Wire Foam Factory and Bob Mellen at Flyingfoam. These folks represent what makes this industry so unique: great service, attention to customer needs and products that can't be beat.
Hot Wire Foam Factories is your go-to RC hobbyist supplier for hot wire foam cutting. If you have ever wanted to design your own plane (or other project) and explore the intricacies of hot wire cutting and sculpting using Foam Factory's adjustable 24” to 48" bow cutter and knife with included power supplies and permanent, waterproof Foam Fusion EPS glue, please read on. Whether you are cutting Depron, EPP, or EPS foam this is the best and most affordable equipment on the market.
Flyingfoam.com is one of the premier suppliers of EPP foam in bulk sheets, but they really shine when it comes to CNC foam cutting. They can basically cut anything you want and do so with extreme precision and quality control. They also offer their own line of combat flying wings (with two in the 43" wingspan size and one at 83"), color tape and many great tips for building your own model.
Join Dr. Dave as he works to build his first plane with Hot Wire Foam Factories great foam cutting tools.
The adjustable bow cutter can cut from 24" to 48" and it comes with its own power supply. Included as well are extra cutting wires and clamps for holding your extensions. The bow is equipped with its own power switch, and the power supply has a variable rate dial that you can adjust to meet the needs of your cutting material.
I also received a hot knife that is very handy. It cuts through the foam easily and quickly. I used it to punch through the fuselage for wiring, and for servo cutouts. The hot knife comes in its own case and includes the 8 inch knife, power supply, and how-to DVD for all types of cutting. The knife also has a switch like the bow cutter.
In addition to the bow cutter and hot knife they also provide an awesome foam glue called Foam Fusion that is the ultimate EPS foam glue with waterproof capability. The formula is easy to clean up because it is water based and glues most porous materials. They also have Foam Coat that hardens foam surfaces and Boost that hardens foam even stronger than the Foam Coat.
Check out their complete catalog full of great foam cutting products. The Hot Wire lineup cuts all types of foam including Expanded Poly Styrene (EPS) Styrofoam, Arcel, BlueCor, CellFoam, Depron, and EPP foam.
My goal in this project was to build a plane - nothing fancy and nothing really engineered. I have built plenty of planes so I figured I would use what knowledge I had and explore the nuances of foam cutting.
The great people at Flyingfoam sent me a huge box of EPP foam. Honestly I love this stuff. It is easy to cut, EXTREMELY flexible and paintable. You have to get your hands on some and work with it to fully appreciate its properties.
I decided to build a plane that would take advantage of the foam properties, have low wing loading and hopefully fly well. I have scratch built balsa planes, but never a foam plane. In a way, this is the root of this hobby; you get a chance to design and build using these great tools and EPP and make something that sort of tests your ability.
I decided to use a NACA0018 airfoil that was thick as I could stand, and I also wanted the wing to be a constant chord. I know tapered wings would be lighter, but I wanted lift from the root to the tip, a characteristic that I thought would eliminate some tip stalling and wing rocking. It does not look as streamlined, but just wait.
For a template, I used another great software product for making airfoils called Profili2 created by Stefano Duranti. The basic product is free, but the fully function version is only $20 - what a deal!
I used a hard, heat-resistant Formica counter top material to place the template against. The properties are not perfect: It can chip, and one chip and your template is ruined.
I used ¼” plywood to make a holder for the Formica, and it worked fine. I cut the plywood opening larger than the template making sure to leave enough room so the wire did not touch the wood.
I attached some side braces to screw the template down to my work surface. My work bench is plywood so it was not a problem to put a screw into the surface. I also placed an aluminum angle on the edge of the bench to make sure things stayed square.
My goal for this project was a great flying plane using some excellent tools and materials. I am providing video for you of the cut, but not the actual cuts; I figured I would make mistakes so I did not video the originals. But as it turned out, I only made one mistake. If I can do it, you can too!
I started by trimming a piece of EPP. I needed a square cut on the end to place against the front of the table, so I used a flat piece of plywood and then mounted two squares to the board. Once the foam was in place and square with the two squares, all I needed to do was move the wire along the squares straight down and through the foam. Note that the hot wire gets red hot within about 5 - 10 seconds; Touch it and it will burn severely.
To start the cut, in a well ventilated area, I dialed up the power and turned on the power switch mounted on the bow. When I finished, I turned off the power.
I placed the templates with some EPP foam between them and screwed them down square with the front of the foam. At one end of the template, I made space for the wire to enter and exit the template. This shape determines the shape that the cut will be. I made sure that end of the template did not spread as I pulled it through the hot wire. I pushed down and cut the lower airfoil and then around the leading edge, lifting up to make the top of the wing. There will always be some flex in the hot wire. I gave myself enough room to keep the wire tight as I moved around the template, making sure the template was high enough above the work surface.
Once the wing airfoil was cut, I used the straight bow cutter and trimmed the foam, keeping things straight and square.
I used a band saw to cut the fuselage, rudder and elevator. The EPP foam cuts very well, and the band saw made a smooth flat cut. I used the bow to cut the wing saddle. I placed the bow on the table edge straight up and down and moved the fuselage around to make the cut. I twisted the bow tube slightly to tighten the wire. The wire expands some when hot.
The tail cuts in the same way. This is a smaller cut, and for this project I used a NACA0012 airfoil. I wanted an airfoil on the tail and rudder rather than flat.
My plane was not designed, but rather created. There were a few considerations: I wanted it light (around 600 grams), a wing loading less than 10 oz./sq. ft, a fuselage that could hold the motor and wings that created lift along with the tail.
|Wing Area:||342 sq. in. sq. in.|
|Weight:||20 oz. / 576 grams|
|Wing Chord:||Constant 9.5"|
|Wing Loading:||8.4 oz/sq. ft.|
|Transmitter:||Futaba 9 Cap Super|
|Receiver:||Corona RP8D1 Synthesized|
|Battery:||1800 mAh LiPo 11.1 Volt|
|Motor:||AXI 2808/24 1190KV|
|ESC:||40 amp (pulls 37 amps)|
There really is nothing you can't do with the tools from Hot Wire Foam Factory and Flyingfoam - tapered wings, flying wings, constant chord or any flying surface you want. With the addition of a hot knife (and I recommend a hot wire scroll cutter or a band saw), cutting foam just like the pros is not a problem.
I definitely plan on building more planes. If you have not flown or had any experience with EPP foam you have to give it a try: It's lightweight, flexible and durable. While there may be limits, I am not sure what they are. The combination of EPP and Hot Wire tools is perfect.
I really think the Hot Wire products and the Flying Foam stuff can’t be beat. I was very pleased that when I was finished, I had an airborne plane of my own design and style. It's just fun to work with, forgiving and it is equipment you will have around for along time. So if you ever thought you'd like to try to build a plane from scratch in a few days, this is your chance. I am sure your friends will be amazed when you tell them your newest aircraft was homemade!
Special thanks to Dave and Bob for helping me with this project.Last edited by Angela H; Feb 17, 2009 at 03:33 PM..
The price does seem a bit steep for a simple hot wire bow.
How is the bow tensioned? Rigid bow with manual tensioning?
The way you did the templates will work alright but an easier way that also works very well unless you're going for extreme precision is to attach the templates to the foam core using 2 or 3 nails. Then you can omit the plywood parts entirely. I would consider template holders and a few other refinements if I was cutting highly accurate glider cores but for most purposes the simple approach is perfectly satisfactory.
The only bits that might need some knowledge to source and cost a few euro/dollars are the variable power supply and the wire itself.
A power supply and wire kit would be a much more practical and cost effective commercial product. The producers of this item might consider that as an alternative offering alongside the product presented here?
Last edited by Aio_1; Feb 18, 2009 at 05:03 PM.
I am a DIY guy. I look at things and make them. I was all over the internet looking at this deisgn and that design and they are too complicated for what I wanted. I built a plane in the time it would take to build the components if not not less time. The bow is lightly tensioned. The wire is perfectly measured to fit in the bow with just some pressure. Too much and your wire will break.
Templates have to be square. As well they simply can not move or your cut is ruined. I fixed mine as I saw in many places as I had to keep pressure on the bow to follow the template. More than you might think.
Price a few of these systems and you will find this one is way down the line with great quality for what you pay. Switches, variable power supplies and safety all included.
I have a home made hot wire which has been used to cut many cores over the past twenty years. I made a new bow several years ago and if I recall correctly it really did take me about 20 minutes. It still does a perfectly good job. The tricky bit is getting hold of ni-chrome wire although as mentioned earlier you can apparently also use a guitar string.
Templates can either be internal or external (i.e. the wire runs inside a hole as you did or around the outside of a template as I usually do. The advantage of the external method is that any errors with the bow result in leaving excess material not removing it. That means a correction is possible should you have problems. Also the template can be less bulky without a tendency to deflect from the wire, with the exception of the trailing edge.
You can also use plywood templates (1/16" is best) but they'll get damaged with repeated use.
made surf boards and windsurfboardsfor years
got into rc planes 5 yer ago
power guest pro charge - boat charger
output 12 vdc @6 amps got at flee market 10 bucks
4 bows 2 ft 3ft 4ft 5ft 1 small about 4in for tight work
wire 45 lbs fish wire
60lbs for 4ft 5ft
play with wire for foam
Last edited by joethrasher; Feb 19, 2009 at 07:27 PM.
I made a hotwire myself, too, but by the time I paid for a power supply, purchased the right kind of wire and consider my time, too, getting one for that price seems like a bargain. But then again, designing and flying planes is my hobby, not fiddling around with hardware trying to make it work, so I might have a different focus than some of you.
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