Lee's Blog

Free Foam Cutter Plans

by Lee, February 24, 2005

FREE FOAM CUTTER PLANS

Here is a simple, inexpensive, safe foam cutter you can make and use that really works. With a little practice, you will be able to cut excellent quality cores. I've also included plans for the power supply and accessories that can make your cuts look like they were cut by a CNC.

On January 27th 2005, with two of these cutters cutting wings and one cutting the trailing edge, 6 of us set up a production line and cut 53 EPP "WILD WINGS" or 106 EPP halves in less than 2 hours with only 2 single panel rejects which were both caused by operator error and not equipment error.

I'm including free plans for my EPP "WILD WING" which is one of the most surprising and enjoyable planes I have flown in my 33 years of flying. It is an excellent slope soarer, and glides well even carrying a motor and lipo battery. I have had 1.5 hour flights with the motor off. Powered slope soaring is a new experience. The motor makes it so you don't have to go chase your plane because you can power back. Slope soaring is still fun when there isn't any wind.

Under power the "WILD WING" is fully aerobatic and a great stunt and EPP combat plane for your local field. We have some planes that will do unlimited vertical, 90+ mph and roll rates of more than 6 a second with a brushless motor and 3-4 cell lipo batteries. With the J250 motor we have used the plane as a nearly indistructable trainer in our club. It is a glider remember.

The construction of the "WILD WING" is described through the text to help teach each technique as it is discussed. I hope you like it. It will be a good project to try out your new foam cutter. It's simplicity makes assembly quick and easy. You will find specific assembly instructions for the plane on our club site.

Don't be afraid of the cutter, but don't hurt yourself by being careless. No matter how many instructions are given, nothing can replace your common sense and safety-minded use of this tool. I have cut for 22 years and have never been shocked, but I have been burned several times by a drip of hot plastic off of the cutting wire. Sometimes things don't look hot that are hot.

Think of foam cutting in the same way as you think of welding. If you are welding you take safety precautions and have safety gear and no one gets hurt. If you have questions, get on the internet or talk to an expert and find some answers.

I hope this information will be helpful. I'm a hobbyist not an electrician or an engineer. What I'm going to tell you is the way I've 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.

The following ideas will help you design a system that is safe.

FOAM CUTTING SAFETY CONCERNS

1. Electrical shock
2. Hot wire burns
3. Inhalation of toxic fumes

TO PREVENT ELECTRICAL SHOCK

1. Have safe habits in handling power.
2. Always use a GFI outlet.
3. Have a warning light to tell you if the power is on.
4. Have easy access switches to turn the power on and off.
5. Use a low voltage power supply.
6. Put the GFI, dimmer, and outlet in a receptacle box with a cover plate and silicone the transformer connection points so you have no exposed high-voltage or low-voltage contact points.
7. Have your hot cutting wire electrically insulated from the bow so you have less chance of making accidental contact.
8. Check your work area and remove or cover all grounded tools or equipment that could ground you and complete an electrical circuit through your body.
9. If your wire breaks do not touch it until the power supply is off, the bow switch is off and the power supply is unplugged from the wall because both ends of the wire could still have power!!!
10. It is possible to have the power on, but you cannot see that it is on, because the dimmer is set so low. Turn off both off switches on the bow and on the dimmer then unplug the power supply from the wall if you are finished cutting. When I'm done cutting I plug the power cord into the GFI on the power supply to let me know for sure the power cannot still be on.
11. Don't cut standing barefoot on concrete or any damp surface. Wear insulating shoes.
12. Some of the assessories are made of metal. Metal carries electricity. Insulate most of the exposed metal assessory surfaces as you can with clear or duct tape to prevent accidental contact. 13. Do not use wire on the automatic swing arm cutter to pull the cutting wire through the foam. It will carry power off of the cutting wire to the swing arm where you don't expect power. Use a non stretching non electrical string such as a heavy Spider Wire fishing line.
14. Have everyone else move back when the power is on to keep them safe and to keep them from distracting you.


TO PREVENT BURNS

1. Don't touch anything that is hot. Some things don't look hot but are.
2. Have a warning light so you know when the foam cutter is on and the wire is hot.
3. Have adequate working space around the foam cutter.
4. Watch out for the hot plastic drips that can occur on the wire and table when cutting.
5. Wear protective gear such as welding gloves if your hands are close to the cutting wire.
6. Move flammable paper, plastic, cloth and liquids from cutting area.
7. Slow down and think about what you are doing and what you are about to touch.

TO PREVENT INHALATION INJURIES

1. Only cut in well ventilated areas.
2. Don't breathe the toxic smoke off the cutting wire. Avoid the smoke. Think of it as dangerous.
3. Use a fan to bring a supply of fresh air around the cutter and an exhaust fan to blow the toxic smoke away. I use both.

THIS IS MY CUTTING SYSTEM


The electrical schematic will be added as this site is assembled.


POWER SUPPLY ASSEMBLY See the attached schematic of the foam cutter.


1. THE POWER CORD. Cut the female plug off of a 3 wire extension cord with ground. Leave the male plug and at least 4 feet of wire.

2. THE GFI. Expose 4 inches of the internal wires and strip 5/8" on all three wires; connect to the power source side of a GFI outlet. The small side of the plug goes to the hot connection, and the large side of the plug goes to the common. Make sure the ground is also connected. The GFI will not cut the low voltage power to the bow from the transformer but it will cut the high voltage power inside the power supply and to the transformer. Use an outlet power checker to make sure you wired it correctly.

3. THE DIMMER ON/OFF SWITCH. The dimmer is both the power control and one of the two on/off switches in the circuit. The dimmer will have three wires in most cases, two black and one green. The hot side line out (or load) of the GFI is connected to one of the dimmer's black wires. The other black wire goes to the hot side of a regular wall outlet (the small slot side). The green wire connects back to the ground connection on the GFI outlet. I have built 3 of the power supplies as described and have found I like the slider version of the dimmer switch better than the rotary version. The slider version is the same shape as the GFI and a square face outlet can also be used to make the final product look better and fit under a readily available triple switch plate or outlet cover.

4. FUSES. It has been recommended that a fuse be place both between the dimmer on/off switch and the transformer and between the transformer and the cutting bow. I have not used fuses in my present power supplies but would like to pass along this safety idea.

5. THE WALL OUTLET. The household outlet will be controlled by the dimmer along with the transformer. The hot side (or small plug side) of the outlet is connected to the second black wire from the dimmer on/off switch. The common wire from the load side of the GFI will attach to the common wire side (or large plug side) of the outlet. Connect a wire from outlet ground back to the ground on the GFI. I plug a 40 watt bulb that is in a two prong plug adapter in this outlet to let me know that the power is on and if the power is reduced by the dimmer.

6. THE TRANSFORMER. There are many styles of transformers on the market. I have tried four styles that have all worked well. A 24-volt 5 amp transformer is preferred. I tend to use around 4 amps when cutting with the single strand 0.020 wire on a 40" bow. The 3 amp transformer seems to handle 4 amp output well but it is above it's rated limit. Your transformer may have different wiring than the ones I have used. Some transformers have solder tabs and others have wires that are permanently attached. If you don't know what you are doing please get help. Check your amperage and voltage before cutting. The 120-volt connections on the transformer are connected to both sides of the wall outlet. Polarity doesn't usually matter. Use the screws on the sides of the wall outlet for easy connections. The three tabs on the reduced volatge side on the transformers that I have recommended will be labled 12V - 0V - 12V. To get 24 volts you connect both of the wires going to the bow to the 12V tabs. You might have to solder wires to the transformer connection points. When you mount the transformer on its wood base, make sure you install a ground wire from the frame of the transformer back to the GFI ground. Silicone all exposed wires or connections to prevent accidental contact. Sources for the transformer are listed later in these instructions.

7. THE CUTTING BOW. The bow is made from a 1" x 4" x 54" pine board. I drill a 3/8" hole at 90 degrees two inches in from each end the entire 4" depth. In each of these holes, I gently tap in a 12" landscape spike that is sold at local hardware stores. Do not slant the spikes, because if you do, the rubber bands tend to slide up the bow as it is being used. Longer bows can be made as needed. It only costs about $5.00 to make a bow. I have five different bows all for different purposes.

8. THE BOW SUSPENSION. The bow is suspended by a nylon cord tied through two holes in the bow. This is attached to a triple chain of #64 rubber bands that reach up to an eyehook in the ceiling. A triple chain means you make a rubber band chain with three rubber bands at a time. This chain will connect to an eyehook in the ceiling and needs to be long enough that the bow will gently rest on the table in an upright position. I like the rubber bands because they are inexpensive and simple. This suspension method lets the bow float as though it had little weight and is much simpler than the weight and pulley systems I have seen. This suspension system uses very little space and is what I used back in my apartment days. It works so well I keep using it.

9. THE CUTTING BOW POWER SUPPLY WIRE. Make sure you connect to the 24 volt connections on the transformer. Cut off both ends of a regular two-wire 13-amp 1600-watt extension cord wire. Attach 12-15 feet of the wire to the bow. Alligator clips with insulating covers are recommended for attachment to the cutting wire.

10. THE SECOND ON/OFF SWITCH. I put a house light on/off switch on the end of the bow without the rubber bands. (See the schematic.) Put a regular switch plate on the front of the outlet. Make sure you silicone the back of the switch so you cannot ever touch the bare wires. This switch lets you control the power without letting go of the bow.

11. THE CUTTING WIRE. I like single strand 0.020 chrome nickel alloy fishing line. The 0.018 is rated at 69 pound test. The 0.020 is rated at 88 pound test. This wire keeps the amps to 3-4.5 on the transformer. Check the amps before you cut whichever wire you choose. You don't want transformer failure. The cutting wire is wrapped around the chain link a couple of times and then around itself several times. Try not to kink it because it will be weak. A broken wire can cost you a foam core or a knuckle or two especially while stretching the rubber bands. A source for this wire is listed at the end of the instructions.

12. ELECTRICALLY ISOLATE THE CUTTING WIRE. You need to try to electrically isolate the wire so that you can only make electrical contact with power by touching the cutting wire itself. Insulate each of the spikes with heat shrink or electrical tape and wrap a strong small cord through the chain link several times; tie and superglue it so it isolates the cutting wire from the spike by leaving a small gap. Make sure this connection is strong because there will be tension on the wire.

13. RUBBER BANDS AND CHAIN LINKS. There will be one 1.5" chain link on the switch side of the bow and two of the 1.5" chain links that are still connected on the rubber band side of the bow. I leave a 4-6" gap to put the #64 rubber bands across to properly tension the cutting wire. I usually have 2x-4x #64 rubber bands doubled through the chain link and stretched around the spike. The rubber bands automatically adjust the tension as the wire stretches and have enough stretch to tolerate the anchor for the bow that will be described later. If you have repeated breaking of the cutting wire loosen the tension on the cutting wire by decreasing the gap between the spike and the chain link. When the wire is hot it will stretch and break if the tension or temperature is too high.

14. THE OUTLET RECEPTICAL BOX. I have installed my GFI outlet, my dimmer on/off switch and the wall outlet in a regular three fixture plastic receptacle box. I use a matching face plate to cover all electrical wires. I wish I could also get the transformer to fit in the box but I haven't figured that one out yet. I mount the box on a piece of wood and mount the transformer next to it making sure the transformer frame is grounded to the GFI. I also put silicone or hot glue on all exposed transformer connections to prevent accidental contact. No bare wires should be exposed anywhere on the power supply.

LINKS TO BUY TRANSFORMERS, WIRE AND EPP FOAM

The power supply kit sold by Aircraft Spruce works well. It is recommended by Burt Rutan for cutting passenger-carrying, full-sized homebuilt aircraft. The parts from this kit can be used in the power supply I use. This is a 24 volt 3 amp transformer. Most of my cutting wires draw around 4 amps and this transformer can deliver it but it is above it's rating. Try to find a 5 amp transformer so you can stay within it's rated limit. This system does It does require assembly and the purchasing of a common household outlet and a GFI outlet. If you don't understand the plans, get help building the cutter from someone who does:

http://www.aircraftspruce.com/catalog/cmpages/hotwirekit.php

The transformer listed below has a 24 volt 5 amp rating. You can buy this one at All Electronics and get the dimmer, GFI and the wall outlet at your local hardware store.

http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item;=TX-245&type;=store

Heating this wire is the sole purpose of this power supply. If you look at the link above Aircraft spruce also has some cutting wire. The wire they offer is 0.032 and 0.041 gauge. The wire cuts well but draws higher amperage than the transformer is rated for on a 40 inch bow. I have had it draw as much as 9 amps with the 24 volt, 5 amp transformer.

There are many kinds of wire and everyone has their favorite. My favorite is single strand chrome nickel fishing leader sold by Mason Tackle Company. Fishing leader is a good cutting wire because it is small and strong. I have tried multi strand wire and had it cut well, but it does not slide over the jigs as well and tends to draw more amps than the transformer is rated for.

Here is a source for the chrome nickel fishing leader. Thorne Bros sells the fishing leader in many sizes including 0.022, 0.020, and 0.018 gauges. The 0.020 is a good wire to start with if you are making a 40" bow. It comes in a 25 foot package or a 1/4 lb roll.

http://www.thornebros.com/muskie/terminal_tackle/leader_components/lc_mason.html

Here is a source for EPP foam. I usually order sheets of the 2" x 24" x 36". This is enough foam for 3 "WILD WINGS" if you don't make any mistakes.


http://flyingfoam.com/foamsheet.html


FOAM CUTTING ACCESSORIES MAKE CUTS LOOK PROFESSIONAL

In order to help you understand the different tools and techniques we use, I am going to tell you how to set up the tools to cut a "WILD WING" which is our club contest and combat flying wing. It is a technical cut and uses many different tools and methods that we have refined. These techniques can be applied to any wing you want to cut.

THE ANCHOR.

The anchor is the device that anchors one end of the cutting wire so that it will not move. It is a simple device with no moving parts. One end of the wire is anchored; the other end traces a single jig. Because one end of the cutting wire is connected to a fixed point, every movement of the other end of the bow will cut a perfect taper its entire length of any airfoil you choose to cut.

The "WILD WING" is cut with an anchored bow set up. The foam cut is 24" long and a 9" to 3" taper. To date we have cut over 124 Wild Wings, or 248 halves, of this plane to date with only 5 halves wasted due to operator error, and one wasted to a broken cutting wire.

Be advised that because the cutting wire at the tip of the wing is moving 1/3 of the speed as the root of the wing, there will be a slight overcut caused by extra foam melting at the tip of the wing. At first I worried about this, but the plane looks and flies great without any tip stall characteristics, so I stopped worrying.

ANCHOR CONSTRUCTION

1. Purchase a 4 inch flat "L" corner bracket at your local hardware store. It will usually have two holes on each angle.
2. On one side of the "L" corner bracket drill 1/4" holes every 1/2" of an inch. The two holes from the manufacturer are two of the holes you can use.
3. Screw the other side with two holes to the 4" end of a 1" x 4" x 10" piece of wood so the side of the "L" bracket with the holes stands upright in the air.
4. This wood will be "C" clamped or screwed to the table and then connected to the chain link that has the rubber bands through it with a bolt, two washers, and a wing nut.
5. The hole you choose to put the bolt through will decide the dihedral of your cut. The higher the hole on the "L" bracket, the greater the dihedral in the finished wing.
6. The two chain links act as a hinge and allow some movement and take some of the pressure off of the cutting wire.

THE CUTTING BOARD.

If you want to have the ability to mass produce a specific cut, you have to control all of the variables. I have a few wing shapes I cut on a regular basis. For these shapes I make cutting boards.

The EPP foam is expensive, so I try to determine the best layout of the plane in the foam to have minimal waste. The "WILD WING" is designed to cut both halves out of a 2" x 12" x 24" block of foam. I cut this block diagonally on a 9" to 3" cut giving me two similar pieces out of the one piece of foam. The "Wild Wing" is swept to 37 degrees and I cut that angle into both the root and tip. After I have decided what wing I want and how to fit it in the foam with minimum waste, I cut 2 pieces of 3/4" particle board the exact shape of the foam to be cut.

I write with permanent markers on the foam to help prevent mistakes. (I make sure the longest edge of the foam is the front of each wing core. This is the edge that was cut on the diagonal, otherwise the wing comes out short.)

One piece of the particle board goes under the foam to lift it high enough for the bow to cut the bottom of the airfoil without hitting the table on the switch end of the cutter. This piece of wood also has the airfoil jig attached to the root end of the board.

The other board sits on top of the foam to hold it flat and secure. I put a weight on it during the cut. I've found that weights set on top of the foam without the board can cause variations in the cut because there are variations in the pressures the wire has to pass through. I've had some foam that wasn't flat when I got it and other foam flex during cutting. The top board with weights helps to eliminate these variables.

The alignment with the wire anchor is easier because these boards are the same shape as the foam. When I am cutting 53 of the same core, I screw the anchor and the bottom board to the workbench, (or at least a board that sits on the workbench). When I align the back edge of the foam to the wing shaped board, it automatically aligns the anchor, jig, and the dihedral. We have reduced our cutting time by about 75% and drastically reduced mechanical and operator errors.

When we cut large numbers of wings I set up power supplies, bows, anchors, jigs and boards for both right and left wings. This way we get more people cutting and do not have to make changes in the set up during the cut.

ONE PIECE JIG AND ANCHORED CUTTING WIRE DESCRIPTION

A one piece jig is an airfoil shaped hole in a piece of wood. You trace the airfoil on the inside of the jig rather than the outside of the jig. This makes it so you do the entire wing with one cut and one jig.

If you are cutting tapered wings the one piece jig is more accurate. It does not have to be changed halfway through a wing core eliminating accidental repositioning of the foam and it does not require an automatic cutter for smooth cuts. It is probably 5 times faster than an automatic two-jig system. It only works on an anchored bow.

You will need an airfoil to cut. Here is an airfoil library. There is a great deal of discussion about which airfoils to use. There always will be. Look closely at the airfoils on this list. Notice how different they are. Some of the best flying airfoils I've ever seen were something that someone just drew. The airfoil is important, but your building skill and the weight and balance of your plane and your attention to detail have as much to do with how your plane will fly as the airfoil.


http://www.aae.uiuc.edu/m-selig/ads/coord_database.html

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 1/4" plywood.
6. The one piece jig has to be strong. It has to be big enough to not flex when the cutting wire is tracing it. I leave 1/2" 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 1/4" 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 1/4" 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 1/2" 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 entering the airfoil on 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 wing 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 right and left sides of the one piece Formica jig are the same because one side will be cutting the right wing and the other side will be cutting the left. 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 for my satisfaction.

HOW TO CUT WITH A ONE PIECE JIG

1. Before you try to cut EPP foam practice on some EPS foam. Test your cutter. Learn how fast to cut and how hot to set the temperature.
2. 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.
3. Wax the jig with a candle or ski wax where the cutting wire will touch.
4. 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.
5. Attach the anchor to the table with screws or 2 "C" clamps.
6. Align the foam with the trailing edge of the cutting board.
7. Put the top board and weights on the foam.
8. 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.
9. 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.
10. Align the wire with the back edge or trailing edge of the foam.
11. Place the cutting wire in the slot of the jig.
12. Turn on your ventilation system to protect you from the smoke and fumes.
13. 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. EPP foam will cut about half the speed as the EPS foam.
14. 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.
15. Do not let the wire come off the jig or the cut will be ruined. This is where most errors occur.
16. 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.
17. Turn off the power after the wire has totally exited the jig.
18. Remove the foam from the cutting board.
19. 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 pull the core free it can tear the trailing edge of the wing.
20. If you get a tear, use a low-temperature hot glue gun and glue the piece back in.
21. 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.

THE GUILLITINE AND THIN SHEET FOAM SLICER DESCRIPTION

The guillotine is a frame that guides the cutting wire in an accurate vertical cut. It uses the bow which has already been described. The bow is still suspended by the rubber band chain from the ceiling. It is used for cutting the foam sheet into usable blocks. It trims trailing edges perfectly. It can also make thin foam sheets. I use this tool on every wing I cut.

The guillotine uses 4 flat "L" corner brackets stood back-to-back and screwed into a wood base to guide the cutting wire in a vertical cut. This cutter is designed so the cutting wire drops through the foam and into a slot in the platform so the foam can be removed with the hot wire out of the way.

The guillotine also will cut thin sheet slices out of thicker foam. The same corner brackets that control vertical cuts keep the wire from moving horizontally. The wire can be accurately suspended any distance you want off of the table and it will slice thick foam into thin foam sheets by moving the foam through the cutter like a table saw. I can cut EPP thin slices any thickness I want.

I set the depth one of two ways. I can raise or lower a flathead screw that is just inside the corner brackets and the wire sits on the head of the screws; or my favorite: I put a piece of brass tubing the thickness of the foam I want on each end of the base and it sets the thickness of the cut.

I have one guillotine that uses 6" x 6" flat corner brackets and my favorite guillotine that uses 12" x 8" carpenter framing squares. The 6" brackets cost $1.00 each. The carpenter squares cost $5.00 each but the 12" carpenter squares give you the ability to store the bow between cuts by setting it on top of the squares while the 6" does not. This helps to control the hot wire and is much safer to use. To me it is worth the extra cost.

You don't need to have a large platform on the guillotine. A smaller platform can trim trailing edges and chop blocks of foam. A large platform is helpful if you are going to cut more than one wing and you want to put jigs on the platform so you do not have to measure each cut. A big base is also helpful if you are going to make thin slices of EPP for thin foam planes.


The squares are made of metal. Metal carries electricity. You need to electrically isolate the brackets or squares by covering them with clear or duct tape except for on the edge that touches and guides the hot cutting wire so there is little chance of you making electrical contact with the cutting wire.

The construction described is for the large cutting platform with all of the bells and whistles.

HOW TO MAKE A GUILLOTINE FOAM CUTTER

1. Cut three 24" pieces from a straight 2x4.
2. Using a flat 3/4" particle board, cut a 38" x 15.5" and a 38" by 8" cutting platform. (If this board is warped and you use it for slicing thin sheets of the foam, the foam may be thicker at the ends or in the middle.)
3. The 2x4s will be positioned north/south while the platform pieces will be positioned east/west on top of the 2x4s with one on each edge and one in the middle.
4. Leave a 1/2" gap between the two platform pieces. This gap is where the cutting wire goes and hides after it passes through the foam.
5. The corner brackets will sit on top of the 2x4s next to the sides of the particle board platform, so leave the side 2x4s 1/4" wider than the platform.
6. Drill pilot holes, countersink the heads of the screws, and attach the platform to the 2x4s.
7. Drill holes in the carpenter's squares on the 8" side to screw the squares to the side of the 3/4" thick platform.
8. Put a layer of clear plastic tape or duct tape on the metal squares to prevent electricity from being transferred to you. Cover the entire square except for 1/4" along the edge of the square that touches the cutting wire.
9. Center the squares so the cut occurs in the middle of the 1/2" space between the two platform pieces.
10. Set the squares on top of the 2x4s and next to the sides of the platform.
11. I use a piece of Formica to set the gap between the carpenter squares so there is enough space for the wire to travel without binding.
12. Screw the carpenter's squares in place.
13. Screw a flat head screw in the slot near to the gap between the squares to keep the wire from dropping onto the wood 2x4s. Leave the screw up about 1/4". This is the screw that you can raise to set the thickness for the thin sheet foam cuts.

THE SPAR SLOT CUTTER MADE OUT OF A SOLDERING IRON

1. To cut a slot in a foam wing or fuselage for a carbon spar.
2. Take a 25-40 watt Radio Shack soldering iron and grind the tip flat.
3. Slide a wheel collar up the shaft of the tip to the depth you want the cut.
4. Use a metal straight edge and trace the edge the length of the spar.
5. Use low temperature hot glue to glue in the spar.

AUTOMATIC SWING ARM CUTTER DESCRIPTION

If you want to cut constant cords or slightly tapered wings you need to cut in the more traditional way with jigs on each end of the foam and a mechanical device to pull the wire through the foam. The power supply and bow remain the same.

I started cutting foam in an apartment and needed something that not only cut well but would store well. This is the method I've used to cut most of my wings over the years.

The swing arm works by transferring gravitational force of a weight dropping to strings connected to each end of the bow that pull the cutting wire through the foam. Tapers are cut when you connect the strings to two different points along the swing arm that have different ratios of movement transferred to the cutting wire.

In other words, one end of the cutting wire moves farther than the other end because one end of the swing arm moves farther than the other. You design your jigs, calculate the ratios you want to cut, set them up on the swing arm and you get a wing.

Each wing is made by passing the wire twice over the foam to be cut, once to cut the bottom of the airfoil and once for the top. The jigs have to be changed between the two cuts. This requires the cutting of four jigs for each wing cut because there are top and bottom jigs for each end of the wing.

Your cuts will be faster and better if you use a wood platform with a jig mounted on each end of the wood with a wood weight on top of the foam.

I have had to invent some of the vocabulary used in describing the system. The "platform" is the main board to which everything is attached. The "swing arm" is the moving piece of wood that also acts as the weight to pull the cutting wire through the foam that is on the front of the platform. "Strings" are any type of string, fishing line or other non stretching line that transfers energy from the swing arm to the cutting wire. The "cutting board" is the piece of wood the foam sits on during the cut

HOW TO MAKE TWO PIECE JIGS

The cutting wire will always cut on the top side of the jigs when using the automatic foam cutter.

Two different jigs will be used. One to cut the bottom of the airfoil and then it will be replaced with one that will be used to cut the top of the airfoil.

Both jigs have screw holes in the base that screw into the cutting board to align the foam and the two jigs.

The jig is made with 1" of Formica that is cut on the center line of the airfoil ahead of the airfoil and 1.5" behind the trailing edge of the jig to help with wire positioning and starting the cut and also with finishing the cut and getting a good trailing edge.

1. Determine which airfoil will best meet your needs for your design
2. Cut a Formica pattern of the exact airfoil you want to make. Cut two different patterns if your root and tip are going to be different sizes or airfoils. You can cut washout with an automatic cutter by tipping the tip airfoil down when making the jig.
3. Cut 2 pieces of Formica for each end of the cut that are 2.5" longer than the jig and tall enough to give the needed clearance above the cutting board for the jig.
4. I like to lightly glue the two pieces of Formica together for the first steps of cutting. They will be separated later so do not use too much glue.
5. Square the bottom edge.
6. Draw a line at the level of the top of the cutting board.
7. Lay the Formica pattern on the jig to be cut and line it up so it is parallel with the cutting board line.
8. Leave at least and extra 1/4" of foam for the cutting wire below the jig.
9. Draw a parallel line to the cutting board line that goes through the center of the jig and is at least 1" ahead and 1.5" behind the airfoil pattern.
10. Trace the jig pattern onto the Formica with the extension lines out the front and the back.
11. Drill the holes that will mount the jig to the cutting board. I recommend that you carefully center the holes and make them so that you can flip the cutting board for making both right and left wings using the same cutting board.
12. Using a band saw cut the top of the airfoil.
13. Separate the two pieces of Formica and only on the half with the pattern cut the bottom of the airfoil.
14. Your pattern and the bottom jig should be a perfect fit on the top jig. They do not have to be cut larger like the single jig is, because you cut the bottom first the foam will drop and no gap will have to be accounted for.

HOW TO MAKE A SWING ARM STYLE AUTOMATIC FOAM CUTTER

1. You need two pieces of wood a 1" x 4" x 48" for the platform and a 1" x 2" x 44" for the swing arm. Both need to be cut of straight smooth wood.
2. You will need four 2.5" 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. You can also use sewing bobbins with a screw through the middle if you like. Bobbins are less expensive but don't position the strings quite as well. 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 not to stretch at all. Stretching causes the surface to cut in small jerks that show up in the final product. I've used heavy "Spider Wire" fishing line with the best success. It contains no wire. It is a high tech non stretching fishing line. Do not use any type of wire for the strings. Wire carries electricity and can shock you by bringing the power to you from the cutting wire. 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 is the same as the cutting ratio 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 need to be slightly held back on the bottom cut and assisted up on the top airfoil jig because it will catch on the steep climb of the leading edge.
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. You will need to assist the cutting wire with a nonmetalic guide to start the leading edge. On the bottom the wire will not always follow the airfoil for the first inch and on the top the wire will like to hang up on the rise of the leading edge.

EVALUATING YOUR CUT

I highly recommend that you always do test cuts on less expensive foam and scrap to get the bow movement and function right before attempting to cut the more expensive foam. Make your mistakes during the learning process not on a critical cut.

Cutting foam is a learning process. Look carefully at every cut you make and work to improve it on the next cut. There are many variables that can make a significant difference in the quality of your cut if you are not getting the quality of cut you want. This applies to both the single jig and automatic cutting systems. If you are not satisfied with your cuts or you are breaking your wire here are 10 ideas to try:

1. Change your cutting temperature.
2. Change your wire tension.
3. Change your cutting speed.
4. Try different cutting wires.
5. Raise or lower the cutting board.
6. Try a different foam.
7. Loosen or tighten the tension on the rubber band suspension of the bow to the ceiling.
8. Move the ceiling connection point forwards or back to improve bow movement.
9. Route the strings on the automatic cutter to the bow differently.
10. Add weight to or remove weight from the swing arm on the automatic cutter.


I hope this information has been helpful. I am a hobbyist not an electrician or an engineer. What I've told 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.


FREE "WILD WING" PLANS

1. Cut a piece of EPP foam 2" x 12" x 24".
2. Split it diagonally making a 24" x 9" to 3" cut making two identical pieces.
3. You need to cut an angle on the 9” end of each core that will sweep the leading edge of the wing back 38 degrees. The easiest way to get close is to lay the two pieces of foam side by side so that the 9" sides are together. The longest side of the foam pieces is the leading edge.
4. On the trailing edge which is the flat edge, measure over 4" on each side of the back from the center. Draw a line up to the other corner on the 9" end of the wing. Double check and make sure before you cut that you have the right side of the wing and the right angle.
5. Cut the foam and check your angle.
6. A parallel matching tip angle should be cut
7. Make a cutting board out of 3/4" particle board that is the exactly same shape as the foam to be cut.
8. Make your one piece jig as described in the foam cutting text using the top of the SD7032 airfoil over the bottom of the SD6060 enlarged to 9".
9. Screw the jig to the 9" edge of the cutting board with the leading edge to the front and the trailing edge 1/4" forward from the trailing edge of the cutting board.
10. C-clamp or screw the anchor to the table as described in the text, with the flat corner bracket to the front.
11. Put a bolt through a hole in the anchor 1"-1.5" above the top surface of the cutting board. Put this bolt through the chin link on the cutting bow that has the rubber bands through it and secure it with a washer and a wing nut.
12. The bow should be able to move with the pivot of the wire taking place at the two chain links and the rubber bands adjusting the slack.
13. Put the foam block on the cutting board.
14. Put the weight board on the top of the foam with a weight (brick) on it as described in the text.
15. Align the wire on the cutting bow with the trailing edge of the core, with the core near the far end of the bow. Lift the cutting wire over the cutting board and foam to the leading edge of the wing and check the leading edge alignment.
16. Scoot the cutting board and foam towards the anchor until the angle of the foam is the same as the wire on both the leading and trailing edge. Make sure the wire will not exit the foam leading edge on the tip when tracing the one piece jig at the root.
17. Turn on your ventilation fan. Do not let the smoke off of the cutter rise into your face. I also use a small fan in the room to help clear the smoke.
18. Set the cutting wire in the back slot of the jig preparing to cut.
19. Turn the cutter on.
20. With your hands on the landscape spike and the top of the bow where your thumb can reach the on/off switch, trace the jig cutting the bottom of the airfoil first then circle the leading edge and cut back over the top of the airfoil and exit the foam.
21. Your cutting speed will be totally by touch but very crucial. If the cutting wire hesitates it will leave a groove root to tip on the core. If you do not trace the jig exactly you can end up with all kinds of defects. It is important to make sure the cutting wire is caught up with the bow as you go around the leading edge so the leading edge comes out straight.
22. If your wire breaks, turn off the thumb switch, turn off the power supply switch and unplug the unit from the wall before you touch either end of the broken wire. The wire will still have power even when it is broken until the power is turned off. Wires do not break very often, but when they do they are the greatest danger in foam cutting.
23. Separate the core from the foam it was cut from, which we call the bed. Work over the top and around the front to separate the core. There will be spots where the melted foam will stick the core to the bed. Most are easily separated. We tend to have more trouble on the trailing edge where the foam is thinner and the cutting wire exits the foam. Use an exacto knife as needed. If the core tears or pieces come out use a low temperature hot glue gun and glue them back in.
24. Remove the core from its bed and use the guillotine foam cutter to trim the trailing edge of the wing so that the entire trailing edge is 1/8" thick.
25. Follow the instruction on the "WILD WING INSTRUCTIONS" on "LEE'S BLOG" on www.utahflyers.org for complete building instructions for one of the best little planes you'll ever fly.

I hope you enjoy the foam cutter and the "WILD WING". Please post pictures of your planes on the UFO club thread on rcgroups.com if you build a "WILD WING". You will find a link to the thread on the www.utahflyers.com club site.

Lee

Trackback URL: http://utahflyers.org/lee/bblog/trackback.php/4/