View source for Hot Wire Foam Cutter

__TOC__

[http://www.eaa974.org/wiki/resources/pdf/PrintFriendly-FOAM_CUTTER_PLANS_AND_INSTRUCTION.pdf Printer Friendly PDF of this page]

== FOAM CUTTER PLANS AND INSTRUCTION ==

Please respect the rights of the designers and the manufacturers who have products on the market.  It is important to not copy or market others work. These foam cutter plans do not give permission for you to copy the planes we market.

These videos and instructions show how to build and use a foam cutter in your home.  With a little practice, you can cut excellent quality foam wing cores. This includes plans for the power supply and accessories that can make your cuts look like they were cut by a CNC.

Do not be afraid of the cutter, but do not 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 25 years and have never been shocked, but I have been burned by a drip of hot plastic off of the cutting wire.

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 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.  If you don't understand basic electrical wiring get some help from an expert.

== FOAM CUTTING SAFETY CONCERNS ==

* Electrical shock
* Hot wire burns
* 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- or low-voltage contact points.

Have your hot cutting wire electrically insulated from the bow so you have less chance of making accidental contact.

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.

If your wire breaks do not touch it until the power supply is off and unplugged from the wall because both ends of the wire will still have power!!!

Have everyone else move back because they haven't read these instructions.

== TO PREVENT BURNS ==

Do not touch anything that is hot.

Have a warning light so you know when the foam cutter is on and the wire is hot.

Have adequate working space around the foam cutter.

Watch out for the hot plastic drips that can occur on the wire when cutting

Wear protective gear such as welding gloves if your hands are close to the wire.

Move flammable paper, plastic, cloth and liquids from cutting area.

Slow down and think about what you are doing and what you are about to touch

== TO PREVENT INHALATION INJURIES ==

Only cut in well ventilated areas.

Do not breathe the toxic smoke off the foam cutter.

Use a fan to bring a supply of fresh air around the cutter and/or an exhaust fan to blow the toxic smoke away. I use both.

== <u>THIS IS MY CUTTING SYSTEM</u> ==  
[[File:foamdiagram.jpg|400px|Foam Cutter Diagram]] 
 
== POWER SUPPLY ASSEMBLY ==
- See the attached schematic (above) of the foam cutter.

1.      <u>THE POWER CORD.</u>  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.      <u>THE GFI.</u>    Expose 4 inches of the internal wires and strip 5/8 inch 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 power to the bow from the transformer but it will cut the power inside the power supply and to the transformer.  Use an outlet power checker to make sure you wired it correctly.  The power supply shown below in the picture was one of the early designs and plugged into a GFI that was in the wall outlet.  It was closed with another piece of wood to prevent accidental contact with the wires.

This is one of the later power supplies that has several features built into one box.  I am now using a 5 amp  transformer now and I prefer the rotary dimmer rather than the slide.  I often use a nightlight instead of the house bulb. All of the electrical connections on the transformer have silicon over the solder joints to prevent accidental contact.  All of the rest of the contacts are inside the electrical box. 

3.      <u>THE DIMMER ON/OFF SWITCH.</u>  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 rotary version of the dimmer switch better than the sliding version.  The slider version has been left just barely on in several cases where the operator thought it was off.  The rotary dinner is a push button switch.

4.      <u>FUSES.</u>  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.      <u>THE WALL OUTLET.</u>  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.      <u>THE TRANSFORMER.</u>  A 24-volt 3-5 amp transformer is preferred.  The 120-volt connections on the transformer are connected to both sides of the wall outlet.  Use the screws on the wall outlet for easy connections.  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 any exposed wires or connections to prevent accidental contact.  Sources for the transformer are listed at the end of the instructions.

7.  <u>THE CUTTING BOW.</u>

How long does the cutting bow need to be?  The longer the bow, the more the wire will stretch and bend as cuts are being made.  If the wire fluxuates even 1/8" and it does it on both top and bottom you will be dissapointed in the cut.  The long bows are not as accurate.

The bow shown is a 72" bow with a 66" cut, but my most used bow is only 54" long with a 42" cut.  The shorter bow is the one you can see in the foam cutting videos seen in the video selections on this site. 

My most used bow is made from a 1" x 4" x 54" pine board.  I drilled a 3/8" hole at 90 degrees two inches in from each end.  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 slant the spikes, the rubber bands tend to slide up the bow as it is being used.  Longer bows can be made as needed for slicing up 4'x8' sheets of foam or long wing cuts.  It only costs about $5.00 to make a bow.  I have five different bows all for different purposes. 

8.      <u>THE BOW SUSPENSION.</u>  The bow is suspended by a nylon cord tied through two holes in the bow.  The bow should balance when held at the center point of the nylon cord.

This cord is then tied so the bow cannot slip and shift weight to one side or the other during a cut.  The bow is then attached to a quick link and then to a light weight bungee cord or 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 bungee or 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.  The rubber bands and bungee cords do stretch out and dry out and crack over time and need to be replaced occassionally. If the bungee cord is too heavy and  strong it will not move properly during the cut.

What you can't see in the picture is the nylon cord has different attachment heights in loops tied in the nylon cord that allow me to raise and lower the bow the change the downward pressure during cutting.  The bow has to be able to gently touch the table or it will stop half way through a cut.  In long wingcuts the bow needs enough slack to be able to make the entire cut without running out of slack.

9.    <u>THE CUTTING BOW POWER SUPPLY WIRE.</u>  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.  <u>THE SECOND ON/OFF SWITCH.</u>  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.  <u>THE CUTTING WIRE.</u>  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.  <u>ELECTRICALLY ISOLATE THE CUTTING WIRE.</u>  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.  <u>RUBBER BANDS AND CHAIN LINKS ON THE BOW.</u>  I use rubber bands to create tension on the wire.  The rubber bands automaticly adjust for the normal stretching of the cutting wire as the power is turned on. 

I put 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 6" gap to put the #64 rubber bands across to properly tension the cutting wire.  I usually have 4 or 5 #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.  

14.  <u>THE OUTLET RECEPTICAL BOX.</u>  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 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.

[[File:cutter12.jpg|400px|Electrical Setup]]  

 
 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.

== 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.   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

If you want a transformer with a little more power, buy this one at All Electronics and get the dimmer, GFI and the wall outlet at your local hardware store.  This transformer has a 24 volt 5 amp rating and is the same size at the 3 amp transformer at Aircraft Spruce.

http://www.allelectronics.com/make-a-store/item/TX-245/24-V.C.T.-5-AMP-POWER-TRANSFORMER/-/1.html

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 between 7-8 amps. 
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 ¼ lb roll.

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

This is how I adjust the power to cut foam.  Since each foam cuts at a different temperature It is best to do some testing.

I like to hook up an amp gauge to see how much power I am running.  

Start at 0 press a piece of foam up against it and start turning the power up until you start to see it cut.  It will smoke a little.  After I figure how much power it takes to cut I then turn it up until it breaks the wire so I know the maximum power it can handle.

Each different kind of wire is different as to how much power it will need and how much it can handle.  The .020 wire I use likes about 4.2A whether I am cutting with a 6" wire or a 60" wire.  Other wires use less and other wires use more.

Because the length of the wire directly affects the resistance the power needs go up as the wire gets longer.  I have a hack saw and a coping saw that I have converted to hand held cutters and for many projects they are easier to use than a fixed vertical wire.  I have a vertical cutter and 5 long cutting bows and 5 different power supplies that I juggle cutter to cutter depending on which cutter I am using.

This cutter has been used to cut EPP, EPS, Pink, blue, fanfold, white bead and plastic sheet.  the most common cuts we do are with the EPP.  Here is a source for EPP foam.  I usually order sheets of the 2.5" x 24" x 36".  This is enough foam for 3 Pinatas if you don’t make any mistakes

Foam Sheets

 

== FOAM CUTTING ==
 
[[File:cutter8.jpg|400px|Cutting Foam]] 
 

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.

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 have 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.ae.uiuc.edu/m-selig/ads/coord_database.html

 

[[File:cutter14.jpg|400px|Guillotine Cutter]]  

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 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.

== 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 have 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.

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 jig of the exact airfoil you want to make. Cut two different jigs 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 a 2 pieces of Formica 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 ¼" 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.

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.

12. Using a band saw cut the top of the airfoil.

13. Separate the two pieces of Formica and only on the one 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 will cut the bottom first the foam will drop and no gap will have to be accounted for.

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 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 yours here are 10 ideas to try:

1. Changeyour cutting temperature.

2. Check your wire tension.

3. Change your cutting speed.

4. Try different cutting wires.

5. Route the strings on the bow differently.

6. Raise or lower the cutting board.

7. Try different foam.

8. Add weight to the swing arm on the automatic cutter.

9. Loosen the tension on the suspension of the bow to the ceiling.

10. Move the ceiling connection point forwards or back to improve bow movement.

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

'''I have cut alot of different kinds of foam with a hot wire over the last 28 years.'''

'''White bead foam''' is still a good foam to build with. I wouldn't build a combat wing out of it but If I was going to balsa sheet the foam or vacuum bag it with fiberglass it would be the foam of choice. It is light, It is cheap. It is easy to get. It doesn't soak up water like EPP. It cuts very well and is what I use to test my new jigs to make sure they are working well before cutting the more expensive EPP foam. I used to build most of my planes out of it. It covers well with low temperature iron on coverings without the 3M77 or 3M90. Once it has a covering on it it does better than balsa in an accident and is easier to repair than balsa. Don't overlook it as a good building material. I have cut over 100 wings out of white bead foam.

'''Blue or Pink foam''' is 1/4 the price of EPP. It is strong and easy to cut. It is easy to find. It does dent more than white bead foam but if you heat it with a monocoat covering iron most of the dents will pop back out. I have built combat planes out of it. It doesn't crumble like the white bead foam in an accident. It doesn't soak up water like EPP so it is good for seaplanes. It weighs more than the white bead and is close to the weight of the EPP foam. There are tricks to building that we use with the more brittle foams. I will put a carbon tube or dowel leading edge to prevent the denting you get with heavy use and I cover most of the white and blue foam planes. I have cut about 50 planes out of bluefoam.

'''Blue fanfold foam''' is a foam used to insulate foundations but it make a great building material. I still use it and recommended it when I designed a modification of the Capricorn. I called the Capricorn Evolution. I recently cut 28 planes out of it for our club. It is a great building material but sometimes hard to find. I am able with my foam slicer to slice thin foam if I can't find it at the stores. Another good reason to build a foam cutter!!!!

'''EPP's durability and repairability make it my foam of choice for many of my designs.''' I have cut hundreds of wings and planes with this foam. I have cut many designs out of EPP that I don't cover but leave the raw foam exposed. It soaks up water so it is not the foam to use in a seaplane. It is the most expensive foam discussed here. It paints easily but has a waxy surface that won't stick to coverings without 3M77 or 3M90 adhesive. The 3M77 stays sticky and the 3M90 dries but still provides a good surface for iron on coverings. It can be hard to get. My mailman stopped and asked my wife what I was doing with all of the foam I was ordering. He asked if it was just styrefoam. I don't know why he was wondering. I only ordered 60 sheets of it in one year. 

Most foams are not strong enough without some form of reinforcement like carbon tubes or rods or my old cheap wood dowel methods. I will cut a grove in the foam with a soldering iron and then hot glue gun a tube in the wing. If I want the wing to be extra strong like the Q planes I will put a tube or rod top and bottom in the wing and it gets stiff as a board. Look at the photos in the bottom of post #1. The Q-trainer has a carbon tube on the bottom hidden in the black pinstripe. In combat planesI encourage the builders to add some reinforced strapping tape to critical areas to hold the plane togeter. A "iron on covering" adds alot of strength to a plane. It does far more than make the plane look good and improve aerodynamics. I want you to see how tough the EPP planes can be.

== Source ==
Information from http://www.utahflyers.org/build-mainmenu-33/27-foam-cutting/37-foam-cutter-plans