Friday, 30 October 2015

EPP Foam Cutting and Shaping

Working with EPP Foam
  • Like Depron Foam and HD Foam cutting can be done with a paper cutter.
  • Hot wire cutter also can be used.
  • Like Depron Foam , HD Foam and Balsa Wood sanding to shape is difficult with EPP Sheets.
  • EPP sheets are elastic in nature, so to keep them in shape you have to use carbon fiber, balsa strips , aircraft grade ply or bamboo sticks as frame works and reinforcements.
  • Fiber tapes or other types of tapes can be used for attaching control surfaces and other parts.
Gluing and taping EPP.
  • Epp is more resistant to solvent than is eps (styrofoam, depron, fanffold, bluecor), but some solvents will attack epp.
  • Solvent free glues are the safest to use.
  • Epp is harder to stick to than is styrofoam.
These glues work well:
  • Beacon's Foam Tac, Similar to Welders Glue but doesn't yellow with UV exposure. 
  • Welder glue. Sloper Steve says "It is the goop type. Has outdone all others tested and costs less too." 
  • Hot glue - the quicker sticker, strong bond.
  • Urethane glues (Sumo, Gorilla, Probond) - strong bond, light weight, slow setting. Fills gap due to foaming.
  • CA, foam safe or regular - good bond, sticks epp to fingers very well, quick, more expensive.
  • Spray a little accelerator on one piece, a thin bead of CA to the other, bring together for a quick bond.
  • 3M spray 77 contains some solvent.
  • Use as a glue or as a primer for film or colored tape covering.
  • Also spray both foam parts and let dry then bring together as a contact cement type bond.
  • Here is some good info on the various Goop products.
  • Epoxy. 
  • UHU Creative/Por Good contact cement for epp and slightly flexible
Glues that don't stick too well:
  • Water based wood glues like Elmers glue.
Glues that may eat the foam:
  • Glues that are made with really strong solvent may eat epp or may cause it to swell. Sometimes if you use these types of glues sparingly you can get away with it.
Cutting forming and shaping epp
  • Like anything else, epp will cut better with a sharp tool. Razor blades, utility knifes, scalpels are all good tools for cutting epp foam.
  • If they are dull, the knives will tear the foam rather provide a clean cut.
  • I use a finger nail emery board to sharpen my utility knife blade. I can sharpen it in a few second; faster than replacing the blade and cheaper!
  • Use a metal straight edge to get nice straight cuts.
  • To cut large blocks of epp such as for a fuselage, a band saw is great.
  • You can mark and then cut the top and also the side profile. 
  • Epp can be tougher to sand than styrofoam. If you use to much pressure when sanding, the foam will tear.
  • For fast work, use a belt sander or a disk sander with a medium or coarse grit.
  • Mount the belt sander somehow. Handle and manipulate the foam not the power sander.
  • Don't use too much pressure.
  • For finishing touches  hand sand using sanding blocks, emery boards etc.
  • You need to experiment to find out what works best for you. 
  • A good hand tool:-
  • Useful tip: "You can sand EPP with sandpaper or power tools such as a belt sander, but often times will be left with a peach fuzzy surface.
  • Use a sealing iron (like the ones used for covering models with Monokote and such) to gently remove the fuzz.
  • Start out at a low temperature and slowly raise it until the fuzz starts to disappear.
  • If the EPP beads begin to swell,  just press them down and smooth them out with a cold, flat piece of metal."
  • Some people do the rough shaping by carving the block of epp with a sharp knife. 
  • Rounding the leading edge;we can round our LE's with the hot tip of a hot glue gun held at a 45degree angle...secures the skin too , actually we can do it to the whole plane ... especially the hinge areas with skin ...
  • Sandpaper will work on FFF but leaves the skin edge ... "fuzzy'' ... glue gun tip takes care of that too ..."
Hot wire cutting:
  • Epp can be cut with a hot wire.
  • Beautiful airfol shaped wing cores can be cut with this technique. 
  • Epp Hobbies has good step by step instruction on cutting wings this way.
  • There are tons of other sites with information about hot wire cutting also.
  • A google search for "hot wire epp" will give you hours of reading on this subject. 
  • Don't want to hot wire your own wings, but still want an airfoil epp wing??
  • These guys can hot wire cut wing cores for you.
  • A soldering iron can be used to poke holes or gouge out battery bays.
  • Do this in a well ventilated area, it does create some fumes. 
  • Here is another tool that is half excato knife and half soldering iron. Check out this link for a clip of the tool in action. -
  • Drilling holes, even really long holes is possible.
  • Make a foam drill bit by selecting a thin wall metal tube of the required diameter. 
  • Cross cut one end at a small angle. 
  • File this end of the tube to remove any burs. 
  • This "drill bit" will easily cut the foam and produce a nice clean hole. 
  • Dremel tools have been used to shape epp, especially for cutting groves and channels.
  • Milling epp to create really light weight airframes can also be done pretty easily and without sophiticated tools. 
  • RCSuperpowers has excellent on line video building instructions. His technique for creating the tunnel for the reinforcing rod works well with epp also and doesn't require any special tools and is quick. This the technique I use.
  • Here is his Youtube "how to" videos. It makes finding the video you need a bit easier. 
  • Here are several more videos created by tallflyer for cutting and assembling epp planes.
Stiffening and reinforcing epp
  • Epp is a pretty flexible foam. 
  • Stiffening is often required to get an airworthy plane built with epp.
  • There are a few techniques for stiffening:
  • Embedding rods/tubes.
  • Typically carbon fiber tubes and rods are used.
  • Another good choice is bamboo "natures high strength composite". 
  • Light, almost as strong as carbon fiber, and commonly available from bamboo skewers, window blinds, chopsticks,floor mats, and others?? 
  • To make a nice clean job, make a tunnel for the rod to fit in.
  • For a quick and dirty reinforcement, just tape the rod to the foam.
  • Thicker foam will be stiffer than thinner.
  • If you don't have thicker foam, you can laminate thinner layers together. 
  • One technique is to laminate a second layer in the front half of the wing. 
  • The KF wing builders do this for better flight performance and gain strength and stiffness at the same time. 
  • Typically the front 50% of the top wing of the front 40% of the bottom of the wing is doubled.
Using strapping tape to form a truss. 
  • By using fiber reinforced strapping tape on the top and bottom of the foam (make sure they line up well) you will form a sand which composite truss.
  • To work well the tape has to stick really well to the foam. 
  • Here is a visual demonstration of what the tape can do.
  • Curving a flat sheet will add a lot of stiffness. 
  • Cambering the wing to give it an airfoil shape for instance will add to the wings' stiffness. 
  • It may not replace the need for other stiffening but it will help.
  • Epp stiffneres can be glued on to a wing to stiffen it in the direction of airflow. The SFO shows this technique and incorporates the stiffener as part of the twin vertical fins.
  • Here is a very good post by Sloper Steve on the strategic use of strapping tape for reinforcing and stiffening:-
  • "Here's a cheap trick ... on the high stress areas like fuselage bottoms ,noses and wing LE's... run a tiny bead of hot glue along the edges, and smooth out with a wet finger, careful, it's HOT...the hot glue really strengthens the edges and is a lot easier than a strip of some kind... did you ever try to pull a strip of Hot glue apart ... strong plastic..."
  • Building hollow box sections or tubes will also add stiffness.
  • This technique is used in building fuselages. 
  • One advantage of this type of construction is the extra torque stiffness that is produced...good for avoiding fuselage twist induced by the propeller. 
  • Have a look at the Silent Mite plans for really light well built hollow epp fuselage.
  • If your using hot melt hinges, you can add sheer strength by cutting a slot across the hinge line at each end and hot melt in a short piece of string.
  • To stop tearing at wing leading edges, etc., cut a shallow slit, insert the string, pull tight, run a bead of hot melt and smooth with the side of your gun tip or use a Monokote trim tool.
  • These methods have been 'combat tested' in the real world. Guaranteed to work, or double your money back......
  • Links to working with epp- Sloper Steve's "Why aren't you building with epp" thread, loads of good info:
Hinging control surfaces, attaching servos, horns, motors
  • Hinging:
  • SuperflyRC has good illustrated instructions on the hot glue hinge method.- /SuperFly.pdf section 8
  • Logical Psycho's Flopsalot thread has a build video with an epp hinge, no tape no glue.-
  • Cut and bevel the control surface and then tape it in place with SloFly super sticky epp tape... forms a good solid hinge.
  • Here is a good technique for cutting the bevel for your hinge.
  • Tallflyers's hinging tip
  • Goldguy's hinging tip
  • Attaching servos:
  • The easiest way to attach a servo is to simply stick it in position using glue.
  • The quickest glue for this is hot glue.
  • I've also found that when it is time to move the servo for the next project, the hot glue can carefully be peeled from the servo. 
  • Apply the hot glue to the servo then press the servo into position on the foam.
  • UHU Creativ/Por, this a good contact adhesive for Epp and is slightly flexible. Usefull for attaching servos.
  • Put a patch of Blenderm on the servo and glue to the plane; can be removed and the servo recycled if needed with no damage or marks on the servos."
  • I have had some success with using double sided tape.
  • It has to be very tacky tape to stick well enough to epp. 
  • You can use 3M VHB doule sided tape. 
  • I don't know how long this bond will last. 
  • With epp planes, you can count a longer life for your airplane so long term bonding is important. 
  • The double sided tape I use has a bit of a foam core. 
  • By stretching the tape, it comes off the servo fairly easy and cleanly.
  • To get a really aerodynamically clean and strong servo install, cut out a snug fitting servo bay in the foam. Trace your servo onto a piece of cardboard to make a template. 
  • Leave room for the servo arm movement.
  • Use this template to mark out the servo bay on the foam. 
  • This will allow you to cut out a nice precise fitting bay. 
  • After pressing the servo into the cut out, use some glue to prevent it from working loose.
  • Attaching control horns
  • Here is a techenique regardless of the type of horn you are using. This technique works well, is strong, and is quick.
  • First carefully mark the position you want to set you control horn in the foam. 
  • Then poke the holes, cut the slot or whatever is required to allow your horn to fit into the foam. 
  • Dry fit the horn into the foam.
  • Remove the horn and spray some CA activator directly on the control horn. Make sure not to spray the activator on the foam. 
  • Put a drop or two of CA on the horn position on the foam.
  • Press the horn into place and hold for several seconds until the CA sets up. The pins or slats that end up embedded in the foam will drag CA into the holes/slits as you press them in place.
  • You can use other glues too. Just do steps 1 - 3 and apply your favorite adhesive.
Coloring and painting and decorating epp
  • Any water base paint should be safe to use on epp. 
  • Krylon H2O spray paints and similar products will work. 
  • Brush on acrylic latex (water based) craft paint also work.
  • Many solvent based paints can be used on epp if they are applied sparingly.
  • Always test your paint and technique on a piece of scrap epp.
  • You can prime and seal the epp with water based products such as water based urethane clear finish, either spray or liquid. 
  • Once you have sealed the foam almost any paint can be used.
  • Here are some great painting techniques for those special effects:
  • Sharpies/magic markers/felt pens are another wary of adding color to foam. 
  • They are great for detail work and are one of the lightest ways of coloring foam. 
  • Epp foam can be coated with products such as monokote and other films.
  • I don't have first hand experience, but the little reading I have done indicates you can get a really nice finish, and the film adds strength to the build.
  • Colored packaging tape is a poor mans method of covering epp with film. 
  • Typically, in order to get the colored tapes to stick, a light coating of 3M spray 77 is applied to the foam. 
  • This is a common way of covering the epp flying wings such as Zagis etc. 
  • The tape adds strength to the build.
  • SDParkFlyers' water slide decals for epp-
  • Firetrapp's thread for making these decals for epp:-

 Use of fiber tape
 Carbon fiber and balsa sticks reinforcements.

 Wing structure.
 Fuselage construction.

 Cutting 45 deg angle for control surface

 Copntrol surface attachement using fiber tape

 Hot wire cutting

 Folding the wing over single spar.

 Using stencils for Wing profile.

 Wing construction by folding.

 Wing Structure 
 Cutting techniques.

 CNC cutting machene

 Silent Might - Full EPP Foam Plane.

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