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Old Aug 28, 2009, 08:59 PM
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cutting foam

Hi everyone, I have a question about foam, I have access to a CNC Mill and was wondering how well the foam used in model aircraft construction cuts.

The mill is designed to cut metal but I don't think it will be a problem, at the very least it's worth a shot.

Thanks the input,

vandallas
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Old Aug 28, 2009, 09:57 PM
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Insert a hot wire instead of the "cutter' and you will go where others have gone before you.
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Old Aug 28, 2009, 10:03 PM
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Welcome to RC Groups!

There are SEVERAL different types of foam, and here's each that I know of (someone please feel free to correct any of this):

EPS (Extruded Poly Styrene):

A hard foam that is easy to mold, and is consisting of small foam beads. A lot of the smaller EDF jets use this foam, but it basically explodes on impact with the ground if the crash is hard enough. Small crashes usually result in the foam breaking cleanly. 100% NOT regular CA safe. See the Phase 3 Squall!

EPP (Expanded Poly Propelene):

A tought foam that is similar to a sponge, but won't absorb water well. It will basically bounce off of anything, and usually tears when it does break. Always easy to put back together. 100% regular CA safe. See any combat wing type aircraft.

EPO (Uhh, I'll get back to you on this one ):

A tough foam that is usually molded and consists of large, tough foam beads that allow the structure to bend a lot. When it breaks, it'll break cleanly almost every time no matter how hard the crash. 100% regular CA safe. See Hobby Lobby Jet Tiger.

Elapor (Multiplexs name brand foam):

Similar to EPO, but with smaller beads and a slightly oily feeling surface. This stuff is tough, and also bends rather than breaks. As EPO does, it will generally break cleanly, and leaves no small foam beads behind. This foam can only be glues using regular CA or other glues that tend to "wick in". See Multiplex Twister

Depron (laminated foam sheets):

A VERY common material for use with small parkflyers, or the occasional jet. It's a hard material that usually bends before it snaps. When it breaks, the break is 100% clean, and is in easy to glue back together pieces. This material is also a prime material for a CNC router to cut, as it usually is cut out clean. A lot of the 3D foamy companies use this material for their aircraft, such as DW Foamies or Fancy Foam, or Charger RC. 100% NOT regular CA safe. See YardBird RC pusher jets.

I believe that is all of the basic foams that we use. The only foam material that can be cut cleanly with a CNC router would be Depron and also I beieve EPP can be cut, but it's got a slightly fuzzy edge rather than a clean one. EPO, EPS, Elapor (if you can possibly find it) all don't cut very well with a router bit, and usually are molded
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Old Aug 29, 2009, 12:27 AM
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Hi

I use standard tools for metal on my mill with great success. The key is the combination of cutting speed and rpm of the tool. This is foam depending. for polystyrol foam extruded type I use a cutter with ball head, dia 8, 6, 4 and 3 mm, each having 2 edges. RPM varies but is slow (can,t measure it though) and cutter speed is rather high. This is to avoid melting of the foam and get clean cuts. I do not use any cooling, though some people indicated cooling by compressed air (helps keep the bit free of dust too).

For depron, I use a tool that has a single cutting edge, dia 1 and 3 mm.

Further you need to make sure the cut foam dust gets away well, by using a powerful dust remover or industry vacuum cleaner.

hth chris
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Old Aug 29, 2009, 03:15 AM
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There is a difference between " Extruded" and "Expanded" foams. "Expanded" has beads , but can still be machined. " Extruded" machines very nicely for most foams , except for some DOW blue, but the rest of the blue does well also.

Its just a matter of finding out which works best for you. For me Pink foams hot wire the best, than expanded styro . Machining can be accomplished in many ways , including various types of sanding ie Sanding drums or discs . Ive had good luck with routers and drums with expanded styro ! As well as pink foams

One foam that I do not like at all , in anyway shape or form is CellFoam 88 !!

Blue Skies................R Dub

BTW Doesn't Mr. Wan of RC Landers CNC cut the prototypes?
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Old Aug 29, 2009, 01:14 PM
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Thanks for the replies, I like the sound of the Depron. About the foams that can't be milled, what about freezing them before cutting? That might give the rigidity needed for the tool to bite into the material cleanly.

I also found this

http://sketchup.google.com/3dwarehou...4f2d24bb38b7d1

google has free 3d models for download. I looked it up and these can be imported directly to mastercam. I will have to double check the airfoil and make a few modifications, but this saves a whole lot of designing time.


Actually, come to think of it, there must be a niche market for foam molds for model aircraft, would be a nice way to make a quick buck...
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Old Aug 29, 2009, 02:45 PM
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I don't think freezing will help. Foam has insulating qualities , its kinda meant to take the cold as well as some warmth. Like I said you have to find what works best for you ! I remember when I first started hot wiring, about 30 years ago, I sure made a lot of good foam into scrap !! Kinda bothered me, then I started trying different things and next thing I knew I was making wing cores as good as the ones that you can buy!!

Grab some foam and have at it!!! Don't be afraid to experiment !!! Go with your gut feelings, what have you got to lose ? Just some foam. I still experiment !!
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Old Aug 29, 2009, 04:29 PM
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hmmm, if anyone has a chunk of model airplane type foam laying around can you please perform this experiment...

put said piece in the freezer,

wait 3 hours,

take piece out and try cutting it with a knife,

observe results

thanks a lot,

vandallas
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Last edited by van.dallas; Aug 29, 2009 at 04:35 PM.
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Old Aug 29, 2009, 06:27 PM
Carbon fiber is our friend
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The RCLander prototypes are cnc foam.

http://www.rcgroups.com/forums/attac...mentid=2599203

You can see the tool marks in this pic. In most of the pictures, you can't see it.

There are those of us who would love to have cnc cut molds (from aluminum or RenShape) if the price is low enough. Most cnc guys in the US want so much nobody can afford it, but you see lots of stuff coming from Europe and now China.

Steve C
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Old Aug 29, 2009, 06:44 PM
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what would be a reasonable price?

if you wanted to keep the cost down then steel would be the best material, alluminum can be pretty expensive
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Old Aug 30, 2009, 11:25 AM
Carbon fiber is our friend
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I've never heard of anyone using steel for a composite mold. I think it would take a long long time to cut and would weigh so much you can't move it around without a forklift!

Steve C
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Old Aug 30, 2009, 04:49 PM
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PhlatPrinter EDF Aircraft Plans with G-code

http://www.phlatforum.com/viewforum.php?f=36
EDF Aircraft Plans
Usually there is a SketchUp .Skp file, as well as some G-code generated by the PhlatScript included in the plan download.

The PhlatPrinter is made to cut sheet Fan Fold Foam, but the G-code could be used to drive a mill. (You may have to reverse the Z axis directions, the PhlatPrinter has the cutter below the surface, instead of in a gantry above the foam).

-Steve
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Old Aug 30, 2009, 10:44 PM
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About 3 O:clock this afternoon I put a Piece of Pink foam,Depron, EPP from a Honda bumper, White Beaded Styrofoam and a piece of Dollar Tree foam Board in the freezer.

A few minutes ago I got them out and cut them all with a Knife They all cut a little nicer except for the white beaded styro and Dollar tree foam which cut much better !

Next I took my dremel with a 5/16 router bit to it and they all had nicer finishes than without freezing ! Especially the white beaded styro.

I guess you can teach an old dog new tricks! Thanks !

Blue Skies................R Dub
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Old Sep 02, 2009, 06:17 PM
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Ha ha, I thought freezing the foam would work.

I just got back from camping so I've got some work to do on mastercam.

Speaking of, what would be a good twist to put in the wings? I was thinking 8 degrees since tha'ts what the horton had, but if anyone knows what works best for RC that'd be great.

Stay tuned, I'll post screen shots when I get the design banged out.
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Old Sep 11, 2009, 08:43 PM
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finally got inventor up and running... only took 3 days, two upgrades, and a clean Vista install.

Drawing up Horten 229 now. Haven't been able to find a way to import .skp files into autodesk inventor, if anyone knows how please let me know.

What would be the best Airfoil for this craft? I would like it to be a glider/thermal rider if i could.
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