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Feb 12, 2020, 11:45 AM
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Methods for curving FFF?


Good afternoon! Iíve spent some time searching on this section a bit with varied luck to find some how toís on forming fan fold foam. Maybe Iím not so great with the search function but I seem to be pulling a bunch of random build threads and always the kfm thread. I have a hair dryer and a heat gun at my disposal and Iíve tried a few times but I seem to wind up getting it too hot where it shrinks down and gets brittle. Iíd appreciate any help you guys can offer. Thx!
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Feb 12, 2020, 03:15 PM
treefinder
springer's Avatar
Search for the "bendfoamm fixture" thread. This simple fixture is a great help in achieving a consistent curve either cold or with a bit of heat. When you are using heat, play the gun over the entire area you want to curve to just warm it up. If it starts to "glisten" you are too hot (the surface has reached the styrene melt point.)

With the bendfoam, once you slide the foam between the round dowel and back plate, you can play the gun just above the dowel to make bending easier.
Feb 12, 2020, 06:57 PM
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Thank you for the reply. Iíll have a look!
Feb 13, 2020, 12:04 AM
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tspeer's Avatar
This is probably overkill for what you intend, but FWIW, here's my foam bending brake.

There is a bar in the shape of an inverted T that clamps down on the foam and forms the edge around which the foam is bent. The T is reversible, with a rounded bull nose on one side and a sharp edge on the opposite side. The bull nose has a steel rod at the apex, and the foam is compressed against it as it is bent.

The base has a hinged piece that brings the foam up and around the T bar. The hinge axis is above the base, at the level of the bull nose. The bending plank has is own stringer for reinforcement, to keep it from bowing as it compresses the foam. Two steel bars are mounted under the plank as handles.

There are two uprights over which the T bar slides. These are dowels over steel rods that rotate in the base. The dowels are off center from the rods, forming eccentric cams. Rotation of the cams moves the T bar closer or farther from the bending plank, to adjust for the thickness of the foam. The T bar has bolts and wing nuts to tighten it onto the cams to hold the foam in place.

In practice, the brake is clamped to the workbench. The T bar is loosened and lifted on the cams to allow the foam sheet to be slid under it. The T bar is then dropped down onto the foam sheet, and the sheet is positioned for the bend before the T bar is tightened onto the clams. Then it's just a matter of lifting the bending brake to fold up the foam. For sharp bends, like a leading edge, it's often necessary to remove the foam, turn it around, and bend it again from the other side. Although I built it mainly to bend leading edges, it can also be used to make more gentle bends, bending, sliding the foam forward, bending some more, etc.

Although the brake presses the foam against the bull nose as it bends it, it is still a good idea to put packing tape on the back side to prevent cracking of the foam.
Feb 13, 2020, 07:43 AM
Registered User
https://www.rcgroups.com/forums/show...hlight=ki%2046

This will show you how to make fully formed compound curves in foam.
Feb 13, 2020, 07:53 AM
Danish? Don't U eat that??
DKChris's Avatar
This is how I Lo-tech put single direction curves into Climapor, which is a german version of depron (Just as stiff but ever so very slightly less brittle - probably a bit like FFF, which we do not have here?):

1) Apply packing tape in an even layer across the "outside" of the foam piece that needs curving. Overlap should be ~1cm or so everywhere. The tape is there to keep the outside from splitting.
2) Slowly form a curve into the material by "rolling" it over a soft curved edge of a table or similar by hand, while applying a bit of pressure to lightly deform the foam where it touches the table edge. Do not press too hard, or you will put an indent line into the foam, creating a weak spot/line. Try to shape it evenly. And take your time, rushing thing will end up in a split panel.
3) If needed be, the tape can now be peeled off the foam.....or it can be left as the outside surface of your construction. If leaving it on, you can also use stuff like sign vinyl, iron-on covering or even glue on paper in stead of the tape.

That's it. My suggestion would be to grab some large FFF scraps and experiment to see if it's the right method for you.

For better illustration of how it's physically done, you can have a look at how the Flite test guys do it with DTFB for their master series planes, just remember the the DTFB foam is less brittle and a bit softer than FFF, so they can go a bit faster and curve quite a bit tighter this way. But you'll get the idea...first curving bit starts about 14 minutes in:

How to Build the FT Master Series Spitfire // BUILD (2 hr 48 min 31 sec)
Last edited by DKChris; Feb 13, 2020 at 08:03 AM.
Feb 13, 2020, 06:06 PM
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Thread OP
Excellent! Thank you for all the info! I’ll grab some test parts and start trying out the different methods.
Feb 19, 2020, 08:44 AM
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Zipman's Avatar
Here is a free form example to curbing fff.
https://www.rcgroups.com/forums/show...7#post10723209
Feb 21, 2020, 01:36 PM
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Thread OP
Sweet! I spent a lot more time on the fuselage of my build than I expected so I’m hoping to have time this weekend to experiment more!


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