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Old Feb 05, 2013, 06:00 PM
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NighthawkF-117's Avatar
Minnesota
Joined Jan 2009
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I would stay away from blue foam as I've heard when you cut a core with it, it likes to warp. This is due to the way it is extruded at the factory. I use pink foam and have never had any problems with warping or strength.
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Old Feb 05, 2013, 06:26 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
20,841 Posts
I have cut plenty of blue foam cores, and none of them warped.

Its not the color of the foam that causes warps.

R,
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Old Feb 05, 2013, 06:29 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
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I've been skinning 1/8" off the top and bottom of the blanks before cutting the cores. Most of the residual stress is in the skin and if you take that off it should not warp.
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Old Feb 05, 2013, 06:36 PM
Master of the Wind
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United States, CA, San Jose
Joined Sep 2008
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All the really big planes I have built were made with 40 lb foam from Whitecap. I would be reluctant to make something this big with 25 lb foam as the finger dent resistance is not that good. 60lb will work also but is trickier to cut.

http://www.rcgroups.com/forums/showthread.php?t=1256550

http://www.rcgroups.com/forums/showthread.php?t=1073259

Also check out this thread for how to make a big hi aspect wing.

http://www.rcgroups.com/forums/showthread.php?t=1149551
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Old Feb 05, 2013, 06:37 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
20,841 Posts
Quote:
Originally Posted by G Norsworthy View Post
I've been skinning 1/8" off the top and bottom of the blanks before cutting the cores. Most of the residual stress is in the skin and if you take that off it should not warp.
^^^^^^
+1.
Also, using the least thick plank of foam that suits your needs is helpful as well.

If a plank seems curved before using for a wing core, I usually find the concave side and sand the high edges a bit with some 60grt on a block, until it sits well on the bench.
Then, slice off the convex top to flatten it.
Then, flip over and slice off a bit more to flatten that.

Then you should have a true, flat, relaxed blank to work with.

It does appear that the pink foam of the same density both cuts better and produces less hairs than the blue foam though....

R,
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Old Feb 05, 2013, 07:47 PM
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DLGjunkyard's Avatar
Canada, ON, Puslinch
Joined Apr 2010
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Quote:
Originally Posted by G Norsworthy View Post
I've been skinning 1/8" off the top and bottom of the blanks before cutting the cores. Most of the residual stress is in the skin and if you take that off it should not warp.
What he said This is good practice with most any material you want to shave down . Even with metal on a mill
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