|Jan 09, 2013, 07:12 PM|
Cutting foam wing cores
I have cut a few cores in my building escapades with mixed success. I am designing some core templates now for a plank style winged bird.It seems that the most difficulty I have is the leading edge, particularly on a tapered wing. If the slopes aren't in sync it flattens the top LE. I seem to have more success cutting from the LE to the TE as the distance is shorter and less error accumulates. I mark the lines with scaled numbers to keep the wire at the same point in the respective ends. Do most people cut from front to back or vice versa. Is there tricks to help cut more accurate cores. I am using 1.9 EPP.
|Jan 09, 2013, 08:32 PM|
Keep the wire super tight. I use 1/4" music wire in a bow so as the wire heats up and stretches, the music wire legs will take up the slack. Keep the legs kind of short, maybe 8 inches or so. I cut from back to front and have a helper on the other end of the bow. If you cut too fast the wire will lag in the middle and give the effect you describe. Don't get in a hurry I think is the key. I'm using some 120 lb test stainless leader wire. It's a tad thick but you can pull it super tight. My power supply is a 4 AMP, 12 volt battery charger. Cutting a 30 inch core it lacks a bit but gets the job done. A thinner wire would help a bit but a 24 volt transformer would be better for the long wire.
|Jan 10, 2013, 07:59 AM|
Good to see you're getting some model building in.
You may be interested in these links, all FREE!
An article I wrote for RCSD called "Build an Automated Foam Wing Cutter". It talks about the bow as well as the automated part.
Tailwind Gliders is offering a FREE 12-minute instructional video on cutting highly tapered wing cores using a Pivot Cut method.
This is a 618Meg download. It is in a zipped .mp4 file format.
To answer your question I always cut from the leading edge to the trailing edge and I always cut the bottom airfoil first then the top. If you cut the top first then you're airfoil will be thinner by the thickness of the wire.
|Jan 11, 2013, 07:58 AM|
Joined Oct 2005
I cut everything front to back and agree with the advice to cut slowly to avoid wire lag in the middle of the cut. Also you didn't say what span you were trying to cut. It really is hard to get a good cut on more than 24 inches or so with a hand held bow. If you google "foam wing cutting" there is some really good advice out there.
|Jan 11, 2013, 10:36 AM|
I will be cutting with a 24" bow. I use about 120 lb steel leader. It is not unusual for me to break the wire. I am wondering how to determine the correct temperature. How do you test for correct temp. I always test on a scrap, but a full length cut requires more heat as the foam absorbs some of it.
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