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Composite Core types

Posted by Duct Tape 
Composite Core types
August 25, 2015 11:38AM
For my first post here (thanks for all of the great info!) I thought I would post a review summary of the various core options I found helpful in getting up to speed here. Maybe it will be of help to other newbies here.

http://www.compositesworld.com/articles/getting-to-the-core-of-composite-laminates
Re: Composite Core types
August 25, 2015 12:40PM
Good link. Thank you!

I'll make this thread sticky at some point. Haven't read all of it yet. But I will. Glad to see they mention end grain Balsa Wood. Balsa wood burned me too many times for use below the water line. It soaks up moisture. Honeycomb core is better. But above the water line it's extremely handy. If you want to make curved parts it's real easy to work with. Make a cardboard and hot glue gun form. Put some balsa wood on top. Fiberglass it. Most manuals tell you use a preliminary layer of (not woven) matt first. And then fabric. But it isn't necessary. You do have to thoroughly wet the balsa wood first, and putty up any widely gaping seams. And then lay down the fabric. It works well. For compound curves it's great. As long as they're above teh water line.



Re: Composite Core types
September 16, 2015 11:42PM
Sandy, do you have any photos of layup work with balsa? Was wonder why end grain? Why not just cut lengths and make a balsa plywood?
Re: Composite Core types
September 17, 2015 01:31PM
I made three or four boats with end grain balsa wood back in the late 1980s. First in 87. The year after I built my house. I was a dumbass and didn't make any photos.

Balsa wood has no compression strength at right angles to the grain. You can squash it down between your hands. Some anyway. But it has remarkable compression strength the end grain way, parallel to the grain. And it weighs very little. It comes in 2' foot by 2' foot sheets of little 2" inch by 2" inch end grain blocks lined up nicely tight together, and held that way by being lightly glued on one side, to a scree of very loosely woven fiberglass fabric.

Because each sheet consists of lots of little end grain squares ( 1/2" inch to 4" inches thick ) it can bend to contour over compound curving surfaces. If you bend it over a sharp bend gaps do open up between adjacent end grain balsa wood squares, but the few wide gaps that might form can be troweled with epoxy putty prior to layup.

The manufacturers recommend wetting the balsa first. And then to lay down a single layer of uni-directional, not woven fiberglass matt. And then your layup. What ever it is. You can skip the matt but you have to be careful not to let a first layer of glass get resin starved. It is fine above the water line. Not expensive and easy to work with. The easy ability to work over compound curves is a blessing. It's used a lot for racing sailboat hulls. I think Plascore can be purchased (for extra money) that has a grid of slits cut into one face of the Plascore, so it too can bend over a compound curve.

You do not want to use balsa core below the water line. Sailboats don't pound rocks. And even they have water absorption problems. Balsa is ONLY for above the water line.
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