# How to make an epoxy fillet



## paint it black (Nov 3, 2007)

Good stuff!


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## Brett (Jul 16, 2008)

I only have one minor opinion to add.  

I think fillet radius should be based on the type of fiberglass material to be used,
and the thickness of the adjacent plywood panels.
Calculating the radius from the panels, the fillet radius
should be 3 times the thickness of the thinnest panel.
Also it should be, at a minimum, the radius of the fiberglass material
when allowed to make it's own curve in a hard 90° bend.
any tighter a radius, the glass will begin to resist,
bubbles will occur weakening the laminate and joint.

example...5.6 ounce tooling cloth when allowed to relax into place
takes a natural 3/4 inch radius...


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## firecat1981 (Nov 27, 2007)

Good point, I'm using about a 1/2"-5/8" radius (depending on how you measure) which worked out well last time, but my panels are just 4mm, and with the flair the corners are much less then 90 degrees, so a larger radius isn't needed. The 6oz biaxial tape I'll be using over it flexes like tissue paper so I don't have any issues there. I used 6oz cloth tape last time and it worked well still, Heck I even proved no failures cause I saw them from the inside when I cut her up into 1ft pieces :'(.


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## firecat1981 (Nov 27, 2007)

I'll add a note to the bottom of it


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## Frank_Sebastian (Oct 15, 2007)

Here is a quick peek at fiberglass cloths. Please note the strength of the various weaves. For any structural laminates "S" glass is a good choice with "E" glass about 30% behind.

http://www.aircraftspruce.com/menus/cm/fiberglass_cloth.html

Best regards,
Frank_S


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## firecat1981 (Nov 27, 2007)

Good info and this quote is why I went with biaxial this time instead of woven cloth. 20% is alot of added strength on a small lightweight rig.

"Knitted fabrics are a relatively new format in composites. The performance of the glass is greatly enhanced by removing the interstices of the woven fabric and the crimped condition. E-glass in woven goods normally has 22,000 psi tensile strength. Layered nonwoven goods give 27,000 psi which is about a 20% improvement. Knitted glass offers greater ease of fabric orientation and saves time over multi-layered wet lay-ups."


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## SKIFFGUY (Jan 14, 2008)

Well done how too...


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