Re: egads

Posted by Laszlo on Oct 9, 2005

Actually, I'm not sure if it's so much smarter as that I'm spending time that I should be using to practice eskimo rolls reading reading mechanical engineering books.

Anyway, Mike, you've run into exactly what I was talking about. The tape doesn't want to stay in a sharp corner because it resists bending and the only way to make it stay is to crease it and hold it in place while the epoxy cures, which gives you your stress concentrator. If you don't force it, it'll just peel away leaving a bubble. The prescribed way to fix a bubble is to use a syringe to inject epoxy into it, which is just another way of smoothing the fillet to the minimum bend radius.

What you say about the fillet volumes is exactly what I meant when I said that the weight will take care of itself. On obtuse angles the amount of epoxy will be less and on acute ones more, but in all cases it'll be the minimum for a good fillet. It's pretty much just a matter of practice. The more fillets you make, the easier it becomes to do this. Beginners should worry more about properly wetted tape, a smooth fillet and a good bond. Save the optimization for the second or third boat.

As far as filleting putty materials, anything that bonds well to epoxy and supports the glass will work. The trick is determining if it will bond well to epoxy. Wood flour is cheap, light, compatible with both the wood and the epoxy and has a decades-long proven track record. Why use anything different, especially when it's what the designer recommends? (BTW, talc is heavier than wood flour and absorbs water).

Anyway, happy building to all,


In Response to: Re: egads by Mike D on Oct 8, 2005