fibreglassing corners question

[journeyman Mick]

Not strictly a boat building question as I am glassing a tool box for the back of the ute, but I figured this was the best place to post. I've made some ply boxes and am laying woven glass matting on them. I'm not sure of the weight/weave of the glass, but it's fairly light, not much thicker than a light cotton shirt (ie not as thick as a king gee work shirt). I'm using epoxy resin and have taken a rounding over bit to all the edges. I'm just wondering how one gets the glass to sit nicely at the corners (ie where three faces meet). I've tried cutting the glass so that I can wrap it around the corners, which would work neatly if the corners were square, but as the corner is rounded off the glass tends to peak in a small point, rather than wrapping around. :?:?

Thanks in advance,

Mick

[Eli]

My suggestion would be to do the corners separately, with a layup of smaller pieces just for the corners. I think I might try a small square piece pulled out into a diamond, and laid on the bias. So long points of the diamonds would be pointing inward towards the center of bottom, and up outside upright corner.

You could also build up the corners with narrow rectangular strips, some laid diagonally across the corner. For thin glass I'd think you'd want two layers at least anyway, for increased wear area.

If you build the corners first, then do your big glass up over them, they'll fade in better.

[journeyman Mick]

................If you build the corners first, then do your big glass up over them, they'll fade in better.

:doh: Too late. Thaks, will try that tommorrow.

Mick

[Boatmik]

Good advice Eli! That's what I would do too. It is enough advice to solve 95% of the problem.

So use that method Mick.

Some other things that might make it easier ...

The bigger the radius - the easier it works.

Another trick that may help a lesser amount is that you can cut the glass slightly differently - cut it so the threads that cross the long edges of the box are at 45 degrees to the edge.

http://www.storerboatplans.com/Faq/doublebias.jpg

This is cutting "on the bias".

Bias cut glass is much better at accommodating curves that happen in two directions at once.

It is better at less abrupt changes than corners but it might be useful in this context. too. It will be most useful for longer tapes that cover the edges and go around the corner at the end. When doing the little patch for the corner itself as Eli suggests it won't make much difference - as the corner approximates a sphere so is equally curved in all directions - so orientation of the threads will make no difference to that part.

It is also a bit of a pain to handle as if you pull it lengthwise it gets narrower - so you can cut something square and it can end up all sorts of funny shapes if you handle it inconsiderately.. So when cutting on the bias it pays to cut the glass a little oversize - or with narrow tapes cut them wider than you need - that way they will stay wide enough even if they get pulled out a bit.

Michael

[Eli]

:doh: Too late. Thanks, will try that tommorrow.

Mick

It doesn't even matter, they'll still fade in to a certain extent. Pretty forgiving. Remember if you don't like it, just grind it a bit with a flap pad, clean it really well and glass it again.

[bloggs1968]

Mick,

if its not too late, get some peel ply and use it on the corners. Make sure the piece of peel ply is large enough so that when it is sqeegied(sp?) out, there is enough surface tension to hold the corner down. Still dart the glass at the corner then use the peel ply. Also, make sure you give the ply a good drink of epoxy on the end grain before you lay up as it can stave the corner/edges of resin if you don't.

regards,

AD

[journeyman Mick]

AD,
thanks, what's peel ply? BTW too late for this project but it was just a training run for when I build my slide on campervan.

Mick

[bloggs1968]

Mick,

see here for info on peel ply - http://www.atlcomposites.com/pdf/peel-ply.pdf

Imagine if you could hold the sticking out corners of your job with masking tape, well this stuff will do the same.

If you want to try a small amount, send me a pm with address and i'll post some up for you.

regards,

AD

[journeyman Mick]

AD,
thanks, sounds worth getting for the camper project, any ideas on price?

Mick

[bloggs1968]

Mick,

You can get it in various widths but 1270 wide is about $4 a lineal metre inclusive.

regards,

AD