working with kevlar
Brad
avoid or at least to control the fuzzing when sanded or trimmed?
am interested in getting the trailing edge of a kevlar control surface
nice and straight.........
thanks,
Brad
Mike Bamberg
It's very easy, never take the kevlar to the edge! Replace the kevlar
of the layup with with equal thickness glass or carbon within 1/2 of
the edge. Be sure there is a "tune-able" (read that sacrificial)
layer over the kevlar if you expect to sand the surface.
If you really need to take the kevlar to the edge of a surface, the
best way to trim it is with a shear, no rotary cutters or sanding.
Log onto several of the model soaring forums and look at the
structures they are creating with Kevlar and carbon.
Mike
Martin Gregorie
> If you really need to take the kevlar to the edge of a surface, the best
> way to trim it is with a shear, no rotary cutters or sanding.
>
Agreed: my (limited) modeling experience with Kevlar says never sand it.
Weight for weight Kevlar usually is a coarser fabric than glass and so is
likely to leave a textured surface if its the outer layer but you can
loose a lot of that merely by using light glasscloth (25 gsm, 0.8 oz/yd)
as the outer layer. As a bonus, that also gives you something to sand if
you really must.
The light stuff (70 gsm or less) is hard to cut cleanly because the
shears or sharp knife tend to distort the weave. Putting masking tape on
one side of the fabric and cutting down the middle of the tape helps a
lot.
> Log onto several of the model soaring forums and look at the structures
> they are creating with Kevlar and carbon.
>
Good advice.
--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
uncl...@ix.netcom.com
I have had some luck sealing the fuzz with cyanoacrylate(Zap is model
brand- use thick stuff) to satnd up the fuzz and permit sanding.
This should get you by for what you are working on now. Best bet is
avoid by ending Kevlar layer just a little short of edge.
Good luck
UH
Uncle Fuzzy
I'm one of the model builders that has also messed with Kevlar. At
this stage, you're already "fuzzed". A possible 'fix' is to continue
sanding until you're a few thousands under your desired profile, then
bag on some light glass cloth. There's no GOOD way to deal with the
Kevlar fuzz.
gliderman
After sanding, you can use a "super glue" (cyanoacrylate) with the
spray on accelerator. Use lot's of accelerator so that the glue
appears to foam up (This makes it brittle and no good as a glue). Then
use a razor knife or an exacto to scrape/cut the fuzz away.
Brad
We did use a mold side E-glass veil to give us a working/sandable
surface, but too bad I did not think about holding short at the TE and
using 7725, that would have made the TE trim a piece of cake instead
of a gin-fuzz......:)
Will let you all know how things turn out. The Kevlar flaperons are
nice and floppy, much more so than the carbon one I made, the carbon
flaperon was very nice to build and easily trimmed but we deemed it
too stiff.
Brad
JohnElliott
http://www.express-builder.com/forum/messages/2/1556.html?1190005809
Exerpt from above thread:
I have talked to several builders trying to use kevlar composites.
Common problem to all of them are the way kevlar behaves when sanding
it.
All edges sanded the normal way gets the look of a "used toothbrush".
This problem limits kevlar use to places where it will be totally
contained inside other structural parts. Now I found out that it is
possible to sand kevlar edges with good result. I used normal water
sanding technique with no:120 grit and this will give you a smooth
edge just as when sanding a fiberglass counterpart.
Don Johnstone
sanding is used on gel coat, which is polyester resin I have not seen it
used on epoxy resin structures. One of the purposes of gel coat/paint is
to prevent water getting to the underlying epoxy structure which is
hydroscopic.