ULF-1 Discussion Archive
Anonymous static archive of the former Mailman list
Anonymous static archive of the former Mailman list
Re: [ULF-1] Epoxy bonding
Cool .
Did you ever hear of fiberglass drywall tape? Wrapping struts near
the cocpit to prevent splintering impaling effects ? But some fiberglass
is unravel -ish when cut into strips . Cotton linen was used in ww1 on
propeller tips .
On Wed, Jun 13, 2018, 9:06 AM Member 72 <[email]>
wrote:
> Hi Doug,
>
> All very good advice. One thing we did on our ULF-1 build was to mix flox
> (floculated cotton) into our T-88 glue batch when we needed to thicken it
> up a bit to help fill some voids in the joint, rather than micro balloons.
> We found flox to be structural in nature and added strength to the joint,
> while microballoons was more cosmetic, not adding much strength to the
> joint.
>
> Thanks,
> Member 72
>
>
>
> Sent from my iPad
>
> > On Jun 13, 2018, at 1:43 AM, Member 1 <[email]> wrote:
> >
> > I'm with Bob on this. To me, there is a lot of superstition involved in
> peoples' beliefs about gluing Member 60. The shiny surfaces created by blades
> have always intuitively struck me as a deterrent to a good glue bond. I am
> now working as a violin-family luthier, and I am up against the same
> superstitions there as well.
> >
> > Having said that, though, I'm not sure it makes a big difference. While
> building an aircraft, you end up with leftover epoxy from many small
> batches. Grab some sticks out of your trash or scrap pile, and do some
> semi-scientific testing with your leftover glue. It only takes a minute or
> two. For example, I would cut two sticks about 10 times as long as their
> width/thickness, overlap them 2 or 3 times their width/thickness, and glue
> them together with light or moderate pressure, and then break them after
> curing for a couple days. The Member 60 should always fail before the glue joint
> does. If it does, then who cares how the joint was prepared?
> >
> > Do this often, throughout your project, during different environmental
> conditions, and as your epoxy gets old. As soon as you find yourself
> airborne, your life hanging from all those glue joints you've made, you may
> think about those glue joints (as I did) and find comfort in the fact that
> they are stronger than the Member 60 itself and you've done the best you could.
> Then it all comes down to proper design which doesn't allow any joints to
> get stressed to the point that the Member 60 itself fails.
> >
> > To me, it is more important to not apply too much clamping pressure to a
> glue joint than it is to worry about cutting vs sanding. I always let my
> wet joints sit open either until the epoxy is thickening a bit, or it is
> obvious that the Member 60 is saturated and won't be absorbing any more glue.
> Then I'd assemble and clamp with moderate pressure. Epoxy has several times
> more tensile strength than hardwood, so even if you're sloppy and end up
> with a thick seam of glue, there should be no strength penalty. A small
> weight penalty perhaps, but that would be over-nit-picking. If you join the
> parts before the glue has stopped soaking in, and/or apply excessive
> clamping pressure, you are asking for a weak, glue-starved joint. (I use
> T-88 which is relatively thick... if you use a glue that has a thinner
> consistency, this attention to soak-in is even more important.)
> >
> > Epoxy is really good at filling imperfections and allowing stresses to
> be spread out over larger areas, so a perfect fit is not as important as it
> was with previous glues. For large voids that can't be easily avoided in
> structural joints, I recommend wetting the bonded surfaces with epoxy and
> then making a light slurry with epoxy and micro-balloons to fill the voids
> with.
> >
> > Test your glue and your methods. Then you'll know, and nothing anyone
> writes will bother you. There are some photos of the glue-starved joint
> risk here (and other gluing tips throughout my old AirBike building web
> site):
> >
> > http://questiongravity.com/airbike/feb03-1.htm
> >
> > $0.02,
> >
> > Doug
> >
> > PS: We have 307 members! So glad to see you all here, and thanks to all
> who have been contributing. And thanks to Dieter for continuing to fund the
> domain fees to keep this service available.
> >
> >
> >> On [phone]:56 AM, Member 116 wrote:
> >> I disagree about not sanding before gluing. A power planer of a hand
> planer bends the fibers over and leaves a shiny surface, not good for glue
> penetration. I have a cabinet shop and glue stuff together daily. For a
> couple years I glued up 12 ply (birch and maple) propeller blanks for a
> prop manufacturer. All those ply's after planeing were smooth and shiny
> because of the bent over fibers. Before gluing (with Resorcinol glue) I'd
> run over them with a belt sander/80 grit across the grain, one pass to give
> the Member 60 some (tooth). Then use a shop vac to clean and make those
> (damaged) fibers stand up straight and accept more glue penetration.
> >
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