Re: [ULF-1] Sanding before gluing

From: Member 1
Date: 2018-06-14 20:56 UTC-05:00
Message: #0629
Good points, Peter.

When I began building airplanes decades ago the EAA had a great book 
about the different adhesives available. They were still talking about 
resorcinol and casein back then, but through the book and other research 
it sounded like they were not being used much any more. You guys are 
welcome to revisit that discussion, but I think it's a dead horse that's 
already been beaten to death in numerous other forums. A little web 
searching will probably turn up all you want to know about the topic and 
more. I'm happy with modern structural epoxies and learning how to best 
use them, so forgive me for being incurious about bygone methods.

Except in the world of violins, where hide glue remains relevant because 
it is easily reversible and more sonically transparent than other glues! 
We do use epoxy for certain repairs that are difficult to close and we 
don't see anyone needing to open it back up in the future.

To be nit-picky, I would disagree that a micro-balloon slurry is not 
structural. I agree that its tensile strength is low, but its 
compressive strength is significant for its weight. Hollow spheres don't 
crush easily, especially when they're being held in that shape by a 
rigid resin matrix. So any use I would have for it structurally will be 
designed to exploit its compressive strength (such as keeping a flat 
part from flexing out-of-flat), and no I would not count on it for any 
tensile loadings. I agree that a flox slurry will have better tensile 
strength, but if we're talking strength/weight ratio and loading in 
compression my money would be on the micro-balloons.

Good discussion guys.

Doug



On [phone]:16 AM, Member 112 wrote:
> Surely the preparation of the surfaces to be glued depends on the glue 
> to be used.  I am a wooden boat builder and my 15ft dinghies have no 
> fasteners - all glued joints.   I use epoxy for all glued joints and I 
> sand all joints before gluing and make sure that epoxy has saturated 
> the end grain or surfaces before making the joint.  Now, if I was 
> using hide glue (let me know if i'm wrong Doug) I would have superbly 
> made joints with an extremely thin, almost invisible, glue line.  Hide 
> glue does not fill gaps and there are many reason why hide glue is 
> used for violins, etc. and not epoxy!
> Just my 2 cents - or 2 pennies!
> Peter