1900 forum posts
Tack it with Cyano then use the phatics
|Martin Harris||18/09/2016 17:57:02|
8807 forum posts
Any reason to prefer aliphatic over cyano? While aliphatic is very good for building, I find cyano far more efficient for piecing together "jigsaws" especially where cracks run along the grain. It's light enough to flood the inside of unreachable areas and the result is almost certainly a lot stronger than the original wood.
|Biggles' Elder Brother - Moderator||18/09/2016 18:52:34|
15748 forum posts
No I disagree about using aliphatic here. If this fracture is as described aliphatics are not the best at all. As has been described put the mating fractured surfaces together into a really close, interlocking, jaged, fit. Then drop very thin CA (as Martin says) onto the "crack". If this works the drop will sit there for an instant and then suddenly seem to "dissapear". What has happened is that capillary action has sucked the glue deep into the fracture zone where it will form an excellent bond - as i say stronger than the original wood and definitely stronger than aliphatics could in this case. Aliphatics are great adhesives, I'm a big fan, but they need some space to work in - not much true, but definitly some. CA thrives where the space between the components is almost molecular in size!! The smaller the better! So if the parts fit back together closely - use CA.
|6032 forum posts|
I suggest PVA such as Evostik Wood Glue ( Resin W ) rather than aliphatic or cyano would make the strongest joint..
No point in debating whether BEB is right or I am right .......just break a piece of balsa into a jagged cut and glue with cyano and another with PVA. When fully dry -24 hours with PVA - test to destruction. The result may vary with different cyano makes and wood type. Some cyano stick like anything others don't stick to really dry balsa. Evostik Resin W seems very consistent while other similar looking 'PVA' such as cheap supermarket makes have very little strength. Maybe the cheap stuff is diluted to look a better deal. Again a test to destruction with scrap wood tells it's own story. If the wood does not fail before the glue then it's not as good as Resin W! By the wood failing before the glue joint I mean softwood or hardwood not just balsa - the grain of a hardwood such as beech will fail before the joint if glued properly. with a good PVA.
My idea of replacing the shattered wood with a new balsa ( after first getting the jagged parts glued back into shape ) might also allow access inside so a doubler can be glued in first. Also consider a two different adhesives - a spot of cyano can be used to hold a doubler in place whilst the main coating of PVA or even epoxy drys. Maybe something ingenious for special jobs - a piece of cotton through a pinhole with something like a button on the end could pull a doubler in place internally and be cut off after the glue drys. Or use a bent piece of thin piano wire to pul linto place and then nip the wire off after it's done its job. Or a screw into a piece of ply could pull the joint into place and the screw removed from outside when dry without leaving much of a hole. ( use sellotape to cover any temporary packing that needs to remain unglued )
|Old Geezer||19/09/2016 17:25:23|
|617 forum posts|
kc - it's only Monday and you're already top contender for 'Lateral Thinker of The Week!'🤔
|Piers Bowlan||19/09/2016 19:04:39|
1871 forum posts
We can all agree to disagree but without a photo of what we are repairing it is all pretty academic! How well the wood mates together, how thick it is, how much filler will be going in to fill the cracks! It is all a judgement call and down to experience and preference. Martin Harris had a good point about stress raisers;- local reinforcement is often not a lot of good unless the load is spread. Like BEB said, a bit of extra weight down the back end is generally not a good thing, as it usually requires a lot of weight up the front end to compensate! However, if it stops the tail falling off mid-flight it is probably not a bad thing after all!. Perhaps building a new fuz is the best solution, - if not the quickest. Decisions, decisions!
Edited By Piers Bowlan on 19/09/2016 19:06:04
|Graeme Poke||11/10/2016 05:24:13|
175 forum posts
After lots of your good advice from the Forum, I have tackled the problem and she is ready to fly again. The forecast for Thursday is good. It looks ok from a distance, a bit rough up close. The only slight concern I have, apart from breaking up, is that the tail plane is not quite lining up with the main plane, about 3 mm out of alignment. I thought of packing up the main wing but thought I would see what happens first. Maybe a bit of trimming will fix it good enough for my mad flying. i have even figured out how to include pictures for your perusal...I think! See how we go. Thanks for all the help.
|Graeme Poke||11/10/2016 05:26:51|
175 forum posts
Ah. I thought it would include the pictures in the body of the post. They are in the 6 photos on the side. Thanks Graeme
|Graeme Poke||13/10/2016 07:29:16|
175 forum posts
The Staudacher flew beautifully today. The only minor trim problem I had was while inverted, I didn't need any down elevator at all. Tail heavy a tad maybe? Other wise fabulous, which surprised me. All held together and flew as always. Very happy lad.Cheers Graeme
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