GLue strength testing worth a look

Got a new way of doing something? Or maybe an old method that needs some clarification.

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tippie53
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GLue strength testing worth a look

Post by tippie53 » Mon Nov 19, 2012 11:01 pm

http://woodgears.ca/joint_strength/glue_methods.html

this can help take the mystery out of how to glue.
While I do use fish and hot hide glue , there is some good info about clamping techniques.
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Nick
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Re: GLue strength testing worth a look

Post by Nick » Tue Nov 20, 2012 6:06 am

Thanks for that John, some interesting results there! Just wondering if you would see different results if the joints were stressed in tension (tried 'ripping' them apart) as opposed to torsional loading...hmmmm. Also his 'mortice' result probably wasn't fair as it wasn't a true mortice & tenon where the glue only has to stop the joint from seperating, the tenon itself usually takes any shear or twisting load in a normal situation. Interesting to see the loading results on the 'gapped' joint.
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tippie53
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Re: GLue strength testing worth a look

Post by tippie53 » Thu Nov 22, 2012 6:28 am

I found it enlightening . Great info base especially for the newer builders
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n~dl
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Re: GLue strength testing worth a look

Post by n~dl » Sat Jan 12, 2013 4:34 pm

That was interesting, I love little tests like this. I wish there was one with an finely-sanded/burnished surface. I can imagine how that one would turn out, but it would have been nice to have seen the direct comparison.
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Kim
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Re: GLue strength testing worth a look

Post by Kim » Sat Jan 12, 2013 11:16 pm

n~dl wrote:That was interesting, I love little tests like this. I wish there was one with an finely-sanded/burnished surface. I can imagine how that one would turn out, but it would have been nice to have seen the direct comparison.
Well..(a proper name would be nice) welcome to the ANZLF. :D

Just to clarify there have been tests done on the topic of glue surface preparation and despite what many assume would be the case, myself included in days gone by, it turns out that for the majority of woodworking glues such as PVA etc, a 'fresh', 'clean', and dead 'flat' surface gives a superior bond to a keyed surface.

I have not assumed from your comment that you are recommending 'keying' or 'toothing' the joint to provide greater surfacer area BTW. Rather I am pointing out for anyone that reads your comment and perhaps assumes that 'is' in fact what you're eluding to, that test show with perhaps the exception of those mechanically bonding adhesives such as epoxy, it simply does not work that way.

This is because PVA type glues bond chemically which is a process that takes place a molecular level. Therefore in order for keying or toothing of the gluing surfaces to be beneficial it would require the hills and valleys of each component to interlock 'perfectly' if it were to have the desired affect of creating 'more' surface area. If the keying of components does not interlock perfectly, then it actually causes a 'weaker' chemical bond because only the meeting 'peaks' of each component would interact as they should with voids between being left filled with glue to become a weak link. If toothing/keying had been created using a course abrasive or a perhaps a rasp or file, the glue joint would perhaps be unreliable.

For PVA derivatives such as TiteBond, or even hot hide glue, the clean 'freshly' planed surface left by a well tuned hand plane is ideal, for epoxies and urethanes, key away.

It is interesting that the test at the link where all undertaken using only softwood meaning the results are hardly conclusive. To be worthwhile you would need to compare apples with apples as kiln dried radiata is like a sponge and this helps in a big way to suck a glue joint dry. When I work with pine I will always flood the joint, but on something hard like jarrah there's no need to and because it won't 'crush' under pressure like pine, you can really crank down on the clamps to end up with an almost invisible glue line but a bloody strong joint all the same. This is important when edge jointing for the face of stair treads or table tops etc and a series of 10lb weights just would not cut it.

There's a reason why they make sash cramps and gluing up bits of pine ain't it. :wink:

Cheers

Kim

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