Thread: Joint Strengths

John

Thanks for the very interesting link.

If you right click on the link and choose "save as" you can save to your computer and then use Acrobat reader to open it. Should save heaps of time!

Yip

JOHN I am a good friend of Mark (he LOVES biscuits-biased ???) & this WAS in F.Wood--but these figures have been disputed in almost any other tests that had been made & published.
I made my own unscientific test & the 2-biscuits came out a VERY POOR second in a st.down--inline rail--shear test in 13/16" ash.
I never tried a sideway shear as I dont think this is near as important.
I think the biscuit would still fail long before a good--properly dimensioned--well made--M/T .

G'day
I'm not particularly fond of any one method, just use whatever is necessary in my opinion to do the job. I did however notice in this article that they said the dowell joints looked dry, and perhaps the glue should have been spread around. Dah?
cheers
Rod

Funny that this subject should come up as I have just finished reading the origianl FWW article. There has been a similiar article since. both seem to show the biscuit as being very strong.
I was interested to see that all the traditional quality methods seem to compare very similarly.
I was also interested to se that the failure point was usualy the surrounding timber, which begs me to ask " Were the proportions of the joints optimal and thus a good comparison.
I recolect seing an artical obout proportions of M&T jounts and their relative strength but can't remember where.

interested to here comments.

Thank God for my screwgun and my big box of screws

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Some days I turns thisaway, somedays I turns thataway and other days I don't turn at all.

I guess where a mortise & tenon is employed in place of biscuits is testament that all our forefathers have unfailingly used these conventional means to provide a safe weight bearing means of construction down through the ages.

I believe biscuits do have a place in modern woodworking but commonsense and practicality must dictate where in joints they are used.

As Woody(Luther), said in a rail application the question of using biscuits in end grain and being capable of withstanding a downward force defies logic and the physics of the joint.

Where a biscuit is used in availing the width of the biscuit going with the grain in edge jointing as in board to board then some reasonable strength is attained and in a quick application.

To truly appreciate good woodworking skills one should have a working knowledge of joints,their uses and limitations.

Just some thoughts
Cheers

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Johnno

Personally I would like to see them try the same test with the frame complete and the panels in place.

I bet they'd get a bloody big shock when a joint finally did go. Would probably take around 500,000 psi or more and what an explosion there would be.

Most joints are only as good as the glue or the timber used, as can be seen in all the photos. Most joints didn't break, it was the surrounding timber that went. Those that did break cleanly at the joint obviously weren't glued properly. Todays modern glues are much stronger than that, even on end grain (at least the Austrealian ones are).

I really don't think they proved much at all, other than they found a great new way to waste a few days and get paid for it.

My 20cents worth.

Cheers - Neil

Whilst I accept your point Neil, I feel a certain degree of healthy paranoia when it comes to relying upon a glue only to hold together a supporting structure.
I am assured that they will hold but there is always a feeling of 'The sword of Damocles' about it for me.

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: http://community.webshots.com/user/iain49

Not advocating a glue only joint but the propper application of the glue to the joint.

A dry or badly glued mortise and tennon, dowelled or or any other joint for that matter, will never be as strong as one that has been well glued.

As some of the photos showed some joints were obviously badly glued as they broke at the joint and not through the surrounding timber. My point is that todays glues are stronger than that and should not have let go at the joint. Either that or their "good ol' Elmers Glue", aint all it's cracked up to be. But I doubt that is the case.

Cheers - Neil