Thread: Will the joint fail?

Hey Zelk,

First a Question what are you making,?

The answer will have a bearing on how to do it.
I would probably use a PVA probably TiteBond, but if there is any load I would probably go for an Epoxy, and a couple of Biscuits or even Dowls

HazzaB

I've not tried butt-jointing timber like that, because every piece of advice I've seen advises against it. It MIGHT work - apparently there are glues which love end-grain - but I wouldn't take the risk.

If there is just no alternative to joining the timber this way, perhaps you could strengthen the joint using some loose tenons ... or perhaps a scarf joint (using an angle like 45 rather than joining at 90) would be stronger.

My other concern will be finishing. This will look UGLY.

If it remains supported as shown for the rest of your life, it will not fail.

Otherwise, it depends on everything else, and your definition of "fail."

I generally rely on glue to hold things in position, while other mechanical contrivances provide structural resistance. Endgrain to endgrain is pretty much the weakest attachment possible. A midline board, spanning the joint, would allow sidegrain contact amongst the pieces, and should be quite robust.

Cheers,
Joe

as others have hinted, what load does the joint need to carry?

I'd be inclinded to reinforce the joint with a loose tongue, think two breadboard ends without a pesky table top in between



ian

Loose tenons would be my first choice for joining end grain to end grain. As has already been said, end grain to end grain is the weakest joint of all. Glue up some scrap pieces & leave them for a few days then put a bit of a load on it, u'll find it breaks pretty easy.

If you partially seal the end grain first with a weak water/glue mixture before you glue you will increase the strength. By how much - don't know but one of the reasons end grain glue joints are weak is that the glue gets sucked away from the joint.

That's a big surface area to join and I can't see a use that would put a sufficient load on either piece that would break a plain glued joint using and good woodworking adhesive eg PVA. The joint will not 'fail over time' if what you mean is does the glue weaken. Depends on the glue, but any modern glue will likely outlive your use of the piece.

As has been said if there is some great load the will apply shear or twisting forces along the two pieces that would tend to have them come apart then you'll need to add some mechanical fastening as other have said - biscuits, dowells or some screws. In any case it is a simple job to drill, countersink and insert two or three screws and then there is not concern on any load (so far as the joint goes).

Originally Posted by Bloss

snip...
In any case it is a simple job to drill, countersink and insert two or three screws and then there is not concern on any load (so far as the joint goes).

not having a go...

using screws to reinforce the joint would require the screws be driven into end grain.
screws into end grain don't hold near as well as screws into long grain


ian

yes it will fail... eventually.
add some interlocking messure... biscuts, dowels etc, and it'll help.

Good luck.

The joint (end grain to end grain) will not be as strong as some other joints. It would help if you made it a lap joint, even with just a 12 MM over lap.

I have made end grain to edge grain joints with TiteBond III that were surprisingly strong. If the final application is not in a high stress application, you may want to try TB III.

Thank you for your replies.

Lets, for the moment, forget about where such a joint would be used. We all know that endgrain to endgrain is a weak attachment.

Lets assume that the pieces are glued to another without reinforcing, allowed to sit indoors as shown in photo 3, exposed to the natural variations in humidity and occasional sunlight and under no load for 5, 10, 20, 50 or even 100 years.

Keeping in mind that the timber will expand and contract, will the joint fail, as it is endgrain to endgrain?

Zelk

half lap the joint with at least the depth of the thickness to provide some bond strength on the long grain. or as they say - loose tenon...

I wouldn't expect much of an end grain to end grain joint.

The normal thing to do is a scarf joint. Any reason you don't want to do that?

Originally Posted by Zed

half lap the joint with at least the depth of the thickness to provide some bond strength on the long grain. or as they say - loose tenon...

Thanks Zed, you're back!

as mentioned, NO reinforcing.

Zelk