To use glue in a trench? Or not?

Imagine making a bookcase. You rout a trench across an upright piece and then put the end of a shelf in that trench.

Can such a joint be glued safely?

A moment's reflection tells you that you are really trying to glue end grain to a flat surface. A glue joint on end grain is very weak, we're told.



Can anyone throw some light on this?

Regards,

Kevin

Most of the strength is from the tight fit of the shelf in the trench. A cross-linking PVA should be strong enough for what you need, even on end grain, but if it's particularly wide you may want to consider screwing all the way through from the outside and capping the holes with timber plugs. If the sides are thick enough you could use dowels instead of screws. In any case, I'd recommend screwing through the back in to the middle of the shelf for some extra support.

why do you want to glue the joint?
to hold the uprights in position? If so, replace the plain rebate with a sliding tapered dovetail.

Quote:

---

Originally Posted by KevinB

Imagine making a bookcase. You rout a trench across an upright piece and then put the end of a shelf in that trench.

Can such a joint be glued safely?

A moment's reflection tells you that you are really trying to glue end grain to a flat surface. A glue joint on end grain is very weak, we're told.



Can anyone throw some light on this?

Regards,

Kevin

---

Yes Kevin, its a joint that is glued, its safe . No different than glueing up a box where the sides are just butted up to each other or rebated then glued .
In the box, they are end grain going up to cross grain and the glue holds up . The grain of the box sides or the bookcase side to shelf is generally expanding and contracting at the same time in the same directions , so you don't get the self destruction that would happen if you glued that shelf in to the bookcase the wrong way around, with the end grain of the shelf facing you . It wouldn't hold books to well either of course:) if you did that. As well as the expansion and contraction of the shelf being the wrong way around.
And yeah , end grain doesn't hold as well when glueing, the thing that is very important in the bookshelf or any cabinet is the back. That's what braces it up well . You try not to just rely on the glue at the end of the shelf to do that.

Rob

Thanks Rob, you've told me things I did not know. Thanks for your time.

Regards,

Kevin

Quote:

---

Originally Posted by auscab

Yes Kevin, its a joint that is glued, its safe . No different than glueing up a box where the sides are just butted up to each other or rebated then glued .
In the box, they are end grain going up to cross grain and the glue holds up . The grain of the box sides or the bookcase side to shelf is generally expanding and contracting at the same time in the same directions , so you don't get the self destruction that would happen if you glued that shelf in to the bookcase the wrong way around, with the end grain of the shelf facing you . It wouldn't hold books to well either of course:) if you did that. As well as the expansion and contraction of the shelf being the wrong way around.
And yeah , end grain doesn't hold as well when glueing, the thing that is very important in the bookshelf or any cabinet is the back. That's what braces it up well . You try not to just rely on the glue at the end of the shelf to do that.

Rob

---

Thanks Ian.

Regards,

Kevin

Quote:

---

Originally Posted by ian

why do you want to glue the joint?
to hold the uprights in position? If so, replace the plain rebate with a sliding tapered dovetail.

---

Thanks elanjacobs, good advice indeed.
Regards,
KevinB

You will find the glue to be stronger than the surrounding timber, thus if you were to break the joint it would be the timber breaking apart not the glue.