Thread: Biscuit Joints Glue or not to Glue

The biscuits are slightly smaller than the slot and are designed to swell.

No glue and you defeat the purpose of the biscuit.

Personally, I've never seen lumps form from biscuits.

Many, including professionals, will tell you that the biscuit adds no strength to the joint and that the sole purpose is for alignment only. If you subscribe to this school then the gluing of the biscuit makes no difference. I glue the biscuit myself, but don't get too fussed about. As for the biscuit swelling and causing a bump on the surface, this may occur if the biscuit is close to the surface as in thin timber.

Thanks for that

Originally Posted by BobR

Many, including professionals, will tell you that the biscuit adds no strength to the joint and that the sole purpose is for alignment only. If you subscribe to this school then the gluing of the biscuit makes no difference. I glue the biscuit myself, but don't get too fussed about. As for the biscuit swelling and causing a bump on the surface, this may occur if the biscuit is close to the surface as in thin timber.

Subscribing to that theory, why put glue on the tenon of a mortise and tenon joint, or on the loose tenon of same. IMHO, the tenon, loose tenon and biscuit all increase the surface area for the glue.

Originally Posted by elanjacobs

Personally, I've never seen lumps form from biscuits.

I have. It happens.

Originally Posted by burraboy

I have. It happens.

Especially with Tim Tams.....more of a bump than a lump though.

Originally Posted by Soredust

Subscribing to that theory, why put glue on the tenon of a mortise and tenon joint, or on the loose tenon of same. IMHO, the tenon, loose tenon and biscuit all increase the surface area for the glue.

Apples and Oranges mate.

Tenons = real wood, large surface area, grain at right angles to the joint, greater depth

Biscuits = compressed rubbish, small surface area, no grain, shallow depth.

Ian

Originally Posted by Ian Smith

Apples and Oranges mate.

Tenons = real wood, large surface area, grain at right angles to the joint, greater depth

Biscuits = compressed rubbish, small surface area, no grain, shallow depth.

Ian

Biscuit Joinery Abstract, Page 1

If the Biscuits are well below the surface then I don't see why not.

Do they add no strength to the joint? Well, people use Biscuits for mitre joints. We know mitre joints are end grain to end grain so they are pretty weak without the biscuits.

Originally Posted by Soredust

Biscuit Joinery Abstract, Page 1

And your point is? - As far as I can tell from that article even three biscuits aren't as good as a single tenon and, in any event, from my own experience I have easily disassembled a "biscuited" joint with a Stanley knife. They cut surprisingly easily.
There's not always room for three biscuits and more often that not I'll bet most only use a single biscuit.
Still, we have to go with what we believe suits us best and, for mine, it's a tenon.

Anyway this thread has the potential to go on and on and on and on and...so I'm done

Ian

Originally Posted by kpphotos

Hi

I'm going to use Haron biscuit joints on Tassie Oak to make panels, and I'm a bit confused as to whether or not to glue the actual biscuits.

From what I can understand the glue swells the biscuits to tighten the joints, but then this swelling may cause lumps in the panels. Are there any hard and fast rules about gluing these types of joints.

Cheers

The OP is a bit old but , Yes there are some, " hard and fast rules about gluing these types of joints." in my book.

First , I have seen biscuit's do some pretty incredible holding of timber under stressful loads, this was were a Elm 30mm thick table top was glued up in which the moisture content was high [ I thought it was dry enough ] it had Bread board ends held on with biscuit's , the table was kept in a sunny position in the house and when the top shrunk the biscuits held and the elm boards 100 x 30 just bent rather than let go at the join.

When I glue them I make sure I don't just put glue in the hole and push in a biscuit , I get a stick and spread it around the hole and then spread it all over the biscuit as well. What happens if you don't do that is , you can get a pocket of air trapped in the hole, every time just about, and you will push a dry biscuit through a small amount of glue sitting on top through to a dry hole.

I wouldn't use biscuits in a panel under say 16 mm thick if it were a polished feature, what I have seen happen where they are to close to a surface , say within 4 mm or 5 mm or under that, is a few months down the track the moisture that was in the glue dissipates and the biscuit shrinks back . I only use them in gluing up tops as an alignment aid and have seen shallow set biscuits shrink back and show up all the way down the top joints very clearly under a polished surface .



Cheers Rob

Originally Posted by RicB

Biscuit Joinery Abstract, Page 1

Good grief ... you provided test data.

Ric, I'm sure you understand that we are all prejudiced in one way or another, and if the facts do not concur with our long held and cherished beliefs, they are likely to be dispensed with.

For myself ... I did my own tests comparing mortice and tenon joints with biscuit joints. The result is that I use both, but for every mortice and tenon joint I make, perhaps fifty to a hundred biscuit joints are made. When strength really matters, like doors that hold a heavy lead light panel, I use mortice and tenon joints, as well as in some areas that are difficult to reach with a biscuit cutter. Otherwise, I use biscuits, and am grateful to the inventor of this joint every time I pick up the biscuit cutter.

Originally Posted by Ian Smith

And your point is?
Anyway this thread has the potential to go on and on and on and on and...so I'm done

Ian

I apologize if by supplying data it has resorted to the old "And your point is?" retort.

Please read the whole post before my link and then perhaps you will get the point.