Why Do Biscuits Hold

[michael case]

According to all woodworking wisdom, tenons set with their faces across end grain should fail. About five years ago I built a red oak platform bed with a hutch. The hutch (essentially a bookcase) has four 1x8" uprights and the top is attached exclusively with biscuits with their faces contacting only end grain in the top. Well they didn't fail. In fact, I can't get them to come apart. I wanted to turn this King size bed into a Queen. I thought I could salvage the hutch. I thought a few good bashes with a heavy mallet would free the end grain attachments on the top. All I received was a shock up my my arm and not the slightest gap or give on the joinery. Traditional tenons do fail in this configuration, but the biscuits held.
All thoughts welcome.

[Dave Gaul]

Biscuits absorb the glue and swell slightly. The biscuit joint is stronger that the wood itself.

[Lex Boegen]

Just a guess on my part, but the grain in the biscuits runs at an angle to the biscuit, whereas the grain in tenons goes along the length of the tenon.

[Neal Clayton]

the reasoning for the tenons is the joint fails gracefully. even when the adhesive is totally shot, the joint still has a structure holding it together, and the joint can always be pulled apart, re-glued, and repaired.

when the adhesive around the biscuit fails, you wind up laying on the floor wondering what happened ;).

[Phil Thien]

I think conventional wisdom has always been that end grain doesn't make a good glue joint.

However, some of the joint tests surprised many when a plain old miter joint with glue proved to be very strong.

And I remember someone (I think Dave from Cairns) indicating that he tested some longer end-grain miters to destruction and it was a challenge. I think he gave up, actually.

I've done a little testing myself, and find that as long as I use two coats of glue on end grain, the joints are strong.

Combine this with the biscuits swelling action, modern glues, etc., and I'm not surprised your joints are strong.

I know they're out of favor for many, but I use biscuits quite regularly. I've had projects that didn't turn out for whatever reason and when I try to reclaim the materials by knocking the joints apart, I can't. I always have to saw though them.

[David Prince]

the reasoning for the tenons is the joint fails gracefully. even when the adhesive is totally shot, the joint still has a structure holding it together, and the joint can always be pulled apart, re-glued, and repaired.

when the adhesive around the biscuit fails, you wind up laying on the floor wondering what happened ;).

I like biscuits, but would hate to rely on them to carry weight with a biscuit and glue only joint. I think they work well for keeping things together and lined up, but a tenon would be better for weight bearing.

[Chris Padilla]

For miters, I always like to use biscuits assuming I can fit one in there. It just feels right to bridge that short joint with a little bit extra.

I like biscuits when I'm gluing real wood to plywood/MDF or gluing plywood/MDF to plywood/MDF. I just don't feel that those engineering wood products glue together as well as solid wood to solid wood.

Biscuits are also useful in alignment/holding situations but can be quite painful in "aiding" misalignment, too.

[Josiah Bartlett]

Some woods, like oak, that have a lot of pores actually have quite a bit of surface area in the joint for the glue to soak into. Combine this with a glue that can take advantage of that, and the joint is probably stronger than the surrounding wood.

[Garrett Ellis]

I like biscuits, but would hate to rely on them to carry weight with a biscuit and glue only joint. I think they work well for keeping things together and lined up, but a tenon would be better for weight bearing.

I also have been told that biscuits are mainly for alignment and not load-bearing.

[Van Huskey]

One of the big keys to this is modern glues. They have gotten REALLY good and you don't even have to buy some fancy smancy glue you have to order in, even the BORGs carry quality wood glues and they are cheap.

[Tom Rick]

I pulled out a biscuit & the grain is very consistently set at 45 degrees to the long axis of the biscuit.
I managed to drop the one I was looking at and the dog got to it before I could pick it up.
Canine tested for strength- nice snap on the grain line @ 45 degrees...

[Van Huskey]

I pulled out a biscuit & the grain is very consistently set at 45 degrees to the long axis of the biscuit.
I managed to drop the one I was looking at and the dog got to it before I could pick it up.
Canine tested for strength- nice snap on the grain line @ 45 degrees...

Now we have to know was it a #00 dog or a #20 dog? :D

[Neal Clayton]

One of the big keys to this is modern glues. They have gotten REALLY good and you don't even have to buy some fancy smancy glue you have to order in, even the BORGs carry quality wood glues and they are cheap.

/agree

i see alot of debates on other sites i visit amongst traditionalists who still try to build things without the use of glue, as they did in the old days when hide glue was all there was. usually i wind up being the sole voice of reason pointing out that modern adhesives are too good to not use them.

[Will Overton]

/agree

i see alot of debates on other sites i visit amongst traditionalists who still try to build things without the use of gluei see alot of debates on other sites i visit amongst traditionalists who still try to build things without the use of glue

I didn't know that traditionalists didn't use glue. What are they using?

From the Natural Handyman;

"Virtually all antique furniture is held together with hide glue. In fact, the use of hide glue goes back thousands of years to ancient Egypt! ..."

[Chris Padilla]

Now we have to know was it a #00 dog or a #20 dog? :D

#FF? Chihuahua? :)