Biscuit Jointing

[Chuck Olson]

I'm really new to woodworking, but I recently saw a TV ad for Kreg Pocket Hole Joinery. It looked like it might be better than biscuit joinery. Any opinions?

[-MIKE-]

Pocket holes are great and pretty darn strong, but leave holes behind. You can plug the holes, but there's nothing to plug or hide with biscuits. Whichever works best for your application.

[B A R R Y]

Sure! I use both.

I use biscuits to align panels. They work well for this and are hidden on all sides.

I prefer pocket screws for face frame assembly, plywood drawer box assembly, case assembly where I don't use dados and glue and one side is hidden, on the baseboard radiator covers I build that move a lot with temperature changes.

It's very difficult to hide pocket holes in visible spots.

I don't use either of them on fine furniture where joinery like mortise and tenon, sliding dovetail, or dovetails are more appropriate. I also prefer M&T or cope and stick on doors.

[phorbin]

Are you talking about laminating?

[Leon]

Try gluing a joint with only glue on the biscuits, that will show you the strength of the biscuit. The biscuit does indeed add strength to the joint however most anything strong enough to break a joint with out a biscuit will break the joint with a biscuit. Biscuits are more helpful for end grain gluing and miter joints. They also some what help with alignment providing the cutter produces a consistent width slot and the biscuits are of uniform thickness. The biggest misconception of the strength of the biscuit is that it is often used for the wrong application.

[Bored Borg]

On Wed, 3 Dec 2008 21:53:07 +0000, DiggerOp wrote (in article ):

My understanding (U.K.) has been that ANY plane surface to plane surface joint is a butt.. i.e. where one abutts the other, with no mechanical interpenetration.

I think that "butt" includes nails, screws and/or glue - All strength comes from the glue or fasteners without which all you have is an "arrangement" not a "joint." That's whether end or long grain. It can be a _reinforced_ butt_ by adding battens or fillets.

I think a biscuit is a sort of a loose tenon of some sort,(Thank you, Queeeekdraw) but is not "fitted" precisely - it ONLY becomes a joint when wetted / swollen with glue so, unlike a pure loose tenon, it is still a (reinforced) butt joint if you follow my logic.

Now a pocket hole....

ARGHHHHHHHHHH !!!

[J. Clarke]

Generally speaking edge grain to edge grain with proper surface prep and clamping using any modern glue of the sorts commonly used in woodworking will be stronger against intermittent loads than the original wood, i.e. the break will be other than in the glue line.

End grain to anything in general the break will be between the glue and the end grain and will occur at a much lower level of stress than for edge grain to edge grain.

This is why a distinction is made between the two kinds of joint.

Now, for edge grain, biscuits bring two things to the party. The first is that if the slots are accurately cut then they serve as positioning aids. The second is that under steady shear load many glues will creep and fail at a stress level much lower than would be the case for a load applied for a short time--the biscuit serves in that case to provide a mechanical obstacle to creep.

For end grain they function as small loose tenons and can add significantly to the strength of a joint that needs all the help it can get.

[Swingman]

"J. Clarke" wrote

Well said!

[-MIKE-]

That was kind of my thinking. They don't seam to add *that much* more strength. And if I need a *lot* more strength, I'm probably reaching for the finger joint bit, no?

[-MIKE-]

There ya go.

[Dan Jefferson]

I use yellow carpenters glue. No problems up to now.

Dan

[Phisherman]

Finger joint trumps the biscuit joint. A scarf joint is fairly strong too, maybe better than the finger joint.

[Bored Borg]

On Thu, 4 Dec 2008 16:41:40 +0000, J. Clarke wrote (in article ):

Well, I'm all for _that_ being the definitive FAQ version.

[nailshooter41]

Sounds good to me. Count me in!

Robert

[nailshooter41]

DOH!

Now why didn't I think of that. What an excellent way to illustrate to the nay sayers that they do indeed bring a little something to the party.

I vote to add Leon's comments to John's in the FAQ. We should just refer folks to this thread when they start up the annual "biscuits are only for alignment" stuff.

Nicely said, Leon.

Robert

[Swingman]

Agreed ... then try this sequence for the "show me" proof:

[nailshooter41]

Some pretty smart fellas in the middle of that thread too, eh?

;^)

Robert

[-MIKE-]

I couldn't have said it better myself. They help "a little" on edge joints. :-)

[B A R R Y]

Yup. Well put.