Following the great advice I got here, I set up my joiner (sorry about calling it a jointer; yeh, I know the difference) and glued two pieces of cherry together with a single biscuit.
Although it took some effort, I was able to break it apart; and was surprised to find the biscuit hadn't swollen noticably. I measured a new one at 0.150" (Lemello #10) and put it in a glass of water for 20 minutes. It only swelled to 0.159", and the width and length didn't change much at all. I was expecting it to swell considerably.
Am I expecting too much, or is it a defunct biscuit?
Was the glue old? Was it Yellow Glue? I did thought about throwing some biscuits into glass of water to see how much it actually swollen. I will try it for myself. Keep in mind that biscuits are mainly for alignment, not strength.
I remember reading that someone from this NG that he get all the slots cut and right away when he apply the glue, he puts his handful of biscuits under running water, then inserts them. Looks like a good idea, although I never tried it. Maybe I will give it a try, since he did not say "do not try this at home." :) :)
What you did was a very good experiment for yourself to actual see what does what.
In my shop we go through over 10K biscuits a year, Lamello brand and they work just fine. If you aren't happy with your joint, perhaps you let the joiner move during the cut and cut the slots too wide.
I'm rather suprised that you could break the joint apart. A yellow glue joint is supposed to be stronger than the surrounding wood. You may want to look into your glueing technique.
The slot made by your joiner should be between 0.160 and 0.165 in thickness. If the biscutt was swelling to 0.159 in the test, then that's about as tight as you want to get without risking splitting the wood.
Make some test cuts and check your slot thickness. Your technique and the joiners accuracy can definately have a negitive impact on the thickness.
The other post with the tip of wetting the biscuts first seems like a good idea. I'll have to give that a try on some test joints.
They don't need to - slots should be accurate and a tiny expansion is enough to hold it. Lamello biscuits _don't_ swell as much as the cheap ones - neither do Tanselli (my usual brand). I assume that they're optimising them for strength, not for foaming up to fill a badly cut slot.
Here's an experiment. I did it last year, when faced with a whinging hippy who didn't like using biscuits because they "weren't strong enough". Take a couple of 2x4 chunks of a strong hardwood (I used oak) and cut a couple of #20 biscuit slots in there. Attach one chunk to the ceiling trusses and stick an eye bolt and a length of rope on the other. Now take a pair of biscuits and assemble them wet with _water_, no glue at all. Give it half an hour to swell, then dangle yourself from the rope.
IMHE, most biscuit problems _in_assembly_ are caused by dud biscuits (or operator error gluing the biscuit instead of the slot), and most problems _in_failure_ are caused by dud slots.
-- What ? Me ? Evil Dictator of Iraq ? Nah mate, I'm just a Hobbit, honest
1) I have been putting glue on both biscuits and slots. Does also gluing the biscuits hurt something?
2) You seem to be disagreeing with the people who say that the biscuits for for alignment only.
Biscuits expand when you moisten them. If you pre-wet the biscuits, you've a real problem getting them in the slots. Store them _dry_ (mine live in the house, not the workshop), keep them sealed up and don't wet the biscuits themselves.
Almost as useful as a biscuit jointer is a glue bottle with a biscuit shaped nozzle. Lamello's auto-dosing one is an insane price, but you can also get cheap squeeze-bottle ones for just a few bucks.
Having two bottles also allows you to keep two dilutions of glue (if you're using white PVA). My slot bottle is always runnier than the roller bottle for doing the face.
Not really disagreeing.
Biscuits are strong enough to hold a joint together, and so is face-gluing it (if it's long-grain to long-grain, or if you're Bay Area Dave). Biscuits also aid alignment. You could make an adequate joint in tension by just gluing either one of these items. As we normally glue both, then the joint shoudl be over-strong. A well-glued biscuit should be comfortably in excess of its tensile strength - i.e. the biscuit will snap if you pull hard enough.
The strength of a good face-glued joint is another reason why you don't need to use huge numbers of biscuits. People made this sort of joint for a couple of centureis before biscuits, and used no reinforcement at all.
There _are_ a couple of cases where it is useful to rely on the biscuit's strength. Edge-glued MDF is often weak (for much the same rasons as end grain) and so biscuiting in MDF needs to be based on the strength of the biscuits alone. Similarly for framing work, where there's an end-to-long grain joint. Less commonly, an edge jointed tabletop can sometimes fail if the outboard board can be bent downwards under load. Particularly in a less stiff timber, this allows the stress to concentrate at the top edge of the glued joint, causing it to break progressively downwards through the whole joint. A biscuit can stop the flexing here that alllows the stress to concentrate in one place.
-- What ? Me ? Evil Dictator of Iraq ? Nah mate, I'm just a Hobbit, honest
I know you're not supposed to do it, but I spread (a thin coat of) glue all over the biscuit before using it. If your cherry board broke along the glue line, something is not right!
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