I was gluing up a panel this morning, I used some biscuits for alignment purposes. I applied glue to the edges and slots for the biscuits, put in the biscuits, and clamped up the panel. Now, I normally don’t put glue on biscuits, and I am wondering is there any benefit to putting glue on biscuits when they are being used for aligning things up?
I saw Norm put glue on some biscuits this weekend. I never really thought too much about it, until now. I have never had any problems with not putting glue on biscuits. Thanks.
Barry
Replies
The water in the glue causes the biscuits to swell, thus locking the adjoining boards together evenly. The point is to minimize planing and sanding that is caused when the mating boards or panels slip. That's why you should store your biscuits in an airtight container. This will keep the humidity in the air from swelling them prematurely.
If you use biscuits, give the joined wood pieces sufficient time to dry before sanding. The moisture from the glue in the biscuit slots will cause swelling that if you sand to soon, will leave a hollow as the moisture from the glue dries out. I had this happen to me on some 3/4" stock a number of years ago.
I very rarely use biscuits anymore, prefering more tradional joinery.
T.Z.
I used to believe that too about biscuits. But living in the mid-Atlantic with its high humidity, I know from work in labs (I'm a Chemist by training) that it is not easy to keep biscuits from humid conditions - dessicator with a tight seal might be the best thing, but who has that in their shop?
So I did a little experiment. I bought a new can of Lamello biscuits, took a few out and measured their thickness with a micrometer. Then I soaked them overnight in water and measured them the next day - with negligible difference in thickness. I had suspected this after cutting down some panel glue-ups that I didn't need anymore. And I found the biscuits were held more by the glue than their thickness swelling.
I don't use biscuits much anymore - they can be handy for alignment but that's about it. And with the recent FWW examination of comparative joint strengths, looks like good old fashioned hand joinery still wins out.
Hmm... this does not match my experience.
Recently I dry-fitted an assembly and forgot some biscuits out when I knocked off at about 9 pm. it was a rainy night, about 9 deg C.The next day the biscuits were a tight fit in the slots. They would not have slid to align themselves during glue up.Could it be differences due to the brand? Mine are a German brand by a company that also makes dowels. Forgot the name & it's too cold outside to go and look.
Barry,
The quality and tolerances achieved by both the biscuit joiner and the biscuits are important.
Many biscuit joiners don't make an exact 4mm slot (because of blade wobble or other slackness in the machine). Some joiners don't make the slots straight with reference to the registration surface. Many biscuits are poory made of inferior material and to poor tolerances.
It makes a big difference and this is why Lamello biscuit joiners are expensive (they are very well made)and why they make their own biscuits (they are equally well made).
Have a look at this post and the one two posts down:
http://forums.taunton.com/fw-knots/messages?msg=31220.17
Biscuit slots should be exactly 4mm wide (not 4.1 or 3.9mm). Biscuits should be 3.9 - 3.95mm when dry and swell to 4.3 - 4.4mm when wet. In a biscuit slot, that expansion is confined by the slot and is what gives a lot of the grip. The expansion is also why you shouldn't use a biscuit within 4mm of a surface, as it will "blow up" and telegraph to that wood surface.
Biscuits used to aid alignment of edge joints can be glued and they will then add a little bit of strength to the joint; but the joint doesn't need that strength so why bother? You could always just wet them so they really do fill the slots tightly; but why bother? I use biscuits to help with alignment (usually 3 - 5 per edge) if the edges have a bit of bow or are otherwise a bit tricky to keep in alignment whilst clamping up. But if your planks are unbowed you may not need help with alignment so biscuits are then redundant.
I only glue biscuits if they are going to be a substitute M&T, like with the cherry cabinet in the referenced post. That post also shows that you can put a half-glued biscuit into a slot and leave it there to stick without the other half of the biscuit expanding. This might be ueful if you have a lot of planks being edge-joined in a large panel, as you can stick a few in to help alignment, do it a few at a time and they won't fall out when you hoist the planks about as you glue and clamp their edges.
Lataxe
I keep my jointer blades sharp and in good shape so the edges mate well. If you do this, the glue-line will be stronger than the wood outside of the glue-line. With that as a given, why bother with improving on that?
When I run my bead of glue down both edges to be joined, I don't worry if glue goes into the slot, but I don't let it slow me down either, then I insert the biscuits dry.
I don't ever use them for other types of joints.
I have used biscuits to make large-stock miter joints stronger (at least I thought they made the joints stronger). The stock was 2" thick and the mating faces were 6" long. The cut angles were 30 to 45 degrees . I used four large (#20) biscuits) on the theory that I was increasing flat grain gluing surface area. Was this a waste of effort ?Tom
Tom, anytime that you do large miter joints, it will of course make it stronger at the time of making them. The problem is, large miter joints are self destructive as soon as the relative humidity changes, and nothing will change that. If the biscuits or whatever fastener is stronger than the wood, then the wood will split if the wood is going down in MC, or crush if it goes up too much. The exception, for large miters is to tilt them up, like in picture frames. This has the benefit of stress relieving a long miter, in that it can tilt in or out with the changes. Your question does not indicate whether you are talking about a closed square or hex. If it is not closed, you would be stronger, but if it is closed, it could be trouble. Many people will claim to have success when they break all of the rules. The problem is, that they may not even know that the time-bomb is ticking, only because the work has not been through the test yet. You can make mistakes with wood at the proper EMC, which goes into a controlled atmosphere, and escape disaster for a long time. But once things leave the shop, you never know. You loose control of their destiny. If they go somewhere like where I live, that the windows may be open for long periods of high humidity, then long dry heat of winter, solid woods WILL move.
I have performed this little test.Measured the thickness of 2 biscuits: 3.8 and 3.9mm respectively. The measurements were identical along the length of the biscuits.Wet both sides by waving them through water coming out of the tap (about 1 sec total exposure).Left them for 8 hrs in a plastic bag.Measured again.They are now 4.0 and 4.3 mm thick.
that's pretty much my method as well. I usually hand plane the boards at one time then glue them up. I will use the biscuits on any panels over 24" long. Other than that i usually just do a rub joint and clamp.
What's even more of a question, do you all apply glue to one edge or both edges on panels?
Edited 3/3/2009 5:45 pm ET by BarryDaniel
Barry, I always apply glue to both edges. If I don't, I usually end up with a little hair-line which shows up later in finishing. My method of applying glue, is to set the board up on edge, like in a vice if the width doesn't make it too high. Then I lay my left forefinger on the edge of the board, with the first joint slightly bent over the edge closest to me. I then put the glue bottle tip right up close to it, then start a bead, then back down the length of the board. With my finger smoothing the glue out across the face evenly in one pass, as fast as I can run the bead, it is smoothed out.
I prefer a little gravy on mine.
Sorry I couldn’t help myself.
My take on your question is; yes I do,
I don’t think it really makes a difference if you put glue on them or not but they always seem to get some on them during my glue ups.
Yes, I agree with you biscuits are much better with gravy. Sausage or Red eye gravy in the morning, brown gravy at night. Yummy.
I guess I should have worded my question differently. You were the only one to understand my dilemma. Not really a dilemma, I just happen to think about it during a glue up. I have used glue directly on biscuits when I first started out, thinking the mo' glue da betta'. I have moved beyond that mentality. I rarely use biscuits anymore, and when I do use never apply any glue directly on the biscuit, just the slot. Seems to work for me.
Furthermore, I usually let panels sit for about 2 hours, then scrape off any excess glue. I usually wait overnight before I sand, scrape, or anything else. learned this from my first project, dips and bumps on all my glue joints, from either not cleaning up or not waiting for the joint to even out.
Barry.
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