This question will (i am sure) show how little I know but here it goes.
I have heard people say here how a biscuit only helps with alignment and that it makes no difference in strength of the joint. how could that be true? How is it that a buiscuit would be any diffent in a joint than a thin loose tenon? I know that it wont add huge amounts of strength, and I know there are much stronger joints. But to say that it does nothing for strength seems like a stretch to me.
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For long grain to long grain joints, with the proper glue, a properly prepared surface and proper clamping, a glued joint is stronger than the wood itself. In other words, when properly cured, a glue joint will not fail. The wood may fail somewhere else, but not the glueline.
So, if the glueline is already stronger than the wood, what additional strength can a biscuit, dowel or spline add?
i agree with you on the glue line if anyone wants to test this theory glue two pieces of pine or any other soft wood together , after the bond has cured try and break it, it will never break on the glueline i've tried
long grain to long grin I concur but long grain to endgrain seems like it would have to help.
For cross grain joints, biscuits or some other type of mechanical support adds strength.
This thread might have some answers. Or maybe not.
http://forums.taunton.com/tp-knots/messages/?msg=15239.1
AJ -
I think your question alludes to a joint where end grain is being jointed to long or side grain such as in a cabinet face frame, etc. The comment "How is it that a [biscuit] would be any diffent in a joint than a thin loose tenon?" would imply this. I think that's the situation that should be considered, not face or long grain to long or face grain. In the latter orientation, as others have noted, the strength of the glue line between properly prepared stock with a well cured and bonded glue, the the strength of the joint is more than the wood itself.
Given that my assessment of the question is correct, a thin loose tenon of hardwood is stronger (my opinion) than a piece of compressed wood fibers in bending and, perhaps shear. Thus it would be my perception that the hardwood tenon would provide more strength in the joint than a biscuit. Along with the fact that the geometry of a well cut rectangular tenon provides more gluing surface area than the small arc of the biscuit.
In any event, when gluing end grain to long grain, a biscuit would indeed add strength to the joint since there is little strength to an endgrain/long grain joint in the first place. But, as I surmise above, the tenon would stil be preferable.
From Beautiful Skagit Co. Wa.
Dennis
This question has come up many times, and there are woodworkers who hate biscuits and woodworkers who love them. I think a lot of the criticism aimed at biscuits comes from woodworkers who believe in doing things the "classic" way. However, I think this is a false distinction. Almost no woodworkers today do things the "classic" way. How many people here can say that they only use hand tools or mix their own hide glue? Why is a biscuit any worse than a power jointer, as far as doing things the "classic" way is concerned?
Now, about the strength of biscuits. In my experience, I have found that biscuits absolutely add strength in certain joints. For example, if you are building a bookshelf, you can use biscuits to support the shelves on the walls instead of using dadoes. Biscuits work great in this application.
When I first started doing woodworking, about seven years ago, I made a couple of tables. I used biscuits to join the table top pieces. These pieces were not jointed. I just used biscuits to connect them, spacing them out about 6 inches apart. Years later, these tabletops are still in great shape, with no spaces between the boards at all.
I also used biscuits to join the aprons to the table legs on those tables, along with a corner brace to add more strength. Again, years later, the legs are sturdy as can be. They've been knocked by the vacuum cleaner, my dog had bounced into them, and guests have banged against the table legs during dinners. The biscuit/corner brace system has worked great.
If you look at woodworking plans published in books and magazines, including Fine Woodworking, you'll find an increasing number of plans that include biscuits to hold together rail-and-stile joints, face frames, shelves, and other elements. This tells me that more woodworkers are coming around to accepting this joint as offering real strength.
About two years ago, Fine Woodworking magazine did an investigation, comparing different joints. The results are pretty involved, but essentially indicate that while mortise-and-tenon joints have the most strength, and survive partial joint failure better, biscuits are plenty strong for most applications. I forget the exact figures, but it takes several thousand pounds of pressure to break a good biscuit joint. Of course, mortise-and-tenon joints withstand a couple thousand more pounds, but how many table legs are going to withstand 5,000 pounds of pressure? In other words, for most practical applications and expectations, biscuits do indeed have good joint strength.
If you consider the ease with which biscuits can be assembled, the strength of the joints, and the savings in terms of machinery expense, I believe any woodworker has to conclude that biscuits are a valuable part of fine woodworking these days.
Here, here,,, could not agree with you more!
Yeah, what he said. I built a pair of 6'h x 4'w leaves for a gate. #2 RW 2x6 flatwise frame with 1 diagonal skinned with dog eared fence boards. Frame attached with 4 #20's per joint, poly and 4 screws. Fence boards attached with deck screws, no glue. No wheels, no corner braces, no turnbuckles, & 5 years later no sagging either and the deadbolt lock still lines up. They are very good for plywood carcase construction as well. I built a loft bed with integrated desk and dresser out of 3/4 ply and every joint is #20's on 6" centers. Tables and chairs I build get M&T's, got to draw the line somewhere. BTW, buy any BJ machine that floats your boat but don't mess with anything other than Lamello biscuits.John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
there is a decided split in this forum ( as well as in life) on the merits vs the purism..vs strength vs speed vs what have you ...all I know is that when I use biscuits for a particular job..they have worked. Not just worked, but wonderfully.
Finding a supply( Lamello are not in the local stores ) of good quality is to be considered ahead of time..I have tried , PC, wolcraft, generic in a bag type and freud and lamello..I now stick with Freud or lamello..makes all the difference.
Wasn't there a FWW article a few years ago where they looked (objectively) at joint strength in a Material Science lab? They looked at the PSI needed to break various joints (MT, buiscuit, double biscuit). I seem to recall that there was really no comparison between the two.
I think biscuits are fine to line things up before nailing or gluing things down, but they aren't structural.
Frank
Edited 1/23/2004 5:20:04 PM ET by BISCARDI
The articles that have been published in FWW regarding strength of biscuited joints vs M&T have been so seriously flawed as to have no meaning.
Like dowel joints, biscuits are an aid to gluing. They do not materially add to joint strength but people almost fervently want to believe that they do.
For years, doweled joints had the reputation of superior joints. Why? Because the furniture industry used them. Forget they held pieces together so they could be rapidly assembled and glued. The average home worker came to an uninformed opinion about them and they came to (erroneously) indicate strength and quality.
Biscuits are a boon to a production cabinet shop. But not for joint strength and the operation really has to be set up in a good production flow to make proper use of the enhancement they provide. In a non production environemnt (greater than 90 % of wood working activities) they are an impediment. The average worker would be much better served learning to make M&T joints at corners and Ts and learning to use battens and cauls for long board glue ups.
But we've all got Lamellos and, the pros use them, right? FWW runs articles on them. What's good for them must be good for me!
It's the Tool Time syndrome.
VL
Well, I'm of the opinion that biscuits *do* add strength in certain cases.
Let me describe the kitchen I just completed. We used prefinished cherry for the cabinets and before the cases were put together we had prefinished edgebanding put on professionally. For the cases that were in the interior, we used glue and screws during assembly. For the cases that were at the end, and where the outside was visible, we used glue and biscuits to join the sides to the tops and bottoms. I'm absolutely certain they added strength. And they aided in alignment as well.
I guess we could have run the plywood through the saw or used a router to put a stopped dado for splines, but I don't think the end result would have been any stronger and it would have been more expensive.
John
John, biscuits and dowels DO add strength to joints in plywood and other composition materials. In fact, biscuit joinery was developed in Europe to manufacture particleboard case goods. Using biscuits in kitchen cabinetry carcases is entirely appropriate.
The also add strength to cross grain joints and depending on the strength needed, they may be the most appropriate and expeditious way to make the joint. However, some other joints are stronger and should be used when ultimate strength is needed.
That leaves long grain to long grain joints in solid wood ie: edge to edge joints. In these joints a properly prepared surfaces adhered with most modern adhesives will provide a glueline that is stronger than the wood itself. For these joints, biscuits, dowels and splines only provide an alignment function. They provide not additional strength to the glueline. As for splines the can actually decrease the strength of the panel.
Venicia,
My experience contradicts what you're saying. Again, I've built bookshelves with biscuits instead of dadoes. I've built tabletops using biscuits to do the long edge glue-ups. And I've used biscuits for table leg and apron connections. All of these projects are several years old and show no signs of weakness whatsoever. For me, the proof is in the pudding in this case. Perhaps the table-tops didn't need biscuits, but the alignment properties are well worth it. In those early days, I didn't even joint the edges of my table tops. So the only real strength is coming from the biscuits.
One other project I didn't mention before is a linen cabinet which is constructed entirely of biscuit joints (except the doors). The cabinet is about 14" deep and over 6' high, with four shelves. The rail-and-stile construction is done with biscuits. The shelves are all held with biscuits. Let me add that when I built this project I knew almost nothing about woodworking. I didn't even prepare the edges for jointing, and I used no screws -- all I used to hold the thing together was biscuit joints! Years later, those joints are perfect, even after my wife has shoved and pushed loads of blankets and heavy linens through the shelves. This is proof enough for me that biscuits add strength.
Edited 1/24/2004 11:49:29 AM ET by Matthew Schenker
FYI... I built a coffe table for myself about 18 months ago and used biscuits for the apron to leg joint. I've already have to re-glue the joint, as it failed once. I now use, only M&T joints at this location. In fact the only thing I've used my biscuit cutter for in the last year is to create slots to fit the table top fasteners in to allow wood movement in the top of the table. As for the added strength to this joint, If done correctly I'm sure it does add strength, it might even double or tripple the strength of the joint, but that's not the important part. We need to ask ourselves whether or not it adds enough strength!
Adam
If your biscuit joints failed, it might be due to the glue-up. Not enough glue? Like I have stated, I used biscuits to attach table legs to aprons, and they have held up perfectly for years. But I also add a corner brace to these joints, which adds a good deal of strength.
I have never seen those "dimples" people mention when using biscuits, even when I have used them for tabletops.
As far as enough strength is concerned, if you look at the pounds of pressure biscuit joints can withstand, and compare that with mortise-and-tenon joints, then yes, mortise-and-tenon joints take more pressure. Also, when mortise-and-tenon joints begin to fail, they maintain more strength, while a biscuit joint loses a large portion of its strength once it begins to fail. But who wants to keep a piece of furniture with a "partly failed" joint -- at that point, esthetically, your piece is done for! Structurally, I suppose there is some value in having the piece "hang on" a little longer, but most of the people I have made things for would probably say that a half-failed table leg is as bad a a fully failed one.
So we are then back to the original question -- how much pressure does it take to cause failure of either a biscuit joint or a mortise-and-tenon joint? To discuss real numbers, I'm going to go back and look at that Fine Woodworking article comparing different joints, and then come back.
I agree with you that finding good biscuits is an important part of the biscuit joinery experience! I have tried Porter+Cable biscuits, which are OK, but they are inconsistent. I find I have to throw away about 1/3 of them because they are too loose or too tight.
Lamello biscuits are great, but you have to order them through the mail. I haven't seen these in stores.
As far as strength goes, Lamello and Porter+Cable seem about equal.
As a technique, it is a good idea to dry fit all your biscuits before glue-up time.
In recent shows norm has not used his famous biscuit joinery and has stated that he has noticed shrinkage mirroring around the biscuit over time. Instead has opted to use just a standard long grain glue joint. which he says is just as strong. Has anyone had this happen to your pieces? I find it hard to believe that he has finally let go of his most standard tool.
Tsk! Tsk! That sounds suspiciously like he's not drying his timber to equilibrium with the environment in which it will reside.
Scrit
More likely Scrit that he's in the habit of hurrying up between the gluing up and the polishing due to the demands of the show schedule. He whacks out a piece in just half an hour (sic)-- well, less really because of the demands of US tellie scheduling. Even the PBS (public broadcasting system) there requires three or five minutes of mentions for the sponsors before and after each 'advert free' show.
It's certainly my experience that if you glue up a table top with biscuits and next day get to prepping and polishing, the biscuits will reveal themselves a few weeks or months later as approximately rugby ball shaped dimples. I put it down to the moisture added to the joint away from the actual edge joint causing swelling, and it seems to be less of a problem if the table top is left to acclimatise and lose that moisture for a couple or three weeks before polish prep and polishing. Slainte.
Website
Sgian
Probably the difference. I tend to pre-sand (sometimes even prefinish) components and glue up in big sessions then leave work for a up to a week before doing the final finishing. Never used biscuits on table tops, I must admit. and I've tended to reserve them for sheet stock projects or rails to legs on lower-cost items. Maybe that's why I've not hit the problems myself. Do you reckon that using a fast setting D3 (my PVA of choice) also has an effect? Just curious.
Scrit
I don't think it's the specific glue, scrit, I think it's the added (water) moisture of the (PVA) glue applied to the mortise or slot cut perpendicular to the edge joint of the planked up table top. It causes the fibres to swell up towards the surface. Given time the moisture escapes the timber, and the swelling goes back to normal. But if you get at it too quickly the shrinking of the wood to where it came from occurs .
I rarely use biscuits for solid wood edge joinery of table tops nowadays, but if I do I don’t put glue into the slots cut in an effort to avoid the problem. Of course any such faults are easily revealed on a horizontal surface especially with a high gloss polish, but any such faults aren’t so easily shown up on vertical surfaces like cabinet sides, etc.. Slainte.Website
I'm a fan of biscuits as are you and many others.If you find "inferior" biscuits that are too large, microwave them for a coupla minutes to reduce swelling.Mmmmmm, hot biscuits.
After all, they're simply compressed beechwood.
BTDT..funny you should mention micros and wood. I had read that you can dry wood in a micro..I had just made a lathe turned mallet (wonker in my parlance) from dogwood..nice hard dogwood. I recalled that you put it in a micro..on for 10 mins, off for10 mins..repeat..till dry. No problem..I thought..my shop was a basement and I went upstairs to our kitchen and promptly nuked the wonker for 10 mins..as I went about my shop work, I heard the **ding**..of the micro. I waited 10 mins, and went up and reset for another 10 min. nuke..next ding..I am waiting and smell smoke..HMMM?..I went up and THE WHOLE house was FILLED with acrid white smoke..my cat's were gagging..I opened the micro and the wonker was just fine..what the?..I took it out and it crumbled in my hands ...the inside was a glowing coal..I opened the door and lobbed it in the snow ...yes, it was winter and the house was closed up good.
Turns out the article said on for ONE minute OFF for ONE minute TEN times..Very Big OOOPS. So, I bought the wife a new microwave, cuz everything we nuked smelled like charred dogwood..oh, yeah..new curtains in the whole house too..and..oh well, you get the point..now I don't nuke wood anymore. The cats lived and so did I , Barely.
Go Stab yourself Ya Putz! Ya think I Parked here?
Sphere -
I learned the microwave-will-burn-wood lesson in the same manner. Only I got impatient.
I put the piece in the oven and gave it about 30 seconds figuring with all the moisture in the (green) wood it would boil pretty easily. After several 30 second trials, I got impatient and gave it about 20 minutes - going about my business in the shop (I have an old MW for use in the shop). I was fortunate in that I smelled the smoke before the wood went into meltdown but didn't catch it before it generated enough smoke to stink up the not only the garage but most of the basement a well for almost a week.
What makes that smoke smell so terrible??!! (grin)
That said, now I put the piece (bowl blanks for turning) in paper (sometmes heavy plastic) bag to reduce the sudden reduction in moisture content in the wood. I can get away with a two minute 'treatment' after which I take the piece, sack and all out of the oven and let it acclimate for maybe an hour. Slow but steady wins this race.
...........
From Beautiful Skagit Co. Wa.
Dennis
Edited 1/28/2004 8:40:14 PM ET by DENNIS
I don't feel so alone now, thanks...<G>
Go Stab yourself Ya Putz! Ya think I Parked here?
I'd say to Norm what I have said here. Tabletops, rail-and-stile joints, and table leg-and-apron joints all holding up after several years of use, and all held together with biscuits.
Matthew
I think that I'm broadly in agreement with you. Much of the work I do is intended for use in a real world environment where cost and longevity are both issues. I've been using biscuits since I got my first Elu DS140 swing biscuit jointer back around 1980 and found biscuits to be excellent in both respects. It would be very nice to live in a world where clients would pay me to produce carcases using hand-planed timbers and secret mitre dovetailed joints, but sadly I (and probably 95% of pro woodworkers) just don't inhabit such a place.
BTW, before using my biscuit jointer on it's first project I did the following test - I made up a box from melamine-coated 3/4in chipboard to hold 12 house bricks with about a 1in space all round. The PVA glue was allowed to set for 4 hours and then the box was thrown out of a first floor (US: second storey?) window about 15 or 16 feet onto the concrete driveway. It took 7 throws out of the window, most onto one or other of the corners, to break the box and even then it wasn't the glue joint or the biscuits which broke. I've never doubted biscuits since.
Scrit
Check out issue 148/april 2001.Strength test: biscuits,dovetails and tenons.
Don't forget leverage when looking at the test results. A 200 pound person leaning against a table that is (round numbers) 30 inches from the center of the leg/apron tenon may put (roughly) 6000 pounds load on the edge of the tenon 1 inch from the center (a 2 inch tenon). This math and model is too simplified, but the point is that we need to be concerned about big loads when there is the leverage of something like a table leg.
I love biscuits for alignment, and for low-load joints like frames and boxes. I still make dados for structural shelving (the shelf that holds the TV in an entertainment center, or the top and bottom of a bookcase), and use mortise and tenons to attach table legs to the aprons. ________________________Charlie Plesums Austin, Texashttp://www.plesums.com/wood
I don't know anyone who engineers wood joints. Ok, I do but the is the exception.
Without engineering you don't know how a joint will break or how to build the joint better.
I do know that yellow glues creep and that a biscuit will stop creeping in 1 direction.
I think i am beginning to form a conclusion on biscuit use. I think i have been using them correctly all along. I have never used them on longgrain to longgrain joints, cant see any advatage there. but what i do use them heavily on are most joints in sheetgoods and short grain to long grain (mostly only on face frames. I would prolly never use them on a structural joint such as a table leg. anyways thanks for all the excellent opinions.
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