Why not biscuits

[Douglas Brummett]

round 2

For round 1 discussion see:
http://www.sawmillcreek.org/showthread.php?t=31971&highlight=biscuit

Okay, background of the question...
Dining table, compact base, poplar
I went back and forth a bit on the joinery for this table. In the end I chose to go the path of expedience and accuracy. So I used a but joint with 2 #20 biscuits to attach the 1.75" aprons to the 3.625" legs. For a little insurance I used 1.125" x 3" glue blocks inside backing each joint.

This fast construction allowed me to go from rough cut stock to jointed, planed, tapered legs, and assembly in a single day.

I ran a sample piece with dual #20 biscuits, but joined. Even after about half an hour the joint took an impressive beating with a hammer before failure. Failure was not on the glue joint, but back in the biscuit socket where the glue hadn't fully cured. So I felt fairly confident in this construction for the table. Note that I did add glue blocks to reassure myself.

It seems that discussion on this topic quickly turns to tests that don't really apply, a naysayer bandwagon, and a whole slough of everything from buy a domino to only mortise and tenon. Opinions are like...
...well, you know. So lets try to avoid going the path of round #1.

For round number 2 I want to see a clean fight. If you have never used biscuits to attach an apron to a leg then please maintain voyeur status on this thread. If you have tried this please let us know the outcome. Personally the table I glued up this way feels rock solid. I have read of accounts of others building many tables this way, one was a furniture maker who claimed he had never had a failure.

So there it is. I am going to go find my flame retardant keyboard :D before it gets to hot in here.

[Bill White]

I'm old and brave.
I've never been unhappy with my use of biscuits. Have used 'em on table tops, leg attachments, etc.
On a rather large and heavy breakfast area table I used M and T.
Two end tables for the DIL I used the biscuits.
Probably try to fit the form to the function if you know what I mean.
Tall cabinet shelves-biscuits.
Bill

[Chris Padilla]

For more fodder, do some searching on Dowelmax. They had some interesting tests.

[Peter Quinn]

I have not made a table this way, or used biscuits for any similar structural application, but I have used biscuits often and am familiar with their strengths or lack there off. I have also not jumped off the Brooklyn bridge, but having walked over it and having fallen from much gentler heights I would advise against it. I enter this conversation in the same spirit.

It is not that biscuits don't offer any strength, but I doubt they have the strength to resist the shear forces a group of my friends and family are capable of exerting on a table during a get together. Perhaps your acquaintances and dining guests are more civilized? I rarely build anything I don't want to serve its purpose for years. I can snap a #20 biscuit in my hands, and last I measured, it was little more than one inch across, divide that by two, you have barely a 1/2" by 1/8" projection into the stock on each side at the deepest point. This may be enough to resist your hammer blows on a small sample, but when ten of my friends and i get to eating and drinking and the fulcrum becomes the span of the table and the base of the leg, your biscuit joint is doomed.

I have built small pieces of furniture like a side table or TV stand with biscuits and had good success, but these are not subject to the same stress over years as a dining table. They are also part of a design that doesn't require more of them than they are able to provide. My own store bought dining table is built with stub tenons and a steel angle bracket pulled together with a hanger bolt at the corners. Your basic factory approach, but it remains solid after years of use. I'm not a purist that will insist on M&T joints as the only sound road, but biscuits may be a lower road than I am willing to trust in the event of a flood.

In your case the glue blocks may add enough strength to keep things together. But I like a table built for those rare occasions when a grown man decides to get up on the table and do the hula dance and several of his friends decide to join him!:D

[Fyrman Dave]

But I like a table built for those rare occasions when a grown man decides to get up on the table and do the hula dance and several of his friends decide to join him!:D
I'm afraid I would "un-invite" any friends that treated my furniture like that.:p

[Phil Thien]

In my testing I've noticed that the biscuit itself is often the point of failure.

I've also noticed that plywood biscuits are available.

In many of the tests I've seen they've used a single, smaller hardwood biscuit. It would be interesting to try multiple plywood biscuits, instead.

BTW, I have no concern about biscuit strength overall. Even in cases like a table with no lower stretchers/stringers to provide additional support (and where the leg can act like a lever), I think a couple biscuits with a glue block could be sufficiently strong.

I'm just saying that plywood biscuits may make the joint even stronger.

[Robert Chapman]

Phil - can you describe the "plywood" biscuit and where you get them? I've never heard of them.

[Joel Goodman]

Years ago, I built a round dining table about 52" diameter with the 5/4 apron attached to the thick legs with I think 3 or 4 biscuits per side. I am amazed but 15 plus years later it is rock solid. The aprons were curved so that there was more width at the ends to join (and biscuit) I have stood on it a few times and it was trucked across the country. I would however go with lose tenons at minimum if I was redoing it today. Not that much more work and stronger -- although I guess strong enough is strong enough!

Woodhaven used to sell a plywood biscuit to go with a router bit but they were a little smaller than the large standard type biscuits so I'm not sure of the gain in strength.

[Rick Fisher]

I used #20 biscuits on a coffee table about 7 years ago. They held the aprons to the legs. The joints eventually let go after about 5 years.

It was probably my fault in some way or another. It was as if the glue just stopped holding.

[Bryan Berguson]

I used biscuits to build a coffee table too only it was about 10 years ago and it has not failed. One of my very first projects and a very special one. The wood (hard maple) came from trees that were cut down from my parents front yard. I made the table as a birthday present for my Mom. It needs a little tlc now on the finish but structerally it has held up well.

Bryan

[Phil Thien]

Phil - can you describe the "plywood" biscuit and where you get them? I've never heard of them.

http://www.woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=138-089&search=Plywood%20Biscuits

[William OConnell]

I use biscuts mostly for alignment issues and really don't rely on them as a much as a mechanical fasteners or joint'
Coffee table maybe , Dining table not me. To much time and effort into the work. Why not pocket hole screws? Just as fast really, and vastly stronger. Or if your a purist a Mortise and Tenon.
Thats my spin on biscuts in this application

[Bond Turner]

In my opinion this is a great representation of how people think today, only for the short term. If the whole idea is to build the table as fast as possible than yeah great, biscuits suit your needs, but they will not stand up over time. The good news is that when you will need to repair it you can do a biscuit again, very quickly, and again, and again...

Part of the joy of building fine furniture or even practical furniture is spending time to build something that will last. To me nothing brings greater joy than orchestrating a perfect fitting M&T joint that I know could handle any number of my friends dancing on the table. It took me a little over 9 months to construct and finish a 12 foot dining room table that I still have 12 years later and it still feels as solid as it did when I completed it after many friends dancing on the table. Take your time, do it right and it will pay dividends in the long run.

I think this belief could extend to the rest of the short sighted...investors, bankers, husbands, wives, etc.

Hope I did not offend anyone.

BT

[Charles Seehuetter Panama City]

Phil - can you describe the "plywood" biscuit and where you get them? I've never heard of them.

It may have been answered already but this is where I get mine and I use a lot of them.
http://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=138-089

I haven't had a failure yet. Some fit a little tight in slots from my Dewalt biscuit jointer but a little tapping sets them in.

[Phil Thien]

In my opinion this is a great representation of how people think today, only for the short term. If the whole idea is to build the table as fast as possible than yeah great, biscuits suit your needs, but they will not stand up over time. The good news is that when you will need to repair it you can do a biscuit again, very quickly, and again, and again...

...

Hope I did not offend anyone.

BT

No offense taken. There is a great article if you google "biscuit-joinery-abstract" (it will be the first hit). They're actually much stronger than most people think.

And I don't think the original poster's table is going to repeatedly fall apart.

[Howard Acheson]

Biscuit joinery was developed in Europe to quickly assemble particleboard and MDF case goods for furniture. Dowels were not sufficient.

I, and the shop I was involved with used them extensively for items we manufactured. Used properly they produce fast, strong joints. They do not have the shear strength of M&T joints but most furniture does not require that level of strength.

That said, if one uses them correctly and likes the way to work and perform, then use them. There are a number of ways to construct furniture and no one way is the "right" way.

[Chris Padilla]

It may have been answered already but this is where I get mine and I use a lot of them.
http://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=138-089

I haven't had a failure yet. Some fit a little tight in slots from my Dewalt biscuit jointer but a little tapping sets them in.

Cool! I've never seen plywood biscuits! However, I don't really wanna buy a 1000 of them. The tubes that Porter-cable sells theirs in would be nice.... No FF-sized plywood biscuits; those are great for picture frames.

[Roger Barlow]

Can't find my issue 148 of Fine Woodworking (scattered everywhere), but that issue has joint strengths for several common ww joints, including biscuit.

[Douglas Brummett]

Alright, this is on par with what I had expected for results. It also agrees with the rest of my internet searches.

People who have tried this typically don't end up with failures. There are a few exceptions, but most look back amazed that they have had no problem. There are those that are adamant that it never will give problems.

People who have not tried will continue to justify their fear and hesitation. They will cling to their m&t with a death clutch. From atop their internet soap box they will preach to the choir of internet lemmings.

Regarding the Bond Turner comments,
Yes, this does have the potential for short-sight. I am curious how long it will last myself. Honestly I do think it will hold up better than the most of the imported junk even with this construction method.

Typically I too would enjoy to dedicate more time to the project. But there is also a time and place for quick projects in my shop. I am not a snob. I am not a fine-woodworker. I am just a hobbyist trying to make better furniture than my local import dealer provides while saving a few bucks.

[Rod Sheridan]

Hi, I make furniture with M&T joints for several reasons;

- it's what I traditionally used
- I have a hollow chisel mortiser
- I don't own a biscuit joiner.

I suspect that many people either don't use biscuits in favour of M&T joints for similar reasons, or favour biscuits because;

- it's what I traditionally use
- I have a biscuit joiner
- I don't own a mortiser.

So my reasons aren't very scientific, I will probably stick with M&T for traditional M&T applications, and will stick with biscuits for traditional biscuit applications.

So now, how do I stick with biscuits for re-inforcing mitres or assembling kitchen drawers since I don't own a biscuit joiner?

I use a Dimar 707N-125-4 cutter in my shaper. (4mm slotting cutter). Obviously it works great for small parts, wouldn't work for huge parts.

I think a lot of woodworking decisions are based upon what we have/are familiar with as opposed to an engineering analysis of strength/cost.

Regards, Rod.

[Chris Padilla]

Good points, Rod.

I plunked down for a Domino so now that is my preferred method and as about as close to M&T as I plan to get.

There are plenty of different situations in which to use various joints and joint aids. One must consider the materials being joined: plywood, MDF, hardwood.

Modern glues are so strong that they are stronger than the materials being joined.

I like biscuits for alignment aids (but they can also throw off alignments if one isn't careful) and for reinforcing mitered joints. I like biscuits for MDF/plywood to plywood/hardwood/MDF applications.

Hardwood to hardwood I would use my domino most likely but biscuits could be used to aid alignment in a long-grain to long-grain glue-up.

Lottsa uses depending upon the situation.

[John Stevens]

In my opinion this is a great representation of how people think today, only for the short term. If the whole idea is to build the table as fast as possible than yeah great, biscuits suit your needs, but they will not stand up over time.

Bond, no sarcasm intended here, I'm absolutely sincere: how do you know this?

Several people who have actually made furniture with biscuits have reported in this thread that it's' holding up just fine. I've made two end-tables with biscuits, and they're holding up just fine, as is a chest of drawers on legs that holds a TV, DVD player and DVDs, probably a couple hundred pounds gross weight. The chest of drawers gets pushed across the floor every now and then when I need to check the connections on the electronics. It's as solid as a rock, with eight biscuits per leg holding the legs to the carcase, and it's showing no signs of weakening. I see no sign that the biscuits in these pieces are going to fail in the long term.

My productivity is up because of the biscuits (now Domino), so my feeling of accomplishment remains high despite the fact that I'm not spending ten times as much time making M&T joints. My aesthetic sense isn't offended by the fact that the hidden joints are biscuits instead of traditional M&T. To each his own, but if strength and longevity don't suffer, then I think the only reason to object to biscuits (or Domino or Dowelmax) is the subjective feeling of accomplishment and the aesthetics of something that's completely hidden. Different topics for a different thread.

Regards,

John

[Jeff Bratt]

Alright, this is on par with what I had expected for results. It also agrees with the rest of my internet searches.

People who have tried this typically don't end up with failures. There are a few exceptions, but most look back amazed that they have had no problem. There are those that are adamant that it never will give problems.

Biscuits are widely used in many applications. Of course they work. I thought the question was how they compared to other joints.


People who have not tried will continue to justify their fear and hesitation. They will cling to their m&t with a death clutch. From atop their internet soap box they will preach to the choir of internet lemmings.

Open minded? Looking for reasoned opinions?


Regarding the Bond Turner comments,
Yes, this does have the potential for short-sight. I am curious how long it will last myself. Honestly I do think it will hold up better than the most of the imported junk even with this construction method.

Typically I too would enjoy to dedicate more time to the project. But there is also a time and place for quick projects in my shop. I am not a snob. I am not a fine-woodworker. I am just a hobbyist trying to make better furniture than my local import dealer provides while saving a few bucks.

The comparative testing that has been done indicates that the strength of multiple biscuits vs. M+T is similar. Done correctly, both are usually stronger than the surrounding wood. Especially for table leg-to-apron joints, however, some people will prefer a joint that won't necessarily fail completely and catastrophically as biscuits can if they do give way. If the extra time and effort is not worth it to you, that's fine. Both are probably better quality than what you get from the "local import dealer", although I find that they sell completed furniture for less than I spend buying raw materials - so it's not really about saving money.

[Douglas Brummett]

Fair enough Jeff :)
I think the lemming comment may be a bit harsh. My searches pretty much lead to 1-2 people per discussion that have actually tried this method for table construction. The rest of the comments come from people that are not willing to even try this approach for one reason or another (open minded, not in this case).

Here are a couple of pictures of what I did. I think most people already get it, but for thread prosperity I will add these.

[Chris Padilla]

Doug,

If you're happy with it, that is all that matters. The variables involved in all this are many such that seemingly identical joints might last 20 years for 1 guy and 1 year for the next guy.

Even you added glue blocks "for a little insurance" and I suspect those are the main strength of the joint because the glue blocks are long-grain to long-grain.

Did you try a biscuits-only joint and subsequent hammer test? That would be interesting....

[Walt Caza]

Good Day to the Creek,
I use many methods, but prefer traditional M&T.
I think there is a place for all approaches, and civility.

Since Doug B. is sharing pics for thread prosperity, I thought I would toss these into the mix.
It is another way to use double biscuits.
The situation called for a quick but strong solution for apron to leg joints.

The Porter Cable 557 comes with a clip-on spacer to help cut the double-wide slot quickly and without fuss.
100269 100270

I tend to overbuild anything I can, but the project limitations were imposed by someone else.
Not sure how much I trusted the biscuits, So I went robust with the corner blocks.
100271 100272

I did some durability testing, and I am ready to say that was one strong frame.
There is no way of knowing how much strength was from the biscuits, and how much was from the corner blocks...
but I do not expect to see that bench back for repair anytime soon.
happy joining, however you choose to do it,
Walt

ps in digging up these old pics, I realized all over again, that it is a crime not to pop those rays.
...but, it was not my call to make... what can ya do?

[David Keller NC]

"Several people who have actually made furniture with biscuits have reported in this thread that it's' holding up just fine."

My take on this is that it depends on what your tolerance for failure is. The fact that several people have chimed in that they've had failures suggests (in my opinion) an unacceptable failure rate. In my case, I made a couple of "tv tables" 8 or 9 years ago with biscuits (both to join boards together for the top and for the leg to apron joints). Both tables have failed at the biscuit joints between the leg and apron. In retrospect, I suspect that may have been inexperience with the technique on my part - they were single biscuits instead of doubling.

That said, I returned to traditional M&T construction, and I draw-bore them. Besides historical accuracy (I primarily build colonial period reproductions), there is no way on this earth that someone's going to tear apart a double-drawbored joint without the wood failing all around the joint, leg and apron.

My basic philosophy is that I want the things I build to have 99% survived intact after 200 years. I won't be around to evaluate the results, so I stick with traditional methods that have proven themselves over millenia.

The issue with loose M&T joints and biscuits is that they just don't have enough history yet. If they largely survive over a 100 year period, woodworkers of that era will look at them as a largely sound method. If the vast majority of them start to fail after 50 years, they'll be regarded as junk.

I don't want to take the chance on the latter.

[Marcus Ward]

I'm going to preach from my internet soapbox of fear and hesitation.

Endgrain to longgrain joints with nothing but a biscuit and glue are going to fail from wood movement eventually. It might take longer depending on where you live, but it'll get them eventually. Sure, it's holding now, it might even last many years, but it's not a well-made piece of furniture. There's a reason the mortise and tenon is so well regarded.

It's because it's hard to make and it makes us internet soapboxers feel snobbily superior to you biscuit normites. Amirite? :P

[Douglas Brummett]

Did you try a biscuits-only joint and subsequent hammer test? That would be interesting....

That was the test. I took a section of apron scrap and fit it up to another chunk of scrap. I did no prep to the end grain, in fact it was the checked and cracked exposed end from the lumber yard. I biscuited it double. The other board was straight from the tablesaw. I glued them up. After a half hour or so I started hitting the golf club shaped sample around. After it didn't break I reached for the mallet and pounded on it for a minute or so before I finally got it to give up the ghost.

Results? Well, the glue joint held strong. The leg split back by the bottom of it's biscuit cuts. The biscuits had not fully cured, glue was still wet in the bottom of the well. I think the result would have been similar once the glue was fully cured from some of the failure tests I have read.

I agree that seasonal movement may be the biggest concern going forward. I think the glue blocks will pick up the slack though.

Walt, excellent solution. I debated about pocket hole screws for a while, but since this table is poplar I thought they could cause cracking and splitting. I like the corner bracket though.

Marcus, you are cracking me up :D
I swear, I am not a normite. Just trying to throw together something in a pinch.

Don't get me wrong people. I am not trying to start a biscuit revolt here. I just wanted to see who had actually done anything similar to my table. There was also an attempt to cull comments from snobby galoots :p

[Joe Vincent]

Good Day to the Creek,
I use many methods, but prefer traditional M&T.
I think there is a place for all approaches, and civility.

Since Doug B. is sharing pics for thread prosperity, I thought I would toss these into the mix.
It is another way to use double biscuits.
The situation called for a quick but strong solution for apron to leg joints.

The Porter Cable 557 comes with a clip-on spacer to help cut the double-wide slot quickly and without fuss.
100269 100270

I tend to overbuild anything I can, but the project limitations were imposed by someone else.
Not sure how much I trusted the biscuits, So I went robust with the corner blocks.
100271 100272

I did some durability testing, and I am ready to say that was one strong frame.
There is no way of knowing how much strength was from the biscuits, and how much was from the corner blocks...
but I do not expect to see that bench back for repair anytime soon.
happy joining, however you choose to do it,
Walt

ps in digging up these old pics, I realized all over again, that it is a crime not to pop those rays.
...but, it was not my call to make... what can ya do?

Walt: Did you use a Kreg jig to drill the pocket holes for the corner blocks? I assume you drill the holes then cut the 45 degree miters? How do you get the positioning just right? Trial and error? Thanks

[John Stevens]

That said, I returned to traditional M&T construction, and I draw-bore them.

...thereby building stress into the joint and removing material to boot. Not many people bother to think that far ahead, but it's a great way to increase the chance that the mortised piece will split somewhere down the road.


Besides historical accuracy...

Different topic.


My basic philosophy is that I want the things I build to have 99% survived intact after 200 years. I won't be around to evaluate the results, so I stick with traditional methods that have proven themselves over millenia.

How can we know with any degree of accuracy how well they've proven themselves? We only see the ones that survive. We have no idea how many failed, or why they failed. They're dust now. Except for the ones that get repaired. My stepdad made a good living repairing antique furniture, including pieces where the traditional M&T joints and DT joints failed. Repairability is an important factor that tends to get overlooked.


The issue with loose M&T joints and biscuits is that they just don't have enough history yet. [snip] If the vast majority of them start to fail after 50 years, they'll be regarded as junk.

Back to repairability. One of the reasons I like biscuit joinery and loose tenon joinery is that it's easily repairable in case of failure. (Unless maybe you draw-bore the loose tenon or drive a nail or screw into it.) The main reason furniture gets "junked" is that it goes out of style. Build a good looking piece that can be repaired, and you can bet that it'll be repaired if and when it fails.

Regards,

John

[John Stevens]

Endgrain to longgrain joints with nothing but a biscuit and glue are going to fail from wood movement eventually. [snip] Amirite? :P

Depends on the glue, right. Glues like Titebond have a little elasticity...maybe enough to withstand the wood movement. If not, a biscuit-joint will be easy to repair with another biscuit or loose tenon. On the other hand, the tennoned piece in a traditional M&T joint will eventually get compressed after enough seasonal cycles of expansion and contraction, just like the handle on an old hammer gets compressed where it fits into the hammer head.

Regards,

John

[Walt Caza]

Hi All,
Thanks for your interest.
I built that bench a looong time ago, and hardly remember....

Joe V. -
I seem to recall that the corner blocks were cut at 45's first.
I would guess at the miter saw.(?)
The 4 main holes which screw into the aprons, were drilled perpendicular to
those angled faces, so that they penetrate the apron square on.
I imagine I made a little 45 ramp to help hold them up at the drill press.

First with a forstner, making a flat bottom hole for the screw heads.
Then a screw clearance hole into the center dimple left by the forstner,
to ensure that the threads do not bite into both pieces, thus screw jacking them apart.

I would have used screws that are flat under the head, probably Kreg self-tappers. I like those.

The center hole, is a Kreg pocket hole, to allow the top to be screwed down
from underneath. The pilot hole did not pierce the top yet.
The top was 3/4" maple plywood, making a 3" border, with a pair of 3" crossbars.
Webbing was strung across, for the upholstered top.
100350
Excuse the huge junkpile. I have a junkpile, but that one is not mine!

The top was 15 seperate squares of fabric, sewn together.
Pulling the buttons down helped to sculpt the top cushion.
100351 100352

The bench was about 4 feet long, if I recall.
The frame proved quite rigid. It worked out to be very comfortable.
I nearly fell asleep on it in my shop!
take it easy,
Walt

[Joe Vincent]

Walt: Thanks for the info.

[Cody Colston]

In response to the OP...yeah, why not?

I use biscuit joinery sometimes. I also use M&T joinery sometimes. It just depends on what I'm making and my mood when I design/build it. If the biscuits fail, they can be repaired if, as previously said, the piece is worth repairing. If not, it goes on the trash heap. Say La Vee

I find it humorous that Norm uses biscuit joinery and gets called a woodworking hack. David J. Marks uses biscuit joinery and is called a fine woodworker. Go figure.

I'll also bet that there would not be nearly as many Domino users and apologists if it had been developed by Ryobi instead of Festool. The $1000 dollar Festool price is actually touted while a $200 Ryobi version would have immediately been labeled as cheap Chinese junk by those same people. I'm not bashing Festool either but rather the tool snobs who think that if it's not green and costs an arm and a leg, it must be useless.

So, if you prefer M&T joinery or hidden dovetail joints or biscuit joinery or whatever, then knock yourself out but don't look down your sawdust filled noses at a different method, especially when you have no personal experience with it.

[Marcus Ward]

Toolsnobs don't sand, they plane. With Brass and rosewood infill planes. So they don't have any sawdust in their noses.

[Peter Quinn]

Hmm, a few people have made a couple of coffee tables, and Europeans have made durable boxes with biscuits. I made a TV cabinet using mostly biscuits, but my TV is a static load. Hey, maybe I should build my next house with them? Skip all those pesky nails and sheathing, just biscuit the whole thing together? And hope the wind doesn't blow?

I think design plays into the failure or success of biscuits as a method of joinery. Forget scrap pieces and hammer blows. Glue up a full size leg/apron joint with two biscuits, make the apron at least 30" long, clamp the leg to something sturdy and stand on the far end of the apron. Give that sucker some real load, simulate the shear forces of a group of people leaning on a table, getting up and down, passing the gravy so to speak. A box has shear strength by using plywood at opposing angles and spreading the load around, no issue there. But a table leg/apron joint?

Has anyone made an unreinforced leg to apron joint using only biscuits that has not failed for a working dining table of at least 30"X60" size? I'm talking no backers, no angle blocks, no screws, just biscuits.

[Douglas Brummett]

Valid points Peter, well except the house bit :)

My test piece was about golf club size. It was a a 2x4x6 joined to a 2x2x30. Prior to hammer testing I did clamp it to the extension table of my TS (extension table is lag bolted to the base, so pretty solid). I pulled on it, twisted it, and got no signs of failure using the 30in leg for leverage. That's when the hammer came out. I think the sharp and intense blows were harder on the joint than my steady wiggle pressure. I was trying to get a feel for the joint as life-like as possible.

From my unscientific testing I concluded that the joint was good, but I added glue blocks for insurance.

[Mike Henderson]

My experience with joinery of this type is that the strength depends upon the surface area of face grain to face grain contact. If I compare the area of a typical M&T joint to one biscuit (actually a half biscuit to be equivalent), I'd conclude that the M&T joint was stronger. I'm sure you can add additional biscuits to get more area, and there's the question of "how much area do you need for this application?"

Since I don't build production furniture (I don't have to crank stuff out fast), I stick with M&T just to be conservative on the strength side. That's not to say biscuits won't work, however.

Mike

[Ken Milhinch]

In the case of a medium to large table, downward pressure on the table top would apply some shear force to the biscuits, but the table legs are taking most of the strain. I suspect the way in which the biscuits might eventually fail would be due to sideways forces on the legs, resulting in racking of the apron to leg joint. A simple reinforcement would be to use corner brackets such as these http://www.rockler.com/product.cfm?page=782 (something I use on all tables I build). Simple to use, cheap and prevent racking.

[Marcus Ward]

Just as an addendum to this conversation: while leafing through some Fine Woodworking mags from 1985 a writer named Graham Blackburn made a whole set of chairs with quite tall backs using nothing but double biscuits to join the legs to the stretchers. No lower stretchers either. They look like, if you leaned back in them, the legs would snap off from those weak little biscuits but the writer claims they're holding up just fine. I'd be curious to see if they're still solid 23 years later.

[Peter Quadarella]

I like the idea that my furniture may last 200 years as a previous poster mentioned. I just tend to think that any joint that relies on glue mainly will eventually fail. The biscuit, without any glue, is not a strong piece of material, and doesn't create a strong mechanical joint.

On things that are not chairs or tables, I would think they are fine, but after thousands of loads and unloads, and seasons, I prefer a joint that can hold without glue also. And regarding the comment about doing the hula on top of a table - it may seem silly, but wouldn't it be worse if a table you made actually fell apart from someone being silly like that?

Of course biscuits are great and useful, but I don't think this is a case of one size fits all.

[Roger Barlow]

Does anybody have issue 148 of FWW around, cause I can't find mine. But the joint tests did have a biscuit joint in it.

[David Keller NC]

"...thereby building stress into the joint and removing material to boot. Not many people bother to think that far ahead, but it's a great way to increase the chance that the mortised piece will split somewhere down the road."

With respect to drawboring, it doesn't substantially weaken a tenon unless the hole created by the bore is quite large compared to the width of the tenon. What one has to remember is that the reason for using a M&T, and its source of strength, is not bearing a vertical static load, it's resistance to racking forces. The resistance to racking forces comes about from the shoulders and the fit of the cheeks in the mortise, not the width, or to some extent, the length of the tenon.

This is one of the primary reasons to use drawboring to assemble a very strong M&T joint that will be subject to a lot of racking - unless the tenon shoulders are really, really sloppy, drawboring pretty much guarantees a tight fit at the shoulders, and for the joint to fail, not only does the glue have to fail, but the wood in the vertical member has to be crushed across the grain. That's a possibility with soft woods like pine, but it'd be an extraordinary load to do this with a hard cabinet wood.

Resistance to racking forces is another reason not to use biscuits alone for something like a table apron or the back of a chair. I'm fuzzy on which mag did this test, but one of them (I think FWW) did an extensive test comparing joint failure from racking between M&T, Loose M&T, dowels, Biscuits, and pocket screws. The authors conclusions were that the biscuits were just as strong as any of the other joints, including M&T, but the failure mode was very different - the M&T joints slowly pulled apart, and the biscuit joints let go with a loud snap and near instant total joint failure.

That mode of failure is not something I'd want to risk in a piece of furniture like a table, or especially, a chair. I believe that was the author's conclusions as well - even though the biscuits were just as strong, they didn't recommend them for critical applications.

Don't get me wrong - I have a biscuit joiner, and I do use it fairly often to align boards for glue-ups, rapidly making utility boxes, and the like. I actually recommended this method to someone on the Neander forum to make a toolbox because he didn't have the tools to make a M&T joint. But I wouldn't use them, nor advise someone use them, for something I was to sell to someone as fine furniture.

[Verne Mattson]

[quote=John Stevens;961807]...thereby building stress into the joint and removing material to boot. Not many people bother to think that far ahead, but it's a great way to increase the chance that the mortised piece will split somewhere down the road.

If you get a chance to visit the Cloisters in NYC, it's highly recommended. They have a terrific collection of furniture made in the 1400s and 1500s. How were they joined, you ask? Drawbored M & T. Joints looked pretty good after 500+ years! I can't imagine any of my furniture lasting that long, but who knows?

Although I personally like to mortise and tenon my work, I don't see a reason why biscuits wouldn't be perfectly acceptable for certain applications. I vaguely remember the FWW article about various joints -I do remember that the biscuit joints failed before M&T. I guess it depends on how much stress you think a joint might take.

I wouldn't ever use biscuits on a workbench, but on an end table why not? Especially if you don't sit on it (like I do my coffee table on occassion).