That's what I hear although I have never see it happen in person.Originally Posted by Mike Parzych
That's what I hear although I have never see it happen in person.Originally Posted by Mike Parzych
Dennis
Mike, thanks for your comments--they're all good for me to keep in mind. Regarding the one point I quoted above, here's my thought. Any piece of furniture with a flat top, whether it's a desk, a bookcase, an end-table, etc., can be expected to undergo two big stresses. One is the stress of a move. The other is that of a fully-grown adult standing on it instead of getting a step-ladder. The first situation is one that only results in property damage. The second situation is one that may result in serious permanent bodily injury or death, so I think that's the more important one to design for.Originally Posted by Mike Cutler
In the second situation, the load of the adult is borne pretty evenly by all of the joints. So if we're considering the case of a four-sided end table or desk with long thin legs joined to stretchers by one biscuit on each end of each stretcher, the load is distributed among eight biscuit joints. If the stretchers are 3/4" thick give or take 1/16" and the slots have been centered in the stretchers, and the stretchers and legs have been butted nice and tight so there's no perceptible gap, then each of the eight biscuit joints are pretty much all exposed 1/8 of the total load, which is mostly tensile and shear forces. I don't worry about biscuit joints failing in this kind of situation.
In the situation where furniture is moved, all bets are off, IMO, because the risk of furniture being exposed to damaging levels of force is very hard to pin down. (I say that based on my experience of having worked from time to time with my step dad, who is a furniture repairman, and on my experience with having moved myself over a dozen times in the past 20 years, and having moved many of my friends, by virtue of being the owner of a pickup truck.) On the one hand, it stands to reason that the stronger the joint, the lower the odds that it will be broken during a move. So, putting aside aesthetics and other intangible values (because they're irrelevant to the narrow issue we're discussing here), the cost-benefit analysis between biscuits or a stronger joint like a traditional M&T is whether the cost of the additional labor involved in making the traditional joint is less than the difference in the cost of repair of damage that will be suffered by each type of joint, multiplied by the probability of that damage occurring during a move. Based on that analysis, I still wouldn't hesitate to go with biscuits.
However, once you figure aesthetics and "tradition" back into your choice of joinery, I have to admit that biscuits are way down with pocket screws. There's nothing like the look of a pinned M&T or through M&T joint, and my hat is off to you folks who have the skill and patience to make joints like that. It's even more than looks--its the fact that more of the "life" of the builder has gone into the piece, and people who truly appreciate furniture realize this. If I had the ability to do make joints like that, I wouldn't use biscuits.
Last edited by John Stevens; 02-28-2006 at 10:34 AM.
What this world needs is a good retreat.
--Captain Beefheart
I believe that it can be a problem if you sand the surface within a day or so after putting the biscuit in - while it is thoroughly expanded, but not yet totally dry in the center. I am not that fast - it is usually many days from the initial glue up to the final sanding. Since the biscuit will be much dryer (but probably not completely dry) by then, I believe this is why I have not actually seen the problem.Originally Posted by Mike Parzych
I bet if you slide a finished table across the floor with a load on the table (can you say cleaning lady), and the leg catches a rough spot on the floor with a lever arm of around 30 inches (the length of the leg) the forces will be far higher than you imagine. Now repeat the process every two weeks (or how ever often the cleaning lady does this), and make it a rough cleaning lady shove rather than a gentle furniture maker slide. That is why I bet on mortise and tenon rather than biscuits, even though I use biscuits for lots of other purposes.Originally Posted by John Stevens
Let's go with your hypothetical situation, and furthermore, let's assume that the force will definitely cause a table made with a single biscuit per stretcher to break at one or more of the biscuit joints. In order to redesign the table so it can withstand this force, we can switch to traditional M&T joinery, a pinned M&T if you like. Or we can increase the thickness of the stretcher to a nominal 4/4" thickness and use two biscuits per stretcher. Or increase the stretcher to nominal 5/4" or 6/4" thickness and use three biscuits per stretcher. No reason to forswear biscuits. We just need to weigh the pros and cons of each design option in light of the cost of our labor, our tools, and our materials, and our aesthetic preferences.Originally Posted by Charlie Plesums
What this world needs is a good retreat.
--Captain Beefheart
Thomas Stender is a furniture maker who wrote a book on how to make several models of tables:Originally Posted by Don Baer
http://www.amazon.com/gp/product/157...Fencoding=UTF8
In that book, Stender says he's been using biscuits in his chairs for years and has never had a chair fail. No disrespect intended to Sam Maloof, but Stender is basing his opinion on chairs he's made and sold; Maloof isn't.
What this world needs is a good retreat.
--Captain Beefheart
I don't understand that statement. Sam Maloof has made and sold thousands of pieces of furniture and many are sent back to his shop for refinishing when by some mean the finish is ruined. As a matter of fact he had a table that one of his former customers sent back because someone had set something wet on it and she asked if Sam could restore it. So I guess that Sam has had the opportunity of seeing how many of his pieces have withstood the test of time. Not all of sams pieces go into musiums. Most go into peoples homes and are used every day.Originally Posted by John Stevens
I have no doubt that biscuts have there place in joining pieces together I just prefer more of the traditional ways.
While I agree, the type of force determines how much strength is needed; gluing a biscuit and pulling it with plier etc applies entirely different forces that in a real joint. And, if you consider the lever arm of a table apron shoulder compared to the length of the leg, you have significantly higher force than what you get pulling on a pair of pliers.Originally Posted by John Stevens
Sorry, I wasn't clear. What I meant was that Sam Maloof, according to your first post in this thread, hasn't made and sold chairs that rely on biscuit joints. My point is that, according to a furniture maker who has actually sold a number of chairs that use biscuit joints, they can be strong enough for that application, depending on the materials and other design factors.Originally Posted by Don Baer
We're all entitled to accept or reject biscuits on aesthetic or traditional grounds, but Jay's original question was whether they were strong enough to use in furniture.
What this world needs is a good retreat.
--Captain Beefheart
Yes, but in use, the force will be distributed among anywhere between two and sixteen biscuits. It all depends on whether the force is borne by one leg or more, and whether the design of the piece of furniture uses one or more biscuits per joint. Maybe I'm also overestimating the amount of force the average person can exert with a pliers. I can deadlift over 300 lb., and I guess I take my grip strength for granted.Originally Posted by Andrew Shaber
What this world needs is a good retreat.
--Captain Beefheart