FWW Joint Strength Test

[Ben West]

I've not yet seen this article, but should soon.

In any event, there have been several of these type tests published the past few years.

In general, be careful interpretting these results. Rarely do magazines implement testing prototcols that are rigorous enough to account for variances in the wood and in assembly procedures. In reality, one would have to duplicate each joint many times to account for these variances.

This FWW article may have done a good job, but that is not the norm with this kind of article.

In the end, does it really matter? I've seen very, very few pieces of furniture with failed joints because they weren't strong enough. It seems traditional M&T, domino, and dowelmax -- if applied correctly -- all produce joints strong enough for all practical furniture making.

[Chris Friesen]

With the bridle joint I'm not surprised that it came in weaker than the half-lap. The "single tenon" piece was only 1/4" thick. If I were making a bridle joint optimised for strength, I'd make the single tenon 3/8" thick, with each of the "double tenons" 3/16" thick. This would balance the amount of wood on each side of the joint, the same way that the thicker mortise-and-tenon joint does.

Their suggested "better way to spline a miter" basically turns the miter into a variation on the bridle joint.

The fact that the thicker tenon gives stronger joints is no surprise...I've seen many sources suggest that the tenon could be up to half the thickness of the piece being mortised, especially if the joint is machine made rather than being chiseled by hand. It's also not a surprise that the pinned/wedged joints were weaker. These additions are there primarily to keep the joint tight over time or to compensate for an initially sloppy fit, not to make it stronger overall.

[Peter Quinn]

I should add to my previous comments that on closer reading of the FWW stress test article I noticed they made and broke five samples of each joint, so the breaking force is an average of five samples which probably nullifies my suspicion that the strength of the individual pieces of wood in question is a strong factor. I still don't like these tests. Just a shame to waste all that beautiful wood when we all know (add your preferred method of joinery here) is the best if done correctly.

Darn scientists. Perhaps they could bring in Pete Townshend to smash those joints guitar style and see how they survive my proposed shock test?

[Steven Bolton]

Was there anything about pocket screws? I like them, but I cannot believe they are as strong as mortise and tenon (as advertised).

Steve Bolton

[Peter Quinn]

Was there anything about pocket screws? I like them, but I cannot believe they are as strong as mortise and tenon (as advertised).

Steve Bolton

Pocket screws took 698# peak load before failure, 1/4" traditional M&T took 717# peak load before failure. Pretty close. A 3/8" tenon took 1475# before failure, considerably stronger. I for one will take a joint that can hold 700# any day. And a 3/4 ton door joint? That's just silly.

[Bruce Wrenn]

Only the butt, and miter joints failed. In all the rest, the wood failed, not the joint. Article could have been renamed " Wood With a Larger Cross Section is Stronger. " DUH?

[Mark Bolton]

I further wonder how each joint may sustain a 'shock' force rather than a long slow crushing as created by the servo-hydraulic testing machine. Suppose a portly friend sits in a chair you have crafted. Will he gently lower himself down, adding weight incrementally? Or will he plop his but down hard and take a load off? Does it make a difference? How about child swinging from a cabinet door? (not that I ever did this as a child mind you...)

I am new to sawmill and this is only my second post but...

As a manufacturer of wood products one can not include such variables in ones work. Operating in the most litigious and warranty laden environment in the world (US) one has to build work in hopes of withstanding the worst possible environment imaginable. More than likely its a situation you never would have imagined. There is no saying "well how hard did the guy sit on my chair when it broke?" As a manufacturer you are charged with the brutal task of foreseeing that possible eventuality.

The simple fact of the mater is we live in a world where someone today walks into a store, within a reasonable period of install, with a cabinet door broken down into its component parts and they are likely to be shipped a free replacement. It matters not whether they reveal that their 150lb kid was using it as a ladder to get to the reecees piecees or not. We as manufacturers in the market have no choice but to compete.

What strikes me as interesting is that standards remain true, simple = better. No matter how badly we all become obsessed with spending obscene amounts of money, a joint we have all been making for years with basic tools performs.

Mark

[Mike Henderson]

Only the butt, and miter joints failed. In all the rest, the wood failed, not the joint. Article could have been renamed " Wood With a Larger Cross Section is Stronger. " DUH?

That was my reaction when I read it. To me the test said, "Modern glues are stronger than wood, so make the joint hefty if you want the maximum strength."

The article was really about which technique has the most "mass" in the joinery, and is why the lap joint came out best.

Mike

[Randy Klein]

I like that they added a blurb discussing seasonal wood movement. That repeated cross-grain movement will eventually stress the joint. And that they acknowledged the test occurred right after the glue cured. It seems that they were expecting some fodder along those lines.

It'd be interesting to add a few decades of time, however unrealistic that may be, to the test and see how they hold up. I'd suspect that the top 2 - half lap and bridle joints wouldn't be the top 2 after that much time.

[Thomas Knighton]

I would imagine that they could put the joints in a chamber that increases and decreases humidity to such an extent that it would mimic a decade or so of time, but that would probably be cost prohibitive...if it truly is possible.

Tom

[David Keller NC]

"Since they used cherry, that kinda sorta cancels out through all the tests. Yes, being a natual product, no two pieces are EXACTLY alike so you have to take it with some grain of salt so add a tolerance of +/- 10% (or whatever) to all the numbers read of the test machine."

Actually, their choice of wood was extremely poor for the purpose for which they designed the test (testing the strength of various joint configurations). The ultimate conclusion of the test could've been phrased correctly that "different joint configurations varied the strength of the individual joint components - almost all of the joints failed where the wood was weakest". Their rather suspect conclusion that a bridle joint was the strongest because it had the most glue area is just flat out incorrect, based on their own test protocols and results.

What they should've done is realized that their wood choice was inappropriate based on the first few test joint failures. There are a lot of common, inexpensive species they could've chosen that would've been less brittle and would have likely allowed them to test the strength of the joint, not the wood. The ultimate one that comes to mind would've been hickory. Not exactly a common cabinet wood, but it would've allowed them to draw a conclusion about joint configurations.

This is, by the way, a common theme that runs throughout FWW's tests and reviews over the last few years. They do come up with pretty good article ideas, but their execution on those ideas is abyssmal. After reading some of the comments by some of the FWW editorial staff on Knots, this doesn't surprise me. They sorely lack appropriate leadership to focus their creativity and apply some logic to how they go about them.

[Greg Pavlov]

"Actually, their choice of wood was extremely poor for the purpose for which they designed the test (testing the strength of various joint configurations). The ultimate conclusion of the test could've been phrased correctly that "different joint configurations varied the strength of the individual joint components - almost all of the joints failed where the wood was weakest". Their rather suspect conclusion that a bridle joint was the strongest because it had the most glue area is just flat out incorrect, based on their own test protocols and results.

What they should've done is realized that their wood choice was inappropriate based on the first few test joint failures.

While you are probably right from a proper test approach point of view, the reality is that a lot more people use cherry for furniture rather than hickory, so the results will have more relevance for them.

[Joe Jensen]

These tests while interesting, don't seem to be of much value in the real world of furniture. I've made tons and tons of cabinet doors and cabinets over the past 30 years. Other than in the first few years, I only do but joints on flat glue ups, and I only use a cabinet set on the shaper for doors. I have never had a failure. I am meticulous on board prep, and fiend for straight flat boards.

[Clifford Mescher]

[QUOTE]

I couldn't let this go by without saying that I like reading Fine Woodworking magazine and I think they do an admirable job.Clifford.

[David Keller NC]

"I couldn't let this go by without saying that I like reading Fine Woodworking magazine and I think they do an admirable job.Clifford."

I still have a subscription, but those of us that have long-term subscriptions and have read the magazine since the 1980's realize that there's been a remarkable dimunition in quality of the magazine, both in the topics covered, the writing, and the completeness of the articles. There was a time when one would never see a tool review in the pages of FWW. While it's true that there's a place for tool reviews, FWW isn't that place.

There are several dozen titles on the subject of WW on the newstands, and it's highly inappropriate for FWW to attempt to dumb down their content in an effort to be more like those mags. There's a place for everything, including magazines filled with nothing but tool reviews and beginner projects, but that title is American Woodworker, not Fine Woodworking. There are many of us that have paid for subscriptions on a 5 year basis that are really, really not happy with the "new direction" of the magazine. It's a race to the bottom, IMO.

"While you are probably right from a proper test approach point of view, the reality is that a lot more people use cherry for furniture rather than hickory, so the results will have more relevance for them."

The problem is the labeling. A correct title would be "strength of cherry in various woodworking joints" not "strength of various glued woodworking joints". Because of this rather glaring ignoring of how the joints failed, the results do not translate to the various joint configurations tested in many other common cabinet woods.