10 ms·

Wood Joint Strength Testing

216 points by UkiahSmith 7y ago

jimnotgym 7y ago
There is another important factor. Wood expands and contracts according to the moisture content of its environment and screws expand and contract according to temperature. The combination of these means that screws work themselves loose over time, often wearing the threads out of the wood. In the UK, stair handrails (for instance) used to be mortice and tennoned with a drawbored peg. This is where an offset holde is drilled through the tennon and a peg driven in to pull it tight. A fashion for cheap construction has seen this replaced by screws in many cases. The problem is that uk houses tend to have wet plaster (or at least a skim on drywall) and high moisture levels at the time of installation. This means that the wood will shrink once installed... and your handrails come loose, the screws are hidden by this time! In a very damp situation, say a wooden gate, this gets a cyclical drying and wetting, yet properly made oak gates can last many years due to their pegged tennon joints. Edit: clarity
- deleted 7y ago
  [deleted]
- exDM69 7y ago
  In addition to wood movement, there's another important factor when it comes to hobbyist woodworkers: accuracy. With modern adhesives and precision machining like Mathias' work will make mighty strong joints even out of the simplest joinery method. A precision made box joint glued with wood glue is stronger than a finely made dovetail joint. But when it comes to me bodging away in my garage with hand tools, that kind of precision is not going to happen. But historical "strong" joints like dovetails and mortises and tenons with wedges and drawbores are very forgiving joints and are quite strong even when they're not made to sub-millimeter accuracy. I can join a decent box with dovetails in about 30 minutes, put it together with a few drops hide glue and fill the gaps with sawdust and it'll work great. But someone with a table saw and a simple box joint jig could join 10 boxes in the same 30 minutes it took me to make one.
  - jdietrich 7y ago
    Modern hand tool woodworking can match or exceed the accuracy of machine woodworking, albeit with a higher skill threshold. You can achieve very fine results with very basic tools. Machine woodworking is undoubtedly faster, however. Tight tolerances are often completely counterproductive because of wood movement. Even with an impermeable polyurethane finish, you'll get significant seasonal movement. Effective fine woodworking is about designing to account for that movement - building drawer runners slightly undersized so they don't bind up, allowing door panels to float in the groove so they don't bow or split etc. One of the key skills of cabinet-making is developing an intuition for wood movement. https://www.canadianwoodworking.com/tipstechniques/dealing-wood-movement https://www.canadianwoodworking.com/tipstechniques/dealing-w...
    - nemo44x 7y ago
      What about torrefying the wood first? Wouldn’t this reduce the amount of movement in the wood?
      - exDM69 7y ago
        You can't really stop wood movement or even reduce the amount it moves. It can be slowed down a little with some finishes (then you have a "wood-plastic composite"). Kiln drying (do you mean this by "torrefying"?) will make the wood dry for a while, but when the temperature and (absolute) humidity will rise on the summer, the wood will absorb moisture from the air and expand and shrink again next winter.
        jdietrich 7y ago
        Torrefaction (more properly, thermal modification) involves higher temperatures than kiln drying, causing chemical changes to the wood that result in permanently lower equilibrium moisture content and hygroscopicity. It improves the stability of wood and drastically improves the resistance of softwoods to decay, but it isn't a complete solution to wood movement. There is a significant tradeoff between stability and strength. https://en.wikipedia.org/wiki/Thermally_modified_wood https://en.wikipedia.org/wiki/Thermally_modified_wood
- aivisol 7y ago
  Moisture expansion cycle creates incredible forces, especially when the construction is used outdoors with large seasonal temperature/humidity changes. Even a wood as soft as pine can easily rip of heads of the screws after a couple of years of use. (personal experience)
- jabart 7y ago
  This is similar to current nails versus cut nails. Round nails help for sheer force, but after a while are easy to pull out. Cut nails are shaped different and work much better. I built two blanket chests using cut nails to hold it together, glue only to make a panel wide enough. Five years later it still is doing great, even with 5+ kids using it as a toy box. Screws would have worked themselves out by now. Also built a workbench with pegged tenons, guess it weighs 100+ lbs, and if you bump it with enough force the whole things moves, but the tenons are still not loose.
- sandworm101 7y ago
  >> The combination of these means that screws work themselves loose over time, often wearing the threads out of the wood. There are also dramatic differences between woods. Even if you use the same wood from the same tree, glues can impact moisture absorption rates. The only totally stable joints are those that don't use either fasteners or glues, the sort of stuff used to build Japanese temples, but these are complex and bulky. There is no perfect joint short of growing a tree in the shape you want.
- MatthiasWandel 7y ago
  Yes, for outdoor applications, the glue usually doesn't hold, though sometimes, for some joints, if its tight enough, the glue can keep the moisture out. See here: https://woodgears.ca/deck/repair.html https://woodgears.ca/deck/repair.html
- newnewpdro 7y ago
  I find this interesting and somewhat in conflict with my experience. I've been doing restoration work on an old home in the desert, and many of the nails in wood exposed to the elements had become quite loose and worked their way out enough to just grab and pull the rest of the way out without any tools. But the nails with with a screw pattern on them which twist as they're hammered in have done much better than the smooth ones. None of these have backed out, and they're all still very firmly set, in the same wood, in the same environment, for the same duration. The builder had used these screw-style nails for hangers, but smooth nails for everything else. I've been using SS deck screws of various length and gauge to do all my restoration work, in part because the reused wood is so old and brittle it's impossible to put new nails into it without splitting, and based on the screw-nails doing so much better than the smooth ones, I assumed the deck screws would be similarly more lasting. If what you're saying is accurate, I would have expected the screw-nails to have backed themselves out. But it was the opposite situation. My interpretation of what happens is the wood swells and contracts from both the temp and moisture changes. The metal fasteners don't change dimension much at all in these relatively insignificant (for metal) temp differences. When the wood swells up the first time, it compresses itself around the firmly held nail, and the nail doesn't budge. When the wood shrinks back down, the compressed wood around the nail stays compressed and now the bore is bigger than before. This cycle repeats itself over the years, and since the nail has a pointy tip, every time the wood swells up and closes in on the nail, it nudges the nail out a little bit before tightening until things shrink again. Based on this model, I think the screw is superior because the depth of the threads is greater than the dimensional difference between swollen and shrunken. The wood is free to go about its seasonal cycles, and the screw doesn't move because the threads are always engaged enough to resist that little pressing force at the pointy tip. I'm a noob when it comes to all this, but that's my impression and only time will tell if I've made a horrible mistake using screws for all these joints. Though it's not like I had many options.
dlbucci 7y ago
Cool article! I've made a few very simple pieces of furniture and have always used screws, so I was surprised to see they were the weakest joint. Guess I'll need to learn how to mortise and tenon!
- newnewpdro 7y ago
  Screws can be fine if used appropriately. If they're loaded in shear rather than tension, there's no issue of the head pulling through for instance.
  - MatthiasWandel 7y ago
    Yes, screws are fine for most applications, but at a right angle, if strength is critical, not the best option.
    - ckcheng 7y ago
      At right angle means the screw is loaded in shear rather than tension right? And that's why screwing in deck boards is good, but not for joists. Use nails for that instead, unless using engineered screws. So I'd be curious if you'd do the same strength test but with nails: end nailing and toe nailing. After all you did end screws and pocket screws... I'll add that your "Smashed deck repair hack job" is very interesting... the deck is attached by mortise and tenon joints? I keep reading about ledger boards and joist hangers, so I'm just... surprised? And you replaced posts in hole with essentially deck blocks! Very interesting... Thanks!
    - newnewpdro 7y ago
      Your failures mostly amounted to the joint pulling apart along the glue interface rather than breaking, I suspect adding a transverse retaining pin will make the failures more interesting with significantly higher loads. Did you consider doing any tests with a retaining dowel or some nails/screws through the mortice and tenon joint?
      - 7y ago
Jedd 7y ago
As someone who dabbles in woodwork, I can highly recommend it as a hobby. Exercising the brain in any new problem domain can often be rewarding in itself, but it's a nice opportunity to blend engineering, practicality, creativity, usefulness. From TFA, I'm (also) surprised that end-grain screws worked at all well. I appreciate the author was trying to minimise variation between the components, but for end-grain I'd use a much deeper thread, as screwing into end grain is often compared to joining into the end of a bunch of drinking straws. Not that I'd ever screw into end-grain. ;) Similarly, the makeshift pocket hole jointer isn't clear from the pictures how they got a recessed hole (commercial pocket hole devices use a t-shaped drill bit, and do not drill all the way through the piece). The recommended bits for pocket holes also have a threadless shaft near the head, so the two pieces pull tightly together. Which leads to the lack of glue in many of those photos. I grew up hearing (but not really believing) phrases like 'the nails are only there to hold it until the glue dries'. Wood glue technology is amazing -- when they say on the bottle 'stronger than wood' they aren't joking. I'd expect to use a lot more glue than shown, and have it significantly affect the results.
- cmroanirgo 7y ago
  > the nails are only there to hold it until the glue dries This is a phrase my brother, a cabinet maker/ jointer, uses... And tests occasionally: Glue 2 pieces of timber together at 90 degrees and clamp it normally. When dry, break the join (by bashing it with a hammer is his general way) to see if it's the glue or the timber. Nearly all of the glue he tests are stronger than the timber (Oz, US and Asian hardwoods), as it's the timber that is ripped apart, and not the glue join. A bottle of standard PVA-B (/ exterior grade) from the local hardware store is pretty excellent. When you think about glue, it's everywhere these days. All timber laminates (eg kitchen bench tops, plywood, particle board, MDF, and finger jointed/laminated timber) are just 'glued'. A lot of this is structural timber (ie designed to last decades). From the article: > This joint failed by the wood in the post shearing along the growth rings This is the most common place of failure when witnessing my brother's "tests", and makes a lot of sense it happens that way too. The glue should have been the strongest part of ALL of his tests. It looks like he 'over clamped' the timber (ie squeezed out all the glue) in few of his photos [0]: which is something my brother has warned me about, as it makes the join weak. [0] https://woodgears.ca/joint_strength/failures.html https://woodgears.ca/joint_strength/failures.html Edit: clarification
djbaskin 7y ago
Yeah, I really need to move away from screws. I recently made a Dialup line if anyone wants to talk about their projects: https://dialup.com/woodworking https://dialup.com/woodworking
Taniwha 7y ago
woo hoo! science!
woofie11 7y ago
A problem is that "strength" isn't a scientific term. You have tensile strength, shear strength, torsion strength, and compression strength. Screws have incredible tensile strength, which this article was testing. Shear strength? Not so much. Hit the joint with a hammer from above, and most screws will just snap. Nails are the opposite -- great shear strength, and no tensile. Glue is stronger than wood, as several comments indicated, but for how long? I've had many glued pieces of furniture fail after a decade of use. In a lot of woodworking, I use multiple types of fasteners. It's overengineering, but it doesn't fail.
- jkoudys 7y ago
  Most of the glued pieces I'll see fail after a decade were using your standard yellow carpenter's glue. It's fine, strong stuff that lasts a while, but it will still soften if it absorbs some water. Some older glues will also brittle over time. There's been a big push recently to waterproof glues that fully cure and can't be re-wet. While it's disheartening to throw out a bottle of clumpy glue (when I've had bottles of the yellow stuff sit around for over a decade and are still good), glues like titebond 2 or 3 should last as long as the wood itself. I'll still use the yellow glue for anything that doesn't hold a load, like thin panelling. These days my yellow glue mostly gets used to repair pop up books my toddler tore apart.
  - lstodd 7y ago
    If you absolutely need a joint to not fail before the wood, use epoxy, mix in some glass fiber cuttings. It's indestructible to the point I wasted considerable amount of sandpaper sanding off a joint I needed to remove. Nothing else would so much as cut it. PVA ("standard yellow carpenter's glue", titebond, etc) is much weaker and moisture kills it over time.
    - jimnotgym 7y ago
      Epoxy comes at a serious cost 1) It costs a lot of $ to begin with 2) Everything you apply it with is ruined within minutes 3) It can cause terrible dermatitis (always wear multiple pairs of nitrile, not latex, gloves). You can become sensitised to the point that you cannot share a room with sanding dust from it! 4) It's open time is short and varies according to the batch size due to the heat it produces. This means you have to spread large batches out in a tray to lose heat or it goes suddenly hard, or indeed melts your tray! 5) Clean up is nigh on impossible. Normally you are left chipping and sanding what is left 6) It has poor resistance to UV light 7) It leaves a residue that can stop paint sticking 8) It is unsuitable for thin glue lines like are used in furniture and traditional joints But yes it is phenomenally strong and water resistant. A better glue for joinery is polyurethane, especially the titebond stuff.
VBprogrammer 7y ago
I'd recommend NOT starting to watch Matthias Wandel's videos. I must have lost years of my life watching woodworking videos on youtube after he got me hooked. It also cost me several thousand pounds in tools and culminated in me buying a home requiring complete refurbishment (not quite finished). Save yourself! (mostly in jest).
- jdietrich 7y ago
  At the very least, watch some Paul Sellers videos to inoculate yourself against the belief that you absolutely must give all your disposable income to Festool and Lie Nielsen. https://www.youtube.com/user/PaulSellersWoodwork https://www.youtube.com/user/PaulSellersWoodwork
  - Bluestrike2 7y ago
    Except for sanders. If you use one of them for a bit, you'll have no problem signing away an organ or two to Festool. And the dust collector, of course. Maybe a Domino joiner. But other than that, you don't have to give them all of your disposable income for your power tool needs.
    - exDM69 7y ago
      Watch enough of hand tool videos and soon you will be hand planing and scraping instead of finish sanding. Buying the sander and dust collector would probably be cheaper than all those hand planes, but there is something in that fine smoothing plane shaving that keeps you coming back.
    - markdoubleyou 7y ago
      I just looked up the Domino joiner. It looks amazing, but good lord, it's $1500 after you add in the different sized cutters.
  - Loughla 7y ago
    Honestly, if you're interested in woodworking, Paul Seller's original 'workbench' video set is how to get started. Cheap materials, can be done with cheap tools, and he's pretty straight forward about what's important to worry about and what isn't. You'll learn whether or not woodworking is for you, and you'll have a handy workbench.
dekhn 7y ago
woodgears.ca is one of my favorite sites on the internet. really inspiring, although it's unlikely I'll ever build a pantograph router.
teacpde 7y ago
It is amazing to find woodworking is such well received topic on HN. I don’t remember how I stumbled on a woodworking video on YouTube about a year ago, and last week I just finished building the Christopher Schwarz knockdown workbench. This hobby is truly addictive, to me, it resembles a lot aspects of software engineering, but in a more vivid and interactive fashion.
- quicksnap 7y ago
  The thing that draws me to woodworking, as a software engineer, is that it resembles many aspects of software, but has a wonderful imperfection inherent to it. The more skilled at woodworking I become, the more I learn that every piece of wood is unique, and does not care about systems and methods. The grain will happily explode in your face if you try to work with it the wrong way. =) It all makes me appreciate the physical aspects of things much more.
- websterisk 7y ago
  I think this is particularly true in the sense that woodworkers (like software people) can make much of their own tooling in their native media. Nothing I've seen on youtube is a better example of that than Matthias Wandel. Need to make a bandsaw out of wood? Here, hold my beer. The Pantorouter... really? Even dust collection! This makes wooden stuff out of wooden stuff out of wooden stuff. Three levels deep, inception style.
yumraj 7y ago
Can anyone recommend any good woodworking books, preferably one that is friendly to beginners.
- takk309 7y ago
  Check out Lost Art Press (https://lostartpress.com/ https://lostartpress.com/) They focus mostly on traditional hand tool wood working. The Anarchist's Tool Chest (https://lostartpress.com/collections/getting-started/products/the-anarchists-tool-chest https://lostartpress.com/collections/getting-started/product...) is a great book to help you get started with what makes a good hand tool and what you need to start doing small projects.
- brixon 7y ago
  YouTube: Steve Ramsey & Izzy Swan both have playlists focused on new woodworkers.
- bradford 7y ago
  I've worked with wood for a few years now, and I wish I would have found Rex Krueger's channel earlier (https://www.youtube.com/channel/UCj4SLNED1DiNPHComZTCbzw/videos https://www.youtube.com/channel/UCj4SLNED1DiNPHComZTCbzw/vid...). I'd say his primary intent is to get you started with the minimal amount of cost, and his videos get to the point faster than many other instructional videos.
- Stephen-E 7y ago
  Lost Art Press is great, but not exactly for the beginner. I'm a huge fan of The Wood Whisperer aka Marc Spagnuolo (https://www.youtube.com/user/TheWoodWhisperer https://www.youtube.com/user/TheWoodWhisperer). He has a lot of content on YouTube that's significantly higher production quality than everyone else, and most importantly he's very good at teaching. He has two books that are great for the beginner: -Essential Joinery -Hybrid Woodworking https://www.amazon.com/Hybrid-Woodworking-Blending-Quality-Furniture/dp/1440329605/ref=pd_bxgy_14_img_2/135-9131879-5402545?_encoding=UTF8&pd_rd_i=1440329605&pd_rd_r=76a03429-86f9-11e9-bd51-9f94d0b120ce&pd_rd_w=egWQx&pd_rd_wg=ak0kW&pf_rd_p=a2006322-0bc0-4db9-a08e-d168c18ce6f0&pf_rd_r=6551523S46P4ZMZ7DPD4&psc=1&refRID=6551523S46P4ZMZ7DPD4 https://www.amazon.com/Hybrid-Woodworking-Blending-Quality-F... https://www.amazon.com/Essential-Joinery-Important-Joints-Woodworker/dp/1940611873/ref=asc_df_1940611873/?tag=hyprod-20&linkCode=df0&hvadid=312128022127&hvpos=1o1&hvnetw=g&hvrand=16834033085502338787&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026803&hvtargid=pla-680778681113&psc=1 https://www.amazon.com/Essential-Joinery-Important-Joints-Wo... While he has a ton of free content on YouTube, his guild site offers even more at a modest price: https://thewoodwhispererguild.com/ https://thewoodwhispererguild.com/ His Shaker Table project was my first "real" piece of furniture that I built. I've since graduated to designing and building my own furniture. Highly rewarding, and I owe a lot of my skills to Marc's wonderful teaching methods.
jugg1es 7y ago
Results are not at all surprising, but it's really great to see it done in a formal way.
zaphod4prez 7y ago
Matthias Wandel is just the coolest. Highly highly recommend watching all of his videos
- MatthiasWandel 7y ago
  That's right :)
MatthiasWandel 7y ago
Hey, cool to see my article on the front page of hacker news. Never expected THAT article to hit hacker news. Got a question, I could answer.
- doctoboggan 7y ago
  Just wanted to say I've been watching your videos for years and I am a big fan. Keep up the great work!
- quicksnap 7y ago
  I love your channel so much, and am so glad to see you here commenting! It's great that you continue to post videos. Thanks so much for combining two of my favorite things: woodworking and engineering!
- longb4 7y ago
  Hey there! Big fan of your articles and videos. I've been building box joints recently and even though the forces they're subjected to are not nearly as pathological as what you tested, I enjoyed your box joints and dovetails strength testing article: https://woodgears.ca/dovetail/strength.html https://woodgears.ca/dovetail/strength.html Quick question: do you recall what wood you used for the box/dovetail article? It looks similar to the spruce from the earlier joint strength article. I suppose using a stronger wood would just get you closer to where the glue is failing more than the wood, but I'm just curious. Less-quick question, feel free to punt/ignore: any thoughts on deliberately building in a very, very slight gap between box joint fingers? I would expect this to reduce joint strength (thanks to reduced force between fingers and surface area in contact) but potentially also mitigate wood stress from movement in service due to humidity. Though I imagine if a work piece is big enough for me to be concerned about movement in service, I probably shouldn't be using box joints!
  - MatthiasWandel 7y ago
    I'm pretty sure that wood was birch. As for gaps in joints, if its a small gap, it doesn't hurt. I actually did some tests in that regard, linked from the article. http://woodgears.ca/joint_strength/glue_methods.html http://woodgears.ca/joint_strength/glue_methods.html A small gap actually helped. Probably because the glue soaks into the wood, so a joint without any gap sort of runs out of glue too quick (my theory). But it suggests that putting glue on and leaving the joint open for a minute may be beneficial.
exabrial 7y ago
Why didn't he join the screwed pieces with glue? I was always under the impression the whole point point of screwed joints is to stress the glue, not to actually bear load (Because of the small surface area and hardness difference of the materials)
- btbuildem 7y ago
  I've never used both screws and glue on a joint. It's either a quick and lame job and I'll use screws, or I'm making something nice and I'll go to the trouble of cutting and gluing joints.
deleted 7y ago
[deleted]

216 points by UkiahSmith 7y ago

There is another important factor. Wood expands and contracts according to the moisture content of its environment and screws expand and contract according to temperature. The combination of these means that screws work themselves loose over time, often wearing the threads out of the wood. In the UK, stair handrails (for instance) used to be mortice and tennoned with a drawbored peg. This is where an offset holde is drilled through the tennon and a peg driven in to pull it tight. A fashion for cheap construction has seen this replaced by screws in many cases. The problem is that uk houses tend to have wet plaster (or at least a skim on drywall) and high moisture levels at the time of installation. This means that the wood will shrink once installed... and your handrails come loose, the screws are hidden by this time! In a very damp situation, say a wooden gate, this gets a cyclical drying and wetting, yet properly made oak gates can last many years due to their pegged tennon joints. Edit: clarity

deleted 7y ago
[deleted]
exDM69 7y ago
In addition to wood movement, there's another important factor when it comes to hobbyist woodworkers: accuracy. With modern adhesives and precision machining like Mathias' work will make mighty strong joints even out of the simplest joinery method. A precision made box joint glued with wood glue is stronger than a finely made dovetail joint. But when it comes to me bodging away in my garage with hand tools, that kind of precision is not going to happen. But historical "strong" joints like dovetails and mortises and tenons with wedges and drawbores are very forgiving joints and are quite strong even when they're not made to sub-millimeter accuracy. I can join a decent box with dovetails in about 30 minutes, put it together with a few drops hide glue and fill the gaps with sawdust and it'll work great. But someone with a table saw and a simple box joint jig could join 10 boxes in the same 30 minutes it took me to make one.
- jdietrich 7y ago
  Modern hand tool woodworking can match or exceed the accuracy of machine woodworking, albeit with a higher skill threshold. You can achieve very fine results with very basic tools. Machine woodworking is undoubtedly faster, however. Tight tolerances are often completely counterproductive because of wood movement. Even with an impermeable polyurethane finish, you'll get significant seasonal movement. Effective fine woodworking is about designing to account for that movement - building drawer runners slightly undersized so they don't bind up, allowing door panels to float in the groove so they don't bow or split etc. One of the key skills of cabinet-making is developing an intuition for wood movement. https://www.canadianwoodworking.com/tipstechniques/dealing-wood-movement https://www.canadianwoodworking.com/tipstechniques/dealing-w...
  - nemo44x 7y ago
    What about torrefying the wood first? Wouldn’t this reduce the amount of movement in the wood?
    - exDM69 7y ago
      You can't really stop wood movement or even reduce the amount it moves. It can be slowed down a little with some finishes (then you have a "wood-plastic composite"). Kiln drying (do you mean this by "torrefying"?) will make the wood dry for a while, but when the temperature and (absolute) humidity will rise on the summer, the wood will absorb moisture from the air and expand and shrink again next winter.
      - jdietrich 7y ago
        Torrefaction (more properly, thermal modification) involves higher temperatures than kiln drying, causing chemical changes to the wood that result in permanently lower equilibrium moisture content and hygroscopicity. It improves the stability of wood and drastically improves the resistance of softwoods to decay, but it isn't a complete solution to wood movement. There is a significant tradeoff between stability and strength. https://en.wikipedia.org/wiki/Thermally_modified_wood https://en.wikipedia.org/wiki/Thermally_modified_wood
aivisol 7y ago
Moisture expansion cycle creates incredible forces, especially when the construction is used outdoors with large seasonal temperature/humidity changes. Even a wood as soft as pine can easily rip of heads of the screws after a couple of years of use. (personal experience)
jabart 7y ago
This is similar to current nails versus cut nails. Round nails help for sheer force, but after a while are easy to pull out. Cut nails are shaped different and work much better. I built two blanket chests using cut nails to hold it together, glue only to make a panel wide enough. Five years later it still is doing great, even with 5+ kids using it as a toy box. Screws would have worked themselves out by now. Also built a workbench with pegged tenons, guess it weighs 100+ lbs, and if you bump it with enough force the whole things moves, but the tenons are still not loose.
sandworm101 7y ago
>> The combination of these means that screws work themselves loose over time, often wearing the threads out of the wood. There are also dramatic differences between woods. Even if you use the same wood from the same tree, glues can impact moisture absorption rates. The only totally stable joints are those that don't use either fasteners or glues, the sort of stuff used to build Japanese temples, but these are complex and bulky. There is no perfect joint short of growing a tree in the shape you want.
MatthiasWandel 7y ago
Yes, for outdoor applications, the glue usually doesn't hold, though sometimes, for some joints, if its tight enough, the glue can keep the moisture out. See here: https://woodgears.ca/deck/repair.html https://woodgears.ca/deck/repair.html
newnewpdro 7y ago
I find this interesting and somewhat in conflict with my experience. I've been doing restoration work on an old home in the desert, and many of the nails in wood exposed to the elements had become quite loose and worked their way out enough to just grab and pull the rest of the way out without any tools. But the nails with with a screw pattern on them which twist as they're hammered in have done much better than the smooth ones. None of these have backed out, and they're all still very firmly set, in the same wood, in the same environment, for the same duration. The builder had used these screw-style nails for hangers, but smooth nails for everything else. I've been using SS deck screws of various length and gauge to do all my restoration work, in part because the reused wood is so old and brittle it's impossible to put new nails into it without splitting, and based on the screw-nails doing so much better than the smooth ones, I assumed the deck screws would be similarly more lasting. If what you're saying is accurate, I would have expected the screw-nails to have backed themselves out. But it was the opposite situation. My interpretation of what happens is the wood swells and contracts from both the temp and moisture changes. The metal fasteners don't change dimension much at all in these relatively insignificant (for metal) temp differences. When the wood swells up the first time, it compresses itself around the firmly held nail, and the nail doesn't budge. When the wood shrinks back down, the compressed wood around the nail stays compressed and now the bore is bigger than before. This cycle repeats itself over the years, and since the nail has a pointy tip, every time the wood swells up and closes in on the nail, it nudges the nail out a little bit before tightening until things shrink again. Based on this model, I think the screw is superior because the depth of the threads is greater than the dimensional difference between swollen and shrunken. The wood is free to go about its seasonal cycles, and the screw doesn't move because the threads are always engaged enough to resist that little pressing force at the pointy tip. I'm a noob when it comes to all this, but that's my impression and only time will tell if I've made a horrible mistake using screws for all these joints. Though it's not like I had many options.

dlbucci 7y ago

Cool article! I've made a few very simple pieces of furniture and have always used screws, so I was surprised to see they were the weakest joint. Guess I'll need to learn how to mortise and tenon!

newnewpdro 7y ago
Screws can be fine if used appropriately. If they're loaded in shear rather than tension, there's no issue of the head pulling through for instance.
- MatthiasWandel 7y ago
  Yes, screws are fine for most applications, but at a right angle, if strength is critical, not the best option.
  - ckcheng 7y ago
    At right angle means the screw is loaded in shear rather than tension right? And that's why screwing in deck boards is good, but not for joists. Use nails for that instead, unless using engineered screws. So I'd be curious if you'd do the same strength test but with nails: end nailing and toe nailing. After all you did end screws and pocket screws... I'll add that your "Smashed deck repair hack job" is very interesting... the deck is attached by mortise and tenon joints? I keep reading about ledger boards and joist hangers, so I'm just... surprised? And you replaced posts in hole with essentially deck blocks! Very interesting... Thanks!
  - newnewpdro 7y ago
    Your failures mostly amounted to the joint pulling apart along the glue interface rather than breaking, I suspect adding a transverse retaining pin will make the failures more interesting with significantly higher loads. Did you consider doing any tests with a retaining dowel or some nails/screws through the mortice and tenon joint?
    - 7y ago

Jedd 7y ago

As someone who dabbles in woodwork, I can highly recommend it as a hobby. Exercising the brain in any new problem domain can often be rewarding in itself, but it's a nice opportunity to blend engineering, practicality, creativity, usefulness. From TFA, I'm (also) surprised that end-grain screws worked at all well. I appreciate the author was trying to minimise variation between the components, but for end-grain I'd use a much deeper thread, as screwing into end grain is often compared to joining into the end of a bunch of drinking straws. Not that I'd ever screw into end-grain. ;) Similarly, the makeshift pocket hole jointer isn't clear from the pictures how they got a recessed hole (commercial pocket hole devices use a t-shaped drill bit, and do not drill all the way through the piece). The recommended bits for pocket holes also have a threadless shaft near the head, so the two pieces pull tightly together. Which leads to the lack of glue in many of those photos. I grew up hearing (but not really believing) phrases like 'the nails are only there to hold it until the glue dries'. Wood glue technology is amazing -- when they say on the bottle 'stronger than wood' they aren't joking. I'd expect to use a lot more glue than shown, and have it significantly affect the results.

cmroanirgo 7y ago
> the nails are only there to hold it until the glue dries This is a phrase my brother, a cabinet maker/ jointer, uses... And tests occasionally: Glue 2 pieces of timber together at 90 degrees and clamp it normally. When dry, break the join (by bashing it with a hammer is his general way) to see if it's the glue or the timber. Nearly all of the glue he tests are stronger than the timber (Oz, US and Asian hardwoods), as it's the timber that is ripped apart, and not the glue join. A bottle of standard PVA-B (/ exterior grade) from the local hardware store is pretty excellent. When you think about glue, it's everywhere these days. All timber laminates (eg kitchen bench tops, plywood, particle board, MDF, and finger jointed/laminated timber) are just 'glued'. A lot of this is structural timber (ie designed to last decades). From the article: > This joint failed by the wood in the post shearing along the growth rings This is the most common place of failure when witnessing my brother's "tests", and makes a lot of sense it happens that way too. The glue should have been the strongest part of ALL of his tests. It looks like he 'over clamped' the timber (ie squeezed out all the glue) in few of his photos [0]: which is something my brother has warned me about, as it makes the join weak. [0] https://woodgears.ca/joint_strength/failures.html https://woodgears.ca/joint_strength/failures.html Edit: clarification

djbaskin 7y ago

Yeah, I really need to move away from screws. I recently made a Dialup line if anyone wants to talk about their projects: https://dialup.com/woodworking https://dialup.com/woodworking

Taniwha 7y ago

woo hoo! science!

woofie11 7y ago

A problem is that "strength" isn't a scientific term. You have tensile strength, shear strength, torsion strength, and compression strength. Screws have incredible tensile strength, which this article was testing. Shear strength? Not so much. Hit the joint with a hammer from above, and most screws will just snap. Nails are the opposite -- great shear strength, and no tensile. Glue is stronger than wood, as several comments indicated, but for how long? I've had many glued pieces of furniture fail after a decade of use. In a lot of woodworking, I use multiple types of fasteners. It's overengineering, but it doesn't fail.

jkoudys 7y ago
Most of the glued pieces I'll see fail after a decade were using your standard yellow carpenter's glue. It's fine, strong stuff that lasts a while, but it will still soften if it absorbs some water. Some older glues will also brittle over time. There's been a big push recently to waterproof glues that fully cure and can't be re-wet. While it's disheartening to throw out a bottle of clumpy glue (when I've had bottles of the yellow stuff sit around for over a decade and are still good), glues like titebond 2 or 3 should last as long as the wood itself. I'll still use the yellow glue for anything that doesn't hold a load, like thin panelling. These days my yellow glue mostly gets used to repair pop up books my toddler tore apart.
- lstodd 7y ago
  If you absolutely need a joint to not fail before the wood, use epoxy, mix in some glass fiber cuttings. It's indestructible to the point I wasted considerable amount of sandpaper sanding off a joint I needed to remove. Nothing else would so much as cut it. PVA ("standard yellow carpenter's glue", titebond, etc) is much weaker and moisture kills it over time.
  - jimnotgym 7y ago
    Epoxy comes at a serious cost 1) It costs a lot of $ to begin with 2) Everything you apply it with is ruined within minutes 3) It can cause terrible dermatitis (always wear multiple pairs of nitrile, not latex, gloves). You can become sensitised to the point that you cannot share a room with sanding dust from it! 4) It's open time is short and varies according to the batch size due to the heat it produces. This means you have to spread large batches out in a tray to lose heat or it goes suddenly hard, or indeed melts your tray! 5) Clean up is nigh on impossible. Normally you are left chipping and sanding what is left 6) It has poor resistance to UV light 7) It leaves a residue that can stop paint sticking 8) It is unsuitable for thin glue lines like are used in furniture and traditional joints But yes it is phenomenally strong and water resistant. A better glue for joinery is polyurethane, especially the titebond stuff.

VBprogrammer 7y ago

I'd recommend NOT starting to watch Matthias Wandel's videos. I must have lost years of my life watching woodworking videos on youtube after he got me hooked. It also cost me several thousand pounds in tools and culminated in me buying a home requiring complete refurbishment (not quite finished). Save yourself! (mostly in jest).

jdietrich 7y ago
At the very least, watch some Paul Sellers videos to inoculate yourself against the belief that you absolutely must give all your disposable income to Festool and Lie Nielsen. https://www.youtube.com/user/PaulSellersWoodwork https://www.youtube.com/user/PaulSellersWoodwork
- Bluestrike2 7y ago
  Except for sanders. If you use one of them for a bit, you'll have no problem signing away an organ or two to Festool. And the dust collector, of course. Maybe a Domino joiner. But other than that, you don't have to give them all of your disposable income for your power tool needs.
  - exDM69 7y ago
    Watch enough of hand tool videos and soon you will be hand planing and scraping instead of finish sanding. Buying the sander and dust collector would probably be cheaper than all those hand planes, but there is something in that fine smoothing plane shaving that keeps you coming back.
  - markdoubleyou 7y ago
    I just looked up the Domino joiner. It looks amazing, but good lord, it's $1500 after you add in the different sized cutters.
- Loughla 7y ago
  Honestly, if you're interested in woodworking, Paul Seller's original 'workbench' video set is how to get started. Cheap materials, can be done with cheap tools, and he's pretty straight forward about what's important to worry about and what isn't. You'll learn whether or not woodworking is for you, and you'll have a handy workbench.

dekhn 7y ago

woodgears.ca is one of my favorite sites on the internet. really inspiring, although it's unlikely I'll ever build a pantograph router.

teacpde 7y ago

It is amazing to find woodworking is such well received topic on HN. I don’t remember how I stumbled on a woodworking video on YouTube about a year ago, and last week I just finished building the Christopher Schwarz knockdown workbench. This hobby is truly addictive, to me, it resembles a lot aspects of software engineering, but in a more vivid and interactive fashion.

quicksnap 7y ago
The thing that draws me to woodworking, as a software engineer, is that it resembles many aspects of software, but has a wonderful imperfection inherent to it. The more skilled at woodworking I become, the more I learn that every piece of wood is unique, and does not care about systems and methods. The grain will happily explode in your face if you try to work with it the wrong way. =) It all makes me appreciate the physical aspects of things much more.
websterisk 7y ago
I think this is particularly true in the sense that woodworkers (like software people) can make much of their own tooling in their native media. Nothing I've seen on youtube is a better example of that than Matthias Wandel. Need to make a bandsaw out of wood? Here, hold my beer. The Pantorouter... really? Even dust collection! This makes wooden stuff out of wooden stuff out of wooden stuff. Three levels deep, inception style.

yumraj 7y ago

Can anyone recommend any good woodworking books, preferably one that is friendly to beginners.

takk309 7y ago
Check out Lost Art Press (https://lostartpress.com/ https://lostartpress.com/) They focus mostly on traditional hand tool wood working. The Anarchist's Tool Chest (https://lostartpress.com/collections/getting-started/products/the-anarchists-tool-chest https://lostartpress.com/collections/getting-started/product...) is a great book to help you get started with what makes a good hand tool and what you need to start doing small projects.
brixon 7y ago
YouTube: Steve Ramsey & Izzy Swan both have playlists focused on new woodworkers.
bradford 7y ago
I've worked with wood for a few years now, and I wish I would have found Rex Krueger's channel earlier (https://www.youtube.com/channel/UCj4SLNED1DiNPHComZTCbzw/videos https://www.youtube.com/channel/UCj4SLNED1DiNPHComZTCbzw/vid...). I'd say his primary intent is to get you started with the minimal amount of cost, and his videos get to the point faster than many other instructional videos.
Stephen-E 7y ago
Lost Art Press is great, but not exactly for the beginner. I'm a huge fan of The Wood Whisperer aka Marc Spagnuolo (https://www.youtube.com/user/TheWoodWhisperer https://www.youtube.com/user/TheWoodWhisperer). He has a lot of content on YouTube that's significantly higher production quality than everyone else, and most importantly he's very good at teaching. He has two books that are great for the beginner: -Essential Joinery -Hybrid Woodworking https://www.amazon.com/Hybrid-Woodworking-Blending-Quality-Furniture/dp/1440329605/ref=pd_bxgy_14_img_2/135-9131879-5402545?_encoding=UTF8&pd_rd_i=1440329605&pd_rd_r=76a03429-86f9-11e9-bd51-9f94d0b120ce&pd_rd_w=egWQx&pd_rd_wg=ak0kW&pf_rd_p=a2006322-0bc0-4db9-a08e-d168c18ce6f0&pf_rd_r=6551523S46P4ZMZ7DPD4&psc=1&refRID=6551523S46P4ZMZ7DPD4 https://www.amazon.com/Hybrid-Woodworking-Blending-Quality-F... https://www.amazon.com/Essential-Joinery-Important-Joints-Woodworker/dp/1940611873/ref=asc_df_1940611873/?tag=hyprod-20&linkCode=df0&hvadid=312128022127&hvpos=1o1&hvnetw=g&hvrand=16834033085502338787&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026803&hvtargid=pla-680778681113&psc=1 https://www.amazon.com/Essential-Joinery-Important-Joints-Wo... While he has a ton of free content on YouTube, his guild site offers even more at a modest price: https://thewoodwhispererguild.com/ https://thewoodwhispererguild.com/ His Shaker Table project was my first "real" piece of furniture that I built. I've since graduated to designing and building my own furniture. Highly rewarding, and I owe a lot of my skills to Marc's wonderful teaching methods.

jugg1es 7y ago

Results are not at all surprising, but it's really great to see it done in a formal way.

zaphod4prez 7y ago

Matthias Wandel is just the coolest. Highly highly recommend watching all of his videos

MatthiasWandel 7y ago
That's right :)

MatthiasWandel 7y ago

Hey, cool to see my article on the front page of hacker news. Never expected THAT article to hit hacker news. Got a question, I could answer.

doctoboggan 7y ago
Just wanted to say I've been watching your videos for years and I am a big fan. Keep up the great work!
quicksnap 7y ago
I love your channel so much, and am so glad to see you here commenting! It's great that you continue to post videos. Thanks so much for combining two of my favorite things: woodworking and engineering!
longb4 7y ago
Hey there! Big fan of your articles and videos. I've been building box joints recently and even though the forces they're subjected to are not nearly as pathological as what you tested, I enjoyed your box joints and dovetails strength testing article: https://woodgears.ca/dovetail/strength.html https://woodgears.ca/dovetail/strength.html Quick question: do you recall what wood you used for the box/dovetail article? It looks similar to the spruce from the earlier joint strength article. I suppose using a stronger wood would just get you closer to where the glue is failing more than the wood, but I'm just curious. Less-quick question, feel free to punt/ignore: any thoughts on deliberately building in a very, very slight gap between box joint fingers? I would expect this to reduce joint strength (thanks to reduced force between fingers and surface area in contact) but potentially also mitigate wood stress from movement in service due to humidity. Though I imagine if a work piece is big enough for me to be concerned about movement in service, I probably shouldn't be using box joints!
- MatthiasWandel 7y ago
  I'm pretty sure that wood was birch. As for gaps in joints, if its a small gap, it doesn't hurt. I actually did some tests in that regard, linked from the article. http://woodgears.ca/joint_strength/glue_methods.html http://woodgears.ca/joint_strength/glue_methods.html A small gap actually helped. Probably because the glue soaks into the wood, so a joint without any gap sort of runs out of glue too quick (my theory). But it suggests that putting glue on and leaving the joint open for a minute may be beneficial.

exabrial 7y ago

Why didn't he join the screwed pieces with glue? I was always under the impression the whole point point of screwed joints is to stress the glue, not to actually bear load (Because of the small surface area and hardness difference of the materials)

btbuildem 7y ago
I've never used both screws and glue on a joint. It's either a quick and lame job and I'll use screws, or I'm making something nice and I'll go to the trouble of cutting and gluing joints.

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