Dovetail joint vs box joint strength test


So I’ve got here
a dovetail joint that I cut out
on my bandsaw when I made the video
about how to make dovetail bandsaw
joints. And, since I have
no use for it, I thought I might as
well test this joint. And I’m gonna test it against
this box joint which I also cut on
the bandsaw. It actually has more fingers but
it’s a smaller level of detail and it was a lot
quicker to cut because the fingers
were straight. And, while I’m at it, I thought
I’d compare it to a couple of finer box joints
or finger joints. That I made on my screw
advance box joint jig. These actually were
the quickest to cut. This one being the quickest
because I could just use my regular
saw blade. So, I’m gonna test these
on my testing apparatus. I’ve got one of the
joints already clamped on to it. And
I’m gonna use this jack to pump this thing
up until it breaks. And I’ve got this 3 to 1 mechanical advantage
on a lever here. So I can measure the force
with my bathroom scale. The bathroom scale only
goes to 300 pounds so I need that lever thing
to cut down the force so only a third of the force
goes onto the bathroom scale so hopefully, it will
still be within range. And I’m gonna
record the weight that I’m pushing on here
with a camera aimed at my bathroom
scale, so that if I miss the
maximum reading, I’ll still have
it on video. So, let’s test
these joints. OK, joint number 1. I’ve got the bathroom
scale…The zero set so that with the weight
of the jack on it, it actually reads zero. So,
I don’t have to subtract the weight of the jack, so
now let’s start pumping. Whoops. 20 – 30 – 40 – 50 60 – 70 -80 135 – 140 145 – 150 155 -160 165 – 170 175 – 180 185 185 This is where
it stops. 185 Yeah, that was it. OK, test number 2. I’ve got one of my box
joints in the jig now. So let’s see how far
this one will go. 150 160 170 170 I think it’s going. 170. There it goes. And there’s nothing
left in that joint. OK, here’s my second
dovetail joint. This time with the
camera very close up. Let’s pump
this one. 40 – 60 – 70 80 – 150 Yeah. 150 150. It just won’t
go past that. 150 And now it’s
completely let go. Now here’s my second
bandsaw box joint. 175 180 That’s gone. And it’s let go. And there’s no… Not much residual strength
left in that one. So, overall the dovetail
joints and the box joints did about the
same in strength. The difference is
really too small given the variations for the
sample readings to say that one is better
than the other. So the interesting thing
will be how well my screw advance box joint jig
joints do against those. And now testing the coarser of the two
joints I made with the screw advance
box joint jig. Now this joint is only half
the size of the other joints. So, if it takes half as much
force as the other joints, it’s actually already
doing pretty good. 40 – 50 – 60 110 115 120 130 130 130 Yeah, 130 is the
limit I think. Yeah, yeah. And this is
interesting, the joint itself
didn’t actually fail. It’s that my
wood came apart. OK, now this is the finer
of the joints that I did with the screw advance
box joint jig. Again, it’s half the size
of my dovetail joints. So, let’s see
how it does. 90 – 100 – 105 110 And there it goes. So that joint is… Yeah, nothing
left on that one. And once again,
interestingly enough, the joint itself stayed together
but the wood came apart. So, examining the
first of my screw advance box joint
jig joints, I did actually have some of the
wood pulling out a little bit. So, there was a minor amount
of joint failure in that one. But for the finer
one, the wood just plain old
tore apart. So, this is definitely wood
failure in this joint. I really couldn’t have made
that one any stronger, with the joint. Now the piece that actually tore
has got a much lighter grain so it’s a lighter,
weaker piece of wood. Which is why that
piece failed. And the other
piece didn’t. So, now comparing the
overall results. I put the two different
types of box joints from my screw advance box joint
jig in the same column. And I have to double
those because they’re only
half as wide. So, that gives me an
average of 240 pounds. Which is quite a bit more than
the other two types of joints. But, I’m actually kind
of impressed with… how close the other
joints came because the screw advance box joint
jigs are about as strong as you can get before
the wood fails. So that the dovetail and the
coarser of the box joints came to within two
thirds of that is actually pretty
impressive.

100 Replies to “Dovetail joint vs box joint strength test”

  1. LOL before you set up any equipment you might want to think about the joint profiles and the direction of forces. All I learnt was that any of these joints are adequate for decorative and general use woodwork.

  2. Thanks in a nutshell the thin fingers are stronger, but it's a choice of looks on the others.this was very helpful thanks

  3. I would like to see this same test done with all same section pieces to give it some control and animal hide glue. A lot have guys have said in the comments the dove tail is a phoney in modern wood working it may well be with all the advances in jointing technology or glue. That said however it's a very old joint that would have been practised when glues were entirely natural and had little strength how then would this test look?

    To the guys that have said that the dovetail is over rated, this is an inherently strong joint if cut well and to the correct slope for the timber. It is something all skilled woodworkers should do as it's something that creeps into a lot of forms of wood working I can show you dovetailed joints in fine cabinets and large building structures.

  4. What if there was a thin nail going alongside the joints all the way trough, or 2 from both sides, would it help the joint break faster or would it actually reinforce it? If you ever retest, I would like to see such a thing. I feel that the nail would be better to have closer to the inside corner.

  5. You have answered a question I have wondered about for a long time.  If I were to have bet, I would have guessed the dove joint to have been much stronger.  I also was surprised that the wood gave before the joint.  Thanks

  6. Next time do a traditional dovetail joint, there are no things like half tails, only a half pin on each side.

  7. @Matthias Wandel Just how strong is the wood? If you just broke a piece of wood on the thing without any joint, holding it in a slot. Would this be interesting to know? I know you can read the number on a chart, but testing a piece of the same wood used in the test might provide a better number to compare against.

  8. Very professionally done.
    The screw advanced box joints can't really be included because they don't necessarily share a linear representation of strength. Kind of like twine fibers to rope or a single toothpick vs a bundle.

  9. It should be pointed out that all these joints are freshly made, with glue that has not had time to dry out and become brittle with age. And Matthias is testing in Ontario, Canada, which is not overly hot and dry. Especially in a hot dry climate such as the southwestern USA, I would expect an old dovetail joint to be stronger than an old finger joint of equal age. The dovetail joint doesn't depend so much on the strength of the glue, so if the glue becomes brittle and cracks the joint still has a chance of holding together.

    Also, I don't buy that there is necessarily a linear relationship between the overall thickness of a finger joint and its strength. That's something that needs to be established empirically (by testing joints of identical design except for the thickness). The mode of failure in these tests was quite nonlinear. A few pounds short of failure the joint was holding fine, and then adding only a few more pounds caused total joint collapse with very little warning.

    It seems obvious to me that a joint's strength depends on both the strength of the glue and the strength of the wood. Therefore a strong joint probably needs a minimum thickness of finger as well as a minimum glue surface to hold against a given pound force.

  10. Hi Matthias, are you sure the test was okay for the last 2 box-joints? The wood broke instead of the joint, so can't we say there is an apex force value to which this test works. Also, I think if the wood used is thinner, the test can be improved since there would be more pressure on the joint verses the corner of the flat wood piece at the joint pushing the vertical wood piece. If there are thinner pieces, then the end of the flat wood can't press on the vertical one as much and the wood wouldn't fail. Hopefully I am making sense. Thanks.

  11. Actually I've been wondering about the stamina of the two different joint types. Thank you for the well-made video.

  12. I once tried something like this on fishing line. I found that knots greatly weaken the monofilament, while using a double sleeve with a cup to cup crimping tool maintained the entire test strength.

  13. when ever i make a box join i tend to put a 3mm rod right down the center do you think its necessary and dose it make it stronger? or do you think it would make it weaker.

  14. the more dense the joint, the weaker the point just before the joint begins. The denser joints aren't necessarily stronger, its just that their 'connection' with the rest of the structure is weaker.

  15. Entertaining experiment, but without any real practical significance, as I see it.

    Wood quality, precision of workmanship, sawing and gluing and last but not least the principle of the lever affects the outcome. The exact position of pressure points, loading points and benchmark points, are crucial for the value of the results.

    Therefore it is hardly indicative, but as I said still entertaining – and much better than watching TV 🙂

  16. have you considered trying to make some  isoloc hybrid dovetails? (maybe by hand because that is supposed to be impossible to do). it could be a good challenge

  17. could you not have re-tared the scale after every 50 lbs or 50kg (your choice obviously) to get around the 300 limit for future tests with more heavy duty things?

  18. it seems like the thinness of the finger make the wood more prone to breaking even though as you said the wood was a lighter grain. Seems like there would be some ideal finger thickness.

  19. I'm curious how much force it would take to break the strong joints if they're built with a harder wood. Likely it would be so much force that it would be dangerous to test with your testing rig.

  20. i assume the dovetail might be slightly stronger because the wood itself its hiting itself agianst the other piece of wood but for the sake of time its probabley ok to just do the box or finger joint

  21. How would one go about testing the strength, or I guess "pressure applied by" a clamp? Would a system similar to this concept work? I ask because the quick-release clamps at my local walmart (hyper tough brand) actually feel like they apply a fair bit of pressure for their low price. Just curious is all

  22. Is there any chance you would retest these joints using much stronger wood?

    It looks like the species of wood was a soft wood that seems to be lest strong than some hardwoods. Or am I off with this train of thought?

  23. a strong joint made from weak wood will hold even after the wood breaks. a better way to test the joint strength vs the wood strength would be to put the jack right against the joint itself, right in the apex, so it rubs against the perpendicular member as it pushes against the horizontal member. eliminate the mechanical advantage.

  24. surely the one with the most fingers would have the strongest hold because there is a much larger surface area with glue on it.

  25. Matthias, I enjoyed your performance tests on glued joints——I would suggest that you should include another column that would compare the total width of all the individual fingers on each piece that failed as the strength of the piece is only as good as the width of all the wood coming out of the joint,——— assuming the glued joint does not fail.
    Keep up the good work!
    Vince

  26. These videos are so great. It puts some science behind the work and helps us to know what joint is better.

  27. I'm curious to see how the finest box joint technique fairs with much harder wood, like Jatoba, and perhaps a stronger glue or some epoxy. Would make an interesting comparison to the cheaper wood. If anything it would eliminate wood failure as a variable and would show purely the strength of the joint. With the wood failure variable eliminated, maybe you could test various strengths of glue as well.

    Very curious on this. Maybe if you run out of creative ideas you could do a bit of testing like this sometime.

    Love the videos and the inspiring creativity in them.

  28. Depending on the wood, there must be some perfect ratio between the number of teeth (hence the glue area) and the strength of the teeth. Wonder it there is a way to calculate that rather than to a lot of tests and draw trend curves. =/

  29. critic is here! thats not same condition. it depend on wood. annual rings. knots… and pressure running time is not same. this experiment cause prejudice. its not scientific experiment.

  30. what happened to the world?
    Doing YouTube search for box joints and getting all this drug related nonsense?!?

  31. No one will understand how upset I just got to see this video and see it was before the improved joint strength test methods. Nor will anyone likely understand why I enjoying watching videos testing differing joint strength

  32. Another critic here 😉 For a change I question the selection of the load configuration. Did you think this kind of load is predominant in a used box/chest? Other reason?

  33. that really only showed the glue strength, and good tight dovetail joints shouldnt need glue. But cheers for showing, great idea using the jack and bathroom scales. simple, cheap and a great idea. Cheers mate

  34. That wasn't quite scientific test. At least, the way you push and speed of jack must be constant, and first crack, second crack and final separation should be considered as well. It will give us a graph which is used in lots o purposes. More glued area in a joint, will change result of a equation.
    I'm a fan and i love your channel so much, Don't consider it rudeness plz
    and sry for my poor eng 🙂

  35. I want to make a cubic box with the edges made of hardwood and the panels of light ply. What is the best way to join three pieces of wood at the corner of a cube? I couldn't find a video showing how to do it, so I'd appreciate a link or search string.

  36. The strength of the joint strongly depends on the number of the "glued surfaces" and hence, to compare dovetale joint with box joint the number of fingers has to be the same. If the dovetale joint reached the same strength as the box joint with less fingers it means that it is stronger. This observation is also explains the reason why the box goints with finer fingers didnt fail at all – they had more glued surfaces.

  37. wow i really thought the box joints at the end would do alot better than the others. hmmm…. i also wonder if you wouldnt' see more dramatic effects by using a much stronger wood like a really heavy maple? then maybe you'd see more results directly from the topology and not the wood fibre failure?

  38. +Matthias Wandel Is it possible to make a three way dovetail joint? For example if you were to make a T shape out of either two or three pieces and they were connected by only dovetails.

  39. Would it be more accurate to calculate the result in NM? What happens with a piece 200mm long will be different from that of a piece 400mm long (roughly half the KgF) but the NM would work out roughly the same. Sure you demonstrate which joint is stronger but it would be interesting to know what the actual forces the joints can take are.

    Long-time listener, first-time commenter. Absolutely love your work, even my GF knows how to build a bandsaw now.

  40. Have you thought about running two dowels across the fingers to prevent the joints from pulling apart? Try it with just a few fat fingers so that you leave more wood for strength.

  41. I thought that the surface area of the latter joints would aide the glue and it did, but I didn't consider that the smaller joints would become points of weakness. Very interesting, thank you for the video.

  42. do you think it makes a difference if you are prying up on the horizontal seam rather the vertical seem? i noticed that was a variable not taken into account

  43. For comparison, it doesn't matter but aren't you measuring torque with the joint as the fulcrum? You don't seem to be pushing straight up.

  44. it'd be interesting if you did the test again, but compared hounds tooth dovetails vs boxjoints, I have found that hounds tooth are much stronger than normal dovetail joints.

  45. Mathias, what type of wood were you using? Do you thing straight grained walnut or maple would of held up better? How well do you think the test would of gone with the addition of dominos?

  46. I like this test but was all the numbers multiplied by 3 to get the actual pounds? I am looking to use a joint for a door in a door shelf system. Which is the strongest?

  47. I honestly think this isnt that accurate… With you only barely tightening the jack release but by fingers u can see the pressure drop every time u pump and i saw higher numbers before any cracking noise but seeing the pressure was dropping u was going with lower numbers.. One for instance is one of the ones u put as 180. That reached 190 before the pop.. I just think b more accurate tightening with pliers or something. But always love ur videos… Keep them coming.

  48. I don't know if someone mentioned it, but it seems that the failure is mostly due to the twisting moment on the joint. In most situations in woodworking, it seems that the twisting moment is not the most destructive force because the wood structure is supported on both sides like a drawer. I wonder if the results change if you support both sides. I love the channel btw.

  49. The wood isn’t as strong as the joint so use oak, ash, or orange orange so wood failure doesn’t happen before joint failure

  50. Technically though, I do work with wood. (thinking to myself about why I watch this channel if I'm not a carpenter) great channel 🤗

  51. you think the numbers would've been any different if you were trying to get the joint to fail in the other direction? if you were squeezing the joint rather than spreading it apart?

  52. Don't you actually have to multiply those numbers by 3 to get the actual load bearing strength of those joints?

  53. There is that old adage that states that the glue is stronger than the wood. All of these joints were glued. Even though some had more contact surface than others they were still glued together. It would seem to me that the glue would turn the wood into a homogenous substance that was basically one solid piece. As though it was never two pieces. All things being equal and in this test they were not as pointed out that some wood had different growth patterns. IF all things were equal, why wouldn't the breaking point be the same on all?

  54. The precision of the joint & the amount of glue bond also matters–as does the wood sawn type & strength of the wood.

    I like your measuring setup.

    Thanks for sharing!

  55. I suppose that wood species may also make a difference, grain structure cellular composition, etc. Is this experiment statistically representative of the wood species or the type of joint?

  56. The pieces of wood are made of different wood strength. If the point is testing only the joints why just dont make the same experience but with a different Material that can be uniform in all pieces in order to be possible to compare properly only the joint force without any Interferenz because of the different wood pieces used. Or try inspect properly the wood used to use pieces as similar as possible . you can just use PVC parts for example. The results will be More acurate. A joint made from wood must have same behavior. That simulates the behavior for a optimal uniform wood but just in other schale.

  57. Everyone is talking about the viable. I'm still trying figure out why he has two half tails as opposed to half pins on his dovetail joint.

  58. Very good and informative. I noticed that you had some glue failures in a couple of the joints.  
    Make sure to always glue both sides, use enough glue on each side, clamp for at least 6 hours, and finally, use a good glue. Glues vary significantly– even among a given type.

  59. This test is a bust. The discontinuities in grain structure don’t make this a valid test. I have yet to see a proper box or dovetail joint fail. Accurate fit up and glue dispersion is the catalyst.

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