Was I Wrong about Glue Joinery?

Sometimes the best way to find things out is to perform your own testing, which is the reason I purchased my Hydraulic Press a few years ago, which didn't cost me a lot and I have used it a few times in testing furniture and other wood joints which of course I share with others so that we all can learn from what I find, which in this case was testing the construction grade 2x4s that I talked about in a video a few weeks before this one, and how that using 2x4s for furniture is not the best idea because of high moisture content, which leads to severe wood shrinkage, and just the fact the softwoods are not very strong, so I joint tested Cross Lap Joint, a Dowelmax Dowel Joint, and End Grain Joint and a Pocket Hole Joint to see how strong each of them was, then I went on to test other laminated wood to see if gluing made any difference to the wood strength with these woods, all very interesting results.
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[@GiovanniPerini]

When you try to bend a beam with a weight in the middle, fibers on top are compressed, and bottom fibers are stretched. Bottom fibers are the ones witch fail first. Oversimplifying a little, fibers in the middle are not stressed at all, so they do not add much to the resistance of the whole; that's why a tube is not much weaker than a cylinder with the same diameter. So the glue layer in your experiment were almost irrelevant for the resistance of the beam. You may try to test an asymmetric joint, with a thinner bottom wooden part, but I suspect that even in this configuration the glue layer would just be to thin to make a difference.

[@billj5645]

There is a horizontal shear stress acting along that joint, but the joint has a lot of area compared to the amount of force it needs to transfer so the shear stress is a low number and easily carried by the glue. In a rectangular beam, horizontal shear stress is actually highest at mid-height of the beam. If you make an asymmetric joint with thinner bottom part, there is even less shear stress on that joint. There is an equation for calculating the shear stress along the joint based on strength of materials principles. The equation is v=(VQ)/(IT).

[@contessa.adella]

Which

[@claudiodigregorio4315]

Years ago I read that wood is stronger in tension than in compression, so in fact the compressed top fibers will fail first. However, we don't notice the failure because the compressed and crushed fibers have nowhere to go, so though weakened already, they will stay until the bottom fibers fail in a visible way. Or so the book said.

[@oldkingcrow777]

Isn't a tube a cylinder??

[@oldkingcrow777]

@@claudiodigregorio4315 wood is cool, that rule is dependent on grain situation iirc

[@TheSuburbanGarageWorkshop]

Colin, thanks for the shout-out about my Power Drill Shield! Greatly appreciated!

[@Ryan_Thompson]

Colin I'm struggling to understand your testing methodology in this one, especially with the "lap" joint that was cut away to lose most of its mechanical strength leaving only the end grain mechanical portion that, if anything, acted as a fulcrum to help pop the joint apart. Were you just wanting to do more testing on (more or less) pure glue joints? Anyway, I must have just come away with the wrong expectation from the first bit of the video, and the pocket hole test, and that's on me. I was hoping you were going to test some actual mechanical joinery with and without glue to see if (and how much) the glue helps. Video suggestion for your rainy day jar, perhaps? 😉 But hey... don't get me wrong. I still enjoyed the vid and learned a thing or two, so that's a win!

[@unholyarmyofone]

From the intro, I was expecting to see something like a comparison between dry fit joints and glued joints and seeing how much of an impact the glue made. Obviously that wipes out a load of joinery that just falls apart without glue, but I was also thinking about the difference between screws only vs screws + glue etc.

[@martinsvensson6884]

It was to test how strong the glue is compared to the wood. Then you cant have other factors unloading the glue stress.

[@petec6690]

I would like to see the difference between glue joints using the same exact joint. One joint is to have glue and be clamped lightly versus one that has been tightened to where glue squeezes out. Most interested in how much difference there is. I've tried clamping the snot out of joints and have never had a failure. I've had joints that were clamped lightly with a spring clamp and those have come apart under pressure. I don't have the equipment to test for myself. Since you're well equipped, I'd like to see those differences.

[@brianstevens3858]

Me and my grandfather tested wood joints of about all types back in the late 60's, and I know that modern glue is far superior to what we were testing, but the only joint where glue actually strengthened the joint significantly was finger/box/ joints. With a good glue up being more important than anything but the actual wood involved.

[@pinkerbot]

i don't understand the 'lap joint' test at all. It was just a test of a glue joint for two boards glued perpendicular to each other, long grain on long grain!

[@ShariHardinger]

I would love to see the lap joint test with the initial lap joint just out of curiosity

[@DavZell]

Right. He's not testing a joint in this one.

[@Mr_Rick]

The lap joint test makes no sense. The meat you cut away in reality still provides tension, compression, and shear strength to the joint. If you're going to test a joint... Test it as it is.

[@christophermcclellan8730]

Yeah, you can’t compare that cut out as a “lap joint” to the dowel joint. The dowel joint had a chance to redistribute pressure.

[@FamilyMentors]

Good point. What makes a lap joint strong is the part Colin removed, I thought.

[@jaayjones5937]

Because you had and interest in testing glue and joints I have a suggestion that would be of wide interest. Woodworkers have different methods of removing excess glue from joints. There are those that let the glue setup and then use a chisel to remove the excess. Others just wipe off the excess and finally there are those that use a wet cloth to remove the excess. It has been stated that using a wet cloth dilutes the glue in the joint and makes it weaker. I think it would be interesting to test that theory. Glue some 1x4's edge to edge and then remove the excess glue using the different methods and determine which break easier. Use several boards for each style rather than relying on just one set.

[@JustinShaedo]

I'd absolutely second this. Wiping with a damp rag gives so much easier and better visual results, but everytime i wonder 'am I weakening the joint?'

[@skipanardoross6805]

I'd like to see that, as well. I am in the wet cloth category and I'm not only curious about weakening the joint but saw where it could sabotage the finish by pushing glue in to the fibers along the edge of the glue line. I haven't noticed that in my projects but I can see how it is possible. I should note that just because I haven't noticed , it doesn't mean it wasn't there. My skill level is intermediate, at best.

[@allwoundup3574]

"I modified this lap joint so that it's no longer a lap joint"

[@jimmacaulay844]

Colin, nice video! The horizontal test does not test the glue joint AT ALL! The glue was entirely in the "neutral axis", as structural engineers call it. In that plane, there is no stress at all and does nothing, assuming it's precisely in the center of the board (as much wood above as below). We saw that the failure was at the bottom, where tensile stress is maximum. At the top, compressive stress is maximum. In the center it's the average of the top and bottom stress, which is zero. Think stress is 1 at the top and -1 at the bottom, and the average of 1 and -1 is zero. There will be some effects of the piston distorting the wood at the small area of contact. For a fairer test you might distribute the load with a small block of wood.

[@aprildegele1510]

Question about the second experiment. I'm assuming you're only testing the glue, but that doesn't account for how strong the glue in that joint is if you cut away the joint. I get the glue test, but it's really not a true test of a glued half-lap. Did you try it without destroying the integrity of the joint? I mean, the glue held perfectly well (larger surface) and only the wood cracked, so that would actually prove that adding glue to a half-lap is effective in strengthening the joint if the glue held in a half-lap that's not a true joint. I also understand that this is a demo as to why soft woods aren't used for furniture, but it's also not a very good experiment to demonstrate the joint or the glue. First, you have no baseline for the difference in wood. And there's no glue comparison with something like Walnut over pine or fir as a visual. What glue did you test? How long did you let it cure before testing? I'll assume at least overnight. I appreciate the demo as it's a very good demonstration, but the stated goal wasn't met because there's nothing to compare it to other than different versions of itself. Just me being picky in pointing out that this experiment, while very useful information, hasn't really demonstrated whether glue makes joints stronger or not. Just sayin'. No offense. A better experiment for the half-lap, for instance, would be to test the glue against the weakest point, which would have been to turn it side ways and see how much pressure it would take to dislodge by pushing down on the wide side. The weakest place for the joint would be if something were sitting on the top-lap joint board to see how long it takes to lift. Physics is important in demos like this.

[@JLneonhug]

Hmm the message was difficult to understand but if you know that wood glue is equal or stronger than wood fibre, the weakest point will always be the wood. It doesn't matter which glue orientation of the glue. The wood grain would play more of a role I thought. I thought that's why laminate sheets they stack it at 90s or 45s to each other.

[@robgullen]

Agreed that it was a bit confusing as to what was really the point of the tests and the video's message . .

[@Dutcharmytent]

Colin, I used to do strength tests for a living in building product research for a major UK company, and you need to suspend a weight off the beam. A bucket filled with water as a weight is good. Using a hydraulic piston will intermittently put pressure on. With a weight pulling down the pull is constant. That’s how we did it and I was building the jigs to do these tests.

[@billj5645]

Regarding your test of the long pieces glued together (laminated)- the strength will be only a function of the outside dimensions of the final piece. We make various types of things with laminated wood for structural purposes such as glue-laminated beams and LVL beams. There is very little stress on a glue joint that is parallel to the length of the member so it is neither stronger or weaker than the wood that it is made from, unless the workmanship in the gluing process is bad. Laminated lumber can be stronger overall than the wood it is made from because the individual pieces that are laminated can be chosen to limit the defects in the wood making higher quality wood than if you just sawed a large beam out of a log. Allowable stresses in glue laminated lumber can be much higher than allowable stresses in sawn lumber.

[@hansangb]

That drill sawdust thingy is awesome. Just ordered one. Thank you!

[@sambiscits6711]

On the half-lap joint, I'm wondering if it could have taken more pressure if the material had not been removed from it. I love Forstner Bits, but they create a lot of chips, and that little box with a vacuum attachment works well. As you plainly showed, I went and ordered one.

[@gregre052]

Another agreement, not much learned. Some obvious some have conclusions that don't give a sure result.

[@1996SST]

Liked the video. I would like to pick up the drill shield but I didn’t see a link?

[@MCsCreations]

Fantastic testing, Colin! Thanks! 😃 That little thing for the drill press is just brilliant! Anyway, stay safe there with your family! 🖖😊

[@vashon100]

Really? He couldn't even read his own pressure gage correctly 600 vs 500. And why bother with that cut up lap joint? And one of his vertical boards for the right angle test was tapered.

[@apmgold]

In the test with the dowels, the dowels provide a mechanical element that works with the glue. Is this not the same principle as the half-lap and glue joint that you originally tested. So if I'm missing something could you please let me know where I've lost track. Thanks for the effort you put into this video, it's really appreciated as are all your videos. I also appreciate the support you have given to Kevin and the production of his drill shields, I hope he has great success with them, they will surely help keep the workshop cleaner.

[@baldeagle5297]

I've used 2 x wides for furniture for years and never had a joint fail. Of course, I only use lap joints and tenon joints with the occasional dovetail and box joint. Well, I have had to glue up tops, but for that, I either mill a tongue and groove or biscuit joint.

[@JackJack-sh2jv]

Something you forgot was having a control piece of how much it takes for a unaltered piece to break so you know if it's the wood or the glue not holding

[@watchman1969]

in my opinion the lap joint do not require that modifications to be tested, in fact, what makes it really strong is exactly those fittings

[@CyberBobCity]

That Power Drill Shield is soo cool!!

[@gnic76]

I've never thought a laminated 2x2 would be stronger than a natural 2x2 only that it would resist warping and twisting better, while being cheaper dur to not having to buy thicker wood.

[@doc2help]

??? did you not cut away the magic of the lap joint in that application??

[@ot9180]

Why would you test any joint one sided? Not attached to another vertical beam?

[@paco473able]

I think a better test of the joints would if the beams were supported at both ends like they were in the latter tests. The first tests are not how a glue joint would normally be stressed in a real application. The numbers would be much higher.

[@whadafoxhat]

ironically the joint you expected to be the strongest, is the one least likely to be affected by the glue content, insomuch as the bottom of a loaded beam is in tension, and the top is in compression, and the centerline is in effect neutral. The Glue therefore has no impact on the parts of the beam that are subjected to the greatest forces, and are less likely to impact on it's overall strength. The "vertical" gluing will have minimal effect, simply because the cross-sectional area impacted by the glue is relatively small. So the overall differences between the examples shown would be predictably small [as they were]. Assuming, as it appears, that the glue is actually stronger than the wood, then the biggest impact would be to glue a strip of wood, top and bottom of the beam, in the "horizontal plane", hence moving the glue to the region of highest forces experienced by the beam

[@dj-bn1fj]

Your half lap joint was no more then a 2x4 glued on the side of each other as you cut out about 90% of the support for a half lap, I use half laps for my wood storage with a lot of heavy weight and it don't move at all. Could you retest with a true half lap please, thanks

[@rjtumble]

It's awesome when you test your own assumptions, thanks for doing this. I wonder if that lap joint failed as quickly as it did because of the knot that was very close to the split? The drill press thing was pretty cool, I'll check it out, thanks.

[@chalcedony6858]

Great experiment! I really loved watching this.

[@cindyharrison4191]

Your not telling the joint. Just crossed grain glue

[@peterdejoseph5197]

Your lap joint lost its integrity when you cut away the areas on your test piece. You should have done it in one piece. I did the same test and it broke where the joint met each other.

[@Bapuji42]

A factor not being accounted for here is the difference between slowly increasing pressure, and a sharp impact.

[@geiraarum2900]

Thank you sir. I enjoyed the experiment.

[@richardmilner4392]

You have a long tip marker you use. Can you tell me the make and model of it please.

[@hassanal-mosawi4235]

Thanks for sharing those tips and the make!

[@erallen97]

Great test, the results were interesting.

[@stephendonathan6782]

Great test thank you for doing this! You should check out Patrick Sullivan's test on glue joints. Take care and GOD BLESS 🙏!

[@TheS4ndm4n]

I was going to say the same thing. Patrick did a really good job of testing the strength and value of glue joints as scientifically as possible within a reasonable margin.

[@DanielHalsey]

Love your videos, Colin, and I know you're not using literal or even figurative tons of force on the press, but please wear your safety glasses where they'll do their job if needed, not just around your neck.

[@joebrown1382]

Very informative Colin thanks.

[@squarelevelplumb]

I think the piston needs to be the same distance for the vertical board

[@jimcy1319]

Looks to me on the lap joint test that all your testing is the glue. 🤔

[@thomasconetsco361]

Did you test different glues?

[@stevej00]

Colin, great video. Testing with a press is always fun. I hope Kevin has filed for a patent. Great idea!! However if you really want to test with the press it may be more useful to translate the psi into foot pounds of force. If the portion is 1.5" dia. 200 psi is around 115 true final psi. So 115 psi at about 6" is about 57 # at 12". Translating this into real world applications could be really handy. I'm a hack engineer so I may be entirety wrong but may make for some interesting comments.

[@farrier2708]

It would be even better if Colin used Newtons, which is the Standard International (SI) system of measurement,

[@tonysheerness2427]

The old story you can break one twig or two twigs but a bundle you can not. On your experiment you were testing the wood not the glue. You need a set up that tests the glue

[@martinsvensson6884]

"625 pounds of force"... per square inch. I'm assuming. If you're going by the gauge. Would be more relevant to know the actual force. So the number needs to be multiplied by the pressing area.

[@rayheinrich1504]

what is the name of that tool for the drill press you showed and where can I get one thank you

[@tysonkoehn1]

Although this is interesting information, it is probably the least scientific testing I have seen on this topic. Barely any useful information since there was no specific data given about any "test." None of these were under normal building scenarios, especially the lap joint test with all the wood cut away. The dust shroud is cool though. Seems pretty delicate, but a nice idea.

[@coreyjames5541]

Ok so a couple things gs here number 1 wood is reaaaaaaly hard to strength test. The reason being the grain structure growing co ditions growing location. These tests while a great idea in theory are really flawed. A 2x4 from my area is going to be much weaker than a wetter climate. So many factors go I to this it's nearly impossible to test.

[@epeiusgarage]

I’m sorry but I feel these are not accurate at all. When you removed the wood around the lap joint you removed the key elements that makes that joint stronger. It wasn’t a lap joint at all. Then the horizontal test is not testing the joint at all. It’s testing the wood. Of course that joint would not fail sandwiched between. There was no force pulley that joint at all. Same with the vertical joint. Just my 2 cents.

[@goodyoga]

Glueing endgrain is useless (very weak). Glueing crossing long grain is also useless (still weak). Glueing pallarel long grain is usefull. i.e. stronger than original woods.

[@bobwatkins1271]

My biggest takeaway from these tests is that wood is weak in tension.

[@fernosan]

There's a paradox: The tighter the joint, the better the glue performs. However, I think the looser the joint, the more effect the glue has. Call it the 'shim effect'

[@dymosfet8477]

Thanks, Now i know that laminated guitar necks is not superior to a single piece. Except for aesthetics.

[@charlesbrewer6552]

The lap joint relies on the mechanical interference built into the joint. In my opinion your test philosophy is flawed.

[@jacktupp1427]

Your methodology is flawed, that is, you must use the same piece of timber cut up to make your test pieces. Not scraps from different pieces glued together. Your results confirm this to be correct. Also, you must use the glue the same way with every test piece. Or run multiple of the same (end grain to long grain,) with different gluing, fixing methods.

[@alanrichardson7244]

Common sense tells you the softwood will fail faster than hardwood.

[@Woodwork-Learner]

Your tests show only that joinery joints are better than glue alone. If used correctly all joints work enough to take a fairly large load but will fail if too large a load. Bit pointless first few tests really. The type of wood and grain direction seems to dictate the breaking strain. Saying that without you testing we would not be able to come to that conclusion. Nice drill extractor.

[@baudgaud]

I am really just confused by what I am seeing here. Your pressure point looks to be no more than 1" diameter, so when you pump to 200 pounds of pressure you are exerting FAR FAR MORE FORCE IN A MUCH MUCH TINIER AREA than any real-world source of 200 pounds of pressure. Additionally you have placed that tiny point a few inches from the actual joint itself, and the piece you are testing is not a "crossbrace" as found in real-world applications but is just "an unsupported beam" so you are not testing shear forces or anything actual or even virtual... This presenter is literally testing whether a structure which would not exist in reality can withstand super-concentrated force which would also not exist in reality. The presenter is then calling this some kind of test of strength of a glue joint. All this tests is the stupidity of any viewer who gave the video a thumbs-up.

[@marcbarash6045]

comment

[@themeat5053]

Talk about beating a dead horse. We running out of topics?

[@markg3305]

I respect alot of your videos but this one just needs taken down lol for one why would you ever test a lap joint like that. Two you can't run tests with 0 respect to the mathematical change leverage adds to the mix

[@vashon100]

The silly faces on your thumbnails are dumb.

[@jason4547]

Your testing rig is acceptable but your means of testing was flawed on so many levels Given your age and experience level. One would assume your intuition would be in par. Or maybe you just didn't put much thought into how this testing should've been performed... /shrug

[@Sigmund1924]

I’ve been watching him for years and it’s the only time I’ve been left disappointed. I honestly think he rushed to do this one just to plug Kevin’s chip collector at the end.