A misunderstanding of the end-grain glue "myth" video?

by now many of you have seen patrick sullivan's fascinating video about end grain glue myths which turn the youtube world upside down with its claim that end grain joints are stronger than long green joints i know many of you have watched it because i've been bombarded with requests for my opinion and have held back on giving my opinion up to now for four reasons first my opinion doesn't really matter that much second there's not that much about his video i disagree with other than the conclusion which seems to have confused some folks third i saw that mark over at the wood whisperer channel already responded to mr sullivan's video so i recommend you watch that and i don't want folks thinking members of the community are piling on which brings me to the fourth reason i was hesitant to make this video generally when one youtuber responds directly to the video of another youtuber some folks can misinterpret that or even intentionally misrepresent it as some sort of dispute when that's not what it is but i've received enough comments about this to see that there is some confusion among my audience and i know this is going to come up in the future every time that i say something about gluing things together so i'm just going to get it out of the way and make this short video not to contradict or take issue with mr sullivan's video but to add what i think are some important points to the discussion and to clarify the subject for my audience by the way i'm calling him mr sullivan rather than patrick because i think that's just a show of respect to someone i don't know personally i know that might sound a little formal and awkward but i think it's good manners his end grain gloomy video demonstrated that a joint which contains some long grain such as when two boards are glued side to side or the end of one board is glued to the edge of another will break under less stress than a joint that contains only end grain such as when two boards are glued end to end he demonstrated this with several species of wood in a relatively controlled environment with special equipment it was very impressive i loved his scientific approach and i think it's a very interesting and valuable video i really am anxious to see other glue tests that he promised to do in this video mr sullivan clearly explained why the joints that contained long grain broke under less stress than the joints that contained only end grain but based on the comments i've seen many people seem to have missed those important details and they focus only on mr sullivan's conclusions did this video blow up the myth of ingrained glue for you i hope so but if you go back and you listen more carefully to what he actually said through the body of his video while he was making the tests you'll see that his test did not show that an end grain glue bond was stronger than a long grain glue bond the test merely showed that glue is stronger than lignin something that is well known in woodworking and forms the basis of the common saying that glue is stronger than wood but this distinction is important to understand if you're going to take this knowledge from his virtual laboratory setting and out into your workshop lignin is a natural substance that holds wood fibers together think of a piece of wood as a bundle of straws the direction the straws run is what we call direction of the grain and these straws or fibers are really strong it takes a tremendous amount of force to break a board across its grain because you have to tear all those fibers it takes much less force to break a board along the grain because rather than severing the fibers themselves you need only break the bonds between them those bonds are created by the lignin and this is the true weakness in wood it's why it takes many blows with an ax to cut down a tree but only one or two to split a log the lignin bond is far weaker than the wood fibers themselves so when mr sullivan broke a joint that was part end grain and part long grain it wasn't a test of the glue strength because the lignin in the wood failed well before the glue bond itself was sufficiently stressed the lignin was another factor that compromised any true test of glue bond that he was attempting when he glued end grain to end grain he eliminated that factor from the equation because the stress was then upon the wood fibers themselves which are extremely strong not upon the weak lignin bonding them together so that test could actually measure the strength of the glue bond itself because that's weaker than the strength of the fibers and it's no surprise that a cured glue seem is very hard to break when it is the only factor at play so put simply the first test was really glue versus lignin the second test was glue versus wood fibers themselves and because the wood fibers are much stronger than the glue we could see when the glue actually failed if you really wanted to do an apples-to-apples comparison those aren't the two tests you should compare you should compare the solid wood brick where there was no glue and he just broke the board compare that with the end grain glue test because only those two eliminated the secondary much weaker factor the lignin mr sullivan's video explains how lignin factors in i'm not criticizing his tests but a lot of people seem to have missed that part of the video and focused only on the conclusion and now whenever any woodworker says that an end grain glue joint should be reinforced with a tenon or a spline folks are going to say patrick sullivan proved otherwise but that's not what he proved and that brings us to why this isn't just a matter of semantics but a fundamental principle that woodworkers must understand mr sullivan reminds us that glue surface is not the only factor at play lignin between the long grain fibers can fail under far less stress than the glue itself but mark's video added important context to that discussion he reminds us that what is true in a laboratory setting is not always equally applicable in the workshop and two key moments in their two respective videos really bear this out i think a lot of us were surprised when mr sullivan measured the stress it took to break an end grain to end grain joint if i'm reading his table correctly it took about 350 kilograms or nearly 800 pounds of force from a hydraulic machine to break the walnut version of the joint but in mark's video he broke a similar walnut joint over his knee with what looked like not much effort now mark maybe he works out i admit it's interesting that i've never seen him and superman in the same room at the same time but i don't think he generated 800 pounds of force that easily something else was at play while mr sullivan showed lignin is a bigger factor in joinery than glue mark showed that leverage is an even bigger factor because we don't make furniture from just little pieces of wood the stress is rarely right next to the joint as it was in the tests mark further illustrates that with the example of a person leaning back in a chair and how that is really bad for the chair i'm going to illustrate it with the example of a mitered frame this joint is end grain to end grain in fact it's one of the few times that you would ever have an end grain to end grain joint in woodworking if you grab right next to the joint and try to spread the pieces apart you'll have difficulty breaking this glue seam but if you grip further away from the joint where you have more leverage this end grain joint won't be that difficult to break and it is that latter situation that is relevant to the real world for example who hasn't broken a frame by dropping it lands on the corner which exerts pressure on the ends of the pieces giving you leverage to break the opposite corner however if you introduce long grain to that end grain joint by means of a spline you'll greatly increase its strength so why does the long grain and mr sullivan's test weaken the joint but it adds strength in the miter example because the long grain in a spline crosses the long grain in the frame itself and it spans the glue seam as well so lignin is not a factor in that joint nowhere can it just break along the grain for the joint to fail the wood fibers themselves must be severed that's how good joinery works whether it's splines or loose tenons or other forms of mechanical joinery they take advantage of the strength of the glue and the nature of the wood itself which is strong within its fibers but weak within the lignin bonds between those fibers so if all you took away from mr sullivan's video was that he debunked the idea that end grain joints are weak you're going to be in for a rude awakening when you actually apply that to a project glue may be stronger than lignin but leverage beats glue and the natural cross grain strength of wood fibers trump everything a successful woodworker must know how to utilize all three of these factors to his advantage finally i think the most fascinating part of mr sullivan's video seems to have been kind of skipped over through a series of magnifications he showed that glue seeps into the pores of end grain potentially creating a stronger bond than may have been expected conventional wisdom holds that the open pores in the end grain reduce the total surface per square inch as compared to long grain which is a continuous surface this is a large part of the basis for the age-old claim that end grain glue joints are weak i'm not going to give away too much about his findings because i want you to go watch this video for yourself but this part of the myth definitely could use some more testing and i think mr sullivan is exactly the person to do that see you next time it's just a couple of cuts your ears will be fine right it will be if you have your isotunes bluetooth earbuds in because you'd already have your ansi certified hearing protection on because you're listening to your favorite music and podcasts and you're 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Channel: Stumpy Nubs

Views: 121,399

Rating: 4.926393 out of 5

Keywords: woodworking, stumpy nubs, tips, workbench, table saw, scroll saw, drill press, quick tip, band saw, bandsaw, lumber, hack, hand plane, sharpening, tormek, worksharp, diamond stone, water stone, wood turning, bowls, lathe

Id: dwLWmoGh59g

Length: 10min 32sec (632 seconds)

Published: Mon Sep 13 2021