Do Splines even DO ANYTHING?? You will be surprised!
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- Опубликовано: 13 июл 2024
- Miter joints are very common in woodworking, especially in picture frames. These joints are said to be weak because they are essentially end grain glued to end grain, so they are often reinforced with a spline.
Do splines add strength to a miter joint? Everyone assumes yes, but in this video I test whether or not that is true, and the results really surprised me.
I am very interested to hear what you think of these results, since they are very counterintuitive. Please leave your thoughts in the comments below, and perhaps I can improve this experiment and shoot another video on this subject.
Thanks for watching!
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Statistic guy and woodworker here. I actually did this for a project in my one college class. Tested this same thing in a similar way with similar results. I found that using epoxy (5-min kind) as your glue without a spline was the strongest joint. My thoughts are the epoxy is thick enough to fill in the end grain and seal the pieces together.
Awesome, I'm a statistic guy and woodworker too, also named David K 😅 Very interesting theory with epoxy filling end grain! Thanks for sharing.
I am not statistics guy hahaha, but same experience here, epoxy expanding glue like gorilla brand makes marvels in end grains joints like that. Anyway, splines are beautiful and I will still use it anyway 😆
I have never seen a picture that weight over 100 lbs. that’s why I know that the splines are only to Make a frame looks good.
Maybe you should could test the joints with force applied perpendicular to the face of the miter as well. I bet it is stronger with splines when tested that way. It seems that with splines, they should not pull out if fit and glued properly. They should break before the glue joint fails as was shown in your tests.
Agreed. That's a good idea Rick I will try applying force from different directions next time 👍
@@dkbuilds watch Patrick Sullivan's videos, it's most definitely not the end grain (unless the glue is shit)
I only have a minor problem with your test and that's how you broke the joint, you applied pressure from the inside of the frame instead of the outside. The difference being that it's meant to resist outside force not inside soooo I'd really love a retest
Ryan _ this was my thought. Spline joints tend to pull away from each other. So testing this force would be the best way to answer the question.
I don't think it matters. Consider an infinitely thin miter joint (imagine two sticks connected in an L-shape) and note that regardless of the direction of the force, the torque magnitude is the same. The only difference is the direction of the torque produced, given by the "right-hand rule" when you take the cross product.
I want a retest too. I logged in just to comment about that. This was really good
Thank you for making this video and testing it out!
Thanks for watching! I love that toy helicopter you recently made on IG. I plan to make a similar wooden toy as a gift in the near future so I'll be coming to your page for inspiration and instruction!
Fantastic video David! So glad Kalika finally told me about your channel!!
Haha thanks for watching Kyle!
I was watching closely, but couldn't see if the splines were breaking. The grain of the spline should run across the miter. And as some other fella pointed out, they should have been clamped to compress the splines in their grooves. But I myself have wondered about how much strength they added. But I couldn't bear to bust one of mine up. I did glue up a 1/4 thick walnut frame that I cleaned the miters up on a shooting board before gluing. That makes for a real nice gluing surface. I couldn't break the frame apart after it dried with my hands. I think there's a lot of variables in deciding if splines are really good. But like you, I'm gonna keep using them . Nice video guy
Great video, I have always wondered about this
I was under the impression that the friction of splines also helps with reducing the movement of the joint over time with humidity as well, which is much more difficult to test for. In theory they also help wirh reducing the impact of any torsional flex of the the joint.
Maybe placing a clamp on the spline (the face and back of the frame ) would increase its strength?
Yeah I noticed that, and how easily they slid in to begin with.
Maybe the glue needed more time to gain full strength?
Strength is not necessarily the purpose for splines, in the sense that the addition of a spline increases the overall strength of a joint. Though I will disagree in that like any joint, if a spline is done properly for the particular design, it will increase strength, even if minimal. But you have to consider what the project is and determine the best joint per purpose. A drawer will almost never be mitered, because it is inherently weak especially when compared to a dovetail. Picture frames are decorative, with the standard if you will to have a miter joint adding in uniformity and a pleasing result. Application is key when determining what joint you will be using for any project, so it is a weight of aesthetics and strength.
Picture frames do not typically see activity, nor experience any force requiring strength similar to what a drawer would. Accepting the aesthetics, your intent is not necessarily increase strength where it is unnecessary, but instead create a joint that will increase the life of the project, meaning last longer without failure. Since they hang on the wall, or sit on a desk, the forces picture frames typically experience is environmental, being temperature, moisture, etc. This is why it is also critical to finish/seal your entire picture frame, meaning front and back. We all know wood moves, and that movement can have a greater impact on lesser joints like a miter joint, so the spline if done properly will actually help prevent lateral and opposing movement by holding the position of the wood in place and minimizing failure of the joint. Popping the frame appart like in your test is not really applicable, in that it is not real world forces that the picture frame would see. Instead, as you later said, even with abuse of dropping a picture frame, the spline will hold it together, which helps prove my point that you are merely trying to prevent failure, and minimize movement, not increase the overall strength of a joint that will never unless abused see the forces required to bust the joint. Especially with moisture, most joints tend to allow the most moisture into the wood more here than the wood itself, and end grain will see the most movement, expanding greatly. The spline not only limits this, it also helps keep the joint aligned, allowing less movement, which means less stress on the joint. So in effect, even if your test shows a black and white concept of no overall gain in strength, this is just not true. Splines do offer incredible value if done properly, and are visually stimulating as well.
I have woodworked my entire life, and even received a partial scholarship in it (bet you didn't know those existed). I have projects I built 40 years ago with splines that still are holding, where other joints that should be stronger show failure. In the end, the most important factor in achieving a durable and strong joint outside of what joint you use, is accuracy of joint. That is to say ensuring the joint mates perfectly and joined together without stress (more clamp pressure). Joints don't have to be perfectly 45 degrees to mate together, and especially with picture frames can be difficult. This is why building a miter, or picture frame jig can offer the best results, even if you don't hit that perfect 45 degree mark. Instead, you need to ensure the frame fits perfectly, meaning the length of the sides are identical, and it is perfectly square. To do that you just make sure you cut the mating parts on the opposite side of the jig, meaning if you number every joint on your frame, you cut odd number on one side of the jig, and even on the other. Often people will try to make up for less than perfectly matching parts, be it a less than perfect miter angle, lenght, or whatever by increasing clamp pressure. That can work for a while, but in doing so, you have already created a joint that has much stress working against it and fighting it, so add moisture, temperature, or even just time and it will fail. Clamp pressure is the enemy of a good joint as it not only makes up for imperfect components, it squeezes more glue out. Depending on wood, edge grain (not end grain), should be almost if not as strong as the wood itself, so this is one joint that should never fail, yet to much clamp pressure, or an imperfect mate will do just that. In fact, many would be surprised to learn that I will often use tape when gluing miters on boxes and even picture frames. To do this, you lay the inside of the miter down on the surface, and line all the parts up against a flat edge. Butt together while pressing firmly and simply apply blue tape over the ends. it can be doubled for strength as well. If your parts are cut perfectly, and it is square, then once you add glue, you can simply close the frame, tape the last corner, and you will have a joint that will stand the test of time, but will also be perfectly square.
That brings me to my final note. Project durability and strength comes down to not just the joints and construction techniques chosen, but the quality of those cuts. In school, I would often be pressed by other students, because before using the equipment that was abused by many, I would always dial it in, meaning brake out the square and indicators adjusting it to make it perfect. It is every bit as important to ensure your tools are accurate, so that your joints and cuts will be accurate. Glue up is not the time to makeup for inaccuracies, or hurried cuts, and will be the difference between a bad, good, or excellent project that stands the test of time. So, add a spline, or add a mechanical joint, but recognize neither will work, or even be as strong as the lesser option if done improperly.
Thank you for the extremely detailed and well thought out response BP. Lots of great points in there. Hopefully other viewers see this comment and learn from it, like I did!
Something I always just took for granted that splines added quite a lot of strength. Very interesting to see that isn't necessarily the case. Seems (as you point out) that the "strength" comes mostly, if not all, from *not* having a total failure. Damn glad you did this, Dave. It was a very well done video, covering every aspect of this topic I can think of. Always love your video style.
Pretty much the same as you, I will continue to use splines for the aesthetic as much as the strength factor. They just look cool, whether there is any other added benefit or not.
Thanks Don! All I want out of my videos is to spread knowledge and share things I have learned myself, so I am particularly glad to see your comment here. Keep up the good work yourself!
@@dkbuilds Just trying to keep all my fingers hehe.
I should point out that what the testing showed is that reinforcing a softwood joint with hardwood probably does improve the strength of the joint a little.
To really test to see if splined miter joints are stronger you'd have to test using softwood splines in a softwood miter joint and hardwood splines in a hardwood miter joint. What is more, it should be the same wood as being used for the miter joint, not just a hardwood or a softwood.
I would expect a joint reinforced with hardwood to be stronger than a joint which is not reinforced with hardwood.
It would not surprise me if in a proper test the splines actually weaken the miter joint. Maybe that won't be the case, but I think that is what your testing suggests to me.
Most of the glue you put on the splines was rubbed off when you inserted them. There needs to be sufficient "slop" between surfaces for glue to have some space to occupy.
Interesting that splines add no strength? I was quite surprised. I think overall they do add something to the equation, especially as you say if dropped. Quite an interesting experiment.
I don't think the purpose of the spline is to add structural strength, its only purpose is to keep that joint together and add a touch of beauty to that miter joint.
Great video. I have been wondering about this lately....so here I am. DD
Thanks Dennis! Glad you found it useful!
Thank you
Super interesting and entertaining video! One thing I noticed though is at 0:39 you said that you ripped an old Pine cutting board. I'm fairly certain that this was Oak. The only reason I mentioned this was because it got me thinking about how different species of wood would hold up to this testing. I think it would be super cool if you did a follow up video testing out different species!
Great channel btw. Subscribed!
Excellent comment! Yes I'm actually not sure what wood it is. Maybe it is oak, it didn't seem like oak (or pine, to be honest) to me so it's a little unknown. I bet different wood species have different strengths... I'll think about a follow up video in the future for sure. Happy to have you on board as a sub!
Pine or oak, either one wouldn't be a good choice for wood for a cutting board. Better used for science! 🍻
@@TheGrantAlexander Agreed! And my wife wanted to "throw it away" pfffft
@@dkbuilds You can't tell wood species?? Even my kid at 5 could tell the difference between oak and pine.
@@oldmanfromscenetwentyfour8164 Why aren't you and your kid making videos?
well... lets say you dont break structural integrity of the frame to perform a test, hang and drop it from a typical height (with a painting in it), I bet it would fall flat on the bottom part of the frame or whatever. So what kinda of force would be in play here. More importantly the structure itself would kinda work together and it would require much more force than in this experiment to break it. Anyway cool vid... I guess not much glue gets in there with the splines and they're not clamped either down either. So the gain is not this much and you sacrifice part of the joint to make it, In the way you pulled it, the spline is not in an orientation to offer any resistance and it would probably not be in most drop.
Would be more accurate if you didnt have to hand tighten the jack, could skew the weight as you are pressing up or down when tightening.
Yes that is a very good point Sam. Hopefully I am skewing the weight in the same direction for each trial, so that the results could still be interpreted the same way. Also if I am indeed skewing, I'd imagine it would only be a pound or two at most, which would impact the force needed to break the joint by a few percent. Regardless, good catch! I should have addressed this issue in the video.
Not really sure why you would be putting that much pressure on a picture frame in the first place. I'm pretty sure the splines are more to help keep the miter from opening up over time.
Good point. I always assumed it was to help keep the frame together if it fell or something. Hadn't considered the usefulness in keeping the miters closed long term!
What about splines at an angle, or dovetail splines?
This was a worthwhile test, but honestly, I don't think the test evaluated the intended use of a spline. A spline is intended to add strength during wood movement. Wood does not move in a way that was done in the video. In my humble opinion, if you had one piece clamped, and then just pulled the other side straight away from the angle, that would be a true test. Again, this is just my opinion.
Thanks for sharing Kevin! I think I might disagree with the purpose of a spline -- I don't think a spline is intended to add strength during wood movement, I think it is intended to add strength to a joint which has suboptimal glue surfaces (like a miter joint which is kind of half endgrain-to-endgrain). I do agree that wood does not move in the way shown in the video -- there is very little wood movement in picture frames unless it's a really wide frame. Clamping the wood and pulling on it like you suggest would be a really interesting test though, I'll consider that if I ever build a follow up video. Thanks for taking the time to comment!
Clearly not enough glue on the splines. If glue were to have been placed inside the grooves and on the splines they would not have slid out like that.
I'm guessing you would have different results if you applied force along the z axis rather than the x and y. It looks like you're just separating the joint as much as actually breaking it. I could probably break any mitered joint that's simply glued together by hand and definitely could over my knee but not sure if it would be so easy with a spline.
If you could apply downward or upward force at the joint itself and kept the ends clamped together. I'd be curious to see your results.
Swanson is proud.
👨 🙏
The direction of the force matters
Good point HSCT!
Maybe confirmation bias but that totally lives with my experience...
🙃
“Lance, you look like a strong, young pup. Why don’t you see if you can give that a nice tear.”
😂
I've been lied to my whole life!
Tbh if an unreinforced frame takes 100lbs to break id say thats good enough. Its pretty uncommon to have a 12 y/o child sit on your picture frames
Hah I couldn't agree more. Though if a frame falls off the wall and lands on a hard floor on its corner, I'm not sure what the force on it is. Could be more than 100 pounds but only for a millisecond or something.
Dovetail splines
Mathias would be proud. Great vid!
Thanks! It's pretty much my life goal to one day have Matthias tell me he's proud of me. Always love seeing you around the comments sections of my videos, TK!
dk builds 2.7 subs dude! That’s pretty impressive progress for such a short span of time. Keep’em coming. :)
@@teekaypew6538 Thanks I'm trying hard over here! :)
to be fair though, the 2 splines one the wood broke on the top half of the miter not the glue
🤔
The spline orientation you created is incorrect for this test. In order for the spline to add strenth it must be at an angle with the force being exreted on it. You should have added your spline the other way.
That’s a good point. I agree that a spline in the other direction would add more strength, however this is the direction the splines are always used in picture frames, which is why I chose this orientation.
Don't take this the wrong way but I think the experiment would be more valuable if the splines were done correctly
Thanks for the input! How would you have done them differently?
Great experiment thanks for sharing your info. I would have lost that bet for sure. However, they are actually keys not splines.
More people call them splines than keys. Majority isn't always correct, so I'm curious why you call them keys? Also, there are a few other names for them, including terms that include both key and spline.
torsional strength should have also been tested
Good point Ian. You mean rotating the top piece in/out of the plane of the picture frame?
End to end grain joinst are actually the strongest joints. 45 degree miters are not end to end grain joints. They are in between end to end (strongest) and side to side (weakest). Still they are not "weak" joints. Long lengths with small glue surface cause the weak joints. There's no way, I don't think, if done properly that the splines would come out without breaking. Try again with full cure time and accounting sufficient space in spline cut to allow glue not to be squeegeed off the spline insert. Also there is a sweet spot for the spline location (where the miter would begin to fail without a spline). Great video! I am not a RUclips creator and so my, grain of salt, opinion is of less value than your experiments.
Thanks for the comment James! I'm not sure I agree that endgrain to endgrain connections are the strongest joints. I know there is a viral video now explaining that they are stronger than most people thought, but I haven't watched it. Is that where you got that idea?
I like your suggestions for extensions to the experiment, I will consider them if I make a follow up video to this one!
@@dkbuilds Thanks for the response! Typically, end to end grain pieces are narrow and long creating a lot of leveraged pressure on a small glue surface. If, however, you were to cut a wide, short board across the grain and glue, that joint would be stronger. We've all heard that "glue is stronger than the wood". This is true. The failure on a well glued joint isn't the glue, its the wood beside the glue. For a better image, picture a 12"x12" board. Now cut 1" inch strips across the grain. Glue the ends together. The result is a very fragile joint. Now, make the same cuts along the grain. Get it?
@@dkbuilds I would love to see a follow-up video!
You're not doing the tests correctly. You're testing the side without the support and strength of a spline. This is like testing a shorter width and height mitre joint over a longer width and height mitre joint. The spline needs to be engaged from the start of the test, not when the rest of the joint has already started to fail.
Ace what a great idea! You should do a test the way you are suggesting and then make a video so we can see the actual results! Thanks so much!
@@jolenethetoolwomantaylor5973 I don't make videos.
its because they weren't snug enough
Hmm good point, thanks Kezza
Who cares if the one without the splines comes apart at the seam between the two miters if you can just put the joint back together?
I guess that is true, but if I build a picture frame for someone and it breaks, maybe they don't know how to glue it back together.
Miters are stronger than dominos
Interesting, I didn't know that!
I like how he said he was using pine from a old cutting board. The wood he was using was ash.
Good call, thanks Victor!