Let this be a lesson to you, folks. If Matthias could have found a cheaper way to make those bandsaw, he would have!! 😆😆 I'm still kind of amazed that you can make a bandsaw out of mostly pine.
I worked in a lab where we tested particle boards and OSBs and there are big differences among the different types that are produced. Some boards are 2-3x times stronger than others when it comes to bending. We also tested vertical ripping, surface strength, volume changes after boil etc.
Where a bandsaw frame needs rigidity I think the test may have just as well been done measuring not fracturing but deflection to 3mm. Nice video as always Mattias.
My takeaway is that you *could* build a very strong bandsaw out of Baltic Birch, and maybe even just using Baltic Birch in strategic locations would work well, but for the cost, Pine is plenty strong.
I just realized, that these videos all would make a perfectly fine article/paper. :) So much scintific work behind that. keep up the great content, Matthias.
A paper would in many ways be easier, cause it's just the facts. For a video, there is the added challenge of presenting it so that people find it moderately entertaining.
Love these test videos! I was waiting for the results for crossgrain baltic birch ply as I was forced to use a 21mm sheet that way for my current speaker project. No-one had the sheets in long grain.
I love these videos with quantified tests of different things. Minor nitpick: I am pretty sure the strength against bending is proportional to the cube of the thickness, not the square as Matthias suggests at about 3:40. So a twice as thick piece would be eight times stronger (assuming a homogeneous material). Further reading can be found e.g. under "Second moment of area" and "List of second moments of area" in Wikipedia for anyone interested.
Stiffness varies with thickness cubed. Fail strength with thickness squared. Note how the birch samples lined of different thickness lined up so close with the square law adjustment
@@matthiaswandel for those that want the equations: stress = M*y/I, where I = (1/12)*base*height^3. For 3-point bending, M = (1/4)*Force*length. Setting y = height/2, stress = Ultimate Tensile Strength and rearranging gives: F = (2/3)*(1/L)*UTS*b*h^2
Great video and test results. I am sort of blown away at the number of comments claiming the results are flawed as so many people do not understand the relationship of the geometry of the piece and how that relates to stress and strain under bending. The methods used in the video to normalize the results are correct from what I could see. Stiffness dictates total strain under a loading condition and the failure of the piece in this test is dictated by the compressive and tensile strength of the extreme fibers of the test piece. Great video.
I refer to them as fire hazards... I tell anybody doing construction for me that if they bring any of those materials on site, they will catch fire overnight.
Wouldn't the most important strength for a bandsaw application be within the plane of the plywood? I didn't see that tested. Essentially, I'd be curious to see how plywood would fare in that device when rotated 90° around the long axis.
Thirded. No wait, Fourthed. Yeah, I'm not sure his tester can take the stresses, but in-plane (good nomenclature, I couldn't think of the right term) testing of the plywood is what's needed. Matthias, I work in a materials lab. Send me the samples and I can test them.
No, it's bending of the column. When the blade is tensioned, the far side of the column is actually under almost as much tension as the near side is under compression, because the bending moment dominates.
A lot of people think strength is a cubic because of I = (1/12)*width*thickness^3. But they're forgetting the stress equation (stress = M*y/I) has a thickness term (y = thickness/2) that cancels out and makes it a square law. When you substitute M = (1/4)*Force*Length and stress = Ultimate Tensile Strength, you get: F[max] = (2/3)*(1/L)*UTS*w*t^2
personally I think you’re wonderful too. I love watching your stuff. You’re one of the best artisans I’ve ever seen. Wish I had your talent. Keep it up man I love it.
In mechanical engineering stiffness is usually more important than ultimate strength so I think that would be a more interesting measurement. Usually once a structure is made stiff enough, the strength is more than enough. Of course wood is not isotropic and is weaker in compression than in tension, so there are some applications where this is less likely to apply.
I think this test is also going in the wrong direction. The forces would be going across the length and width of the boards in the structure rather than through its thickness.
Exactly. Using any wood product as a structural member, the stiffness is in the long axis. You don’t use a 2X lying flat. Think about glulam beams. I really don’t see the point of testing like Mathias did.
Engineer here (Mechanical and Electrical). The strength and stiffness of a beam is mainly in the faces experiencing the tensile and compressive forces. That's the reason for "torsion box" construction. The strength and stiffness is the 3rd power of the beam depth and proportional to the width. I've always wondered why Mathias has always used solid frames for his bandsaws instead of slightly larger hollow boxes. If I was to build a wooden bandsaw, that's what I'd do with good plywood face grain running in the primary stress directions. Personally, I'd use tubular steel sections.
I keep seeing comments about it being proportional with thikness cubed. This is true if you keep the member square, for example, so doubling thickness also doubles the width. But if you only double the thickness, it's squared. Steel is a bad example though cause you can double the thickness of a hollow member but not the wall thickness. Then the it will be less than 4x as strong.
@@matthiaswandel Probably a mixup because stiffness is proportional to the thickness cube. Stress is proportional to the thickness square : Stress = M*c/I = (F/2)*(L/2)*(h/2)/(w*h^3/12) = 3*F*L/(2*w*h^2).
Maintaining the full tension strength of the wood all along the outer part of the 'C' shaped main beam would not be possible with plywood. I think what might make sense is building it in low-cost soft wood with a radiused shape, and then laminating some high quality knot free layers along the tension pathway on the outside. Or, for that matter, just put one or two layers of fiberglass tape on the main load paths.
I recently got some 1/4" 2x8' sheets of pressed hardboard that is dry-erase on one side and chalkboard on the other from the cull lumber section of my local House Station. 70% off, some rough edges but otherwise good. I've been using it for drawer dividers, but the dry-erase side is very smooth and hard like melamine, so router table top, blower impeller disks and cabinet doors you can put notes on. Big chunks of Masonite too, almost a whole sheet of 3/4" for $7.
Hey Matthias, thanks for the test! this is quite useful! I have two questions: - Does it makes any difference if you rotate the plywood 90 degrees? - I see that you are measuring the total strength, but what about the stiffness of the material (young's modulus)? For building machines, that's probably more important than the total strength
I am not sure I am using the right words since I am not a native english speaker.. The material physics is pretty straight forward. The strength of your probes rise with the thickness^3. Also one side is in tension while the opposite side is in compression. This means the middle fibres carry no load (which is over simplified!). Also this means with plywood the inner grains may lay in the wrong direction, but this doesn't matter much since only the most outer ones carry the load. For semis you want things to be light but heavy duty; best things therefore are sandwhich panels; outer layer of sheetmetal (steel or aluminium) and in between light (and thus weak) foam of some kind. (maybe you see the similarity to plywood) fun fact: car springs can hold significally longer with the right paintwork; since it is always on the outside, it may carry quite a lot of the load if it adheres good enough and the material properties of the paint are good.
Stiffness rises with thickness cubed, strength with thickness squared. The solid birch samples, all from the same board, showed how consistent that worked out. If I'd used the wrong equation, my results would have been all over the place
Most plywood failures I've had were from poor quality control of gluing the layers. Thanks for the video. Now I need to find a supplier of Baltic Birch plywood near me.
How does the stiffness compare? Looks like MDF should be pretty stiff among these? Which agrees well with some of its applications (stiffness, weight and damping, like for speaker boxes). Regarding anisotropy, would be interesting if they made plywood with thicker core plys and thinner surface plys -- well, they usually do, but more like having veneer on top of a couple thick core plys. I mean like having several alternating layers of thin, yet quite strong material -- like, a coarse 1-3 ply pine core in the middle of 3-4 layers each side of Baltic Birch or the like. The core could be even weaker woods for that matter; it only needs to handle some compression keeping the outer layers from buckling, while the outer layers handle the bulk of the tension/compression load. Same concept as honeycomb- or foam-core fiberglass construction. They probably don't for production cost / complexity reasons (hence Baltic Birch being thin layers all the way through); or the consistency makes it better suited to joinery too. And I don't suppose you'll be very interested in making your own plywood to test the idea, hah, but just a thought -- in particular, it's interesting that the cheap 5-ply is so much weaker across-grain, basically because the outer layers don't count for anything while the inner layers, bearing the load, are effectively so much shorter, like a 3-ply, 12mm or whatever, piece would do.
I seem to remember that MDF is used in speaker units because it is consistent throughout the board, which might have effect on acoustics. Companies tend to care about repeatability, and mdf provides consistent results.
MDF is used in speakers because it tends to be acoustically "dead" (non-resonant). It's also inexpensive and easy to machine. It's not particularly strong. And don't ever get it wet.
the DeHaviland Mosquito was constructed with a 3 layer plywood construction of a thin birch ply on the outsides and a thick balsawood core. the modern equivalent for aircraft today would be glass fiber with a honyecomb core.
MDF is not stiff at all; it will deform easily if under transversal loads (ex., shelves) and will slowly lose its ability to return to the original shape. It's reasonably strong in the longitudinal direction (ex., vertical side panels). Also, as mentioned above, will will swell up and delaminate as soon as it gets wet (unless you use moisture-resistant - typically green - MDF). Always seal the edges (ex., with diluted PVA glue) - and preferably the faces as well - if there's any chance that any liquid will get spilled on it.. Note that varnish and paint will only work until there's the slightest crack, and then water will get through and ruin the MDF. PVA, sealants and some primers will actually soak into the MDF and form a thin waterproof layer.
@@RFC-3514 Also a good point about creep -- this test only shows short-term deformation, but things can go differently over long time scales, and with temp/humidity cycling.
Not surprising results for strength testing, but what about testing in regards to the forces applied to the bandsaw? In an assembled bandsaw, the main force is going to be vertical from the blade tension mechanism, right? That's parallel with the large surface of the material. I'm still curious if MDF be strong enough in that regard. The forces you tested are essentially as if you clamp the neck of the bandsaw to a rigid structure and pull the top and bottom wheels toward you. That said, it's probably still cheaper to use solid pine instead of MDF due to engineered panel costs. Hmmm.....an MDF CNC'd version...
The force is pushing down, but... offset from the main column by quite a bit. As such, there is bending force, and the force along the grain as a result of bending will far exceed the actual downward force of the blade. The far side of the column will actually be under tension when the blade is tightened
Ever played around with edge ply? I used some cement form work support stuff to build a desk and it's super strong. It's all single direction so I cut it into strips, then sandwiched them together like an enormous butchers block. The strips were super flexible sideways but had almost no play on a vertical plane.
The strength of the solid wood may depend on which way the growth rings run (whether the wood is plainsawn or quartersawn). This occurred to me when another comment mentioned making up beams of plywood or OSB so the plyies are parallel to the stress. This would reduce the tendency to delaminate like many of the failed samples did. On the other hand this is not very useful because of the trouble of using any built-up wood in a project like your bandsaw.
It seems like you have tested the plywood only with pressure perpendicular to the layer lines. I would love to also see a comparison that is in line with the layer lines.
Materials like playwood and OSB are used in construction for taking loads ALONG the material - stretching - in shear walls, not across it like in beams as you test it
Not really, as already with this test to some degree you are comparing apples to pears. Plywood is made mainly for dimensional stability, so unless real wood which with moisture will swell and shrink mainly in one direction (perpendicular to the grain) the layers in different directions compensate for that. When you look into construction, where structural strength is required you will find either solid timber beams, or glue laminations, but we are talking about completely different dimensions here and using certain cuts of wood to reduce impact of grain and get beams exceeding dimensions you can just get from a mill today, among other things. Plywood is plenty strong if used for cabinets, or as sheathing as intended. Same with OSB, which is just a cheaper alternative creating something with properties of both plywood and particle board. Particle board, I don´t know if that is actually good for anything other than cheap (in the worst sense of the word) cabinets and one time packaging. MDF, by reducing the particle size again has superior qualities over particle board. less compressible, more rigid, easier to coat/paint. MDF also due to its high density is quite good for speakers. So except in case used as sheathing, none of those boards are intended to be really structural. They are solid enough as floors and walls on joists and studs, especially on walls they provide in combination a lot of strength in one pane. They may work for cabinets, if used right. But using the example of a bandsaw, most people may already be surprised that a saw without a metal frame is stiff enough at all. But in this case, with right dimensions and taking into account the grain direction, it gets kind of structural and solid wood or glued laminations are the way to go. An enigneered box frame made out of plywood would likely work as well looking at rigidity. (just not sure if it would hold up).
Matthias might consider using the beam stress equation Mc/I and comparing stresses instead of factoring loads around. He's using an interesting method of normalizing results, but it's not exactly the same as what you'd see in a standard three-point bending test. Also I'd like to see a tensile strength test as well but that requires a different test setup. Big props for generating your own material strength data! That's amazing dedication.
@@Bob_Adkins only if you're using the same size wood everywhere. If you made an A-frame from framing pine or LVL but made the bottom member from dowel, then knowing the tensile strength will allow you to use the smallest dowel diameter.
@@toolscientist I know what you're saying, but wood in tension is so much stronger that if you made it smaller, there would be no reliable or practical way to fasten it. So wood in tension will always be WAY larger than it needs to be. That said, not much wood is used purely in tension in normal construction.
@@Bob_Adkins a through hole and thin dowel glued in will be strong enough at a certain diameter to hole length ratio. But yeah, you need fairly specific examples that aren't often used in reality, so your comment is right in 98% of cases 😉
For a rectangular cross section, Mc/I reduces to 6M/bt^2. This is where he's getting his factor. If you double the thickness, you reduce the stress by 4.
I'd also test plywood strength by pushing along the layer lines as this is how the plywood frame wood have been constructed - pieces of plywood glued back-to-front, not right-to-left of the frame.
Not far from where I used to live was a school furniture manufacturer, and they got some 10 ply Russian plywood to make the furniture from and it was nice stuff. I made a bookcase from some scraps, and it was really nice to work with. It was 3/4" or 19mm, and was a very nice product. It would be interesting if you could test some of that.
I've found the engineering lesson that is most relevant to woodworking is bending moment of inertia. Whenever I have to use a weaker material for something critical, I orient it so the bending moment of inertia is maximized
Matthias, have you ever experimented with making hardboard out of cardboard. There’s a lot of Amazon and Walmart shipping boxes lying around these days. I wanted to see what could be done with the stuff besides discarding or burning it. I soaked six small pieces in cheap yellow carpenters glue and compressed it firmly. It produced a very tough material. I also coated it with glue and it produced a durable finish. It has a lot of possibilities.
I've experimented with laminating cardboard with fiberglass and either Titebond III or high quality epoxy. You can make some strong and durable composites out of it.
Excellent video as always! 👍 It's great to see, that Baltic birch playwood is so strong.. No wonder about price and that lots of it is going to export..
@@johncoops6897 Yes, it is compressed in its thickness when it is made. It seems that it creates more strength in the thickness direction than in either of the other directions. In other words, it is not an isotropic material like metal, it is a little more like wood, even though it has no visible grain.
@@johncoops6897 Thanks, though I did not say it had grain. I elaborated on the first half of TMMs comment, for anyone that didn't get the idea he was trying to get across. The second half of his comment, the main point in my mind, I agree with.
"The ancient Egyptians and Greeks cut wood thinly and glued it together in layers with the grain in perpendicular directions as fine wood was in short supply. This is believed to have been done purely for cosmetic and economical purposes but it turned out to be a great alternative to pure wood as it reduced flex, making it a versatile building material." "One can thus presume that rotary lathe plywood manufacturing was an established process in France in the 1860s. Plywood was introduced into the United States in 1865 and industrial production there started shortly after. In 1928, the first standard-sized 4 ft by 8 ft"
what if the laminations were in the same direction...all long grain? curious about them pushing and pulling against the glue/epoxy...assuming they would be fighting against that.
Its more for plywood being more homogenous and less at risk from bending overtime than wood, not for the strenght if i think correctly. Also it is easier to buy a sheet of ply and then cut the shapes than buy wood and make ot i to shape.
Bending due to moisture changes (or improper drying of the wood), sure. But the plywood is more likely to bend from physical loads (ex., weight on a shelf).
Can you do a test with for example pine 10mm thick and take the readings when it brakes. Then put two similar pieces on top of each other and take the readings. And finally a third set of similar pieces but glued together.
As a child I built a slingshot out of particle board, because it was the first chunk of wood I found in my dads shop. Shortly afterwards, I learned that particle board is quite weak 😄
Hmmm.. technically if you consider bending dominant behavior (planar strain profile) with a maximum stress failure criteria, the strength of the section is proportional to cube of the section's height. Given that extreme wood fibers usually *break* first, this is not a bad assumption (a linear strain profile) - this is what we call *allowable stress design* method. For a material that *yields* and has a large inelastic range of strain (i.e. it is ductile), the strength is proportional to the square of the section height (but the strength comes out as a larger number for the same section as well).
Thank you very much for your video. I wanted to ask you if you can help me understanding cross grain vs long grain in OSB. What I have to pay attention? Thank you so much. Carlotta
I think that if you put inner layer with the plywood cut in diagonal it would be stronger. And if you added some fiber glass roving and used a quality urethane glue with good curing pressure.
Also proves why you never make something that will receive force cross-grain, the strength of the pine was pitiful. This is something that 3d printing people should have learned by now as 3d printed objects are far stronger along the grain than cross-grain much like wood; all the time I see 3d prints in which the print orientation makes it receive force cross-grain.
Have you substantiated the width correction factor? Interesting results. Plywood certainly has its uses since it's not completely useless across the grain like solid wood, but good to see a comparison.
Not that it changes any of the conclusions, but it appears the crossgrain pine failed cleanly along a glue joint -- not the wood. See the failure at 2:11 and commentary at 2:19 for what appears to be grain discontinuities.
While strength is important for many applications stiffness is even more important. As the testing machine records travel getting a stiffness chart should not be too difficult. May be in an follow up video?
This is very interesting Matthias. It's a common technique in shelf-making (for example with book cases) to reinforce a shelf from deflection by rabbeting a piece of solid wood and gluing it to the front edge of the shelf. This is supposed to make a plywood or MDF shelf less likely to bow from the weight of the books. I wonder how a plywood or MDF shelf prepared in this way would compare to just a solid piece of wood?
Most of the support will come from the solid piece of wood, cause that is also a lot stiffer. Basically, the stiffest material takes most of the load, even if the stiffest material was not the strongest
@@matthiaswandel this reminds me of a horizontal dough mixer I used to have to work on that was duel belt drive (one belt on either side). The driven center shaft was far stiffer torsionally that the drive shaft, and since the power was applied to the drive shaft way off center, one of the two heavy duty timing belts took the lions share, if not all of the load. It was also a nightmare to balance the two belts since their relationship to each other changed at different loads.
@@matthiaswandel Makes a lot of sense. I just watched a video over on Rob Cosman's channel where he created a double mortise and tenon joint. In that video he suggested that having 2 tenons would give the joint better ability to resist leveraging on the joint than a single tenon would (even if the sum of the widths of the two tenons and the gap in between them is the same as the width of a single tenon). If this is true, then I'm not sure why -- maybe doubling the number of shoulders is superior at resisting racking even if it sacrifices some glue surface? What are your thoughts?
Saying that half the grain is oriented the wrong way is sort of like saying 2/3 of an I beam is in the weak orientation. That’s just not how it works. I think the major difference is that generic pine plywood comes from the outer grain of speed grown trees while dimensional pine comes from the center of bigger, older trees. As a counter example, LVLs are significantly stronger than the same size pine lumber. That is due mostly to being oriented so that they are loaded on edge where plywood is strongest.
I'm curious to know how you converted the force to a uniform thickness. In theory it seems to be a simple scaling factor but in reality the stiffness in flexion (which is the engineering term for what you are measuring here) depends on the moment of inertia of the section of the boards, which for a rectangular section is (width*height^3)/12 if i remember correctly.
You are correct that I = (1/12)*b*h^3, but there is another 'h' in the stress equation that cancels and makes it a square law. I showed the equations in another comment, but the final result is F[max] = (2/3)*(1/L)*UTS*b*h^2
I'm a student from Brazil and you can help me with a project, can we talk? What load cell model did you use? And how did you read on the computer, besides? Have you used a microcontroller other than Arduino?
This is video I've been looking for, thank you man! Forgive my ignorance, but how do you tell grain orientation in OSB? I always assumed it to be chaotic random grain orientation
But why did you assume double the thickness is 4 times the strength? Moment of inertia is calculated by B*H³, so you should have assumed it to the 3rd power.
The plywood could be used on-edge. TJI beams are used in construction and are vertically oriented like this. It would be interesting to build some I-beams (so they don't buckle) and see how they do on the same jig.
Yeah, I would never use plywood with significant force in the direction that Matthias tested in this video. Instead I would design so all major forces are in the plane of the plywood, in which it is the strongest.
Hi Matthias: there's actually a cube law between thickness and strength when it comes to rectangular beams; so a beam twice as thick would be 8 times as strong, not four.
A cube law to thickness and stiffness. Your beam twice as thick would also be twice as wide, so then it becomes a cube law (and 4'th power for stiffness)
@@matthiaswandel I have the same concern as Chlorate. Your reply seems a bit cryptic, something about changing the widths of the beams? Might be a miscommunication about units of measure, maybe force (Kilogram) versus internal stress/strain (Newton)
@@matthiaswandel I would also agree with Chlorate, namely the maximum stress in the sample would be inversely proportional to the second moment of inertia (a.k.a. area moment of inertia) which is linear in width but cubic in thickness. So a twice a wide sample could handle twice as high of a load, but a twice as thick sample should be able to handle 8 times the load.
What about flex without breakage? If the forces involved aren't enough to break a material and stiffness is a primary concern in the application, then the material that is stiffer is the better choice even if it has a lower breaking point.
for solid wood, flat or edge on are going to be the same, but for plywood I could see it being very different (don't know if it would be better or worse than flat plywood, but I expect it would be noticeably different)
Haven't read the comments, maybe it is mentioned somewhere. What if a piece is cut at 45deg angle from plywood so all the grain impacts strength the same. Wasteful but interesting. Or corners and ends going to be weakest points
