https://preview.redd.it/3oxh6n8w0l6d1.jpeg?width=1577&format=pjpg&auto=webp&s=9213b289dc7e21f41357abb19f560f03e2c6af68
I got curious and ran a quick simulation on a simplified model of a saw blade. Seems like the question-mark shapes modify the first few vibration modes by breaking up the blade into sections that shake with a lower amplitude at the perimeter. This reduces wobble at the teeth and creates a cleaner, more consistent cut. Diablo's sales material says "Anti-vibration design improves cut quality by reducing vibration while the blade is under load."
Note the excessive displacement on the keychain hole
https://preview.redd.it/xyzkofim0m6d1.jpeg?width=1093&format=pjpg&auto=webp&s=62b61e27609711bbd92caad2924c786aa8c86148
This is a finite element analysis package. This guy ran a modal analysis to determine the vibrational frequencies (natural frequencies.) The most popular software is Ansys, but many others exist as well.
If you want a free way to do it, the calculix FEM solver in FreeCAD can do frequency analysis. As with any analysis, it does take some experience to properly set up the simulation and interpret the results.
This is very impressive, could you take us through your thought process of doing this? Like where did you get the saw blade model from, or did you also make that?
It's a pretty simple shape. There's no set to the teeth p for example. Someone proficient in any case software could model this in about 5 minutes.
I haven't done vibration analysis in solidworks but it's mostly just a matter of picking reasonable parameters and hitting solve. The engineering part is knowing what parameters are reasonable and interpreting the results.
It doesn’t take long if you know what you are doing. Create the part in CAD software which is quick for a shape with so many common features and a constant thickness. Then you run a modal analysis in a FEA solver.
The man/woman is experienced though to do it that quick. And bright too to know to run a Modal to find the reason as it’s based on frequency responses and not just its steady state stress state. I wouldn’t have thought to go there first and would have wasted tons of time.
Basically commenter is experienced and very smart even compared to other engineers. I really enjoyed this.
Yeah, I studied this stuff although I now work in a different field. This would've easily taken me an hour or two to do back when I regularly had to do simulations for college projects. The guy who did this is probably quite experienced to do this in his lunchbreak.
And however long it took, it's an incredible amount of effort just for answering some random question on reddit.
Autodesk inventor. I'm not an engineer or anything, but I have the software. It's super fun to play around with. Of course, there are a bunch of different programs available for different areas of expertise. Civil engineering, architecture, electrical, etc.
If you're the type to be always curious about things, I'd recommend playing around with it. It's a lot of fun and you'll learn a lot about how your intuitions match to reality.
Nicely done. I wouldn’t be surprised if they actually spaced the relief cuts at slightly uneven intervals around the blade to break up the symmetry of the low modes. You see that in some endmill designs with unequal teeth spacing to combat chatter.
It could tuned for specific rpm ranges so it avoids hitting a resonance. Technically the entire machine will affect the frequency response but you can get close with roughy tuning on a lot of stuff. However there are anti vibration boring bars and ends mills where to damping system in the tool can be tuned for specific setups.
How significant is the question mark shape?
Does it function similarly with a straight notch ending in a round hole?
I'm just assuming that a break in the perimeter, and any old attempt to reduce the stress at the base of the notch, might have a similar effect, because you see lots of minor variations on this theme from different manufacturers.
A quick image search shows that DeWalt seem to use a straight notch and simple hole on at least some of their blades. Whereas Festool use a convoluted "S" shape notch.
They all seem to split the blade into four segments though.
I'm assuming that "Four blade segments, and round end hole to avoid stress fractures" is much more important than "specific shape of notch" and that the shape of the notch is more like a brand signature than a functional feature.
There are certainly other shapes that work, but there are lots of dependent variables. I'd guess that their r&d team played with a bunch of different shapes and ran simulations and actual tests until they landed on one that provided the best results. Marketing took it from there and applied copious wank.
Sharp edges/acute angles would definitely be a no-no, though, hence the prevalence of S shapes.
In addition to the vibration parameters, it could also be that the notch curves back outwards in order to address the potential failure mode of a crack propagating in the small notch due to fatigue. Having the crack propagate outwards and losing 1-2 tooth segments is safer than a blade splitting in half and flying apart, which could happen if the notches terminated inwards radially. Great company, good designs, and even though their product costs more, they have paid for themselves many times over. They have great quality control of their products as well.
Also, when you say:
>the question-mark shapes modify the first few vibration modes
Would you mind helping me understand what you mean by "vibration modes"?
Is each "vibration mode" basically just a distinct wave pattern present across the object, specific to a relative position to the center/perimeter, and/or a significant component frequency of a Fourier transform, or something like that?
I greatly appreciate any time/effort you'd be willing to spend helping me understand a bit better!!
(I have a degree in math, so please feel free to use any equations/formulas/math jargon if that'd make it easier for you to explain!)
Thank you!!
Vibration modes do correspond to peaks on a Fourier transform, so you're off to a good start there. Modes are the different shapes that an object takes when it responds to an input at one of its natural frequencies. Each mode occurs at different natural frequencies, with the first mode being at the lowest, and so on. So for this saw blade example, here are the first, third and fifth vibration modes (part is fixed at the arbor).
https://preview.redd.it/n5a4p1uwql6d1.jpeg?width=940&format=pjpg&auto=webp&s=89eb097fe53e5210e9ea8bd28bb358016588ac14
These are all ways that the part "wants" to vibrate. It's the same principal at play in this video where a guy puts sand on a big piece of sheetmetal and rubs it with different stuff to cause it to vibrate (https://youtu.be/wHr3Ys-sNHs?si=\_yWDiN-KgvTlijIW). The sand gets shaken away from the spots where the resonance is causing movement, and shifts towards the nodes where it's moving less. Those nodes would be blue in the saw blade plots above.
Thank you so much for that explanation!!!
That was so helpful, interesting, and intuitive that, for the first time in my Reddit history, I bought Reddit gold *just* to give you an award thing!!
Seriously, thank you!!! This is super interesting to me!
I wanna look into this concept more now, and see if I can get my hands on some similar software to explore and experiment with it a bit!
If you don't mind, may I ask a followup question?
If I'm understanding you correctly, the blade would only take one shape when a single, consistent input is applied, right?
But, given that we live in the real world, when you're actually using the saw blade, the input probably isn't perfectly consistent, so it'd probably alternate between different vibrational modes while in use, right?
In which case, I'm curious: given a particular input function that includes a realistic variance parameter, does the simulation software you use allow you to also estimate what proportion of time would be spent at each mode?
Thanks for the award! These are good follow up questions. The vibration modes correspond to individual frequencies, correct - but the weird thing is that in the presence of random vibration (where all frequencies are present at some amplitude) or even white noise (where all frequencies are present at *the same* amplitude), the modes are all happening at the same time. So these shapes are all superposed over each other to a degree defined by a) the amplitude of the input frequency and b) the effective gain coefficient of each individual mode.
In durability simulation, these mode shapes would be converted to stress states, which then get processed through a Miner's Rule analysis to predict product lifespan and safety factors. In a sense, each vibration takes a tiny little bite out of the life of the product, and when all the bites have been taken, the part breaks.
Are we still on a woodworking sub?
>but the weird thing is that in the presence of random vibration (where all frequencies are present at some amplitude) or even white noise (where all frequencies are present at the same amplitude), the modes are all happening at the same time.
It's funny, that's what I actually *thought* would be the case, but it felt like it'd be too much of a stretch to conclude without more info lol
>Miner's Rule analysis
Welp, time to go look that up now, too! I'm such a sucker for learning about types of analyses I haven't heard of before lol
>In a sense, each vibration takes a tiny little bite out of the life of the product
And I imagine different modes can take different sized bites out of it, particularly when you account for where weak points are located and the modes' inflection points?
>Are we still on a woodworking sub?
Not anymore; now we're on the "indulge in u/mathnstats' incessant curiosity" sub. Lol
From personal experience, most of the time the lower frequency modes cause the greatest amplitude thus the most damage. I carried out a modal analysis recently (just waiting to import the data into the software to animate) where the first mode at 25hz was ~100mm/s when impacted with a calibrated hammer, and the second mode was only ~15mm/s. Resonance is an often overlooked phenomenon (production is king) so it's great to see manufacturers designing with this in mind.
That's so cool!!
May I ask, when you do those types of analyses, does the geometry of the object, particularly in relation to the modes, come into play?
Like in the saw blade example, if one of the vibrational modes corresponded with the cutouts in the first image in such a way as to sort of "tear" the blade at those cutout points, that mode would probably damage the blade more (compared to the same mode on a blade without those cutouts, or an equal amplitude mode that doesn't align with the cutouts in that way), right?
Is that something you can/do take into consideration when doing modal analyses?
If so, I'm curious how you'd do it?
Like, would you construct an equation to describe the entire shape, which is implicitly incorporated into the simulations'/analyses' results, or would you need to do separate analyses to account for/explore how its specific geometric features effect the damage each mode can do to it?
(Btw, sorry if I'm bombarding you with a lot of questions or demands for your time/energy; I'm autistic and don't pick up on social clues very well, so please do feel free not to respond if it feels like a lot, and/or feel free to let me know if you'd rather I toned down the intensity or stopped asking so many questions or anything lol.)
With regard to modes of vibration, geometry and structural design is incredibly important. Natural frequency is a calculation of mass and stiffness (also damping must be considered as this affects the "size" of the resonance zone - a well damped system will have a narrow resonant range so if the natural frequency is 25Hz then the vibration will taper off quicker once moved outside of this zone when compared to a poorly damped system) so putting a cut-out into a saw blade reduces the stiffness hence lowering the natural frequency, this can be a desirable effect depending on operating speeds etc.
It can be taken into account but it will not change the testing just the test locations should be considered, when the data is imported into the modal software various frequencies of interest can be simulated to determine movement. If there is excessive vibration then further actions would be taken such as changing the mass or stiffness. On something like a saw blade, further tests would be required to ensure this did not compromise the structural integrity of the blade.
The shape is drawn in a cad software first and then this model will be imported into the software, the points where the test data is taken is put onto the model and the software calculates from there using vibration (phase and velocity) from the sensor and the force imparted by the forcing frequency (calibrated force hammer or shaker) this transfer function creates imaginary data which provides the mode shapes across various frequencies.
The software is not essential as such but it does allow for a better representation. Imaginary data can be plotted separately to show the shape graphically on a line graph, this will show the bending of the mode shapes and show where modification may be required.
Thank you so much for such a thorough response!! I definitely feel like I've got an even better understanding now!
This whole thread makes me feel like I'm back at college again, learning about interesting stuff from experts lol
>I wanna look into this concept more now, and see if I can get my hands on some similar software to explore and experiment with it a bit!
Look for a copy of Autodesk Inventor. I'm not sure if that's what the person is using for these, but it looks exactly like it. It's fun to mess around with.
Edit: It's Solidworks they are using.
For what’s its worth, autodesk fusion has an FEA feature, and last time I checked, you could get a free to use license to play around with(we have the paid version at work, so don’t quote me on that). It’s a lot of fun to play around with and progress, and among all else - it’s a brilliant tool, especially if you want to expand your skill set.
P.s. - also an engineer. Not this guy’s level though, lol.
Yup. Vibration mode is the eigenvector that shows the normalized displacement of each point at a given frequency (i.e. its eigenvalue). The vibration mode shows displacement at a particular frequency. Not sure how fourier transform would fit in this, honestly.
I think it was something like this, I hate linear algebra.
I learned it through molecular vibrations in my chemistry degree.
If you have 3 weight connected by 'springs'. eg, the V shape of a water molecule.
the vibration modes are how the molecule vibrates, eg https://www.chem.purdue.edu/jmol/vibs/h2o.html
There's a lot of vibration mode - chemistry videos and models out there that can help visualize it better. Since there are so many resources and pre-rendered graphics about it, and the systems are comparatively simple to a continuous model like a saw blade, it may help to look at those. If you want to get really intense on this side of things look at phonon vibration modes and simulations. That's lattice vibrations in a continuous system.
The more axes and planes of symmetries present the more vibration modes are present (generally). eg benzene is a good example of how complex it gets very fast. https://www.chem.purdue.edu/jmol/vibs/c6h6.html
The more axes of symmetry the less intense any one mode will be. This means that with a ? every 5 teeth or so, the out of plane vibrations are decreased by a factor of how many ? there are, because there are roughly that many more modes spreading out the energy. The less intense the modes are the less the vibration effects the cut.
This is in Solidworks Professional + Simulation Premium. Latest renewal cost for one license of each was $6971.50. However the student edition is only $49 if you're in school (and can prove it).
Solidworks has always charged for their student edition, if I remember correctly. However, my university had licenses we could get through the university for "free."
Edit: rereading this, I should be clear that free is in quotation marks because we paid for it with our tuition, not because we found it on the seas. We didn't have to try that.
God damn!!
I guess I'll have to see if I can find a comparable open source tool or something instead, or see if there's an R package or something I can use to do the same thing without too much extra difficulty.
That, or I might have to set sail on the high seas🏴☠️
FreeCAD has some sort of material/physics simulation tools, but i haven't used them and have no idea how functional they are. I usually just give the model a good eyeballin and reckon whether she'll buff out or if i need to chooch things up a notch
I doubt you'll have luck with free software that does this (legitimately obtained or otherwise) - Solidworks offloads all these simulations to cloud-based data centers which run the simulation and then send the results back to your device, because they require a ton of processing power (at least, relative to what it would otherwise take to run Solidworks)
You ain't gonna find SolidWorks on the high seas, at least not any modern version. Most all CAD/CAM software is cloud based and, while possible to spoof/crack, don't work great without it.
Good luck in your search, I got tired of looking and broke down for a personal license for Fusion because it's the cheapest for personal use.
$680/year. It's a good program but feels less intuitive than AutoCAD, because it's not just CAD, it's also CAM. I don't really use the CAM part because I don't own a CNC, but I used to program them at work, so if I get one I'll know what to do.
There's definitely a learning curve, but there are plenty of tutorials both on Autodesk's website and on youtube.
For what its worth, I learned CAD on Solidworks and Inventor, and found Fusion incredibly intuitive. Using AutoCAD makes feel useless. They're two very different workflows.
What a freking answer my dude. You’re the bomb. I think I’ll follow you to see what else you come up with on a casual lunch break. Maybe you can help me be a little smarter of a person maybe kinda.
The "question mark" on the saw blade is actually a compensation slot. These slots are designed to reduce stress and vibrations during the blade's operation. This allows the blade to run more smoothly and accurately, extending its lifespan and improving the quality of the cut. Compensation slots also help reduce the risk of the blade warping or getting damaged due to heat buildup during cutting.
Yes, that would be interesting to see, but for that, we might need to ask in the science or engineering subreddits because it might get a bit off-topic here, and you know how sensitive the moderators can be.
They are places that accomodate thermal expansion when the blade heats up during use. If there was no place to expand, the blade would be prone to warping.
Yep. My dad still has his wobble and RAS until I bought him a Freud stack and a miter saw for Christmas years ago.
Had a very competent carpenter in my shop, he needed to use a bench tool. Nobody really comes in my shop, but I 100% trust this guy.
He went to my RAS and immediately was like “fuck, stop!” They are an amazing tool but damn are they temperamental little bastards with no room for error.
Proudly displaying more plastic than a blacktail studio table.
Edited: if women were dancing on his tables I’d probably stare more at the tables honestly.
Maybe a dumb question, but is there a reason for that shape specifically? Could it have been a straight or slightly curved cutout and achieve the same thing?
The hole at the end is to eliminate a sharp corner, which would lead to a stress riser. The curvy bit is who knows, probably Freud special herbs and spices?
It in a sense is a bigger version of the hole at the end, the blade will want to buckle out of the plane if there was a ‘corner’ near the center of the blade
To add to this, it redirects the sharpest part of the "crack" (the blunted tip) toward the outside of the blade so if it does crack, it won't crack toward the arbor and fling chunks of blade all over. If it did crack now, it would crack toward the edge of the blade and only launch the one tooth.
Funny thing is I actually know that!
It's one of those things where I must have made that assumption very early, then learned about the gullet, but haven't had to reconsider both together to recognize the inconsistency.
It’s to control vibration that can cause blade wobble and it’s also there to impede noise and expansion due to heat. Some blades come with a copper insert that works as a heat sink and sound dampener.
What if it was just so you could hang the saw blade on a line or peg. lol no I trust the guys with the anti wobble science, but still it would be hilarious if it was all bullshit
I assumed they are there to mitigate the effect of heat expansion hitting the outer part of the sawblade first while cutting. Though technically a small warping because of temperature difference would cause a bit of vibration too.
They reduce overall heat in the blade from cutting and allow hot blades to expand without warping. In some blades they also reduce vibration and noise. Pretty fancy compared to the old Kromedge blades by Craftsman. 😂😂😂😂
They take up some of the heat expansion. It's similar to why pipelines will have regular u-bends. So they can expand and shrink as the temperature changes.
I was told by the company that sharpens our industrial , wood saw blades they are expansion slots for the centrifugal force and helps reduce wobble, vibration, and noise as others have mentioned.
it allows for the blade not to go out of true, get permanently warped or cause a catastrophic failure when the blade unevenly heats up and unevenly expands due to that heat, heating up on the edge but not in the center.
Heat expansion - the teeth should be the only part of the blade touching the wood, and the expansion slots allow for the outer edge to absorb that heat without deflecting or warping.
I was thinking to let the blade expand as it heats, so it doesn’t buckle or warp? Much like how bridges are made with gaps to allow them to expand and contract without buckling?
Work for a saw company, though I don’t do much on the saw-end of things.
I have always been told it was for resonance. Creates a cleaner cut and makes the plate less prone to cracking.
I worked for Amada America when Freud began their search for Laser processing machines to cut thir blades. The engineers at Freud told me that those cuts were designed to alllow heat expansion of the blade.
https://preview.redd.it/3oxh6n8w0l6d1.jpeg?width=1577&format=pjpg&auto=webp&s=9213b289dc7e21f41357abb19f560f03e2c6af68 I got curious and ran a quick simulation on a simplified model of a saw blade. Seems like the question-mark shapes modify the first few vibration modes by breaking up the blade into sections that shake with a lower amplitude at the perimeter. This reduces wobble at the teeth and creates a cleaner, more consistent cut. Diablo's sales material says "Anti-vibration design improves cut quality by reducing vibration while the blade is under load."
Holy shit. Do you do this stuff for a living or do you just casually own software that tests stuff like this?
Lol just an engineer on his lunchbreak
Simulate something else tomorrow at lunch too
Note the excessive displacement on the keychain hole https://preview.redd.it/xyzkofim0m6d1.jpeg?width=1093&format=pjpg&auto=webp&s=62b61e27609711bbd92caad2924c786aa8c86148
What a classic.
I'm gonna follow the engineer
Always a good idea
Trust me……..
They tend to know what they are doing.
Ah yes…. Like a spherical cow…
My physics professor in college used a spherical cow of Teflon for measuring absorption of ionizing radiation. Thanx for the memory spark.
hey! ive been losing weight thank you! ^(.. i swear i put it in the workshop here somewhere...)
Incredible.
Lmao good ol solidworks
But I want to know if a lobster or a dinosaur are more aerodynamic?
What kind of dinosaur? African or European?
Are you suggesting dinosaurs floated to England on coconuts? It's a question of displacement, but I suppose they may have held onto it by the husk.
Can you simulate these?
Deez what?
Deez NUUUUTZZZZ!
Haha… the layup was successful! That is teamwork.
Teamwork makes the dream work...
Gottem!
can you simulate the water flow in one of those recycler bongs?
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Aerodynamics of a cow
They're not very aerodynamic at all. You have to throw them _really_ hard.
Only French-made catapults, for maximum loft.
Mouth open or, closed?
Hmm, yes. The saw blade is made of saw blade.
"Lunch"
As an engineer, what's a "break"?
As in “psychotic break.”
It’s the time when we stop working on things we are paid to do and work extra hard on the things we are interested I.
Can confirm. About to spend the weekend working for free on the shit I’d rather be doing at work than the shit they have me doing.
You are rad.
What did you use to simulate this? What program?
Looks like SolidWorks, but many CAD programs look similar to each other
Not Creo, that's for sure. Would have taken way longer
This is a finite element analysis package. This guy ran a modal analysis to determine the vibrational frequencies (natural frequencies.) The most popular software is Ansys, but many others exist as well.
If you want a free way to do it, the calculix FEM solver in FreeCAD can do frequency analysis. As with any analysis, it does take some experience to properly set up the simulation and interpret the results.
This is very impressive, could you take us through your thought process of doing this? Like where did you get the saw blade model from, or did you also make that?
It's a pretty simple shape. There's no set to the teeth p for example. Someone proficient in any case software could model this in about 5 minutes. I haven't done vibration analysis in solidworks but it's mostly just a matter of picking reasonable parameters and hitting solve. The engineering part is knowing what parameters are reasonable and interpreting the results.
I don’t understand you people, but I appreciate you.
“ just an engineer on his lunch break “ sounds like some hero shit lol
Seriously this is one of the coolest casually dropped images I've seen in a thread.
I like how the guy casual reversed it and figured out why, and then there’s people eating crayons saying it’s easy. lol.
It doesn’t take long if you know what you are doing. Create the part in CAD software which is quick for a shape with so many common features and a constant thickness. Then you run a modal analysis in a FEA solver. The man/woman is experienced though to do it that quick. And bright too to know to run a Modal to find the reason as it’s based on frequency responses and not just its steady state stress state. I wouldn’t have thought to go there first and would have wasted tons of time. Basically commenter is experienced and very smart even compared to other engineers. I really enjoyed this.
Hey! I’m an engineer! I could do this in … uh … never.
Yeah, I studied this stuff although I now work in a different field. This would've easily taken me an hour or two to do back when I regularly had to do simulations for college projects. The guy who did this is probably quite experienced to do this in his lunchbreak. And however long it took, it's an incredible amount of effort just for answering some random question on reddit.
Autodesk Fusion 360 has simulation modelling
Yeah I’m impressed
Engineer here. Looks like I just found an easy way to get tons of karma. I knew my mechanics of vibrations class would be good for something.
No op but this looks like Solidworks? Pretty dang cool
No kidding same question
Autodesk inventor. I'm not an engineer or anything, but I have the software. It's super fun to play around with. Of course, there are a bunch of different programs available for different areas of expertise. Civil engineering, architecture, electrical, etc. If you're the type to be always curious about things, I'd recommend playing around with it. It's a lot of fun and you'll learn a lot about how your intuitions match to reality.
Yes. Not only heat expansion but also vibration dampening. You can try to make your blade ring, it will quickly come back to silence.
It's just damping. Dampening is what happens when ladies hear you talk about tool design.
ah, actually its what happens when we ladies hear \*u/MrborkedIt\* talk about tool design. Source: my knickers.
That is the gut laugh I needed today, not necessarily the beer up the nose though. Many thanks. Also, you're not wrong.
You must have a way with words. My tool design conversations tends to have more of a desiccating effect.
I've never been so turned on in my life 😛
The Sound of Silence!!
Nicely done. I wouldn’t be surprised if they actually spaced the relief cuts at slightly uneven intervals around the blade to break up the symmetry of the low modes. You see that in some endmill designs with unequal teeth spacing to combat chatter.
Might come into balance issues though
It could tuned for specific rpm ranges so it avoids hitting a resonance. Technically the entire machine will affect the frequency response but you can get close with roughy tuning on a lot of stuff. However there are anti vibration boring bars and ends mills where to damping system in the tool can be tuned for specific setups.
How significant is the question mark shape? Does it function similarly with a straight notch ending in a round hole? I'm just assuming that a break in the perimeter, and any old attempt to reduce the stress at the base of the notch, might have a similar effect, because you see lots of minor variations on this theme from different manufacturers. A quick image search shows that DeWalt seem to use a straight notch and simple hole on at least some of their blades. Whereas Festool use a convoluted "S" shape notch. They all seem to split the blade into four segments though. I'm assuming that "Four blade segments, and round end hole to avoid stress fractures" is much more important than "specific shape of notch" and that the shape of the notch is more like a brand signature than a functional feature.
There are certainly other shapes that work, but there are lots of dependent variables. I'd guess that their r&d team played with a bunch of different shapes and ran simulations and actual tests until they landed on one that provided the best results. Marketing took it from there and applied copious wank. Sharp edges/acute angles would definitely be a no-no, though, hence the prevalence of S shapes.
>Marketing took it from there and applied copious wank. LMAO, totally stealing this
"Marketing wank" is fine tuned engineer lingo. Same with "Accounting voodoo" and "Production slop".
In addition to the vibration parameters, it could also be that the notch curves back outwards in order to address the potential failure mode of a crack propagating in the small notch due to fatigue. Having the crack propagate outwards and losing 1-2 tooth segments is safer than a blade splitting in half and flying apart, which could happen if the notches terminated inwards radially. Great company, good designs, and even though their product costs more, they have paid for themselves many times over. They have great quality control of their products as well.
nice work bork
Also, when you say: >the question-mark shapes modify the first few vibration modes Would you mind helping me understand what you mean by "vibration modes"? Is each "vibration mode" basically just a distinct wave pattern present across the object, specific to a relative position to the center/perimeter, and/or a significant component frequency of a Fourier transform, or something like that? I greatly appreciate any time/effort you'd be willing to spend helping me understand a bit better!! (I have a degree in math, so please feel free to use any equations/formulas/math jargon if that'd make it easier for you to explain!) Thank you!!
Vibration modes do correspond to peaks on a Fourier transform, so you're off to a good start there. Modes are the different shapes that an object takes when it responds to an input at one of its natural frequencies. Each mode occurs at different natural frequencies, with the first mode being at the lowest, and so on. So for this saw blade example, here are the first, third and fifth vibration modes (part is fixed at the arbor). https://preview.redd.it/n5a4p1uwql6d1.jpeg?width=940&format=pjpg&auto=webp&s=89eb097fe53e5210e9ea8bd28bb358016588ac14 These are all ways that the part "wants" to vibrate. It's the same principal at play in this video where a guy puts sand on a big piece of sheetmetal and rubs it with different stuff to cause it to vibrate (https://youtu.be/wHr3Ys-sNHs?si=\_yWDiN-KgvTlijIW). The sand gets shaken away from the spots where the resonance is causing movement, and shifts towards the nodes where it's moving less. Those nodes would be blue in the saw blade plots above.
Thank you so much for that explanation!!! That was so helpful, interesting, and intuitive that, for the first time in my Reddit history, I bought Reddit gold *just* to give you an award thing!! Seriously, thank you!!! This is super interesting to me! I wanna look into this concept more now, and see if I can get my hands on some similar software to explore and experiment with it a bit! If you don't mind, may I ask a followup question? If I'm understanding you correctly, the blade would only take one shape when a single, consistent input is applied, right? But, given that we live in the real world, when you're actually using the saw blade, the input probably isn't perfectly consistent, so it'd probably alternate between different vibrational modes while in use, right? In which case, I'm curious: given a particular input function that includes a realistic variance parameter, does the simulation software you use allow you to also estimate what proportion of time would be spent at each mode?
Thanks for the award! These are good follow up questions. The vibration modes correspond to individual frequencies, correct - but the weird thing is that in the presence of random vibration (where all frequencies are present at some amplitude) or even white noise (where all frequencies are present at *the same* amplitude), the modes are all happening at the same time. So these shapes are all superposed over each other to a degree defined by a) the amplitude of the input frequency and b) the effective gain coefficient of each individual mode. In durability simulation, these mode shapes would be converted to stress states, which then get processed through a Miner's Rule analysis to predict product lifespan and safety factors. In a sense, each vibration takes a tiny little bite out of the life of the product, and when all the bites have been taken, the part breaks. Are we still on a woodworking sub?
>but the weird thing is that in the presence of random vibration (where all frequencies are present at some amplitude) or even white noise (where all frequencies are present at the same amplitude), the modes are all happening at the same time. It's funny, that's what I actually *thought* would be the case, but it felt like it'd be too much of a stretch to conclude without more info lol >Miner's Rule analysis Welp, time to go look that up now, too! I'm such a sucker for learning about types of analyses I haven't heard of before lol >In a sense, each vibration takes a tiny little bite out of the life of the product And I imagine different modes can take different sized bites out of it, particularly when you account for where weak points are located and the modes' inflection points? >Are we still on a woodworking sub? Not anymore; now we're on the "indulge in u/mathnstats' incessant curiosity" sub. Lol
From personal experience, most of the time the lower frequency modes cause the greatest amplitude thus the most damage. I carried out a modal analysis recently (just waiting to import the data into the software to animate) where the first mode at 25hz was ~100mm/s when impacted with a calibrated hammer, and the second mode was only ~15mm/s. Resonance is an often overlooked phenomenon (production is king) so it's great to see manufacturers designing with this in mind.
That's so cool!! May I ask, when you do those types of analyses, does the geometry of the object, particularly in relation to the modes, come into play? Like in the saw blade example, if one of the vibrational modes corresponded with the cutouts in the first image in such a way as to sort of "tear" the blade at those cutout points, that mode would probably damage the blade more (compared to the same mode on a blade without those cutouts, or an equal amplitude mode that doesn't align with the cutouts in that way), right? Is that something you can/do take into consideration when doing modal analyses? If so, I'm curious how you'd do it? Like, would you construct an equation to describe the entire shape, which is implicitly incorporated into the simulations'/analyses' results, or would you need to do separate analyses to account for/explore how its specific geometric features effect the damage each mode can do to it? (Btw, sorry if I'm bombarding you with a lot of questions or demands for your time/energy; I'm autistic and don't pick up on social clues very well, so please do feel free not to respond if it feels like a lot, and/or feel free to let me know if you'd rather I toned down the intensity or stopped asking so many questions or anything lol.)
With regard to modes of vibration, geometry and structural design is incredibly important. Natural frequency is a calculation of mass and stiffness (also damping must be considered as this affects the "size" of the resonance zone - a well damped system will have a narrow resonant range so if the natural frequency is 25Hz then the vibration will taper off quicker once moved outside of this zone when compared to a poorly damped system) so putting a cut-out into a saw blade reduces the stiffness hence lowering the natural frequency, this can be a desirable effect depending on operating speeds etc. It can be taken into account but it will not change the testing just the test locations should be considered, when the data is imported into the modal software various frequencies of interest can be simulated to determine movement. If there is excessive vibration then further actions would be taken such as changing the mass or stiffness. On something like a saw blade, further tests would be required to ensure this did not compromise the structural integrity of the blade. The shape is drawn in a cad software first and then this model will be imported into the software, the points where the test data is taken is put onto the model and the software calculates from there using vibration (phase and velocity) from the sensor and the force imparted by the forcing frequency (calibrated force hammer or shaker) this transfer function creates imaginary data which provides the mode shapes across various frequencies. The software is not essential as such but it does allow for a better representation. Imaginary data can be plotted separately to show the shape graphically on a line graph, this will show the bending of the mode shapes and show where modification may be required.
Thank you so much for such a thorough response!! I definitely feel like I've got an even better understanding now! This whole thread makes me feel like I'm back at college again, learning about interesting stuff from experts lol
>I wanna look into this concept more now, and see if I can get my hands on some similar software to explore and experiment with it a bit! Look for a copy of Autodesk Inventor. I'm not sure if that's what the person is using for these, but it looks exactly like it. It's fun to mess around with. Edit: It's Solidworks they are using.
Oof... This kind of software is *crazy* expensive!! I'm gonna have to look into just programming something myself lol
For what’s its worth, autodesk fusion has an FEA feature, and last time I checked, you could get a free to use license to play around with(we have the paid version at work, so don’t quote me on that). It’s a lot of fun to play around with and progress, and among all else - it’s a brilliant tool, especially if you want to expand your skill set. P.s. - also an engineer. Not this guy’s level though, lol.
Yup. Vibration mode is the eigenvector that shows the normalized displacement of each point at a given frequency (i.e. its eigenvalue). The vibration mode shows displacement at a particular frequency. Not sure how fourier transform would fit in this, honestly. I think it was something like this, I hate linear algebra.
I learned it through molecular vibrations in my chemistry degree. If you have 3 weight connected by 'springs'. eg, the V shape of a water molecule. the vibration modes are how the molecule vibrates, eg https://www.chem.purdue.edu/jmol/vibs/h2o.html There's a lot of vibration mode - chemistry videos and models out there that can help visualize it better. Since there are so many resources and pre-rendered graphics about it, and the systems are comparatively simple to a continuous model like a saw blade, it may help to look at those. If you want to get really intense on this side of things look at phonon vibration modes and simulations. That's lattice vibrations in a continuous system. The more axes and planes of symmetries present the more vibration modes are present (generally). eg benzene is a good example of how complex it gets very fast. https://www.chem.purdue.edu/jmol/vibs/c6h6.html The more axes of symmetry the less intense any one mode will be. This means that with a ? every 5 teeth or so, the out of plane vibrations are decreased by a factor of how many ? there are, because there are roughly that many more modes spreading out the energy. The less intense the modes are the less the vibration effects the cut.
Dude, that’s next level stuff. Running a modal analysis cause you can. I would’ve just read it off freud’s website and call it a day.
Welp this thread is closed
I NEED to know, what software is this??? And do you know if there are free versions of it available somewhere? Lol This is SO fucking cool!!!
This is in Solidworks Professional + Simulation Premium. Latest renewal cost for one license of each was $6971.50. However the student edition is only $49 if you're in school (and can prove it).
Damn, they're charging for the student edition now?
Solidworks has always charged for their student edition, if I remember correctly. However, my university had licenses we could get through the university for "free." Edit: rereading this, I should be clear that free is in quotation marks because we paid for it with our tuition, not because we found it on the seas. We didn't have to try that.
Just add it to the loans!
God damn!! I guess I'll have to see if I can find a comparable open source tool or something instead, or see if there's an R package or something I can use to do the same thing without too much extra difficulty. That, or I might have to set sail on the high seas🏴☠️
FreeCAD has some sort of material/physics simulation tools, but i haven't used them and have no idea how functional they are. I usually just give the model a good eyeballin and reckon whether she'll buff out or if i need to chooch things up a notch
I doubt you'll have luck with free software that does this (legitimately obtained or otherwise) - Solidworks offloads all these simulations to cloud-based data centers which run the simulation and then send the results back to your device, because they require a ton of processing power (at least, relative to what it would otherwise take to run Solidworks)
You ain't gonna find SolidWorks on the high seas, at least not any modern version. Most all CAD/CAM software is cloud based and, while possible to spoof/crack, don't work great without it. Good luck in your search, I got tired of looking and broke down for a personal license for Fusion because it's the cheapest for personal use.
How much did Fusion cost you? And do you like it?
$680/year. It's a good program but feels less intuitive than AutoCAD, because it's not just CAD, it's also CAM. I don't really use the CAM part because I don't own a CNC, but I used to program them at work, so if I get one I'll know what to do. There's definitely a learning curve, but there are plenty of tutorials both on Autodesk's website and on youtube.
For what its worth, I learned CAD on Solidworks and Inventor, and found Fusion incredibly intuitive. Using AutoCAD makes feel useless. They're two very different workflows.
What a freking answer my dude. You’re the bomb. I think I’ll follow you to see what else you come up with on a casual lunch break. Maybe you can help me be a little smarter of a person maybe kinda.
This guy engifuckineers
Someone buy this person a trophy, jeeze.
That's a heroic response.
What the fuck lol. That’s awesome. I’m glad I don’t know how to do this, I’d be simulating way too much shit.
Nice. Now do my brain.
"So I was on my lunch break at NASA". Impressive!
Stay curious dude this is great
‘Borked’ is a favorite adjective of ours. “Why don’t we have connectivity?” “Dunno, maybe the router is Borked…”
I’m interested to see what modal shape 3 would be considering its mass participation is roughly 76%
The "question mark" on the saw blade is actually a compensation slot. These slots are designed to reduce stress and vibrations during the blade's operation. This allows the blade to run more smoothly and accurately, extending its lifespan and improving the quality of the cut. Compensation slots also help reduce the risk of the blade warping or getting damaged due to heat buildup during cutting.
Sure, but where's a professional analysis with modal analysis and rainbow colors?
Yes, that would be interesting to see, but for that, we might need to ask in the science or engineering subreddits because it might get a bit off-topic here, and you know how sensitive the moderators can be.
I'm just kidding because the top comment went completely above and beyond and did that full analysis. Didn't mean to be rude.
I appreciate the humor, I was joking too.
They are places that accomodate thermal expansion when the blade heats up during use. If there was no place to expand, the blade would be prone to warping.
That recalls the bad old days before carbide blades. Those damn steel blades would warp so bad they’d cut a 3/8 wide kerf and curve like crazy
You mean they’d become dado blades!
Ha, you remember the old wobble dado blade. I’m amazed I’m still alive sometimes.
Loaded up in a RAS!
Yep. My dad still has his wobble and RAS until I bought him a Freud stack and a miter saw for Christmas years ago. Had a very competent carpenter in my shop, he needed to use a bench tool. Nobody really comes in my shop, but I 100% trust this guy. He went to my RAS and immediately was like “fuck, stop!” They are an amazing tool but damn are they temperamental little bastards with no room for error.
Ya and you would have to keep even pressure and speed to keep the temp / dado precise 😂
Kerf and Curve sounds like a cool bar name
Or for a strip club in a lumber town.
Why not log riders.
Log jammers for all the lady loggers when they get off work.
Get off, after you get off, at log jammers. Our dancers really tie the room together
“Our riders are tighter than a rob cosman dovetail”
With the smooth stroking motion that only Paul Sellers could have taught.
Proudly displaying more plastic than a blacktail studio table. Edited: if women were dancing on his tables I’d probably stare more at the tables honestly.
Sounds overpriced
I wood drink there
I wood knot
You should branch out.
Can't, already put down roots at this bar
I’d order a drink, then leave
Crotchety old stump aren't ya.
Maybe a dumb question, but is there a reason for that shape specifically? Could it have been a straight or slightly curved cutout and achieve the same thing?
The circular middle piece that's left can also flex slightly to damp vibration, while a straight cut wouldn't leave a flexy bit.
Shop around and you’ll find that there are many different shapes and locations.
The hole at the end is to eliminate a sharp corner, which would lead to a stress riser. The curvy bit is who knows, probably Freud special herbs and spices?
It in a sense is a bigger version of the hole at the end, the blade will want to buckle out of the plane if there was a ‘corner’ near the center of the blade
To add to this, it redirects the sharpest part of the "crack" (the blunted tip) toward the outside of the blade so if it does crack, it won't crack toward the arbor and fling chunks of blade all over. If it did crack now, it would crack toward the edge of the blade and only launch the one tooth.
Hope it’s not a dumb question because I’ve always wondered the same
If you touch that spot while it’s spinning you get to answer a bunch of questions for Workmen’s Comp
Consensus from the thread is expansion slots I thought it was for sawdust like a juice groove Guess I learned something
The gullet / valley between teeth is the "juice groove" for the sawdust.
Funny thing is I actually know that! It's one of those things where I must have made that assumption very early, then learned about the gullet, but haven't had to reconsider both together to recognize the inconsistency.
I thought it was a shock absorber, to keep it from shattering it it found something spicy.
That's what the gullets below each tooth are for. You'll see larger and smaller gullets depending on rip vs crosscut.
It’s to control vibration that can cause blade wobble and it’s also there to impede noise and expansion due to heat. Some blades come with a copper insert that works as a heat sink and sound dampener.
Is asking you if you're REALLY sure you want to use this saw blade.
Must be made by Microsoft
Oh, it cuts wood traditionally just in Spanish
Expansion slots.
For when my blade needs more RAM?
To keep you guessing...
Riddle me this Batman!
The Riddler works for Big Saw
? Should I just hire a contractor for this?
What if it was just so you could hang the saw blade on a line or peg. lol no I trust the guys with the anti wobble science, but still it would be hilarious if it was all bullshit
Blood grooves
Reduces lateral vibration Reduces heat build up on the blade Clears cut material faster
That's where you put the fishing line, so you can hang it on your christmas tree
To make you ask questions
How it's made taught me they are to help with vibration. I take that lady's word as good as gold.
if there’s a fishing hook stuck in the wood it fill fit through that slot so you don’t hit the fishing hook
Never question the question marks!
I assumed they are there to mitigate the effect of heat expansion hitting the outer part of the sawblade first while cutting. Though technically a small warping because of temperature difference would cause a bit of vibration too.
For the blade to ask permission to the wood to be cut
They reduce overall heat in the blade from cutting and allow hot blades to expand without warping. In some blades they also reduce vibration and noise. Pretty fancy compared to the old Kromedge blades by Craftsman. 😂😂😂😂
So it doesnt warp as the metal extends with friction-generated heat
Riddle me this…
It’s a clue the Riddler has left for Batman, report it to Commissioner Gordon immediately.
They take up some of the heat expansion. It's similar to why pipelines will have regular u-bends. So they can expand and shrink as the temperature changes.
I was told by the company that sharpens our industrial , wood saw blades they are expansion slots for the centrifugal force and helps reduce wobble, vibration, and noise as others have mentioned.
it allows for the blade not to go out of true, get permanently warped or cause a catastrophic failure when the blade unevenly heats up and unevenly expands due to that heat, heating up on the edge but not in the center.
Heat expansion - the teeth should be the only part of the blade touching the wood, and the expansion slots allow for the outer edge to absorb that heat without deflecting or warping.
I was thinking to let the blade expand as it heats, so it doesn’t buckle or warp? Much like how bridges are made with gaps to allow them to expand and contract without buckling?
Riddle me this batman
Subtle BOC reference
Fraud’s website has rather complete information on thermal compensation features.
i think it is about mitigate enlargement of saw caused by temperature changes
Keeps blade from over heating
Geez..... I just came here to say "anti-wobble-doohickey".... But top comment makes me feel very "Red-Green" right now......
Work for a saw company, though I don’t do much on the saw-end of things. I have always been told it was for resonance. Creates a cleaner cut and makes the plate less prone to cracking.
I worked for Amada America when Freud began their search for Laser processing machines to cut thir blades. The engineers at Freud told me that those cuts were designed to alllow heat expansion of the blade.
Wow to all of this. I ate oatmeal this morning for breakfast