Is this really why a Bandsaw Sawmill Blade won't cut Straight?

I had some thoughts about why a bandsaw blade might not cut straight and then had an epiphany. Could this one equation explain all you need to know about setting up a sawmill?
Thoughts?

[@WhatDennisDoes]

I should have pointed out, because of the 4 next to T, blade tension has the greatest effect on reducing deflection. Four times as much as reducing length. So tension is the most important thing according to this equation.

[@jaed660603]

Tensión must be enough to support cut, but sharp and setting gives direction up or down in horizontal, left por right in vertical sawmills.

[@Cloudkicker000]

Question to you about your saw, in redoak video I could see the waves you are taking about. I just wonder how parallel is your cutting blade to the motion on the rails? Should it ideally be parallel? Or would a angle create a counter force pulling the in place?

[@VKMilling]

@@Cloudkicker000 I will almost guarantee the reason this happened is the front and the back of the blade are not parallel to the rail surface.

[@rok1475]

You are over complicating it and mixing a lot of misinformation. 1. The blade must be properly tensioned. Commercial sawmills tension a 1” blade to 16000-17000 psi. Assuming the width of the blade from the bottom of the gullet to the flat edge is 0.8” and the blade is 0.042” thick you need to stretch that blade with a force of 530-570lb. The tensioning mechanisms must therefore exert a force twice as high. A simple 1/2” threaded rod/nut tensioner can easily create much higher force so the problem of blade tensioning is reduced to knowing how much tension is on the blade. Hydraulic tensioner have a gauge and the force can be calculated easily. For small mills compression springs are a good solution. They compress by specific length with given force applied so by measuring the length of the compressed spring one can quickly calculate the force on the blade with fairly good accuracy. 2. Blade tracking: alignment of the wheels must be near perfect. Wheels must spin on the same plane. If wheels are off by even a small fraction, blade will wander. 3. Blade guides: the guides must be aligned so they actually guide the blade with downward tension to keep it parallel to the plane of the tracks of the sawmill, not just skate on the surface in case the blade wants to wander off. Adjusting the guide rollers is not difficult but requires fair amount of precision some woodworkers are not used to. Get a 6” digital height gauge, lower the blade close to the tracks, put something flat across the tracks and measure each side of the blade , front and back. If every point of the blade is within few thousands of an inch, guides are aligned well. Then move the adjustable side of the guides to different points and repeat the measurements. They all should be very close. If not, adjust the guide rail. Well tensioned blade running on wheels that are aligned to the same plane and guided parallel to the tracks plane will cut straight. There is no magic to it, just physics. There force exerted by wood on the blade should be parallel to the plane of the blade. Any down or up force is an indication of incorrect alignment and tension. A perfect alignment can be thrown off in seconds by sawdust particles sticking to the blade, wheels and roller guides. Good lubrication of the blade helps. Small teeth produce finer sawdust that tends to stick to everything, big teeth produce miniature toothpicks that fly out and not cause trouble. Use blades with bigger teeth, but feed it into material so those teeth produce large chips not dust. If the motor can not handle the load, get bigger one or live with the consequences of fine dust or build some scrubber and screen to reduce the sawdust deposit, clean the blade frequently to maintain good tracking of the blade on the wheels. Wheel size is important for blade life. 12” wheels will be fine for cutting a few logs a year, not so much for running commercial milling businesses. Aluminum alloy cast wheels can easily cope with the forces needed to tension narrow blades. It’s the bearings that do all the heavy work. And this is where thicker shaft helps-it lets you use bigger bearings that can take bigger load. But also thicker shaft will deflect less with blade optimally tensioned. Less flex=better blade tracking and less material fatigue. You don’t need to worry about material fatigue if cutting few logs a year, but tracking is always important.

[@WhatDennisDoes]

This was flagged as spam, so I didn't see it right away. I released it from the queue. I think I'm in agreement with pretty much everything you said. I'm not sure how the wheel alignment matters for the blade wandering in the cut, though. The guides should keep the blade parallel to the cutting path. The alignment needs to be good, but not perfect. The kerf will be thicker than the blade so as long as it stays within the kerf it should be good. Of course blade set needs to be considered but in my experience the teeth are never perfectly ground to be perpendicular to the blade. In any case my problem wasn't that the blade always cut up or down, it was that it wandered and followed the grain of the wood. I hope I don't sound like I'm preaching because I hope to just present these thoughts for discussion. I like what you have to say, thanks for the comment!

[@tomoverholt5123]

I was a little surprised that you didn't mention logs with soft and hard grain like pine, from my experience the blade prefers to follow the soft grain which is difficult for it to do if the tension is right, the guide's are close and the blade is sharp, but if the blade is dull it will be very difficult to keep it from following the soft grain so you have to keep going slower and slower to keep it straight until you change the blade. Waviness isn't as much of a problem with harder wood because there is less soft grains to pull the blade.

[@WhatDennisDoes]

Great point!

[@onewyatt1]

Blade speed needs to be about 4,000 feet per minute. Thin curf wonders less. Feed rate of wood must not be above blade capacity to cut and clear. Blade guides shouldn't add more than the slightest tension, they are for blade alignment only. Blade size and type are determined by factors mill manufacturers can give guidance on. Wider is better as is thickness but availability is a factor.

[@andrewbuis98]

That 4 comes from approximating the curve of the saw blade as a parabola! The slope of the parabola is 2 times the eccentricity divided by the length. When that length is half of the span (L/2), your equation becomes t =4dt/L.

[@stephenanderson3056]

Another thought on blade wandering. I forgot to tighten a blade guide on my saw. It had been cutting Oak perfectly till the top teeth (The ones that had been set facing the top of the cutting edge) hit the guide. After that the blade dived like a submarine due to the lower facing teeth being set properly and upper teeth losing set as well as being dull. I thought I would sharpen the blade to see what would happen. The cutting improved as did the diving, but it was not perfect. I put a brand new blade on and cut a 14" oak log perfectly. It appears that the sharpness and quality of the tooth set is really important. I was looking on a video by a sawmill owner (which I recommend) and he said that he changes blades every two hours. I am working on an automatic blade sharpener and using this blade as a test blade after I reset all the teeth and sharpen it a couple of times I will let you know what happens.

[@rjlchristie]

Little t (deflection force) will also be dependent on blade speed and tooth kerf and the uniformity and density of material being cut. my 2c

[@curtiswagner834]

I know this post is old but I feel the need to add a new dimension to all the comments. First of all a blade needs to be sharp, set properly, and tensioned well. (I like your guitar string comparison..... I used to tension my small shop bandsaw using a guitar tuner while plucking the blade like a guitar string.) I see a lot of comments on blade GUIDES..... I do not see much about blade SUPPORTS. There is a big difference between the two. If your blade supports are not lined up properly it will cause the blade to actually bend...putting pressure on the front of the blade causes the metal compress in the front and the back of the blade wants to stretch. These two opposing forces tend to make the blade buckle.....try it. Take a blade with your hands and try to bend it width wise. You will see it buckle. Granted ....if all the other factors are in good shape this will reduce that tendency, but that force is always present. LASTLY ..... you cannot force a blade that is dull on one side to cut straight. I like to see how other people think so I enjoyed your video.

[@progamer-hy5fs]

congratulations my friend, thanks for the effort to discover interesting ways of work better,. I liked a lot your video

[@curtlemons4211]

I've been cutting Australian Pine with a janka hardness of around 2900. - It's not for beginners. And I will tell you, thicker and larger blades make the biggest difference. I've tried it all.

[@VKMilling]

I'm aware that this video is now a year and a half old. That said, I run a bandsaw mill every day. Usually culprits of cuts that you are showing are: at some point, your tooth side (front of blade) and the spine side (back of blade) become no longer co-planar. Usually this is because of either A) your wheels or guides are deflecting either the front or back of the blade out of alignment with the opposing side or B) you have material build up between the blade and the wheels; one side of the blade tooth profile has lost its set (you hit something that pushed the teeth out of whack); Tension. Blades heat up when you're cutting. Doesn't matter how much lube you are using, doesn't matter what that lube is. There is a change in the temperature of the blade and thus causes the blade to stretch. When it stretches, you have to apply more tension. Also, adding more blade ABSOLUTELY decreases your chance of deflection. Not only because it reduces the deflection by force, but also because the spine of the blade, being wider, acts as a rudder in the cut and helps keep that cut flatter and straighter. If you cut a lot of very knotty material, you want to use the widest, thickest blade your sawmill can handle.

[@harrymusgrave2131]

A handful of things come to mind.. Are your blades too long for your saw? Next. The blade could be getting hot. For most cutting we use water to cool the saw. Next. Wimpy or worn wheel bearings. Any play at all will mess you up. Also. You may have to slow down on the feed. You have a small saw. And last. Check your saw guides for wear, and or improvement. It might be time to change up to some bay bailer parts.

[@skilomodelista]

I built one. Initially I thought that high speed was a good deal, but it burns the saw teeth’s even with heavy water flux. The waving is a persistent problem. Now I will replace, from 3hp2 pole motor to 10hp 4 pole motor + pulley belt reductor monted with a heavy bearings to get a lot of tention on the saw blade.

[@wrathofsocrus]

That's always handy when you can find an equation for one purpose that also works for something different. I remember setting up drip irrigation and wanting to find out the flow rate for a given pressure and it turned out that a fuel injector calculator gave the same numbers as I got from testing. All of those thoughts are on point. The board being cut @1:35 really tells the story of how outside forces can manipulate the blade, as it is following the same path as the previous cut on top. The only tip I have is that you can run the saw and use a sharpening stone or similar on the sides of the blade to help with any minor imperfection. If the teeth or the weld protrude a tiny bit they can deflect the blade. I'm pretty sure I saw it on one of Matthias Wandel's bandsaw videos.

[@sosebee12nadc13]

Undercover Adam Savage? Lol thanks for the info!

[@arbenibraimi6584]

Sir also my bandsaw doesnt cut straight can i ad some bearings and is it ok to aproach the bearings at max so can the bearings touch the blade all the time because my blade makes a lot of crackings when do this can you explain what to do because i have no choice thanks a lot

[@ledenhimeganidleshitz144]

You have the wrong equation. Try the equation for flutter. Re.aerodynamics.

[@mk-jf1ux]

way out west a youtube channel has a cheap car wheelans axlex based video series published a year before you first one still good today

[@paulandreboisvert8467]

from what I have experience is where the blade travel on your wheel ,forward is more stable.

[@davenopeapottimus2590]

10:07 - 10:15 Hashtag that's what she said. Everything else right, then tooth set.

[@gaminawulfsdottir3253]

I think I like this guy.

[@mareknosek996]

Most blades need a little pitch on the roller's thats how you get a better cut.

[@Lumber_Jack]

I think you realized this, but thicker and wider blades can handle higher tension, so that is how they would factor in to helping. Blade size doesn't enter into the equation directly but it influences the "T" in the equation. Bigger wider blade means you can run larger values of "T" in your equation, and that will reduce blade deflection.

[@dukedez1]

I put B56 belts on my 18.75” pulleys. Very tight fit but way less vibration when spinning full speed cause it was more balanced being nice and tight on the pulleys. Lots of elbow grease to get them on. But worth it. Lol

[@WhatDennisDoes]

Oh good to know! I'll try the 56 belts

[@scottstuart9158]

Thank you for this video. You made so much sense!

[@fabian075]

Hi, I´m building one, but I have proble with vibrations, when the engine is running, the blade have too much vibration, do you know why?, did you have that problem or not?, thanks

[@WhatDennisDoes]

I never had that problem. My first thought is that a wheel is not balanced or a bearing is bad. A couple things to try: does it vibrate without a blade on? Does it vibrate with a different blade?

[@sylvesterdombroskie7823]

I owned a circle sawmill for 26 years and I believe if you went with larger wheels thicker and wider blades as well as more set in the teeth and further tooth distance you would saw straight and faster if you don't believe take a look at shop bandsaws the smaller ones don't cut as good as the larger ones. Look at the large bandmills and resaws why do you think their bands are so big. If these bansaw sawmill builders would make a mill that would cut good and fast i'd buy one. In the meantime I'll keep building one that works right.

[@aadilchauhan5782]

Can small sawmill cut straight??

[@timberdoodles4647]

Okay, comments, I hope I get a response. This was hard to listen too, not being a math geek, more of a trial and error common sense kind of guy, anyway. You touched on the the issues but instead focused on the math. Yes, teeth per inch is important, angle of the tooth is as well, so is set, and the geometry of the gullet. These all need to be in order for a good cut to happen, then you need to ensure the band teeth are sharp. Logs size and species, hard or soft wood all have different requirements so know you stuff. if any of these items are in compromise you will get funky cuts. These funky cuts are more likely to be over ridden by some guy tighten the band more, wrong call! Just fix the most likely item first, dull band, the tooth angle then set. Over tightening the band will only cause bearing wear and shaft wear, which lead to unnecessary repairs and increasing time and money input. Oh, the lubrication isn't lubricating the band, or cooling it, the "lube" is a cleaner, that is its primary use, sure if you dump a gallon of water on a band it will cool it maybe too much, what the "lube" does is clean the band, its a cleaner, cleaning the pitch and sawdust build up off the band so it can run at a proper tension and free, the band is actually air cooled, a clean band will run cool, also over tighten a band will cause it to heat up, heat is bad for band life and doesn't solve the dip and dive problems. Some food for though.

[@wazzazone]

At 2:35 all you need is a blade guide

[@ThoenWorks]

what I found - is if you are (for some reason) limited to a certain amount of "force", then you are better off running a smaller blade so your max force gives you more "strain".

[@askquestionstrythings]

Off hand and without looking at any references I would think the psi of a saw blade would be related to the tensile strength and yield with consideration to the Fatigue cycles. (Would totally have to look at some strength of materials references to check that assumption) As for that equation for the guitar string, if I remember correctly from PDE there is a big assumption in the derivation where the string is assumed to be infinitely thin and massless. I've never dived into the deep end of the pool with vibrations where they toss out the big assumptions and deal with objects that have mass, inertia, etc. But the basic thoughts you proposed are right in line with what I would expect you would need to do. Closer supports, proper tension, thicker blades (cross section), etc. I have to wonder if the equations relating to cutting force, etc for machining apply to wood... (we only did the equations with metal, but they should apply to plastic and possibly to wood)

[@TheJunkyardgenius]

I think your overthinking this far too much. Massive resaws have 2-3inch wide blades to reduce twist and wander where as small 1/2 inch blade are used for cutting curves. Its easier to cut curves with a smaller blade, its easier to cut straight with wide blades. Its been proven for a long time, fit wider wheels and get a wider blade and tension your bandsaw properly.

[@onewyatt1]

PS: Always a good idea to build mill that standard blade sizes will already fit. Makes getting blades easier and faster. No need to custom order blades. I am by no means an expert, never even owned a bandsaw mill. Have studied them for decades and designed many after doing deep dives on everything related that the internet could provide. :)

[@viking1ur]

I have some experiance but I am fare from an expert. However there are some basic rools i learn. 1. the size of the wheel and band actually does not matter that much (Look at Milwaukee M18). 2. U learn from when u where small that when sawing u let the saw do the job and dont stress it or push it. If the saw didnt do the job it was something wrong with the saw (blade). Sawing dry hardwood is very hard for the blade so cooling and light pressure is important and a small and short blade will have less meter of running capasety than a longer blade. And when the blade get dull it cant take any stress at all and will quickly get bad and brake. So the most important thing I learn is to use time on the blade to keep them very sharp and to "Wikk" them (It is in Norwegian - dont know what u call it in US - it is about every second teeth sticking out to the left or right). The correct wikk will alow the blade to runn free true the wood with no side stress and it will not rise or dive. I got a electricsharpner with my bandsaw when i bought it 2. hand and it come in handy. The wikk I do with a small handtool. The bandsaw is a Lennartfors powered by a Jonsered chainsaw engine. It is small but works perfect as it is strong enough for the quit large grove in the blade. Very large grove in the blade or large timber like diameter over 60cm would be a larger job for my engine but Idont saw much of that and if i do I need to trim them down to get them prosessed. So the saw - meaning the blade here is the issue. Wish u luck with your projeckt. I also have had plane for many years to build a large bandsaw on truck chassis and use it as a mobile sawmill.

[@swdweeb]

And here I thought you were headed towards reducing 'l' when the log size allowed it. Great discussion and thought process. Of course to get the views you want you needed to smash a watermelon with it ;-)

[@WhatDennisDoes]

Yeah not a barn burner for sure. I did almost whack my head with the whiteboard though, that might have been entertaining. Next taking head video I'll make sure to light something on fire. ;)

[@mildyproductive9726]

You're pretty much exactly right, IMO. Use the biggest blade... that your saw can tension properly; hence, you get the highest T that your saw can handle. And if you still have problems, use the fewest number of teeth you can get for your blade. In wood, you really can't go too low in TPI. If you did both these things, and your saw still can't cut straight, you still have another option! (Besides beefing up your saw). In your video, you said that you need wider blades as you go lower in TPI, because the gullets get deeper. But the gullets don't need to be deeper. "Skip tooth" blades have a relatively low tooth count with relatively shallow gullets. I think they get their name because, say, a 4 TPI 1/4" skip tooth blade might have the same gullet depth as a typical 8 TPI 1/4" inch blade; so it's like every other tooth has been removed. They are often used for making contour cuts in thick wood. But you should be able to do the same thing on a saw mill. If you can't buy the blade off the shelf, you can make it yourself. The typical saw mill blade has a 3 tooth set pattern. You could remove every other tooth, with a grinder! This will allow you to make straighter cuts (and with less horsepower). But you will likely have to reduce your feed rate, because each tooth can only remove so much material per pass.

[@willowmina6745]

Alignment is critical from my experience with blade sharpness and wood density, hardwood versus softwood. The force that is used to move blade needs to be minimized. I even increased my frame stiffness to insure little to no frame deflection, which could contribute. Your frame like mine is not robust.

[@RADMAN752]

I am going through the exact same thing with my mill... perhaps its the tension and distance from the guide bearing to the log like you are saying. running 1 1/4 blade and i find that the blade wanders too far back on the wheels and guide rollers and maybe it is taking the set out of the blade causing it to pinch and wander. i think i can fix this with flanged guide bearings and more tension. Cooks sawmill makes good stuff for homemade mills. thanks for posting

[@mikenute7477]

The other factor I’ve always assumed had a lot to do with it is whether the blade was angled parallel to the ground (or to the track, really). I can’t remember but I’m guessing you had an adjustment to set that? But the other points here on tension, sharpness and feed rate are also good and worth exploring. I can tell you I’ve bought lumber from a guy with a giant woodmizer that is usually high quality but for whatever reason the day he was cutting this cherry was wavy as hell, so even the pros can have these issues. Keep at it and keep us posted!

[@howjwattan3146]

My personal experience, the setting of the saw blade tooth determine whether the blade will drift or not. When a blade start to drift , blade guide could not do much to get it straight. If the bride drift upward, try set more tooth downward, you will see improvement after that. How much tooth need to be reset is all by try and error.

[@wymershandymanservice9965]

Set up your tension hydraulically with a gauge so you can monitor the tension your keeping on the blade. Loss of pressure will show you blade stretch due to heat or as the blade gets dull. This allows you to see real time results on blade.

[@Sn33zuS]

I love to learn from your learning, it puts my knowledge into a mathematical equation as well as pinpoints the importance of tension and workload when figuring out how to build your own for yourself. Thank you, it puts things into perspective and leaves a few things to think about! 🤙🏻

[@jamesspears5127]

Blade tension, the flatness of the blade, blade sharpness, and sap buildup on your blade, are what I have found too cause the blade too wander

[@robertlamka708]

Just a thought. The closer the blade guides are to the work piece the less the blade should drift. Maybe, just a thought

[@billychurchill]

I was thinking that if you sandwich the blade between 2 sets of rollers and keep it close to the wood it would not deflect as much.

[@michalrimmerak1646]

Wheel diameter is very important. Thickness of the blade shoud not be greater than DIAMETER of wheel/1000 for ideal lifetime of the blade (information from www.pilana.cz, blade manufacturer). If you are using smaller wheels then recomended for the blade, you are shortening its life due to bending it too much. Another important information, that many people didnt know. Bandsaw blade must rest. It is recomended to cut 2,5hour, then resharp the blade and let it rest 12hours. So If you want to be cutting 8 hours /day, you must own 4 blades. It may be strange, but try it. I was cutting 8 hours at once and blade is cracked every 15cm (with one final crack).

[@michalrimmerak1646]

...but, as you can see on Woodmizer Timberly, band wheels are 400mm, and recomended (sold with machine) blades are from 0,9 to 1,07mm. So it is not STRICT rule. You are only shortening lifetime of the blade.

[@camreed7073]

i just got the same wheels today liked the video

[@HoneyDoHomestead]

larger bandwheels (theoretically) also give you more kinetic momentum to tear through a rough cut, where as small light weight wheels are relying completely on the HP of the motor to push through the cut.

[@frankdeegan8974]

I don't know but HP leverage torque speed momentum all need to be in balance, a person needs to be an engineer to get this right to be able to saw a flat board. I guess I would have downloaded and studied some of the manuals for store bought sawmills an did things the Chinaman's way and copy copy copy . LOL

[@BofhJohn]

Just a thought... when ripping wood, the grain is also contributing side load. if your blade is dull, it'll round the corners of the point of the tooth causing grain following to be the path of least resistance until the tension overcomes that and you plow through the grain causing the blade to "wander" back in the other direction. Put a dull blade on your vertical saw and rip a hardwood board against the fence to watch this in action. Good find on the formula!

[@WhatDennisDoes]

Good point!

[@dreweaton2154]

Blade tension is key obviously. Too much and you will prematurely break blades. Sharpness is important too etc. You didn't mention tooth set ( I don't think) which is critical or horsepower. Fewer teeth means each tooth cuts more thus requires more hp to stay up to cutting speed. Feed rate and blade speed are important even on sharp well tuned machine. Generally I think this is why mills tend to rely on robust designs rather than taking the engineering to the limit. This way more factors can be less than perfect and we can still obtain decent results without being broken down. $0.02 from a sawyer.

[@WhatDennisDoes]

Yes, well said! "More factors can be less than perfect and we can still obtain decent results". As a hobbyist I can afford to spend time fiddling around in order to save money but I'm starting to grow tired of pushing all the limits. Maybe I'll just push a few of them. I already want to make a follow up video to address tooth geometry, kerf width, etc.

[@rok1475]

Drew Eaton rigidity of the machine is the key to cutting material. You learn this very quickly when working with hard materials like steel :-) Milling logs produces forces most woodworkers are not used to so there is steep learning curve and a lot of surprises along the way. But the end result is well worth the effort.

[@danharold3087]

Good video Dennis!

[@tedsykora1858]

There has to be some internal resistance to bending of the blade if thicker because a thicker blade would be stiffer feeling. Just like a thicker bar of metal is stiffer than thin. Great bunch of points raised.

[@WhatDennisDoes]

Hmm I didn't think of that, good point

[@rok1475]

ted sykora to overcome the force pushing the blade up or down the blade would have to be as thick as the steel bar. Those forces can not be overcome with the strength of blade material, but they can be eliminated with alignment and tension.

[@tedsykora1858]

@@rok1475 not suggesting thickness being the ONLY modification. Just one of several. I would be conceivable that a blade that is twice as thick would flex half as much. Just a possibility.

[@joegillitzer6239]

Amazing!

[@stephenanderson3056]

Veeeeery interesting!