Sawmill blade tension measuring

Band sawmill blade tension

[@2ndamendmentwa74]

Loved the step by step breakdown. Thanks for taking the time. I had to experiment a bit to figure out my "sweet spot" with blade tension. I ended up changing the bearings and shaft on both wheels to 1.25" because I was noticing more flex than I was comfy with on the shafts. While doing that, I switched the steel shaft from a cold rolled mild steel to 4140 (if memory serves) for even less flex. It looks like your mill supports both sides of the wheels : This is one of the main things I am thinking about each time I see that beast of yours. Your mill wouldn't flex like mine (and most that I have seen) if it is double supported.

[@practicallyIndependent]

Thanks a lot for this video! I know it's an older video, but this really helps a lot. I been wanting to make sure my blade tension was set correctly but didn't want to waste money on an expensive measurement tool.

[@ThoenWorks]

Thank you! And love your Instagram feed.

[@practicallyIndependent]

@@ThoenWorks Thanks! I have a bunch of videos coming on YT soon. Just need to take some time to do some editing, lol. I really like your content as well.

[@my83roadster4me]

This man is smart.I have no idea how to begin doing any math other than add,subtract and multiply.

[@rok1475]

You can get heavy duty compression springs that are rated to compress to specific length by given force (i.e. 25% at 980lb, fully compressed at 2100lb). Calculate what force is needed for the size of the cross-section of the blade you have, double that amount and find a spring that covers the range you need. Install the spring between the frame and the tensioning nut and squeeze it until the length of the compressed spring corresponds to a required force. One of the commercial sawmills use this method. Just remember the force on the spring hast to be double of the recommended tension for the blade cross-section since the force at the tensioner mechanisms is balanced by “top” and “bottom” parts of the blade.

[@ThoenWorks]

I have been wanting to do something like this. More to eliminate rigidity in the system than to figure out tension. For now, the rubber tires provide "forgiveness"... May also use a stack of belview washers (wrong spelling probably)..

[@rok1475]

OneVeryOrdinaryMan the compression springs are made of special steel that retains its flex under stress over long time. Spring washers are made of ordinary spring steel that deforms over time under stress (the washer becomes a bit flatter than when it was new). McMaster-Carr sell those compression springs. With rigid wheels the springs also maintain constant tension as the blade guide is moved in and out (which changes the geometry of the blade) and when sawdust particles get stuck on the wheels and the blade. Not a problem for sawmill with rubber tires, though. I posted the comment for the benefit of others watching your video as I think is easier and more accurate. Measuring the stretch of the blade to establish the relationship between the force applied and number of turns of the tensioning nut has a wide margin of error. Those compression springs have narrow tolerances (=are fairy accurate and consistent) and measuring the length of the compressed spring can be quickly accomplished with reasonable accuracy in the field with simple tools after every blade change. Also, since setting proper tension is quick and easy, one is more inclined to remove the tension when the sawmill is not in use, which extends blade life.

[@ThoenWorks]

Like it.. good input. 👍👍

[@rok1475]

One more thing- fabricate a washer for the compression spring from a chunk of 3/8- 1/2” steel. 1000-2000lb force will deform standard flat washer.

[@thomassellers7613]

Just a thought... you’re comparing the 2 blade’s thickness difference and it equals about 16%... however, the actual amount of blade contacting the wood is the thickness plus the set of the teeth. For example if the set is .020” on the teeth in both directions, that would be .040 plus .035 = .075” for the smaller blade and .082” for the thicker one. Thus the difference in the cut would be about 8.5% if I did my math right. Of course it’s just like peeing in the ocean; every little bit helps! Very well done however,... thanks for sharing.

[@ThoenWorks]

Those are good points Tom. If by some chance I still have those blades I might have to put a caliper on it and measure it just out of curiosity. Of course somewhat water over the dam now as I've moved on to different setup.

[@curiouscarly1148]

Perfection is insanity’… Or is it the pursuit ?

[@SuperHurdman]

Hi do you think when a person gets the right tention in order to get it back to the correct tention could a person use a guitar tooner? I am thinking why wouldn't it work! looking for your thoughts on this subject?

[@ThoenWorks]

Could theoretically work as long as certain things such as blade thickness, width, and length between wheels was always the same. Believe you would still have to initially perform a "standard" tension measurement to calibrate initially. Most tuners may not work, but maybe something like a Snark, which uses vibrations could work. I have a couple and will have to try an experiment.

[@2ndamendmentwa74]

This is one of those far out ideas that could be most excellent. I have one of those tuners around here somewhere... I'll try this when I find it also. I expect that the "note" will be a little muddied because of the rubber tires (my wheels use rubber belts.) I'd love to hear if this ends up working for anyone.

[@ThoenWorks]

Maybe next 1-2 videos, I will try the guitar tuner thing.

[@SuperHurdman]

Thanks for the input. Why I asked I have my mill with scooter tires and how I am tension my blade is add air more tension more air I have been guessing but the other day snapped a blade. My tires are con-vexed so as not to take the set out of the blade I am wondering does your wider tires not take the set out of the blade? Are you Canadian?

[@ThoenWorks]

I am not Canadian, but have a couple Canadians married into family - so I've had to learn the language, aye!😁. I think getting a digital caliper and being able to clamp it to the blade is the most ideal way to set tension without spending an arm/leg.

[@jamesgulrich7416]

Not the stupid milli meters! Love it!

[@ThoenWorks]

+James Gulrich I cant argue against the fact that metric is much more logical, But still....

[@rok1475]

James Gulrich if you consider metric stupid, why do you use decimal fractions of an inch (1/1000) for precision machining rather than 1/1024 ? It would seem logical to to continue to divide an inch into 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1024 yet not a single American machinist does that but rather they all use decimal fractions. It seems ironic that a country founded on the idea of independence clings so hard to a system of measures of its former colonial masters.

[@ThoenWorks]

Relax people James is just referring to a joke I made.. humor, joke, tongue in cheek, not serious, all in fun, friendly ribbing..... That kinda thing.. 😉

[@cliffordthomas9623]

TKs for the info.

[@AltonMachineCom]

Great video Thanks.

[@ThoenWorks]

AltonMachineCom Thanks for watching. One day I will fabricate a fancier meter, but the crude method works ok for now.

[@paublusamericanus292]

I spent the day watching cooks measurements, on steel wheels, ground smooth, with wheel bearings for structural rigidity as the pillow block could not stand 10,000 lbs for more than 5 hrs. they use a tension meter, by flexing the blade with a very hard pointer, thus measuring not youngs modulous, which with spring steel is huge, and the measurement of stretch will not in your case be youngs modulous, because by pulling the center out away from the blade, will just pull it in straight, maybe still measuring stretch length, but not being snapped on super tight will certainly slip more than one can believe. I have seen 10,000 lbs on tires like that, and they smash way down with that much weight. If it runs good for you, good on you, but youngs modulous of strength, hmmmmmmm. those tires will do more than just supporting the blade, but will smooth the kerf on one side by bending the teeth straight, thus causing if too tight to try to track down in the wood. Your mill seems to cut well, so good on you, but youngs modulous of stretch, is a stretch to me.

[@ThoenWorks]

Admittedly, may not be translating you comment to my understanding correctly. I am not applying anywhere near 10,000 lbs force on the tires. More in the realm of 10,000 to 15,000 psi on the blade. I am only applying around 1700 lbs to the tires. (plus or minus).. the bearings I'm using are rated for ~2500 lbs load (each) at given RPMs - and there are 2 per side. So room to go.

[@scor440]

Why do this? I dont get it

[@ThoenWorks]

Perhaps not much of a reason to do this if you have a manufactured mill and specific instructions that came with it. However, in a case such as mine it was critical to get some sort of baseline blade tension to find out where I was at.

[@rok1475]

Gary Rosema the blade needs to be tensioned property for straight and consistent cuts. 15000psi (narrow blade) to about 25000psi (wide blade) is the typical range. Commercial mills apply 16000 to 17000 psi for 1” blade.

[@olitomesek9677]

Metric !,!!