bandsaw tension guidelines

[Edwin Santos]

The two major issues with the flutter method is it is not very repeatable and it (the way most people apply it) leaves the blade significantly under tensioned compared to the manufacturer's recommendations and yes, like a passenger car tire inflated to 20psi it will likely get you from point A to point B but it will not be operating at peak efficiency.

I have grown weary of recommending proper bandsaw blade tension, I have come to the conclusion that most people use a bandsaw as a blunt instrument, more a reciprocating saw than a circular saw and thus the quality of cut is not of primary concern.



General recommendations are carbon and spring steel (like the Woodslicer) need 15k-17k to operate correctly, much more than 20k psi and they start to go wonky, you can get away with 8-10k psi on 14" cast saws since thats about all they can muster on a 1/2" blade.

Bi-metal and carbide toothed blades like between 25k and 32k psi, the Lenox Tri-master and Woodmaster CT seem to like right at 30K and the Laguna Resaw King works its best in the 26k-27k range. They all start acting weird above 35k psi but not a lot of saws will get this high on resaw width blades.

I think much of the lack of attention to tension is a result of the fact that (significant numbers of) hobbyists owning saws that have significant tension capabilities is a relatively new development.

I respect your deep well of bandsaw knowledge. If I might tack on to your excellent comments - part of the challenge here is that a bandsaw operating at optimal peak performance relies on a whole series of set up factors. I feel blade tension and brand of blade seem to always grab the spotlight, but it really should be shared with guide setup, thrust bearing setup, elimination of drift through proper table/fence setup, appropriate choice of blade for the cutting job at hand, technique and feed rate. Some of the tuning can actually be quite personal (think of a musician who uses a particular guitar tuning)

I feel it is challenging for the blade manufacturers to state one single ideal blade tension that ignores the many variables like those above plus the model of saw and it's unique characteristics. Add to this the common "more is better" attitude we have in American society which makes some think more tension is always better. In reality, I was taught that tension need not be any more than it takes for you to get the cut you desire and, with all the other tuning variables appropriately in place, excess tension is not helpful to the machine or the cut. This said, I tend to use a higher tension for the tri-master blade than I do for the carbon blades I used 80% of the time but I don't think I nearly hit the tension levels they recommend because in my particular case I have not found it necessary.

When the bandsaw is well tuned and set up, it can be a very fine instrument. However, if one has not experienced working on a well tuned bandsaw setup, it is hard to explain.

[John TenEyck]

I'm always amazed that people have no issues using a dial gage to set up their table saw but don't treat their bandsaw with the same level of precision, yet then are frustrated by the poor performance they experience. We all know tension is important. Anything short of measuring it leaves you in the dark. I and others have written several times how it easily can be measured with a pair of 6" verniers and two little C-clamps, which don't cost much.

John

[Ben Rivel]

I'm always amazed that people have no issues using a dial gage to set up their table saw but don't treat their bandsaw with the same level of precision, yet then are frustrated by the poor performance they experience. We all know tension is important. Anything short of measuring it leaves you in the dark. I and others have written several times how it easily can be measured with a pair of 6" verniers and two little C-clamps, which don't cost much.

John

Exactly. I think its a cost thing. A dial gauge in a homemade holder to calibrate a table saw is MUCH cheaper than a tension gauge to properly setup a bandsaw. Since there arent nearly as many cheap options for a bandsaw tension gauge and those that are available arent well known, it makes them a lot more uncommon.

[lowell holmes]

When the bandsaw is well tuned and set up, it can be a very fine instrument. However, if one has not experienced working on a well tuned bandsaw setup, it is hard to explain.

Hey guys my saws work great and have been for the past 20 years. I know from experience when the saw is set properly. For you to assume that because some one doesn't use gadgets to set up their saw, well . . . .

You might want to view Alex Snodgrass and Mark Duginske. I might be wrong, but I don't recall either mentioning tension gages.
Google "flutter method bandsaw" and see what pops up.

[Frank Pratt]

There was a thread a while ago, it might be on SMC, about using a digital caliper clamped to the blade with the jaws 5" apart. The blade tension is just enough to hold the blade straight & then the caliper is zeroed out. The tension is then increased until the blade is stretched the correct amount. I can't remember the details & I can't find that thread now. Anyway, I set mine to .003 stretch, which seems really tight, but with a 5/8" blade I'm getting cuts that are pretty much perfectly straight with no drift whatsoever. The saw is a Rikon 10-325.

If I understand correctly, for a given PSI, all sizes of blades will stretch the same amount. The author of the post used Young's modulus & some math to come up with the right amount of stretch.

Found the thread:
http://www.sawmillcreek.org/showthre...533#post198533

[lowell holmes]

And that article did mention the Timberwolf flutter method. Just saying . . . . . . .

[David Kumm]

Generally Snodgras and Duginske are not working with big saws and carbide blades. The $300 blade mistakes can add up. My less scientific method with a carbide blade would be to tension close and test. If the blade spins the back bearing when under load, I'd tighten until it doesn't. I seldom spin the back bearing on a 1" Trimaster. I broke several prematurely when I used to guess at tension and relied on the bearing. When I quit using the bearing, I quit breaking blades. Don't know if the heat created shortened their life, I just know what works for me.DSC04308.jpg Dave

[Sam Blasco]

I know I don't often reply to many threads, but here is one I may be able to add something useful to. I own three bandsaws currently (two MM24s and an old Delta 14 that was my grandfather's) and have had or worked on many others over the past 30 years I've been playing with wood seriously. And, as many of you know, I have helped quite a few folks get their Minimax bandsaws in the last 12 or so years. One of the things I send to my customers when they get a new bandsaw through me is my take on some of the basics, and blade tension gets its few paragraphs. Some of this will be Minimax specific, particularly when I talk about the on board gauge, but I believe it applies to any bandsaw. Here they are (and please keep in mind I don't believe any of this is set in stone, let alone wood):

First and foremost -- Tension is subjective. I think there are decent guidelines out there, but no hard, fast rules to live by. I have experienced good cutting with the same blade at different tensions. The only reason I say this is to free you up to experiment a little and realize you can’t do much damage by picking the “wrong” tension, since both “right” and “wrong” don’t really exist, only variations that approach optimal. You will find the simple on board gauges on most bandsaws are quite, respectably useful and repeatable, and the MM gauge is no exception. I’ll mention more on that later, but first I would like to discuss tension meters, since they and the numbers they provide are much talked about here and other forums, then go into my personal “feel” method. Regardless of width of blade I tension each blade about the same. Obviously, narrower blades require less spring to get to that “same” tension.

There are four tension gauges I have played with: Starrett, Lenox, Iturra and Hakansson. They are all built similarly and use a dial indicator to determine the psi. I ended up owning the Hakansson gauge as it was a gift. There are many other gauges out there, both homemade and mass produced, but these are the four I have experience with. And when it comes to tension there are so many opinions out there about what proper tension should be that I wouldn't know where to start if I didn't trust my own opinion. Ha. I tension by feel, mostly, and that is even more subjective than using meters. According the above gauges (which guys have brought to my classes over the years) I average about 21,000 psi for all my blades, regardless of type. That is the mean based on equal tests with all four systems, following the manufacturers instructions, as the numbers from one gauge to the next varied considerably (about a 3,000 psi range between the high reading and the low reading. 21,000 psi is fairly moderate tension compared to some of the large numbers that many professed experts have claimed are necessary and have debated about for years (15,000 – 20,000 for carbon steel and 20,000-30,000 psi for bimetal, which would include most carbide tipped blades). Does that mean I am debating now? All tests were done to my pencil line drawn on my on board gauge that I have used reliably for years to tension my blades. Each tension gauge agreed with itself, at least, when tested three times - within 1,000 psi). What does this tell us? I don’t know, but it leads me back to my method...

Come 6" down from the upper wheel, where the blade is about to enter the tire. Tension enough so that there is less than 1/4" deflection with moderate pressure (no body weight behind your finger). Track the blade where you want it. Close the doors and turn on the machine with no guides set and no zero clearance dust block. Check the blade to make sure it is not fluttering side to side. If it is, add a little more or less tension while the saw is running until the blade stops fluttering. Make a test cut on a 6" resaw. Does it cut easy? straight? no wander? If so, you have found a good starting point for tension. Draw a pencil line on your saw's gauge and you can return to that setting reliably for that blade again and again. A 1" blade will require the same tension as a 1/4" blade, but will use much less spring to get there. I have three pencil lines on my saws... 1", 1/2" and 1/4". Typically, for a 1" Carbide Tipped blade, the pointer will be about 1/4" above the last line on the saw’s gauge, or 5/8s of the way up from the bottom of the window. The picture below of my on board gauge is just to give you an example of about where the pointer goes, your own results may vary. The 21,000 psi is between those two upper lines and if I add enough tension to get the pointer just above the top line I'm at 26,000 psi, according to those gauges I mentioned above. The saw cuts very well at both of those points, so I like to err on the side of less tension (this goes for drive belts too). The results confirm my theory that a blade will cut well at many different tensions, and go in and out of "flutter" at many different tensions, too, so beware of the "flutter" test as a sole means of tensioning a saw. Harmonics is an interesting subject. I like to run my blades at the lowest tension they cut well at, since I believe there is no point in over-stressing a system. Would you run your car at the RPM red line all the time because the engine is capable of that? Why over stress a system if you don’t have to. If you feel you ever need more tension for a particularly hard task you know you have some in reserve, right? As for the pointer, itself, you can actually adjust it to point wherever you want it to when you reach a tension you like. Unscrew it from the frame and access the spring and its set screw from the backside. Personally I find it easier to make a pencil line.

Tension-Guide.jpg

[David Kumm]

Good stuff from Sam. I'm not surprised that the sweet spot on his saws is lower than what I consider it to me on my old cast iron frame saws. The characteristics of steel vs cast iron will be different and I should have included that I run Oliver 116 and 217 and a Yates Y20. They also don't have built in scales that are very consistant - or exist at all. Dave

[William Shelley]

Hi all, first post here on SMC.

I've been working on-and-off on a shop-made 19" bandsaw with wood wheels and frame. I decided to go with pneumatic cylinders for tensioning. Pneumatics are really the best way that I found to apply force to the blade. A 4" bore cylinder can apply 1759lbs of force at 140 PSI, divided by two (force applied to wheel is divided over both parts of the blade) gives you 879.5lbs which is good for a 3/4" bi-metal blade.

In a test by Matthias Wandel, he found that the spring tensioning mechanism is hardly able to apply more than about 65 pounds of force, barely enough to tension a basic 1/4" blade.

My saw was designed from scratch to use a pneumatic tensioner but you may be able to retrofit it into an existing commercially-made saw. The great thing is, you can dial the air pressure way down, for example at 10 PSI, the same 4" bore cylinder puts out 125lbs of force, or about 62.5 pounds applied to the cross section of the blade.

[John K Jordan]

Hi all, first post here on SMC.

I've been working on-and-off on a shop-made 19" bandsaw with wood wheels and frame. I decided to go with pneumatic cylinders for tensioning.

That is interesting. Do you have any pictures of your saw and/or the tensioner?

How in the world do you keep the pressure constant? Do you think a small hydraulic cylinder would work?

JKJ

[John TenEyck]

Wendell's spring mechanism must have been sized for a really small blade - or maybe he just got it wrong. Springs can put out all the force a bandsaw needs if it's sized correctly, which is easily proven with a tension gage. An air cylinder would be great, to be sure, however.

John

[William Shelley]

That is interesting. Do you have any pictures of your saw and/or the tensioner?

How in the world do you keep the pressure constant? Do you think a small hydraulic cylinder would work?

JKJ

Here's an old link to my project. It looks a bit different now, and the wheels shrunk to 19" because I didn't oversize them enough when assembling.



The wheel mounting assembly has been tweaked a bit as well.

The really nice part about a pneumatic cylinder is that a cheap regulator is all that's needed to keep the pressure constant. Hydraulics would work as well, we have a really large vertical bandsaw for cutting steel beams at my workplace (it will cut a 24" x 6" x 1/2" I-beam like butter), which uses a hydraulic tensioner. I prefer the pneumatic for my bandsaw because the air can act as a shock absorber.

[John K Jordan]

Wow, you gotta applaud a guy who builds a bandsaw from scratch!

JKJ

[Myk Rian]

While it does not concern you it is very likely your bandsaw is not working in a way that gives you the best cut for the money you have invested in it, if that is OK for you then fine. I think it is important in a tension discussion to point out the flutter method is both low on repeatability and precision and is a poor way to produce accurate and repeatable results. If you not concerned about getting the best cut or the most life out of a blade then accurate tension is unnecessary.

Sounds condescending to me.
I've used the flutter method since forever. Always works, and is repeatable.
I can set my Delta 14" w/riser up in a couple minutes and resaw 12" planks.