Bandsaw tension

[Sam Layton]

There has been a lot of discussion about bandsaws, blades, etc. Not a lot of talk about tension gages. I have just been going by the factory gage on the saw. I don't have a clue how much tension it will produce. I am in the market for a tension gage. I am thinking the Lennox, or the Iturra. It seems that the Iturra gage is more compact, and does not utilize as much blade for measurement as the Lennox. I don't know if that is a big deal or not. It just seems to me that the more blade you measure, the better...

I would like to know how you tension your blades? If you use a tension gage, what brand is it, or is it home built?

Thanks for your help, Sam

[David Kumm]

Sam, I've had two Starretts and an Iturra. There was discussion some time back about inconsistent measurement with Iturra and that gauge took a beating in some posts. I had that problem, sent it back to Louis who fixed it for free. I found a Starrett on ebay for a good price and of course three days later a second came up so I put a $90 bid for kicks and got it. All three gauges were consistantly within 1000 psi - one Starrett was off, the other two matched. I sold the Iturra but would not hesitate to recommend them. I am keeping both Starretts to confirm they still measure the same. doesn't matter how much blade you measure. there are other ways to do it but I like the gauge as I have three saws and each has a little different sweet spot. I would also argue the amount you spend should be appropriate to the quality of the saw. If a saw can't tension a blade sufficiently you only need the gauge once as you will always go to just before the spring bottoms. Dave

[Bill White]

Don't use a gauge other than the one on the saw as a guide. I then adjust by the old "deflection" method. Some use the "flutter" test. Always thought the tension gauges were just another somethin'-to-buy tool kinda like the digital depth gauge still unwrapped and sitting in the tool chest.
Bill

[Prashun Patel]

After reading Duginske's book, I just rely on the saw's gauge. After the blade starts to age, I might turn up the tension a little. In my limited experience, there's a decent amount of tolerance in the acceptable blade tension. I don't notice any change in performance or longevity of the blade now vs. when I was using the flutter method.

[David Hawxhurst]

i measure the stretch of the blade, do a little math to convert it to psi. it is the principle that most the bandsaw tension gauges work on.

[Myk Rian]

I use the flutter method on my 14" Delta 105" blade. Has never failed me with whatever blade I use.
I never trusted the gauge on the saw, as I believe blades of different lengths will affect the reading.

[Van Huskey]

This is one of THOSE subjects. Funny enough you won't much disagreement in the metal cutting world but in the woodworking word tension can be a hot button issue.

Duginski is a voice that set off the firestorm. Although I agree with Duginski on most subjects bandsaw tension is NOT one of them. He was unhappy about the state of tension gauges and I will give you the link to his discussion here and you can read his other info in his book if you like. His final position is just use the gauge on the saw. My problem with that is it can only be correct for one blade thickess and one blade type for any given width, that is assuming it is even graduated in widths or a gauge is even present. In the end I have decided where I fall and I have made it simple for myself and it seems to work fine. I use a set of calipers to measure the stretch over a given length of band and calculate the psi (link to the best walk through of this I have seen follows). In the end I will get a Starrett IF and only IF I ever happen onto a great deal on one short of that I will continue to use my calipers. Once I measure a width/gauge/type of band I make a note of the tension on the gauge, I do this 2-3 times to verify it is coming out the same and just use that number on my saws scale from then on for that exact type of band. I do not use the calipers for anything smaller than 1/2" for those bands I just use my finger and the deflection method, it is just quicker for me and frankly I probably over tension the carbon ones. In the end the most important thing is keep records with whatever method you use so when you find a sweet spot for a band you can reproduce it via what ever method you use to "measure" the tension.


http://www.sawmillcreek.org/showthread.php?50949-Carter-Iturra-Lenox-Starrett-Comparison&highlight=lennox+starrett

http://woodgears.ca/bandsaw/tension.html

[Van Huskey]

I never trusted the gauge on the saw, as I believe blades of different lengths will affect the reading.

Myk, I have never seen a BS that this is true for, though there certainly could be some. To verify this is not the case on a given saw take the blade off then turn the tension knob if you don't see the pointer move as you crank the tension knob you know blade length will NOT effect the saws gauge. You may notice the friction causes some movement right at the beginning but nothing more. The gauge on most saws is designed to move with spring compression not directly tied to the tension screw. If you have a saw that the gauge is tied to the screw movement not the spring compression I would like to know which one it is so I add a caveat when I say blade length doesn't matter!

[Damon Stathatos]

Sam - I always just crank 'em down until they feel 'good and firm' to me. If I start getting a bit of a flex (banana) through the cut, just crank 'em down a bit more for the next cut.

I absolutely hope you DO get a tension gauge however. Bring it on out and show it to me, take some tests on my blades, put it 'through the paces,' so to speak. There's a lunch in it for you and it would satisfy my curiosity as to how close 'my method' gets opposed to where it's supposed to be. Even if you don't get it, there's still a lunch waiting for you 'out here' (in the hinterlands). Best of luck and have fun with your decision.

[David Kumm]

I live pretty close to Mark Duginske and he has been very good to me over the years. I respect him a lot but his experiences with bandsaws to not match mine. Granted I run large cast iron machines but every time I thought I had a good cut at a lower tension I found I got a better one at higher- up to a point. There is no way I can feel the difference between 20000 and 30000 psi with any confidence and trying to do it on different machines with different distances between the wheels is way more than I can commit to long term memory. I don't think it is necessary to know what the tension really is but I'm a numbers guy and I like rulers with numbers rather than just marks for reference. Because I experimented with the gauge I know I get a better cut with a 1/4 bimetal at 30-35000 than lower and the 1" trimaster keeps getting better all the way to 25000 and then it takes better eyes than mine to see the difference after that. Most old saws didn't have built in gauges- for good reason I think. Dave

[Prashun Patel]

How critical is it to have a blade tension that's absolutely 'perfect'? I must be doing it wrong, because I only ballpark mine. What I can't figure out, though, is why my cuts come out fine. While the stock gauge may not be 'right', isn't 'right enough' in this case?

I'm a numbers guy too, but is this or is this not a case of perfect-for-the-sake-of-saying-i'm-perfect? Don't mean to be glib by that.

[David Kumm]

I don't think either of us is right or wrong here. Just choices. Part of the fun for me when running my old saws is seeing how good a cut I can get if resawing an 18" board or cutting a tenon that is a few thousands thinner at the end than at the cheeks. would make no sense in a production world but with me it's only a hobby. If I rehab a 75 year old bandsaw I'm going to test it to the limit. I'm also the guy dumb enough to modify my XKR for another 100 hp, then adjust the suspension. Dave

[Van Huskey]

How critical is it to have a blade tension that's absolutely 'perfect'? I must be doing it wrong, because I only ballpark mine. What I can't figure out, though, is why my cuts come out fine. While the stock gauge may not be 'right', isn't 'right enough' in this case?

I'm a numbers guy too, but is this or is this not a case of perfect-for-the-sake-of-saying-i'm-perfect? Don't mean to be glib by that.

IME once you reach a certain point with any blade (often only about 50-60% of the optimum tension) you get a cut that is pretty close to as good as you will get with that blade/wood/saw combination. The better the finish capability of the blade the easier it is to see the increase in quality of cut past that point. It is my opinion that the majority of the finish issues with lower than optimum tension is a result of the harmonic vibrations in the blade being of higher amplitude, with increased tension you get lower amplitudes as the frequency gets higher. For me I like to optomize what I have paid for especially when it doesn't cost any money and a small amount of time. The one other big tell tale regarding low tension is a barrel cut.

The vast majority of people probably use just the gauge on the saw, which usually will return absolutely acceptable cuts, but I want "what I paid for".

[James Heisbert]

I agree with Patel. I think there is no perfect tension but there is a right tension for different materials. The amount of tension can also be affected by the type of the material. If the material is solid, then greater tension is needed for the blade to stay in track. This goes directly proportional to material dimensions and hardness. Those are my observations so far in my experience as a band saw operator.

[Georg Zudoff]

Hi Sam and all folks!

Last summer after I bought a bandsaw I read a lot of threads here and books, too. For example Lonnie Bird's book about bandsaws. Articles from magazines too. Of course, some of the threads were translated into Russian, because I'm from Ukraine. So, after rereading many time Sawmill threads, and we reread them together with man who sell me bandsaw blades (I can tell by secret that Van Huskey's advices were choosen as 'most valuable') we produced the following tensioning method. I have a mediumsized bandsaw - Makita LB120F - for carbon blades we use bandsaw gauge, for bimetall blades - bandsaw gauge but on the next mark. I.e. - my preffered blade for hardwoods is bimetallic 13 mm width, I tension it for the 10 mm mark.

Probably in the future I will buy some gauge, Starret or Iturra, but right now I have others buts.

Regards,
Georg.

[John Lanciani]

How critical is it to have a blade tension that's absolutely 'perfect'? I must be doing it wrong, because I only ballpark mine. What I can't figure out, though, is why my cuts come out fine. While the stock gauge may not be 'right', isn't 'right enough' in this case?

I'm a numbers guy too, but is this or is this not a case of perfect-for-the-sake-of-saying-i'm-perfect? Don't mean to be glib by that.

I guess it depends what you use your saw for. If you're cutting veneer from a $30 or $40 (or more) per board foot piece of 4A quilted maple then good enough is not neccessarily good enough. I regularly cut 12" - 16" wide veneers and they go directly into the vacuum bag, they're that perfect every time and I don't make test cuts. If that's in your ballpark that's great; I'll continue to quantify my setup in the name of accuracy and repeatability.

[Georg Zudoff]

Hi John, of course you're right and tension gauge still in my wish list. But for my purposes - coarse ripsawing and after I do remaining jog with handtools only, I no need to use tension gauge. For veneer resawing you are right for 200%.

[Sam Layton]

Thank you everyone for your response and help. David, and Van, I have read the information, and views of Duninski. I do not agree with his views in all cases. I think that Iturra got a bad rap in that deal.

I have been using Timberwolf blades. When I resaw with a 3/4" Timberwolf, the results are good. However, the cuts are very rough, and not satisfactory. So I would like to get a carbide blade, and do some serious resawing. First, I am going to work on my saw in order to increase my tension. In addition, I am a numbers guy as well. I like to dial in, and see where I am at. I am just not happy not knowing what tension my saw is producing.

Damon, your on. However, I believe it is my turn to buy lunch.

John, what kind of saw and blade are you using?

Thank you very much for all of the help, I do want to purchase one of the three gages. I am just not sure which one.

Sam

[Thomas Hotchkin]

Sam
Not to highjack your post. But has anyone here used [The Thien Audible Tension Gauge for Bandsaws (Beta)] for bandsaw blade tensioning? Can be found at.
http://www.cgallery.com/jpthien/tg.htm Tom

[John Lanciani]

Sam,

I have a Minimax MM20 with a 1" Lenox tri-master blade. You can see my resaw setup here; http://www.sawmillcreek.org/showthread.php?178546-Veneering-Resawing-questions&p=1838654&highlight=#post1838654 at post #11

[ian maybury]

Must say (as a non expert) that I find this is a very confused subject. I'm another that's all for having an objective and repeatable method of measuring blade tension.

My experience suggests the following:

(1) Tension is a very different matter on your average 14in lightweight saw, and on a large industrial (e.g. Italian) machine.

So far as I can tell it's as much about having a method of finding a setting that avoids unwanted vibration and harmonics as anything on the former. Which given that saws are different probably leads to the often conflicting varieties of black art one hears of for finding a workable tension setting.

On the latter with carbide and larger blades the tension gets high enough that it's tough to judge by subjective means - which points to the advisability of a gauge.

Against that large saws seem to be less bothered about the precise setting once you have 'enough' tension. They don't for example seem (if at reasonable tension levels) to suffer from blade flutter to any significant degree, or to get into the sort of vibrational melt down that occurred on my last saw on rip cuts much above 5in....(no matter what the tension setting - caused by inability to tension the blade enough, and chassis flex?)

(2) OEM bandsaw tension gauges that rely on uncorrected and mechanically indicated spring deflection cannot be accurate over time - there's always going to be the issue of sag in springs that are regularly loaded. i.e. the spring gets shorter in its relaxed full extension condition, and likewise needs additional compression to deliver a given force.

Perhaps if regularly calibrated and the scale marked up accordingly using an accurate tension gauge.....

(3) Friction in the mechanism, and the possibility that it can vary means that (despite our tendency to use it as an indicator) the force to turn the tensioning wheel isn't necessarily a very good indication of what's going on either.

(4) 'Proper' tension gauges that measure blade stretch (technically 'strain') have the potential to work, but only if used correctly, and if the required tension is well above that required to pull all bowing/sideways deflection out of the blade. (which is going to be rather more than at first might appear to be the case) Otherwise all it's going to measure is lengthening between the clamping points due to the straightening effect.

The other issue is that if you do the maths it becomes clear that a tension gauge needs a high accuracy (expensive) dial gauge measuring down to about 1/10 thou if it is to be accurate enough to do the job.

All of which may mean tension gauges are less applicable to lightweight saws...

None of which is 100% satisfactory.....

ian

PS Maybe one of these: http://www.tensitron.com/strap_band.html

[Sam Layton]

Thomas, I have heard of the audible method, but don't know anything about it, nor know anyone that has used it.

John, you have a great set up. That sure is a super resaw set up. I can see that you put a lot of work in that device, and it sounds like it paid off for you.

Ian, I'm with you, it is a very confusing subject to me as well. Everyone has their own theory. A lot of different methods work for a lot of people. So, I guess what ever method works for an individual is good. Like David said, he can not feel the difference between 20,000 and 30,000 psi. For me, I don't know what any psi feels like. So, for me a gage is what I will have to rely on. Even if it is not total accurate, but repeatable, that will be good.

Sam

[Alan Lightstone]

I guess it depends what you use your saw for. If you're cutting veneer from a $30 or $40 (or more) per board foot piece of 4A quilted maple then good enough is not neccessarily good enough. I regularly cut 12" - 16" wide veneers and they go directly into the vacuum bag, they're that perfect every time and I don't make test cuts. If that's in your ballpark that's great; I'll continue to quantify my setup in the name of accuracy and repeatability.
Yeah, but you built the greatest resaw fence/guide in the history of the world. ;)

What's the downside in over tensioning a blade?

BTW, just looked at the price for the Starrett. OMG!!!!

[David Kumm]

Sam. Can you clear some room for PM. Dave

[Sam Layton]

Sure will David

[Bruce Wrenn]

For me, I don't know what any psi feels like. So, for me a gage is what I will have to rely on. Even if it is not total accurate, but repeatable, that will be good.

SamGrab yourself a $9.99 HF dial indicator and a couple of 1" C clamps. With blade only slightly tensioned, open caliper to 5". Clamp jaws to blade. As tension is increased, blade will elongate. A little research will show amount of elongation over 5" to achieve the desired tension. Before breaking out the CC to buy a carbide blade, I would try a bi-metal blade.