Bandsaw Tension - Duginske

[Prashun Patel]

I read Duginske's bandsaw Bible and found it interesting that he recommends just using the mfg's blade tensioning scale to properly tension the blade.

I was surprised.

Is all the hoopla about tensioning just past the flutter point a lot of unnecessary precision?

[Bill Huber]

I don't know, I do know that I have tried the flutter set up but never really got it. I have been just using the scale on the saw and it has worked out very well for me.

I don't have a drift problem and everything cuts just fine so I am not sure what else I could gain with setting the blade different.

There was one time it didn't work to well, I installed a 1/4" blade and set the the tension on the scale to 3/8", the blade broke, I wonder why:D:rolleyes:

[Neil Brooks]

Is all the hoopla about tensioning just past the flutter point a lot of unnecessary precision?

I would say it this way: there's a lot of mythology and lore surrounding bs blade tensioning.

From my (limited) understanding, for any manufacturer that provides a recommendation for tensioning their blades (in PSI), one of the deflection/electronic tension gauges is the only "real" way to get to the manufacturer's spec.

Short of that, Lonnie Bird seems to think you should tension _beyond_ the index on your saw, Duginske seems to recommend that you tension _to_ the index on your saw.

And ... how does either know what PSI that will yield on MY saw, and whether or not that truly gets me to where the manufacturer thinks I ought to go ?

In other words ... I feel like "close is close enough."

For resaw work, though, I tend to go a half-measure _higher_ than my index mark (in other words, for my 1/2" Wood Slicer, I tension half-way to the next wider blade, on the index), but ... only for resaw.

The thing about (for example) the Carter Electronic Tension Gauge, or -- for that matter -- the Ratchet Rod that I bought -- is repeatability.

On the ETG, you can hit manufacturers recommended PSI as a starting point, and adjust from there, to achieve YOUR desired result, based on the cut YOU'RE making.

Ditto the ratchet rod. Because I can attach a torque wrench to it ... if I ever cared to ... I can repeat the tension that I like ... for each blade ... for a given kind of cut ... just by hitting the same torque value, each time.

[Van Huskey]

I agree with Bird and Duginske on using the scale but I have my own variation. I tension to the mark for carbon and to the next blade up for bi-metal and carbide toothed blades. It seems to me that you can not possibly use a saws scale for both since one likes 15,000 PSI and the other two like more like 25,000.

I also agree with Duginski on after market gauges since they were built for the metal working industry and production wood industry and our needed tensions are too low on the scale to be accurate and precise, one could design one but nobody to my knowledge has. Duginski feels the Carter ETG beats the analog hang on gauges but a non-issue for me since I don't have a 14" cast clone.

Prashun, if you have never read Duginski's threads here (some are epic battle threads) search his posts. There is one thread that deals with this very issue.

[Jim Rimmer]

I read Duginske's bandsaw Bible and found it interesting that he recommends just using the mfg's blade tensioning scale to properly tension the blade.

I was surprised.

Is all the hoopla about tensioning just past the flutter point a lot of unnecessary precision?
I found that interesting as well especially after reading teh Timberwolf brochure that came with their blades. I, too, have tried the flutter method with no success. I tried a better blade and the Duginski method and have smooth, straight cuts.

Some times good is good enough. :D

[lowell holmes]

I had the same reaction you do, but I revisited the flutter technique, and now I use it. What I was not doing is to move the guide up as high as possible and perform the flutter technique. If you leave the blade guide down, the system does not work. You want the blade as un-restrained as possible. It works with a 3/8" Timberwolf blade. The resaw capacity is good, the saw doesn't shake and bake, which makes me think the saw is under less stress.

I've never tried it with other blades.

I have an after market Iturra spring in the tension setting mechanism. They say that with a normal blade and with their spring, you should set the tension for a blade size zmaller than the blade. For instance, wwith a 3/8" BC saw blade in the saw, I set the tension at the 1/4" blade setting.

[Ken Fitzgerald]

I've read Duginske's writings and here's my interpretations.

Adjusting tension is relative and the manufacturer's indicator will get you into the ballpark. Let the cut be the final determination of the final setting. In his tests of even expensive measurement tools, IIRC he found enough inaccuracies to present a reasonable argument against spending that kind of money.

I use his general methods and have been happy with the results but I am no expert.

[Van Huskey]

His thread here regarding tension gauges:

http://www.sawmillcreek.org/showthread.php?t=50949

The thead really provokes thought at least in my feeble brain. I think we all too often look for simle answers give me a ____ that fixes my issues, even if we don't have issues to fix...:D

[Ken Fitzgerald]

Van,

In the search for simplifying something we often over look the simple and over complicate the issue.

The object is to adjust the tension for good repeatable results with a given blade and to be able to correct for the blades eventual dulling.

[Van Huskey]

Van,

In the search for simplifying something we often over look the simple and over complicate the issue.

The object is to adjust the tension for good repeatable results with a given blade and to be able to correct for the blades eventual dulling.

My personal problem is I care far too much about the "why" than I probably should. I find if I understand enough whys I can answere a lot of my silly questions that are merely academic for me. In the end it is one of the reasons bandsaws are my favorite woodshop tool since it is as much black art as science. I keep meaning to search out some info or even a person in the flooring industry who deals with the engineering of their bandsaws in a production environment. I had a contact from my guy at Lenox but lost it. My understanding is these guys know more than just about anyone regarding bandsaw blades and interstingly enough they use some of the same band material as high end bands for our vertical saws. The question is how relatable I can make it.

In the end KISS (keep it simple stupid) has always worked for me with BS blades but I have the cerebral need to search for "better" and the answers to "why". I ask why more than a 3 year old!

[glenn bradley]

In the search for simplifying something we often over look the simple and over complicate the issue.

Ah, the birth of the word "simplexity" :). My saw has numbered markings as a reference scale. They make no attempt to index by size when so many variables affect the correctness for a given blade ;).

[Kirk Poore]

My bandsaw, being built about 1915, doesn't have a tension gauge. I just tighten it up until the blade gives a good medium tone when I pluck it.:) I've never had an issue.

Kirk

[John Coloccia]

I tighten mine until it stops shaking..."fluttering" I guess.

[Chris Friesen]

My bandsaw, being built about 1915, doesn't have a tension gauge. I just tighten it up until the blade gives a good medium tone when I pluck it.:) I've never had an issue.

Actually, plucking the blade (either along the back column, or else with the guides retracted) is a pretty good way to check tension. If you ignore the teeth, a 1/4" blade and a 1" blade tensioned to the same PSI will give the same tone.

[Prashun Patel]

Actually, plucking the blade (either along the back column, or else with the guides retracted) is a pretty good way to check tension. If you ignore the teeth, a 1/4" blade and a 1" blade tensioned to the same PSI will give the same tone.

They should make bandsaws with pickups and a mic-out jack. Then I could plug my guitar's tuner into it, tune to G and be done with it.

[Ken Fitzgerald]

Prashun,

Don't need the jack, you can buy a microphone and hook it to a lap top and there is software available to analyze and display the frequency of the "plucked" blade.....:rolleyes:

[Chris Padilla]

I crank it up beyond the gauge...push on it to see the deflection to see if it "feels/looks*" right and cut away.

Real scientific, I know, but I'm happy with my results and ultimately, we all want to be happy with our results. The path to getting happy results may be different for all. :)


* - around a 1/4" is what I aim for....

[Mike Cutler]

Okay. Time to let the cat out of the bag, so to speak.

I did the aftermarket bandsaw tension gauge calibrations and analysis for Mark Duginske.
I tested 3 Iturra bandsaw tension gauges. One Lennox and a Starrett.
Carter also sent me an ETG unit per Mark's request.

Dimensional tests were done on all of the analog tension meters using Young's Modulus to perform a reverse interpolation.
What this means is that each analog tension gauge was fitted with an nist traceable mechanical standard, in this case a Starrett inside mic,and the gauges were calibrated to ideal inputs in the vertical and horizontal plane.

The analog gauges were then fitted into a frame and attached to a section of 1/2" bandsaw blade per the manufacturers instructions. The blade was attached to a NIST traceable load cell and pressure, in lbs. force was applied. The resultant lbs force was converted to PSI, as read on the analog tension gauges.
I performed the test with zero bias, 50% bias, and the manufacturers recommended bias when avaliable.
I also tested the meters in pre-loaded conditions at each bias setting.

All of the analog meters were then fitted onto my Jet 14" with the Carter ETG installed and cross cal comparison was performed. The Carter was tested on a force applicator and found to very repeatable and accurate. Not NIST standard, but accurate enough.
The result were that with repaetable indications on the Carter, both in applying and relaxing tension there was too much mechanical hysterisis in the analog tension gauges to be repeatable.
The results were also compared to the spring tension gauge on the back of my Jet and the results were consistent with Mark's summation that the installed tension indicator on the back is adequate.
Where we have a difference of opinion is with respect to the OEM spring.
The OEM spring supplied with my bandsaw would only produce a usable 8-9000psi .
I have a Carter Cobra Coil installed and it will yield about 16-17,000 psi to the blade.
However the real measure is that no matter what you tension your bandsaw too, there needs to be an air gap between those coils, or you no longer have a bandsaw. No spring, no bandsaw.

It was boring stuff,and took about two weeks solid of nites in the garage to complete.

Bottom line is that the analog tension gauges are being used to low in the range to be accurate and repeatable. Measuring 15-25,000 psi on mechincal devices with ranges in excess of 600,000 psi just doesn't always work out well. If you want to use an aftermarket tension gauge the Carter ETG is the most repeatable of the tension gauges I had available to me.

PS.
Just in case your interested. The blade is really strong.
At 80,000 psi it sheared the stainless steel screws I was using to affix it.m and deformed a cheap c-clamp along the way.
The sacrificial component on a 14" bandsaw is the upper wheel yoke. I promise that the yoke will break before the blade.

PSS.
No, I was not paid to do this work. It was voluntary,and I did not want any form of compensation to potentially compromise the results that I obtained.

[Kent A Bathurst]

Okay. Time to let the cat out of the bag, so to speak............

Mike - hey - how 'ya doin' ?

I've been sitting back watching this thread, waiting for you to open the bag.

Kent

[Prashun Patel]

Okay. Time to let the cat out of the bag, so to speak.

I did the aftermarket bandsaw tension gauge calibrations and analysis for Mark.


And THIS is why this forum rocks.

Thanks!

[Joel Goodman]

Prashun,

Don't need the jack, you can buy a microphone and hook it to a lap top and there is software available to analyze and display the frequency of the "plucked" blade.....:rolleyes:

iphone has an app for tuning stringed instruments "cleartune". Now we just need a "bandsaw" app.

[Alan Schaffter]

Okay. Time to let the cat out of the bag, so to speak.

Mike, I commented and posed questions to Mark in the original thread, but he didn't respond, so I wonder if you could provide your comment-

First, I maintain that the manufacturer's recommended blade psi settings are just rough guidelines. There is no engineering or mathematical process that will get you from blade metallurgy and dimensions to a psi that is guaranteed to result in a good cut in all species and thickness of woods.

Second, I have no first hand knowledge, but I suspect manufacturer recommended psi blade tensions are derived by testing rather than from engineering and mathematics- a bunch of testers (engineers/woodworkers?), use a particular blade to make a bunch of test cuts at various blade tensions. The cuts are examined and some criteria is used to select the best ones which are then used by the manufacturer to decide on a "best recommended" blade psi.

Finally, if my first two points are valid, the only reason for something like the Carter ETG is for repeatable settings- for the user to note at which setting his blade yields good cuts, so he can return to that setting when he remounts that same blade.

Final questions, do bandsaw blades become strain hardened over time from use? I know bandmill blades do. If so, won't that affect the recommended tension setting?

[Steven Hess]

Rikon Tech Support states the tension gauge is their as a feel good indicator. My stock 1/2" blade is tensioned about a 1/3 of the way past the 5/8" blade setting. That's good for that blade. Do the flutter for the Timberwolf blades.

[Mike Cutler]

Mike, I commented and posed questions to Mark in the original thread, but he didn't respond, so I wonder if you could provide your comment-

First, I maintain that the manufacturer's recommended blade psi settings are just rough guidelines. There is no engineering or mathematical process that will get you from blade metallurgy and dimensions to a psi that is guaranteed to result in a good cut in all species and thickness of woods.

Second, I have no first hand knowledge, but I suspect manufacturer recommended psi blade tensions are derived by testing rather than from engineering and mathematics- a bunch of testers (engineers/woodworkers?), use a particular blade to make a bunch of test cuts at various blade tensions. The cuts are examined and some criteria is used to select the best ones which are then used by the manufacturer to decide on a "best recommended" blade psi.

Finally, if my first two points are valid, the only reason for something like the Carter ETG is for repeatable settings- for the user to note at which setting his blade yields good cuts, so he can return to that setting when he remounts that same blade.

Final questions, do bandsaw blades become strain hardened over time from use? I know bandmill blades do. If so, won't that affect the recommended tension setting?

Alan

During the process of testing these devices for Mark, I contacted both Delta and and Lennox to more completely understand the "15,000" psi value.
As near as I can surmise in talks with the engineering support people at Delta, the value applied to metal working bandsaws. The 14" Delta has it's roots in metals fabrication.
Personally, I think the number is somewhat meaningless with respect to the 14" bandsaw. From the testing on my OEM spring and the aftermarket spring from Carter I installed, the OEM spring would be completely compressed and would no longer be acting as a spring, and the Carter would have been near the end of it's application range at 15,000 psi. I know that with the current configuration I have on my 14" Jet. I could not apply 25,000 psi and still have a "working" spring.
I personally want to apply as little force as required to my 14" Jet, so as to not risk breaking the upper wheel yoke assembly.

I don't know that a blade becomes "strain hardened". We'd need a metallurgist to answer that one. I do know that they can become brittle and develop micro fractures eventually resulting in failure.

I an also somewhat suspect of the different PSI recommendations and manufacturers claims based on composition of the blade, or the teeth.
Steel, nominally, has the same modulus within the range of applicability.
A 1/2" blade is a 1/2" blade. The required psi value will be similar for repeatable results no matter who makes the blade.

The Carter is a very nice unit. I don't use an aftermarket tension gauge, but if I were to use one it would be the Carter.
Being able to return to a known applied force would be very beneficial in aiding the diagnosis of problems. The Carter also reads out in "Lbs. Wheel Force. Something a little easier to understand and visualize than psi.



Steven

I have a 1" Lennox Tri Master on my Rikon 10-340. The tension gauge is past the 1" mark, but I still have gaps between the spring coils.

[John Coloccia]

I guess the core question is "what is the purpose of tension?". As I see it, there are three things adjusting the tension does:

1) make it so the blade can be driven by the wheels
2) makes the blade straight through the cutting area and give it some stiffness
3) "tunes" the resonant frequency of the blade

As far as I can tell, 1 and 2 are pretty trivial. You tighten it up, and when it's not flopping around anymore you're good. I think 3 is the only one that's really going to affect cut quality, and that's easily tuned by adjusting the tension until the blade stops shaking and runs smoothly, which I guess is the flutter method. I don't see how #3 gets fixed by hitting a PSI reading unless the idea is to tension it SO much and raise the resonance SO high that it can no longer be excite in any significant way.

Is it really more complex than this? I don't mean that sarcastically. I mean it from a let's get back to basics point of view and decide what the purpose of tension is other than the 3 I've listed.

[Mike Cutler]

Is it really more complex than this? I don't mean that sarcastically. I mean it from a let's get back to basics point of view and decide what the purpose of tension is other than the 3 I've listed.

John

No, it's not. We tend to make it more complicated than it has to be.
I think that people just have a natural tendency to be more comfortable with "order". If we say that "x" value of tension on a blade is ideal and will yield a 100% statistically perfect cut, than that's what people want to grasp and hold onto. I guess we just like hard fast rules.

I have access to some pretty big bandsaws. Do-All.s, Marvels and a really cool ancient Rockwell.
When we make the blades for them and weld them on, all we do is just apply tension until it feels right, and make sure that the springs and hydraulic adjusters have range left.
I've ran steel Box, "H" and "I" beams. Big Pipe, 2" thick plate steel and followed it up by ripping and crosscutting 12"x 12" Oak Dunnage on the same machines, with the same blade. They all came out "statistically uniform" in thickness.
Change the speed of the blade and the feed rate on a Marvel, and turn off the Cutting Fluid and a Marvel has no issue with wood.

Stick the blade on. Apply tension, make a test cut, and adjust tension as necessary. Just make sure that you still have working spring.

[ian maybury]

My background in this is in machine development rather than woodworking, but I've a sneaking feeling (see the parallel post on cast iron vs. aluminium band wheels) that you've hit it there John - that blade tension is critical only on saws with a mode of resonance/vibration that (a) is going to cause problems if it gets going, and (b) capable of being tuned out by precisely hitting a 'sweet zone' on blade tension.

Resonance by the way happens because systems (like the key parts of a band saw) have a particular natural frequency of vibration. You can apply (excite as the engineering term goes) vibrations of almost any frequency to that system with minimal effect, but if the applied frequency equals the natural frequency, then the effect is that the 'push' comes at just the right time every time to drive the system into vibrating through a monster amplitude. The real world examples we are all familiar with are the buzz that comes into a car door at a certain speed, or the shake in an out of balance wheel which does the same, or the vibration that comes into a machine in certain cutting conditions.

Think about it. Blade tension is of course significant to maintaining sufficient rigidity and twisting resistance in the beam that is the blade, but in the end it shouldn't be critical. i.e. the job should get done if the tension is in the right ball park - much as MD says.

A highly developed 'good' saw (like maybe the Agazzani and other models MD runs - where presumably the structure is designed so that its natural frequencies in whatever modes of vibration it is capable of are well away from any likely exciting frequencies that may be around) may not much care exactly what blade tension it's run at within reason. On the other hand a lighter, cheaper and vibration prone model may have a zone or zones such as the above - which may partly explain why blade choice can be so critical too.

Others may be very prone to screeching and the like in various other modes of vibration that prove extremely difficult to tune out.

If you have a cantankerous model that can with care be massaged into behaving itself, then for you blade tension, thickness and maybe other variables will be critical.

Mild steel frames are very prone to this sort of vibration indeed, so it's no surprise that many saws present problems - but it's in the end got to vary from saw to saw (maybe some types are so generic that there are similarities), and with differing set ups.

It's not what you want though in a production type environment - one of the key aims in production or user friendly equipment is process reliability/robustness - and a relatively linear response to changes in input variables is a key aspect of this.

I'm hoping that this will prove to be the case with the Aggazzani B-24/NRA600 I've just bought with the help of many here......

ian

[John Coloccia]

Sounds like what we really need isn't a tension gauge at all. A laser and a detector, aimed at the blade. Decompose the signal and output the amplitude of the peak resonance. Tweak the tension until that's minimized. Hmmm. Maybe I found a project for the winter.

[Will Overton]

From the manual for the Powermatic 14" bandsaw. I imagine other manufacturers use similar language. With most blades I need to go a little higher, but I had one 1/4" blade that I need to go a little lighter. I have no problem with having to tweak a little during each cutting session.




A gauge on the upper wheel slide bracket (C,
Fig. 25) indicates the approximate tension
according to the width of the blade. Initially,
set the blade tension to correspond to blade
width.


3. As you become familiar with the saw, you
may find it necessary to change the blade
tension from the initial setting. Changes in
blade width and the type of material being cut
will have an effect on blade tension. Keep in
mind that too little or too much blade tension
can cause blade breakage.

[Max Coller]

Because my woodworking addiction doesn't quite exhaust all of my income, I also dabble in really expensive pipes featuring internal spiral grooves designed to put bullets in the same hole - in the next township. Benchrest shooters refer to "nodes" in load development - that is, there are harmonic sweet spots inherent to each barrel/action/stock system, and by varying the amount of propellant, a given bullet can be pushed through the pipe at just the right velocity to hit those sweet spots consistently. If the system can withstand the higher pressure, another accuracy sweet spot can usually be found at a higher velocity - the next "node." Additionally, for rimfire benchresters, there's a theory that by "ringing" a barrel, the harmonicly neutral sweet spot can be determined in the barrel - which is then cut off at that spot so that it will be "dead" and bullets will exit consistently from that "dead" spot in the pipe. That's a longwinded introduction for this:

Is there also a sweet spot in tensioning a bandsaw blade - and another above that with more tension (but potentially less utility given the wear on the bearings, tires, blade and wheels?) Or, is it just that tensioning a bandsaw blade to a minimum measure precludes it from resonating at any significant frequency, thereby forcing it to follow a straight path because it is effectively "dead" harmonically?

Does someone have a good beater band saw they'd be willing to subject to a torture test to see if there are harmonics - tune the blade to a low G, for example, and then see if there's an increase in wandering with increasing tension until there's another improvement at a high G - or some other interval? Would that test prove anything other than that tuning a bandsaw is like tuning a guitar?

For the record, I've tried the flutter method but resorted to using the scale on the tensioning knob, plus a little bit for good measure. I didn't try any incantations or incense or small animal sacrifice to make the flutter work better, however, so maybe that's the part I've overlooked in the past.

[Ken Fitzgerald]

Here's my opinion.

Different saws will require different settings for a given blade because of the physical differences between saws. In other words take a blade off my MM-16 and it might require a different tension on your Delta, Grizzly etc.

So what?

Don't make more out of this than necessary.

Realize and respect that the setting used on your saw may not work on somebody else's identical saw or a different saw.

Realize and respect the idea that even with an exact replacement blade you may have to use a slightly different setting because of subtle differences in the blades.

Find what works for you and use it.

The horse is dead.......the bones are dust..........

[Wes Grass]

Re resonant frequency, guide height (unsupported blade span) will have an effect overall, as will the hieght of the upper guide above the work. I've seen a huge change with the latter cutting metal. Too high and it'll screech like crazy.