Audible bandsaw tension gauge

[Phil Thien]

So I took what I learned in that poll of plucked bandsaw blades (at SMC) and I created a web site where I allow the user to take a few measurements of their blade and saw, and determine the optimum frequency of their plucked blade based upon their desired tension.

You can use a $13 chromatic tuner (like this one) to check your bandsaw's blade and see how close you are.

It should be pretty darn accurate. Probably more accurate than any clamp-on gauge.

If you're interested in taking a look, the page is here:

http://www.cgallery.com/jpthien/tg.htm

Let me know what you think.

 

[froglips]

Phil, that is down right amazing.

I knew of the tuning fork sound method, but never understood how you could use it without first having a tension guage.

My hats off to ya!

Jim

 

[Mark Stewart]

Jim this has to do with harmonics. The sound acts as a tension gage just like tuning a guitar. I use a clamp on tuner that my daughter has for her guitar (that she stole from me. guess my playing is not so good).works like a charm. You can also use a pitch pipe if you have good ears they are only about three or four bucks.

 

[ErnieM]

Phil

What an wonderful idea. My bandsaw (ShopFox) has no tension gauge. Looking forward to trying out your method.

Just a thought. Many people have difficulty matching pitches. They say they're tone deaf - but that's another myth for another discussion. For folks like these, a guitar tuner or other chromatic tuner is very difficult to use. Another solution is to use the following:
[FONT=Arial, Helvetica, sans-serif]Korg CA-30 .

An amazing value. A fully chromatic tuner with an easy-to-read LCD meter. Calibrates from 410 to 480 hz, equal temperament and can deliver a reference tone over one octave. Best of all is its ability to lock on to whatever pitch it hears. Batteries included. (4" x 2 1/2" x 1/2") Fits in your pocket!! This is a new model from Korg. $25[/FONT]


[FONT=Arial, Helvetica, sans-serif]With this unit, you can pluck your blade and the machine will automatically tell you what pitch your blade is producing - no guesswork. It can also continously play the tone you're looking for. I haven't tried it with a bandsaw blade yet - but I will and let you know how well it might work in this application. At $25.00 it's a steal. Available at the Harpsichord Clearing House.[/FONT]


[FONT=Arial, Helvetica, sans-serif]Ernie
[/FONT]


[FONT=Arial, Helvetica, sans-serif]
[/FONT]

 

[Alan in Little Washington]

Interesting approach.

I can't tell without seeing the formula, but I wonder however, with all the measurements involved especially small distances and weights, what the affects of small errors might be. I think that was one of Mark Duginske's points in the big (contentious?) thread on SMC a few years ago, when he essentially said the Carter, Iturra, and other tension gauges weren't any good (actually I think he said they weren't any better than the manufacturers marks which he said were generally all that areineed.) I'm not sure I totally buy that, however.

Basing tension on blade specs, you would definately need pitch data every blade. Maybe one of you metalurgists (or harpsichord builders) out there can answer these questions- assuming constant length, do other things besides dimensions and weight affect pitch? Does the type of steel and temper affect the pitch? I think they might, but am not a metalugist so don't know. What happens to the pitch when the blade has stretched, or becomes strain hardened with use? Does the pitch change?

If all manufacturers/the industty could decide on a standardized height setting for calibration, they could do the calculations and testing, and supply the tuning information with each blade. That would make pitch tensioning a real snap for users, at least initially.

I still think a system like the Carter ETG1000 electronic tension system where tension is measured and computed using a pressure sensor under the foot of the tension screw and computed and displayed directly is the right way to go- it is not blade dependent, as long as it is repeatable.

Another, much cheaper method might use a torque wrench. Once you did a one-time math calculation to compute the mechanical advantage and other factors, like inherent friction, etc. of the tension screw and converted that to torque, you could replace or remove the crank handle with a torque wrench. A cam assembly inserted between the foot and the tension screw might work better with less friction. A simple "click" type torque wrench should work just fine. Lke the pitch device, you would need a chart except instead of pitch/blad/tension, you would need a torque vs tension chart.

Frankly, the beauty of Phil's, Carter's, torque wrench, or other such system, is not in the initial tensioning- use the marks on the saw. Within a certain reasonable range, who cares how much tension the blade is under, since most people adjust (or should adjust) the tension so the blade being used cuts that particular species of wood properly. The real benefit of a precision device is repeatability- being able to set the blade to a setting that has worked in the past not some theoretical setting.

 

[froglips]

Would the pitch method also help keep the same tension on a blade that has stretched over time?

I liked my question, no clue if there is any reality behind it though

Jim

 

[Phil Thien]

Interesting approach.

I can't tell without seeing the formula, but I wonder however, with all the measurements involved especially small distances and weights, what the affects of small errors might be. I think that was one of Mark Duginske's points in the big (contentious?) thread on SMC a few years ago, when he essentially said the Carter, Iturra, and other tension gauges weren't any good (actually I think he said they weren't any better than the manufacturers marks which he said were generally all that areineed.) I'm not sure I totally buy that, however.

I think the problem with the gauges they were testing is that getting accurate and repeatable results requires too much luck getting them set on the blades. Clamping them on a blade anything short of perfectly straight is going to result in an overtensioned blade. So you tension the blade a little, to make sure it can support this heavy object w/o deflecting, and now you're starting at unknown tension x, so your readings are still off, and you may still end up with too much tension.

I have broken this down into a simple physics problem, where the characteristics of a vibrating steel string are extremely well understood. Take a piece of steel of a certain mass, suspend it between two points with a tension of x, and we can compute the FF (fundamental frequency) produced with extreme accuracy. Far greater accuracy than required for tensioning a bandsaw, in fact.

Basing tension on blade specs, you would definately need pitch data every blade. Maybe one of you metalurgists (or harpsichord builders) out there can answer these questions- assuming constant length, do other things besides dimensions and weight affect pitch? Does the type of steel and temper affect the pitch? I think they might, but am not a metalugist so don't know. What happens to the pitch when the blade has stretched, or becomes strain hardened with use? Does the pitch change?

Back in high school physics we tensioned wires of different compositions and were unable to detect differences. If there was a difference, we didn't have the gear to find it at the time.

That is why audio transducers of different compositions sound largely alike. Aluminum, plastic, paper, and even Kevlar cones with rubber and foam and cloth and even paper surrounds produce the same fundamental frequencies. The differences come in the harmonics (distortions). All I care about is the FF.

If all manufacturers/the industty could decide on a standardized height setting for calibration, they could do the calculations and testing, and supply the tuning information with each blade. That would make pitch tensioning a real snap for users, at least initially.

Hopefully (due to the reasons above), that won't become necessary. But I will tell you that an area that concerns me is blades with carbide teeth. I need to do some testing there.

I still think a system like the Carter ETG1000 electronic tension system where tension is measured and computed using a pressure sensor under the foot of the tension screw and computed and displayed directly is the right way to go- it is not blade dependent, as long as it is repeatable.

Yes, if one has the $$$ and the 14" saw, the Carter system looks like a great way to go.

Another, much cheaper method might use a torque wrench. Once you did a one-time math calculation to compute the mechanical advantage and other factors, like inherent friction, etc. of the tension screw and converted that to torque, you could replace or remove the crank handle with a torque wrench. A cam assembly inserted between the foot and the tension screw might work better with less friction. A simple "click" type torque wrench should work just fine. Lke the pitch device, you would need a chart except instead of pitch/blad/tension, you would need a torque vs tension chart.

Frankly, the beauty of Phil's, Carter's, torque wrench, or other such system, is not in the initial tensioning- use the marks on the saw. Within a certain reasonable range, who cares how much tension the blade is under, since most people adjust (or should adjust) the tension so the blade being used cuts that particular species of wood properly. The real benefit of a precision device is repeatability- being able to set the blade to a setting that has worked in the past not some theoretical setting.

The primary reason for following-through with this is that it will hopefully provide a gold standard in determining tension (short of the Carter solution, which only works w/ 14" saws). 99% of users have no problem, as you say, with that built-in scale. But when there is a problem or a question, hopefully this will provide a precise method of testing one's current built-in gauge.

For me, once I hear 20,000 on a saw, I can get there every time in the future just from memory. Which is a good thing, 'cause my saw doesn't have a scale.

 

[ErnieM]

For me, once I hear 20,000 on a saw, I can get there every time in the future just from memory. Which is a good thing, 'cause my saw doesn't have a scale.

Wow Phil - That's quite a statement. Do you have perfect pitch? If not, I'd love to know how you do that.

Ernie

 

[Alan in Little Washington]

I think the problem with the gauges they were testing is that getting accurate. . . .

I don't remember if they checked the Carter ETG l mentioned below. Probably not.

I have broken this down into a simple physics problem, where the characteristics of a vibrating steel string are extremely well understood. Take a piece of steel of a certain mass, suspend it between two points with a tension of x, and we can compute the FF (fundamental frequency) produced with extreme accuracy. Far greater accuracy than required for tensioning a bandsaw, in fact.

Back in high school physics we tensioned wires of different compositions and were unable to detect differences. If there was a difference, we didn't have the gear to find it at the time.

Compositions maybe, but not different thicknesses. Stringed instruments have different diameter strings or wires don't they? Something is missing. Or is it a comfort thing? Ernie, can you help out here?

That is why audio transducers of different compositions sound largely alike. Aluminum, plastic, paper, and even Kevlar cones with rubber and foam and cloth and even paper surrounds produce the same fundamental frequencies. The differences come in the harmonics (distortions). All I care about is the FF.

Not the same thing at all. Transducers don't vibrate on their own, they are physically moved by a component that responds to a magnetic field or piezio electric effect vibrating at selected frequencies.

Hopefully (due to the reasons above), that won't become necessary. But I will tell you that an area that concerns me is blades with carbide teeth. I need to do some testing there.

Anything that changes within the measured oscillating distance (between guides)- extra teeth, fewer teeth, added weight/heavier teeth, etc. will change the freq vs tension. Another thing you will need to do is to ensure the distance and anchor point are constant and very accurate. If a blade is tensioned to X psi but the tuning distance is changed, the pitch will change- e.g. a slide guitar. You can compute what effect changing the distance will have on your results. You won' be able to rely on the upper and lower wheel tangent points either.That distance will be different between saws and among blades whose length is not precise.
Tire thickness, etc. will have an effect, also. You will need to use special clamping bracket to be sure you tension you have a fixed length. If you use a clamping device you will need to clamp, test, unclamp, adjust tension, clamp, test, etc.

Yes, if one has the $$$ and the 14" saw, the Carter system looks like a great way to go.

Frankly, I believe the price is high because the demand is low. That unit has a commonly available transducer and likely a single chip driving a readout that costs pennies. The last I looked, it has come down from the $200-$300 range to around $150 which is still too high, but given some competition or volume it could and should go MUCH lower. Look what happened to the price of the Oneida dust deputy :wsmile:.

The primary reason for following-through with this is that it will hopefully provide a gold standard in determining tension (short of the Carter solution, which only works w/ 14" saws). 99% of users have no problem, as you say, with that built-in scale. But when there is a problem or a question, hopefully this will provide a precise method of testing one's current built-in gauge.

I believe when Carter says it will fit most 14" bandsaws they are not excluding 12", 20" or other bandsaws etc. And, despite what Carter says, his unit can be mounted to any bandsaw that has a tensioning device where you can slip the sensor between two parts, including, contrary to their site, bandsaws with quick tension levers- they just haven't designed a mount for it, yet.

Like I said, I think you may be on to something, mainly for repeatable setup, but am doubtful you'll come up with a "gold standard."

In addition to things we have discussed, one of the main reasons I say that is- there is no such thing as a "gold standard." I frankly don't see where any of the bandsaw or blade manufacturers can come up with objective tensioning data- there is no "magic" number- 20 Kpsi might work fine but 27,250 psi might work just as well. I think it is all subjective- they make a blade or saw, and have their R&D folks test it cutting wood. If a particular blade seems to cut ok at 20 Kpsi for some unspecified types of woods, then, wa la, it is a 20 Kpsi blade. What is the tolerance. It certainly won't cut like a dog at 19,500 psi, work like a champ at 20 Kpsi, then like a dog at 20,500!

For me, once I hear 20,000 on a saw, I can get there every time in the future just from memory. Which is a good thing, 'cause my saw doesn't have a scale.

Another thought/question- how will you calibrate your unit initially? How will you know what the tension on the saw blade is when you are showing X Hz on the Chromatic tuner? Without absolutely knowing every single factor, you really don't want to rely on an equation. You will need a gold standard to start with- possibly something like a Carter ETG- a chicken-egg situation? I raised these questions with Mark D. off line, but he didn't answer. In reality, no math is needed to verify your idea- Buy a Carter ETG- check the pitch of various size and construction blades at various tensions, and see if it works and with the resolution and repeatability that is useable.

Crank her up to a high 'C' and let her rip.

Keep us updated.

 

[Phil Thien]

I don't remember if they checked the Carter ETG l mentioned below. Probably not.

No, they praised it if I recall correctly, they just said it wasn't necessary because the built-in gauges work so well. Mixed blessing as far as Carter is concerned, I'm sure.

Compositions maybe, but not different thicknesses. Stringed instruments have different diameter strings or wires don't they? Something is missing. Or is it a comfort thing? Ernie, can you help out here?

Of course the gauge of the wire is the same. I'm saying two wires of different compositions, but the same gauge.

Not the same thing at all. Transducers don't vibrate on their own, they are physically moved by a component that responds to a magnetic field or piezio electric effect vibrating at selected frequencies.

Agreed. But my point is that 100-Hz is 100-Hz. Blade steels are not going to be of such dissimilar composition that it will effect the outcome here.

Anything that changes within the measured oscillating distance (between guides)- extra teeth, fewer teeth, added weight/heavier teeth, etc. will change the freq vs tension. Another thing you will need to do is to ensure the distance and anchor point are constant and very accurate. If a blade is tensioned to X psi but the tuning distance is changed, the pitch will change- e.g. a slide guitar. You can compute what effect changing the distance will have on your results. You won' be able to rely on the upper and lower wheel tangent points either.That distance will be different between saws and among blades whose length is not precise.

If you go through the worksheet, you'll see that I take all that into account.

Tire thickness, etc. will all have an effect, also. You will need to use special clamping bracket to be sure you tension you have a fixed length. If you use a clamping device you will need to clamp, test, unclamp, adjust tension, clamp, test, etc.

I lost you on tire thickness?

Frankly, I believe the price is high because the demand is low. That unit has a commonly available transducer and likely a single chip driving a readout that costs pennies. The last I looked, it has come down from the $200-$300 range to around $150 which is still too high, but given some competition or volume it could and should go MUCH lower. Look what happened to the price of the Oneida dust deputy :wsmile:.

Agreed. They (Carter gauges) are glorified digital bathroom scales.

I believe when Carter says it will fit most 14" bandsaws they are not excluding 12", 20" or other bandsaws etc. And, despite what Carter says, his unit can be mounted to any bandsaw that has a tensioning device where you can slip the sensor between two parts, including, contrary to their site, bandsaws with quick tension levers- they just haven't designed a mount for it, yet.

Yes, it could certainly be adapted to more saws. It doesn't seem like they're doing much with it, though.

Like I said, I think you may be on to something, mainly for repeatable setup, but am doubtful you'll come up with a "gold standard."

Maybe yes, maybe no. I actually don't care about using this for repeatable setup, but rather more for finding 15, 20, and 25k on saws the user is unfamiliar with.

This is pretty basic physics. If you know the mass of a wire, you can compute the fundamental frequency of that wire when plucked, depending on tension. Obviously more testing is required. I'm not willing to claim it as bandsaw law yet.

In addition to things we have discussed, one of the main reasons I say that is- there is no such thing as a "gold standard." I frankly don't see where any of the bandsaw or blade manufacturers can come up with objective tensioning data- there is no "magic" number- 20 Kpsi might work fine but 27,250 psi might work just as well. I think it is all subjective- they make a blade or saw, and have their R&D folks test it cutting wood. If a particular blade seems to cut ok at 20 Kpsi for some unspecified types of woods, then, wa la, it is a 20 Kpsi blade. What is the tolerance. It certainly won't cut like a dog at 19,500 psi, work like a champ at 20 Kpsi, then like a dog at 20,500!

Well, if it becomes any sort of gold standard it will only be insofar as determining tension. I AGREE WITH YOU 100% that the suggested tensions seem quite arbitrary. I used to think they were good starting points, but now I'm not even certain of that, as I've become quite fond of running at what some people would consider very low tensions.

Another thought/question- how will you calibrate your unit initially? How will you know what the tension on the saw blade is when you are showing X Hz on the Chromatic tuner? Without absolutely knowing every single factor, you really don't want to rely on an equation. You will need a gold standard to start with- possibly something like a Carter ETG- a chicken-egg situation? I raised these questions with Mark D. off line, but he didn't answer. In reality, no math is needed to verify your idea- Buy a Carter ETG- check the pitch of various size and construction blades at various tensions, and see if it works and with the resolution and repeatability that is useable.

Crank her up to a high 'C' and let her rip.

Keep us updated.

The equations are textbook, but the application needs testing. Two engineers (users of online forums) are doing some preliminary investigating. But there may be a Carter or some other load-cell based solution in my future so I can can correlate results. I could cobble what I need together at one of the physics labs at UWM or MSOE, but that has a way of becoming a federal project (send item x out for certification because we don't have any paper on it... metrology outfit called and item x needs replacing, but it isn't in the budget... Phil now donating replacement, which some undergrad will drop in two months, rendering it worthless). I wonder if Duginske's materials engineer still has the Carter gauge somewhere? Doesn't Duginske live right here in Wisconsin? Hmmm...

 

[Phil Thien]

Wow Phil - That's quite a statement. Do you have perfect pitch? If not, I'd love to know how you do that.

Ernie

No, probably just average to above average pitch memory.

Actually, I think I'm going to look for an online test for absolute pitch.

Maybe I can be the next American Idol judge.

 

[ErnieM]

Originally Posted by ErnieM

Wow Phil - That's quite a statement. Do you have perfect pitch? If not, I'd love to know how you do that.

Ernie
​

No, probably just average to above average pitch memory.

Actually, I think I'm going to look for an online test for absolute pitch.

Maybe I can be the next American Idol judge.

Phil,

Either you have perfect pitch or you don't. There's no such thing as a person without perfect pitch who can remember a pitch for much longer than 15 minutes. If you can remember the pitch of the blade consistently, you either have perfect pitch or you just think you're remembering the pitch.
Why not have yourself checked for perfect pitch and find out for sure?

Alan,

Back in high school physics we tensioned wires of different compositions and were unable to detect differences. If there was a difference, we didn't have the gear to find it at the time. Compositions maybe, but not different thicknesses. Stringed instruments have different diameter strings or wires don't they? Something is missing. Or is it a comfort thing? Ernie, can you help out here?

I'm so far over my head here it isn't even funny. Phil says they tensioned wires of different compositions and were unable to detect differences. I don't understand what differences they were hoping to detect? Pitch, amplitude, resonance, etc?

Yes, stringed instruments do have strings of different diameters. On a harpsichord, if a Pythagorean stringing schedule were used, where each lower octave has a string twice as long as the octave above, the lowest string on a typical instrument would have to be 16' long or more.
To avoid this, the scale is foreshortened - as you proceed down the strings are made shorter than they should be and the lack of proper length is made up for by increasing the mass of the string by using wire with a greater diameter.

Again, I'm so far over my head here that I don't know if this helps or even has anything to do with what you're talking about. But you asked - so I answered. :gar-La;

Ernie

 

[Alan in Little Washington]

I lost you on tire thickness?

Makes the tangent point sloppy and is just another factor that affects the distance if you don't use some sort of bracket system to define the area of the blade you will test.

Another idea I had awhile ago- simple, non electronic, not blade dependent, no moving parts with the possible exception of a tiny cylinder, etc. if you couldn 't do it with a bladder - a high pressure version of a manometer (no pressure gauge). I don't know if such a thing already exists, but it should be easy to do with a liquid filled mini hydraulic "load cell" and some metal (non-expanding) tubing (1/32" I.D. would get 20,000 psi down to 100 pounds) terminating in some sort of blanked-off calibrated transparent readout tube, kinda like a thermometer, or those pressure indicating tire inflation caps. Without doing the math I don't know if it would give the needed range and precision, but I have a feeling it would, especially if you only wanted 1000 psi resolution over a range of 10-25 kpsi. This is something that probably could be made domestically or overseas for literally pennies- another glorified bathroom scale but simpler and cheaper.

Heck, you could also go the other way with this. Fancy it up, add a gauge, adjustable pressure switch, and a mini-pump to tension the bandsaw automatically, continuously, and precisely, somewhat like they do tensioning belts in wide belt sanders, etc. with pneumatics. Of course, then you have gone full circle, and need to ask yourself, is this level of precision and automation needed.

Maybe the bandsaw manufacturers need to label their marks (the ones who provide marks) in Kpsi rather than in width of blade like they do now (1/8", 1/4", etc.) Any spring, linear, or not, can be calibrated that way- again back to the bathroom scale analogy. I always wondered about the aftermarket tension springs- do they provide the same tension, have the same elasticity, and are they calibrated the same as a new OEM spring? If so how do you know when it is time to change a spring? Is it ever time for a hobby woodworker? Do you really need an aftermarket spring and if you use one, do you need some new way other than the manufacturers marks, to tension it? Inquiring minds want to know.
'

 

[Alan in Little Washington]

Phil,

Alan,

I'm so far over my head here it isn't even funny. Phil says they tensioned wires of different compositions and were unable to detect differences. I don't understand what differences they were hoping to detect? Pitch, amplitude, resonance, etc?

Yes, stringed instruments do have strings of different diameters. On a harpsichord, if a Pythagorean stringing schedule were used, where each lower octave has a string twice as long as the octave above, the lowest string on a typical instrument would have to be 16' long or more.
To avoid this, the scale is foreshortened - as you proceed down the strings are made shorter than they should be and the lack of proper length is made up for by increasing the mass of the string by using wire with a greater diameter.

Again, I'm so far over my head here that I don't know if this helps or even has anything to do with what you're talking about. But you asked - so I answered. :gar-La;

Ernie

Thank you maestro!

I would hope they meant to test pitch (frequency). Your description is exactly what I meant. The problem, as I see it is the variance in blade cross section, from size to size and design to design. A given blade, under a given tension, over a given distance will have a certain pitch, but change any of those factors and all bets are off. Now as to the effects of blade design- gullet, teeth, bimetal, etc. on pitch, your guess is as good as mine and that is where I think any sort of mathematical approach falls apart.

 

[Phil Thien]

Either you have perfect pitch or you don't. There's no such thing as a person without perfect pitch who can remember a pitch for much longer than 15 minutes. If you can remember the pitch of the blade consistently, you either have perfect pitch or you just think you're remembering the pitch.
Why not have yourself checked for perfect pitch and find out for sure?

I don't know the scales. I just know the sound the blade makes when I retension it.

I guess I'll try finding some pitch tests online. Maybe I'm not getting as close on pitch as I think.

 

[Phil Thien]

Makes the tangent point sloppy and is just another factor that affects the distance if you don't use some sort of bracket system to define the area of the blade you will test.
'

I did a quick test...

If I use a blade weight of 84 grams, length of 72.5", thickness of .022", width to gullet of .390", and wheel separation of 19.75" (these numbers from a Blade Runner/WoodSlicer blade for my BS150LS saw), my math says I should "tune" the blade to 91.167-Hz to achieve 20k-PSI.

Now, if I change the wheel separation to 20" (an entire 1/4", not likely to see the tires contribute to anywhere near that much error), while keeping all the other numbers the same, my math says I should tune to 90.028-Hz for the same 20k-PSI.

Obviously we still have to confirm that this works. But if it does, I don't think the tires will contribute much in the way of error. I have concerns in other areas (and ways to address them if they bite me), but I have to jump some other hurdles before I can concern myself with fine-tuning.

 

[Phil Thien]

I have updated the page so I now have approx. 40 MIDI files which will give you a good indication of what I believe your properly tensioned blade should sound like.

Working through the worksheet, you will be given a freq. that a blade tensioned to the PSI you're shooting for should generate when plucked ON YOUR SAW. You can then listen to a sample file of ten plucks that you can use to compare to your actual results.

This largely negates the need for a chromatic tuner. All you need now is a good digital kitchen scale. And if you don't have one of those, you may be eating too many pretzels in one sitting.

http://www.cgallery.com/jpthien/tg.htm