I saw this on LinkedIn.com (tension or strain)

[James Heisbert]

I saw this in a group at LinkedIn.com - http://www .linkedin.com/groupItem?view=&srchtype=discussedNews&gid=1779950&item=140306570&type=member&trk=eml-anet_dig-b_pd-ttl-cn&ut=2g4PVzqjpU3Ro1.

The folks there were having conversation about blade tension. Most of them stated that the right term is strain and not tension. That tension and strain are two different things. I have observed that all woodworkers in any forum site use the term “tension” and not strain. This made me confused. Can somebody tell me what’s right? Thanks.

[Ole Anderson]

I would say that tension is the force that you exert on the blade to stretch or strain it.

[Andrew Pitonyak]

I did not follow the link, but...

One definition of Tension is the state of being stretched tight, or, to apply force that tends to stretch something.

Strain is a force tending to pull or stretch something to an extreme or damaging degree.

So, when I stretch my leg, I put my muscle under tension. If I apply too much tension, I may pull or strain my muscle.

[Erik Loza]

That may be technically correct (though I never really thought about it until now...) but even if it isn't, that would be like taking issue with engine builders or auto mechanics referring to a car engine as a "motor". It technically is not a motor but the term is so commonplace that it's not worth taking issue with.

Just my 2-cents...

Erik Loza
Minimax USA

[James Heisbert]

So by applying tension, you’re actually straining the blade? Is there any difference? I am not neglecting the fact that most of us here are experienced band saw users but those people on linkedIn are big time in machining business or industry.

[Jim Rimmer]

Sometimes discussions like this put too much tension on my brain and put me in a strain. :D

[John Coloccia]

Without reading the whole thing, when an engineer or a scientist talks about tension and strain, they mean:

Tension - the force applied to the object
Strain - the amount the object physically deforms

Generally, strain will be in units of length, is often given as a ratio. Tension will be in units of force. The spring scale on the BS generally indicates tension, and the "tension gauges" for BS blades (with little dial indicators on them) measure strain.

edit: having read through the above
PSI is not a measure of strain. For example, if you have a bolt torqued down with a preload of 1000PSI, if you apply a 500 PSI force trying to stretch the bolt the STRAIN on the bolt is still 0, because the bolt won't budge until you've reached 1000PSI. Hence, one reason it's important to torque down certain bolts properly is so that they have enough preload to resist straining and subsequent metal fatigue. Cylinder head bolts come to mind.

All that said, unless you really need to be precise for some reason, most people will use the terms interchangeably as it pertains to bandsaw blades. Tension and strain on a bandsaw follow each other, so it's somewhat pedantic to make a distinction for most BS conversations. You could say, "I think you need to increase the tension" or "I think you need to increase the strain on the blade", and both mean precisely the same thing.

[Tom Walz]

Tom Walz • Is this a language issue?

In canada they may use the term "dish saws" while the US uses "hammer saws".

From a Phsyics standpoint I would think that putting anything under tension would be putting a strain on the material. Neither Machinery's Handbook 24th ed. or Handbook of Chemistry and Physics 74th ed. define either term.

Over 30 years I have learned that it is incredibly important to find out what someone means by the term they use. (I have never found that telling someone they are wrong helps communication.) We sell a lot of "braze alloy" to folks who call it "silver solder". Of course it is most technically correct to call it "braze filler metal". The same is true with "carbide" which is actually "cemented tungten carbide".

Over 30 years in the business my language has become more and more that of the customer. Maybe 10 years ago I had a peer reviewed journal request a paper on some of my research. I wrote it as I ordinarily would and it was rejected for "over use of colloquial language". I rewrote it so that it was much harder to understand and ti was accepted.

Finally, I know Paul smith Personally and Professionally. I have a great deal of respect for him and his knowldege of the art of sawing as it is actually practiced and described in actial use. However, he is in Texas and the language does vary regionally.

[Joe Kieve]

If you said to your wife, "your face would stop a clock". She'd probably slap yours. But if you said to her, "honey, every time I look at you, time stands still". She'd probably kiss you. Have you not said the same thing?

My 2 cents

Joe

[glenn bradley]

Too much time on minutia, not enough time in the shop :D

[James Heisbert]

This came up with a language issue and I better agree with most of you. I can think of a common saying, “..it’s the thought that counts!”

[bob hertle]

After a 35 year career as mechanical engineer/machine designer here, I can assure you that the guys in that conversation do not have a clue as to what they are talking about!

Regards
Bob

[James Heisbert]

I scanned through Paul Smith and Tom Walz’s profiles. They are both owners of different sawmill companies.
And both have long experience in years.

[Scott T Smith]

I scanned through Paul Smith and Tom Walz’s profiles. They are both owners of different sawmill companies.
And both have long experience in years.

James, I think that you meant to say Sawmill Supply companies, not sawmill companies. I don't think that either one runs a sawmill; rather they sell supplies such as blades and bands to those that do.

[Steve Baumgartner]

After a 35 year career as mechanical engineer/machine designer here, I can assure you that the guys in that conversation do not have a clue as to what they are talking about!

Regards
Bob

Agreed! But rather than increase the misinformation I say: get out any freshman-level mechanical engineering text and read the part about strength of materials. If that's too much effort, then don't fuss the technical stuff.

edit: that sounded like I was criticizing Bob, but I meant the non-engineers out there, not him

[Jacob Reverb]

Strain is a force tending to pull or stretch something to an extreme or damaging degree.

Stress is the force applied upon an object that tends to deform it. Stress is expressed in units of pressure ... like psi.

Strain is the deformation caused by the stress. It is commonly expressed as a percent, signifying the percentage (of the unstressed dimension of the object) that the object stretches or compresses as a result of the stress.

[daniel lane]

http://www.instron.us/wa/glossary/Tension-Test.aspx

This is probably a good description for the layman.

I did tests like these in engineering labs back in the day, and still have a scar on my left hand to prove it! (Mind you, the Instron is a safe piece of equipment - the injury was sustained when I was holding two pieces of a broken steel sample together near the break to get the elongation measurement, and someone bumped my elbow and cause me to shove a sharp piece of steel into my hand. Left a trail of blood all over the engineering building as we looked for the nearest first aid kit!)



daniel

[Lee Schierer]

Regardless of what you call the force acting on the blade, the reason for removing the tension (layman's terminology) on a band saw is to prevent the tires from taking a permanent set, it has nothing to do with the blade stretching.

Any piece of steel that is pulled with a force (tension or strain) such that the elastic limit of the material is not reached will return to its original length. Once you exceed the elastic limit of the material the blade will get longer. It also takes less force than the original elastic limit for it to get longer again. Therefore, unless you exert enough force on a band saw blade to exceed the elastic limit it will always return to the length that it started at when the force is removed. If you exceed the elastic limit of the blade it is a very short and slippery slope to failure, which is why you can break most small blades if you over tighten the tension (again layman's terminology) adjustment.

With that said, there may be some creep that occurs on thin members if the force is left applied for a long period of time, but the greater danger is having the elastomer in the tires take a set and creating an out of round condition on your wheels.

[Larry Whitlow]

Don't know. Don't want to know. Don't care. I just crank the handle before I use the saw and when I'm done at the end of the day.

[Ken Fitzgerald]

I agree with Lee. Removing the tension is more about relieving the load from the tires than anything else.

When I use my bandsaw, I increase tension by cranking it 2 turns. At the end of day when I'm done, turn it 2 turns to reduce the tension......layman's terms.

[Jacob Reverb]

Any piece of steel that is pulled with a force (tension or strain) such that the elastic limit of the material is not reached will return to its original length. Once you exceed the elastic limit of the material the blade will get longer. It also takes less force than the original elastic limit for it to get longer again. Therefore, unless you exert enough force on a band saw blade to exceed the elastic limit it will always return to the length that it started at when the force is removed. If you exceed the elastic limit of the blade it is a very short and slippery slope to failure, which is why you can break most small blades if you over tighten the tension (again layman's terminology) adjustment.




The "elastic limit" of which you speak is called "yield strength," and even for mild steel, it's generally > 36ksi. For the steel in a band saw blade, it's probably > 70ksi.


You'll probably never even remotely approach either of these stress figures using the springs in a band saw tensioner. If a band saw blade breaks, it's probably due to metal fatigue at the weld or at a "hard spot," rather than because you exceeded the strength of the material.


I'm with Ken and Lee: The reason to relax a band saw blade is to prevent forming "flats" on the tires, which cause a "thumping" when the saw is run.

[Tom Scott]

In case anyone still cares...

Force - Externally applied to an object and is generally expressed in pounds (Imperial units). So moving the wheels of you bandsaw apply a force to the blade.
Stress - The force within an object and is dependent on its geometry (F/A). Generally expressed in terms of pounds per square inch (or similar). For example, you can apply a 500# force to a 1/4" blade and have a stress of 20,000 psi within the blade, while the same 500# force applied to a 1" blade may result in a stress of only 5,000 psi.
Strain - The elongation resulting from an object's stress, generally expressed in terms of length. This is dependent on the stress within the object and the material's properties (modulus of elasticity). For example, two blades that look identical, are the same size and have the same force applied to them will have the same stress, but if they have different material properties then one may have a higher/lower strain, or amount of deflection/stretch. This is really what we're most concerned with in regards to our bandsaw blades, but since most blade steels will have basically the same modulus of elasticity, then stress within the blade could easily be the comparison.

I know, more than you probably care to hear.

[James Heisbert]

I came up with the following conclusions:

1. The difference between the terms we use is mainly because of the level of language that each of us have. The “level” of the language that we possessed is greatly affected by factors like society and the field of expertise. Society includes the region you are located, culture, dialect and the technology around you. While expertise is achieved through thorough studies and through experience.

2. People view things differently. A layman may have said the word “tension” but what he really meant was “strain”. Or he might have been thinking that they have the same meaning. No matter how he say it, he’s a layman, a layman speaks the words of a layman. While engineers or machine designers view tension and strain as two different things.

Now, can we change this? I think no is the answer. Without differences, we aren’t humans.
The conversation brought communication issues and I think it’s probably my fault for bringing up this thread. But I have enjoyed the conversation though.

[Alan Schwabacher]

One of the risks of technical knowledge is that it provides more ways to get annoyed, as terms that are important to distinguish in your field are used as ordinary words by those who don't want to make the same distinctions.

For instance "silicon" (the element) and "silicone" (a specific set of structures containing silicon, carbon, oxygen, and hydrogen, and sometimes other things) are not distinguished by most. To my ear they are as different as "curly maple" and "Chippendale highboy". Until now I have been able to refrain from pointing this out.

[Tom Walz]

Dear bob hertle, et al.

You are absolutely correct. Paul Smith and I do own sawmill supply companies. In addition Paul and I both have a long history, many decades each, of actually making saws run better.

The discussion under reference deals, in large part, with the fact that the language is highly imprecise. Your comment “I can assure you that the guys in that conversation do not have a clue as to what they are talking about!” is accurate from your viewpoint because we are speaking a different language. I call it “talking sawmill”. We work very hard to explain things in terms the other person understands.

Also we really try very hard not to argue with people or insult them. I am sure you are a very fine person but the opinion you expressed of me does not make me want to listen to you and certainly does not make me want to work with you.

Besides speaking a different language, we also live in a different world than you apparently do. We actively avoid telling anyone they are wrong. Instead we suggest what might be a better way. We believe that confrontation is a huge detriment to problem solving.

The average hobby woodworker is very intelligent, definitely upper income and generally very successful in life. These people are also very gracious and polite. We never correct them or tell them they are wrong. If they call and ask for a pointy thing to start holes we may suggest a gimlet and send them a picture but we do it in such a manner that we are working with them.

Aw heck, maybe you are just having a bad day. If you are going to IWF maybe we can meet and I will buy you lunch.

Tom Walz

[Jacob Reverb]

Now, can we change this? I think no is the answer. Without differences, we aren’t humans.

OTOH, communication works better when we all agree to use the same word to refer to the same idea ... lest, when we tell someone to "turn right," they steer the car into an oncoming 18-wheeler.

[James Heisbert]

OTOH, communication works better when we all agree to use the same word to refer to the same idea ... lest, when we tell someone to "turn right," they steer the car into an oncoming 18-wheeler.

Yes, that should be our goal to solve communication issues. But that's almost unattainable because someone from another field view the term in a different dictionary. Can we decide that this should be the proper term to use and not theirs? No.

What's important is they get our message and we deliver it to them the proper way that it is most understandable.
When we tell someone to "turn right", they will steer the car to the right direction where they're safe.

[Michael W. Clark]

Lee described the difference between force, stress, and strain accurately. Being a mechanical engineer and in sales myself, I also see Tom's point in that you have to communicate with the customer and know what they are referring to.

I did not read the link, but I have always heard it referred to as blade tension. The tension is the only thing I can read directly off my bandsaw. It is a measure of the spring displacement. Sure, the tension (force) imparts a stress and strain, but I can't read that directly. If I change blades and set the scale to the same number, I have applied the same force, but the stress/ strain in the blade will be different.