bandsaw tension gauge-crazy idea?

[Kurt Loup]

I had planned to make the shopmade bandsaw tension gauge that was in the February 2001 Fine Woodworking magazine, but I decided to try something different. The article states that for every 6000 psi applied to 5" of blade, the steel stretches .001. Instead of making the gauge in FWW, I decided to clamp my inexpensive Harbor Freight dial caliper to the blade. I opened the caliper to 5", c-clamped the jaws to the blade and zeroed the dial. I tensioned the blade until the caliper read just shy of .003 attempting to approximate 15,000 psi, the minimum recommended tension of most blade manufacturers. As I suspected, the saw's tension gauge was not accurate. As far as I can tell, the tension seemed appropriate and I got good results in some resaw tests which was the point of checking the tension in the first place. Do you think this method is half way accurate to determine blade tension?

Kurt

http://www.loup-garou.net/images/caliper.jpg

http://www.loup-garou.net/images/tension.jpg

[Lee DeRaud]

As far as I can tell, the tension seemed appropriate and I got good results in some resaw tests which was the point of checking the tension in the first place. Do you think this method is half way accurate to determine blade tension?If it works, it works. It's not like the Blade Tension Police are going to shut down your shop if the numbers are off by 10%.

[Mike Cutler]

It may not be "accurate" per se, but it's definitely repeatable. If it works for you I say stick with it. I might give it a try tomorrow and check it out my self. A lot cheaper than a tension gauge, that's for sure.
Nice idea, thanks for posting it.

[Per Swenson]

Kurt,

A while back I posted a way to set jointer knives with

magnets. All though it was not a original idea, many

suggested I submit it to the magazines and claim

a prize or tool. Let me be the first to suggest you

do the same. I think its brilliant and a winner.

And unlike my Idea, truly original.

I hope you consider this and good luck.

Per

[Greg Torok]

I have a very nice set of calipers...why didn't I think if this? You've got a great idea. You can also use spring clamps to hold the calipers....

I will certainly try this. Thanks (btw - how's the e16?)

[Dale Thompson]

Kurt,

Your measurements look good to me. :) Strain in in/in is obtained by dividing stress by the Modulus of Elasticity of the material. In this case you used a stress of 15,000 psi. The Modulus of Elasticity of steel is 29,000,000. With that calculation, I get a result of .000517 in/in. Using a length of 5", we would multiply that number by 5 and get a result of .0026". That, in my humble opinion, is "just short" of .003. :D :cool: :)

NICE WORK KURT!! I wish that I could be right once in a while! :(

Dale T.

[Chris Padilla]

If Dale blesses it, it's gotta be good! :D

[Kurt Loup]

Thanks for the comments. I've gotten some additional ideas to think about.

Kurt

[Jim Becker]

I think this is a great idea. Who cares if it's not "exact"...it told you what you really needed to know and that is that the so-called tension guages on all these saws are, ummm....well....you fill in the blank! And as someone mentioned, repeatablilty at the tension that works well for you is a good thing. You'll get more consistant results.

[Allen Bookout]

I think that this is a great idea but I have some questions. Does the 15000 psi figure apply to all sizes and brands of blades? Also it seems to me that the stretch would vary by size of blade, both thickness and width. Does someone have the proper formula to use. Thanks! Allen

[Lee DeRaud]

Also it seems to me that the stretch would vary by size of blade, both thickness and width.As Yoda says, "Size matters not.":cool:
In theory, the width and thickness of the blade are handled by the "per square inch" portion of the equation. How well the theory works in practice is another question, but I suspect there are other factors than size that affect the outcome.

[Corvin Alstot]

Does the 15000 psi figure apply to all sizes and brands of blades? Also it seems to me that the stretch would vary by size of blade, both thickness and width. Does someone have the proper formula to use. Thanks! Allen The 15000 psi is a guideline for blade tension for resawing but personal experience and preferences make this a starting point for resawing. There was an article in one of the latest woodworking magazines that used a low tension for resawing.
I would think that the modulus of elasticity would not change with the size or thickness of blade, its still steel (but I am curious what others have to say).

[John Miliunas]

Kurt, many thanks for this wonderful little tune-up check!:) Went over to the BS this morning and rigged up a digital caliper to mine and, after indexing it at the prescribed 5" mark, I started tensioning the blade. Here's the surprise: I believe that I can now believe my factory tensioning gauge!!! :D As I cranked it up, I got .001, .002 AND .003 on the caliper synchronizing with the 10, 20 and 30 on my machine gauge! :) My initial test was on a Laguna, HD16 with the 1" Resaw King blade. I will now continue to try this with every blade change. This just rocks! Thanks again.:) :cool:

[Larry Copas]

The caliper is a most valid way to check tension on a band. I use the same method to check tension on my bandsaw sawmill. I have checked three different brands of sawmills and there tension gauges were all way off.

Different band manufactures recommend different tensions for there bands...range seems to run from 15,000 psi up to around 28,000 psi. Call the manufacture and they will be happy to give you there recommendation.

[lou sansone]

good post and topic all

I had been planning on posting a similar topic. good use of the caliper. Thanks dale for the info. Here are a couple of thoughts
1. youngs modulus is independent of size and shape of that material. it is defined as the ratio of the stress /strain of the particual material. as dale has said it is about 29x 10^6 psi
2. the 15000psi results in about .05% elongaton of the blade. I guess this must be a reasoanble preload for the steel blade.
3. Although the blade size will have an effect on the amount of spring tension you need, it will not change the .003"/5" that you need to stretch the blade.
4. I usually tension my blades using the "flutter" method rather than the stretch method. It turns out that when I did this test that my ideal blade tension seemed to be about half of what the stretch school of thought predicted.
5. Are there any other creekers that use the flutter method for tensioning their blades?

lou

[nic obie]

Kurt,

Brillant Idea. I wish you would have posted it before I spent the $150 for one of Iturra's gauges. When I get a chance I'll compare the two.

I agree with Lars, send the idea off to FWW or another of the mags before somebody else does.

[Allen Bookout]

I tried the flutter test as that seemed to be the proper way to test according to what I have read. Then I used the dial caliper idea posted here. I did not have time to verify the results exactly but from what I saw the tension seemed to be hugely more using the caliper than using the flutter test setting. Seems like a lot of tension to me but I am surely not a bandsaw expert. I do not know if I was being careful enough but will try it again later when I have the time. Has anyone else compaired the two?

One other thing that I found was that Michael Perata in a post showing simular threads below (Blade Tension Guage) briefly mentioned using a dial caliper instead of a tension guage. He did not expound but there must be at least on other person using this method.

[Dale Thompson]

If Dale blesses it, it's gotta be good! :D

Hey San Josey,
You are a TERRIFIC judge of character and celestial influence! :rolleyes: Contrary to popular opinion, salt water DOES NOT build brain cells, even if it is well iced! :D :) Anyway, thanks for the compliment - I think?? :confused:

Dale T.

[Dale Thompson]

As I cranked it up, I got .001, .002 AND .003 on the caliper synchronizing with the 10, 20 and 30 on my machine gauge! :) :cool:

Hey Spring,
Remember that the same in/in strain(stretch) occurs on BOTH sides of the blade and the "stretch" on the blade is actually double your reading. OK. You already knew that! :) As a good friend, I just wanted to set the record straight. ;) By the way, BS (Badger Stadium) is an ancient acronym. We now call it Camp Randall Stadium. ;) :D

Dale T.

[Dale Thompson]

4. I usually tension my blades using the "flutter" method rather than the stretch method. It turns out that when I did this test that my ideal blade tension seemed to be about half of what the stretch school of thought predicted.
5. Are there any other creekers that use the flutter method for tensioning their blades?

lou

Lou,
Timberwolf recommends the "flutter" method. I've tried it and have no complaints with the results. :)

Lou, we all have skeletons in our closets. :( One of mine is that I SELDOM detension my Band Saw blades. :o That negates the purpose of the whole post for idiots like me. :eek: If there are any "sharks" in the Creek, I am fair game! :eek: :D

Dale T.

[Alan Tolchinsky]

Hi Lou, I use the "flutter method" for tensioning. But isn't that just for low tension blades? Now I just crank it up and check performance.

[Richard Butler]

good post and topic all

I had been planning on posting a similar topic. good use of the caliper. Thanks dale for the info. Here are a couple of thoughts
1. youngs modulus is independent of size and shape of that material. it is defined as the ratio of the stress /strain of the particual material. as dale has said it is about 29x 10^6 psi
2. the 15000psi results in about .05% elongaton of the blade. I guess this must be a reasoanble preload for the steel blade.
3. Although the blade size will have an effect on the amount of spring tension you need, it will not change the .003"/5" that you need to stretch the blade.
4. I usually tension my blades using the "flutter" method rather than the stretch method. It turns out that when I did this test that my ideal blade tension seemed to be about half of what the stretch school of thought predicted.
5. Are there any other creekers that use the flutter method for tensioning their blades?

lou


I have tried the "flutter" method and found it to be the most inaccurate way to test tension. My results yielded tension so low as to be dangerous.

[Richard Butler]

Hi Lou, I use the "flutter method" for tensioning. But isn't that just for low tension blades? Now I just crank it up and check performance.

As far as I am concerned there are no "low tension" blades. Steel is steel and the only reason that I can see for advising low tension is to hide weak welds.

[Mike Weaver]

...The article states that for every 6000 psi applied to 5" of blade, the steel stretches .001. Instead of making the gauge in FWW, I decided to clamp my inexpensive Harbor Freight dial caliper to the blade. I opened the caliper to 5", c-clamped the jaws to the blade and zeroed the dial. I tensioned the blade until the caliper read just shy of .003 attempting to approximate 15,000 psi, the minimum recommended tension of most blade manufacturers.... Kurt,
THANK YOU!
You just saved me a bunch of $$ for a tension gauge. (And, made SWMBO happier to boot).

GREAT Idea and it's so easy, a Caveman could do it. :eek:
-Mike

[Basil Rathbone]

This sounds like a great way to set up the blade in my new Rikon 10-325 that arrived today, but I am wondering at what tension do you start your measuring at and how do you know what that is?

Thanks. I agree with the other posters, if this works, you should get a prize.

[Richard Butler]

I had planned to make the shopmade bandsaw tension gauge that was in the February 2001 Fine Woodworking magazine, but I decided to try something different. The article states that for every 6000 psi applied to 5" of blade, the steel stretches .001. Instead of making the gauge in FWW, I decided to clamp my inexpensive Harbor Freight dial caliper to the blade. I opened the caliper to 5", c-clamped the jaws to the blade and zeroed the dial. I tensioned the blade until the caliper read just shy of .003 attempting to approximate 15,000 psi, the minimum recommended tension of most blade manufacturers. As I suspected, the saw's tension gauge was not accurate. As far as I can tell, the tension seemed appropriate and I got good results in some resaw tests which was the point of checking the tension in the first place. Do you think this method is half way accurate to determine blade tension?

Kurt






Sure it is accurate. It would be more accurate if you had a larger span to measure.

[John Schreiber]

I don't want to rain on the praise parade here, but doesn't this assume zero tension at the beginning measurement? How do you get it to be at zero, but still have the blade straight, so that any further elongation is due to tension?

[Chris Barton]

This is a vintage post and, Kurt did win a prize from FWW and his tip was in the magazine, about 2 years ago...

[Cliff Rohrabacher]

Accurate? I have no idea.

Different steels at different hardnesses will perform differently under stress. So too will the performance change with the width and thickness of the blade as well as little things like tooth and gullet grind.

Over my years in machine shops with band saws I never once pulled out a tension gauge (never saw or heard of one). I just tightened the blade to just the right "feel." However, it is absolutely true that a DO-All or a Grob (common machine shop saws) are stratospherically better (heavier) machines than what a few lousy grand will purchase in the consumer retail market.

Kids new in the trade would over-do the tension such that they'd snap the blades over and over and the machines would be no worse for it.

I rather suspect that that sort of treatment would destroy most made-for-the-consumer band saws. But then you aren't paying 20 grand for them either.

[Eddie Darby]

I've used the TimberWolf flutter test, and am happy with it most of the time, but when I am pushing my saw and thus blade more than usual, I will give it a few more cranks higher. I usually find another flutter free zone, higher up in tension, that I use for the hard cases.

I haven't tried this yet, but I do have the article. Same idea though.

https://www.taunton.com/finewoodworking/Workshop/WorkshopPDF.aspx?id=2702

[Ray Scheller]

Be careful claiming this as your idea as I think I read this in a Popular Mechanics article a year or two ago:confused: . Just my $.02 worth.

[Chris Barton]

I dodn't think Kurt was trying to steal anyone's idea. And, his was published in FWW at about the same time, 2 years ago (when this post first started)!

[Kurt Loup]

Be careful claiming this as your idea as I think I read this in a Popular Mechanics article a year or two ago:confused: . Just my $.02 worth.

Ray,

I assure you that I did not come across this idea from another source prior to my post. Note that this post was started over 2 years ago. On the recommendation of others, I submitted the idea to FWW and it was accepted and published in the tips section a year or two ago. Maybe you saw it there?

Anyway, check out Mark Duginske's post about bandsaw tensioning. He doesn't think this is a good idea for various reasons. I have no reason to disagree. He and others certainly know more about this than I do.

Kurt

[Mark Duginske]

Do you think this method is half way accurate to determine blade tension?

Kurt

Sorry to rain on the caliper for tension party but I see it differently.
This whole idea is based on a number of questionable assumptions.
If you read the other band saw thread that is going on that I started on damage from over tensioning you will pick up information on springs, aftermarket tension (strain) gauges and how they compare and how useful they are.

First, the original FWW article is based on the assumption
that spring weakens and the gauge is thus not accurate. Neither of these is correct. The band saw spring does not weaken or lose its strength over time. Also the gauge is relatively accurate just like the gas gauge in you vehicle.

To test the usefulness of the blade stretch test theory for woodworking I bough all of tension gauges (over $1000) that measure 4 or 5 inches of blade for stretch to determine their usefulness. I first tested them with Aaron Gesicki who has an undergrad and masters degree in metallurgical engineering.

Then I sent them to Mike Cutler, who is a frequent SMC contributor and he did another evaluation which is summarized in the other thread. In short, gauges that measure 4 or 5 inches of blade stretch are not applicable to woodworking machines and are not applicable to blades under 1” wide.

The third wrong assumption is that the clamp on strain gauges are of value for the woodworking band saw tension range. Read Mike Cutler's testing report in the other thread on these gauges. These gauges are designed for very large metal cutting band saws using by woodworking standards tremendous tension. They are like using a gallon jug to measure a spoon of fluid. It is simply not the appropriate scale.

The FWW article was about doing something on the cheap that in reality is not worth doing. I think that the article fulfills the fantasy of doing something, that is the duplication of what a $300 tool does for a couple of bucks. And that is what it is, a fantasy. Even more of a fantasy is that the $300 strain gauge tool is the answer
for woodworking band saw tension.

Wrong assumption #4 is that it is simply a mater of clamping something to the blade and tensioning it. As Mike described it, the 1/2" blade is too flexible to get a good reading. I tried the feeler gauge idea and the caliper idea several times (clamping and unclamping) on a saw with a Carter ETG electronic gauge and was amazed at the differences I got on ten different test.

Sure the blade does stretch and you could measure but there are so many variables that it is beyond the scope of a back yard mechanic. You would need a room full of expensive equipment to measure it accurately. Another problem with blade stretch measuring (blade load) is that it is not as accurate as the saw gauge or the Carter ETG (or the standard saw gauge) which is measuring wheel load.

The number may or not work but it will give you a plecebo effect. It is about as accurate as holding your hand out the widow to measure the speed of your vehicle. Why not use the speedometer?

No field of woodworking has more misinformation than the band saw as it relates to tension and the standard tension mechanism.
Although the feeler gauge and caliper method of measuring tension is theoretically valid the actual usefulness of this technique is doubtful. How many of you measure tire pressure to know how much fuel is in your tank? Theoretically you could measure either your car weight or the tire pressure to determine the amount of gas in the tank. Why not use the gas gauge?

90 percent of the time you can use the gauge on your saw with good results. For cutting thick material or if the blade is dulling
go to the next higher setting. Just like the gas gauge in your car
it is a “good enough” device.

[Kermit Hodges]

Great idea, but afraid it's not a new idea. But it is as accurate as your dial caliper and how well you set it up. (how much tension or slack was in the blade when you started).