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Thread: bandsaw tension gauge-crazy idea?

  1. #1
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    bandsaw tension gauge-crazy idea?

    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




  2. #2
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    Quote Originally Posted by Kurt Loup
    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%.

  3. #3
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    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.

  4. #4

    Submit it!

    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
    "all men dream: but not equally. Those who dream by night....wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible."
    T.E. Lawrence

  5. #5
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    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?)
    Last edited by Greg Torok; 07-08-2005 at 10:31 PM.

  6. #6
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    Bade Tension

    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.

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

    Dale T.
    I am so busy REMAKING my projects that I don't have time to make them the FIRST time!

  7. #7
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    If Dale blesses it, it's gotta be good!
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  8. #8
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    Thanks for the comments. I've gotten some additional ideas to think about.

    Kurt

  9. #9
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    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.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
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    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

  11. #11
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    Quote Originally Posted by Allen Bookout
    Also it seems to me that the stretch would vary by size of blade, both thickness and width.
    As Yoda says, "Size matters not."
    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.

  12. #12
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    Quote Originally Posted by Allen Bookout
    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).

  13. #13
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    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!!! 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.
    Cheers,
    John K. Miliunas

    Cannot find REALITY.SYS. Universe halted.
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  14. #14
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    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.
    Attached Images Attached Images
    Larry

  15. #15
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    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

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