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4X6 Band Saw Blade Tension

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  • #16
    I disagree that bandsaw tension gages are meaningless.
    When/Where did anyone say that? It has been pointed out that at 2 or 3 times the cost of the saw, and 10 to 20 times the cost of a blade they may be a poor expenditure. Not the same thing.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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    • #17
      Originally posted by mickeyf View Post
      A blade gauge such as is found on a typical home shop saw that simply measures the length of the blade is meaningless unless all your blades are exactly the same length, width, and thickness. Most saws will accept blades with a variation in length of an inch or more. Even with identical blades, without a reference to a particular "standard" blade, a gauge won't mean much. "tight as you reasonably can" and "ping" has also worked fine for me.
      That's where.

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      • #18
        Note - "measures the length" - was referring to this. If I am incorrect, and this thing actually measures tension, I apologize. It appears to me that all this can do is indicate how far the adjustment screw has traveled. I don't actually own a saw that has one of these, so I am only able to go by what I see in photos.

        Click image for larger version

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        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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        • #19
          Originally posted by Willy View Post
          Do what works best using all of the above good, albeit ambiguous, advice.
          pfft, what's wrong with ambiguous? It's like how I set the saddle height on my road bike. Keep raising it until my balls hurt, then lower it until my knees hurt and then raise to somewhere in the middle.

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          • #20
            Originally posted by mattthemuppet View Post

            pfft, what's wrong with ambiguous? It's like how I set the saddle height on my road bike. Keep raising it until my balls hurt, then lower it until my knees hurt and then raise to somewhere in the middle.
            Makes perfect sense. If your knees are hitting your balls you need to change something. Yep.
            At the end of the project, there is a profound difference between spare parts and extra parts.

            Location: SF East Bay.

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            • #21
              Now I see what you were talking about. Band tension gages also measure blade stretch. Here is Starrett's:



              Not all bandsaw tension gages cost $300. I got one made by Simonds for a very reasonable price. Don't use it much, though.

              I owned 3 4x6 bandsaws. On all of them, I tightened it about as tight as I could. I don't have the world's strongest hands. But a pluck test resulted in a nice ping, about the pitch you'd get tapping the side of a spoon against a saucer. I never had trouble with blades coming off. Of course, proper alignment and tension is only part of that equation - you also need a good blade. I used nothing but Lenox Diemaster IIs.

              metalmagpie

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              • #22
                Mickey, the last picture with the finger pointing at the slot shows indicators for the width of the blades. It's actually intended as a tension indicator that you simply crank on the tensioner until the moving colored washer right by the end of the finger is lined up with the hack mark that corresponds to the width of the blade. That supposedly is the proper tension for that width blade. I know it sort of looks like travel amounts but it's not. So it can tolerate a reasonable variation in blade lengths since the spring doesn't start to compress until the blade starts to tension.

                Of course all of our cheap 4x6 horizontal and vertical combo saws don't have any of that unless we added a spring like Rich C showed us earlier. In that case we can look up a spec for tension on the size of blade and then if we have a good enough setup to measure the spring we can tighten it until the spring is the proper compressed height.

                It's quite a few hundred lbs of tension though. So not easy to measure and calibrate.
                Chilliwack BC, Canada

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                • #23
                  Heh.......................

                  I am no great fan of Atlas, who seem to have nearly always chosen the cheaper but not so good choice when they made their machines.......BUT...... Their bandsaws are an exception.

                  I have an Atlas bandsaw. Quite well made, not a microgram of "zamak" on it.. What they did for tension was to use a standardized spring for tension. Perfect idea. You adjust the tension knob until there is exactly 1/4" of space between two parts. then you are done. Could not be simpler or more effective (no it does NOT depend on the blade length as long as it is within reason compared to spec)

                  I just made a gauge that is 1/4" thick and adjust until that just fits snugly. has worked perfectly for 25 years now.
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #24
                    the strain on a blade of this size is usually given at around 300 mpa.

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                    • #25
                      BCRider - So that thing is actually indicating how much the spring has compressed - thanks!. Not nearly as useless as I thought! Since the ubiquitous 14" wood bandsaw will usually accept a blade from a lot less than 92" to a fair bit more than 93" that's good to know, although I suspect many of them (like mine) don't have that indicator anyway.
                      "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                      • #26
                        Mike Green's excellent thread on a shop-built bandsaw-blade tension gauge, with input from Frank Ford:

                        https://bbs.homeshopmachinist.net/fo...-tension-gauge


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                        • #27
                          I think a spring that is compressed to a specific distance is the best tension gauge you can get for a small band saw. Springs all have load per unit of compression ratings so we need to simply know how many PSI tensile stress is required for a given blade size and calculate the required spring force to get that. Then select a spring with a rate that can achieve that tension at a reasonable amount of compression. If we get the tensile stress required we probably can pick a standard spring you can buy off the shelf and add it to your saw. Compress the spring by the required amount and you are done. If the measurement changes it is because the blade has stretched and you need to tighten again.

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                          • #28
                            Yep, that is what the Atlas referred to above uses. Spring is similar to a valve spring. I should measure the spring rate and compression sometime if I have it apart.

                            Never a problem with tension. Have had a hassle or two from worn pulley pivots.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #29
                              In my former life as a bicycle mechanic I built a lot of wheels, and used a spoke tensiometer. They are remarkably cheap on Amazon, starting at about $25. A quick internet search suggests that tension for a bimetal blade should be in the neighborhood of 20,000-30,000 psi, or 230-350 lbf for a .025 x 1/2" blade. That's within bicycle spoke range. Perhaps a bicycle spoke tensiometer could be modified for bandsaw use. One would need to make different contact points, since bandsaw blades are thinner than spokes, and possibly change the spring. And one would need make a calibration chart. Could be done by simply hanging weights from a section of blade. I actually built a calibration rig.

                              A couple of examples:

                              https://www.amazon.com/TOOGOO-Electr...9K4RH&pd_rd_r= 6ee9d8ec-d3fa-4908-af86-5db40e174083&pd_rd_w=zKLya&pd_rd_wg=XVOLG&pf_rd_p= 5415687b-2c9d-46da-88a4-bbcfe8e07f3c&pf_rd_r=27PSD0X5GSTZ4V3F2Z9H&psc=1&re fRID=27PSD0X5GSTZ4V3F2Z9H

                              https://www.amazon.com/LIOOBO-Bicycl...ensiometer&qid =1595816155&sr=8-9


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