John TenEyck
02-25-2020, 2:56 PM
I've been helping a friend sort out the tension in the blade on his bandsaw mill. There is no spring in the tensioning mechanism and so there are concerns that it could easily lose tension in use. As I thought about how to determine if that might be the case it dawned on me that the simple tension meter I use on my bandsaw, or even a set of Vernier calipers, can be used to measure the tension on a blade after it has been tensioned just as easily and accurately as it can on a blade being installed. In fact, it might be more accurate because there is no need to find zero tension. And that's why I'm posting it here.
To prove my logic I went down and clamped a set of 6" Vernier calipers (because that's what my friend will use on his mill) to the blade of my large bandsaw which has about 25 ksi on it under load. I set the calipers at 5.9", clamped the jaws to the blade with two small c-clamps, reset the output to zero and then released the tension on the spring. The calipers read -0.005". And that is just over 25 ksi:
30 x 10^6 x 0.005/5.9 = 25.4 ksi
So if you have had trouble determining zero tension with a shop built tension meter you may want to go about it from the other direction. Put the amount of tension on it that you think is right, or have been using, install the tension meter, reset the indicator to zero, then release the tension and note how far the indicator moves. Plug that into the formula above and you will know how much tension is on the blade. And now you can adjust the tension to any level desired, within the capability of your bandsaw.
For more on how to build a tension meter follow this link: https://sites.google.com/site/jteneyckwoodworker/current-projects/bandsaw-blade-tension-meter?pli=1
John
To prove my logic I went down and clamped a set of 6" Vernier calipers (because that's what my friend will use on his mill) to the blade of my large bandsaw which has about 25 ksi on it under load. I set the calipers at 5.9", clamped the jaws to the blade with two small c-clamps, reset the output to zero and then released the tension on the spring. The calipers read -0.005". And that is just over 25 ksi:
30 x 10^6 x 0.005/5.9 = 25.4 ksi
So if you have had trouble determining zero tension with a shop built tension meter you may want to go about it from the other direction. Put the amount of tension on it that you think is right, or have been using, install the tension meter, reset the indicator to zero, then release the tension and note how far the indicator moves. Plug that into the formula above and you will know how much tension is on the blade. And now you can adjust the tension to any level desired, within the capability of your bandsaw.
For more on how to build a tension meter follow this link: https://sites.google.com/site/jteneyckwoodworker/current-projects/bandsaw-blade-tension-meter?pli=1
John