Bandsaw Blade Tension Meter

There are many opinions about how to tension the blade on a bandsaw.  I'm an engineer, and engineers measure and control things.  Turns out, you don't have to spend much money in order to do exactly that with a bandsaw blade.  There are commercial tension meters costing several hundred dollars, but for less than $25 and an hour or so of your time you can make one that works just as well.  Here are the parts of the one I built for my bandsaw.

It's made from a few pieces of 3/4" hardwood stock, a few 1/4 - 20 bolts and thumbwheels, and a dial gauge.  The upper wood cross arm is doweled and glued to the spine.  The lower cross arm has a 1/4" dowel in it and that fits up into an oversized hole in the bottom of the spine.  The cross arms are slotted to fit onto the back of the blade and holes near the front end are drilled for the bolts and thumbwheels that hold the cross arms snug to the blade.  The dial gage is mounted such that it is in the mid range of its length of travel when the lower cross arm is in place.  You likely will need to add a small block on the side of the lower cross arm as a foot for the dial gage, as I did.  Here is the meter mounted onto a blade.

You can make the meter any size you want and of course it would have to be much smaller to fit in a saw with a 6" resaw height.   The distance between the inside edges of the two cross arms on my meter is 12" with a 0.020" spacer between the lower cross arm and spine.  

To use the meter put a small amount of tension on the blade then clamp the meter it to the blade with the 0.020" (not critical) spacer, then remove the spacer.  Now remove all the tension from the blade until the dial gage no longer moves.  Add a little tension back and then release the tension again until the gage stops moving.  Repeat a couple more times until you are positive you have found the point of zero tension - the point where the gage just stops moving.  Set the dial gage to zero and then crank up the tension after reading further below.  

If you are unsure of where zero tension is then you can tension the blade to what you think is correct, where you were setting the blade before you decided to build the meter.  Now install the meter, set the dial gage to zero and then release the tension from the blade.  Note the dial gage reading and plug it into the formula below to find the tension.  

Now you need to know that steel has a Young's modulus (Y) of about 30 x 10^6 psi and a little math: 

Y = Stress/Strain 

We want to know what the Stress (tension) is in the blade, so we can rewrite the equation to:

Tension = Y x Strain

The strain (elongation per unit length) in the blade as we increase (or decrease) tension = dial gage movement (0.001") / distance between the cross bars.  So for my meter, for every 0.001" the dial gage moves:

Tension = 30 x 10^6 x (0.001"/ 12") = 2500 psi

If I want to apply 25 ksi to a blade I simple increase tension until the dial gage moves 0.010" above zero tension.  It doesn't matter what blade I have on the saw.  It will take more or less spring force to move the dial gage 0.010" but there will be 25 ksi on that blade when there is.   

I hope you find this helpful.  I think you'll get more consistent and likely better performance and life out of your blade by using the meter to adjust the tension.