Tensioning Band Saw Blades

[JamesHuntsville]

I had planned to make the shop made 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 digital caliper to the blade. I opened the caliper to 5", c-clamped the jaws to the blade and zeroed the reading. I tensioned the blade until the caliper read .003 attempting to approximate 18,000 psi, within the 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? I was tensioning a 1" blade with 2 1/2 tpi hook. This is supposed to be reasonably accurate for any blade from 1/2" and above. Just for picture taking I did not use C clamps. This was only for setup for photos. I have actually set the tension between .0025 and .003 using C clamps and it works very good. Dont know if this setup will work for the low tension timberwolf blades. I think one should check with the manufactur to see if the low tension blades can be tensioned like this. At least this method would be repeatable and take the guess work out of tensioning the blade every time you wanted to use the saw. Mark the tension scale and return to the mark everytime for the proper tension. Redo the whole procedure when you change blade sizes and mark the scale for the new blade size. What do you think?








JamesHuntsville

[workin for wood]

I think that's some serious blade tensioning you have going on there. I believe you that your scale is inacurate, and I'm sure mine is too. I guess I'm old fashioned, I tension my blade by feel. I push on the front of the blade and the side of the blade...when it is hard to push over 1/8 in either direction, then I call it good, set my rollers and then go to work. You should change your guide blocks to Euro Rollers btw. (Just my opinion). Be sure and remove blade tension after using the saw, that's the most important thing.

Now here is a question to you. you say the blade stretches .001 or whatever. Now you say you can make a mark and re-use it next time around for that blade, but will the blade unstretch after you take the tension off, or stay the same, and perhaps next time you crank the tension on that blade will it stretch again beyond the original stretching, and will this continue to happen until the blade breaks, which inevitably will happen sooner or later. Too complicated for my brain, so I'm just going by feel.

[utbva]

Jeff, from what I remember from my metalurgy classes, steel has what is called and elastic limit where the steel will stretch and return to its normal state. When the steel is stretched beyond the elastic limit it is called the yeild point and at that point the steel will not return to its normal state. Once you go beyond the yeild point it does not take much more force to break the steel.

I agree that that is some technical tensioning of the blade. It is something I may look into for my bandsaw but I just have a 14" Jet band saw so I don't use as big a blade. I have change to ceramic guide blocks and they made a big difference to how well my bandsaw performs but I am going to look into the Euro Rollers. One thing I have not done is to remove the tension after using the saw, I need to either get a turn wheel for the tension adjustment or a tension release lever. I'm just too lazy to turn that little adjustment knob everytime I use the bandsaw.

[William Young (SE BC)]

Bill;

One thing I have not done is to remove the tension after using the saw, I need to either get a turn wheel for the tension adjustment or a tension release lever. I'm just too lazy to turn that little adjustment knob everytime I use the bandsaw

Same here. My Ridgid 14" band saw is somewhere between 5 and 6 years old now. Had a tremendous amount of re-sawing red oak when I was making lots of clocks. I have never slacked off the tension yet except to change blades. Now that I am doing a lot of turning it also gets lots of use cutting out big bowl blanks etc.
I know a lot do not agree with this but mine also requires a lot of cranking of an adjusting knob up on the top of the saw . It has original bearings in both top and bottom wheels and is still working great. The tires are still in new looking condition because I keep them clean and re-clean them every time I change a blade.
I can see the point in slacking off the tension if the saw is not going to be used for long periods of time because it could cause flat spots in the tires on some makes depending on the type of material used for the tires. But I have never had that problem yet so I guess I will continue on just using it as I am. My saw gets used a lot so not much chance of tire damage due to lack of use.
W.Y.