Bandsaw blade tension gauge

[Bill Dufour]

I see a vee belt tension gauge for sale locally. Can this be used to tension a bandsaw blade? I assume the grab hooks will need some shims or padding so as not to bend the teeth.
Bill D
https://modesto.craigslist.org/tls/d...669110329.html

[John TenEyck]

How would you correlate whatever value it records in to psi on a bandsaw blade? Makes more sense to me to make your own tension gage. Less than an hour of your time and for the price of a dial gauge.

https://sites.google.com/view/jteney...ter?authuser=1

John

[Brian Tymchak]

How would you correlate whatever value it records in to psi on a bandsaw blade? Makes more sense to me to make your own tension gage. Less than an hour of your time and for the price of a dial gauge.

https://sites.google.com/view/jteney...ter?authuser=1

John

Thanks for writing that article John. Very informative.

[Johnny Barr]

Or this ...... https://www.eztension.com/buy-one-no...-tension-gauge

I originally thought this was a gimmick but it does the job and gives similar results to using the more traditional push and measure method.

[John TenEyck]

Or this ...... https://www.eztension.com/buy-one-no...-tension-gauge

I originally thought this was a gimmick but it does the job and gives similar results to using the more traditional push and measure method.

With that device you won't know what the tension actually is. It may be OK for some applications and completely inappropriate for others. It's akin to using the flutter method, which relies on first tensioning to the indicator mark for the blade width you install. Again, you have no idea what that tension is and, with a worn-out spring like on my old 14" Delta when I first got it, it wasn't nearly enough. These methods may indeed work on many new saws, but I'd rather have a true, measured number to verify it's correct.

On my newer Grizzly the 1" indicator produced 24 ksi on a 1" Woodmaster CT when I measured it. That is a very good tension to run that blade at, but I still found it pretty surprising that Grizzly would think to put that much tension on a blade. On the other hand, even with an Iturra spring on my old Delta the tension is 12 ksi on a 1/2" blade, much less than I'd prefer to run at, but not possible with that wimpy frame. Without measuring the tension on each saw, I would have had no idea.

John

[Steven Cok]

I picked up an EZtension a while back and played with it some (14” Jet). It always felt like I had to crank the tension up higher than I anticipated, and I was getting decent results at lower tension settings.

I just swapped out the old tension spring for a Carter Cobra, so I thought I’d take a run at the EZtension again. I did more reading of opinions and feedback on the forums, and a thought crossed my mind - EZtension is (from what I understand) set up for 15,000 PSI, a setting that I believe is recommended for resawing. Basically worst case scenario for a bandsaw blade. I’ve read differing opinions, but for day to day work on blades from 3/16” to 1/2” (covers everything I do), settings of more like 12,000 PSI (and maybe down to 8,000 PSI) should work just fine. This matches my limited experience with tension settings lower than the EZtension call for as well.

So I got curious if I could use the EZtension to reliably set tensions lower than 15,000 PSI. I ran a bunch of calculations for 1/2”, 3/8”, 1/4”, and 3/16”. I had to make a lot of assumptions along the way, but I was looking for relative values, not absolutes. I thought the results might be helpful for others, so here’s my (very) rough interpretation of what I saw:

If you step down the EZtension setting one step, i.e. use the 3/8” setting on a 1/2” blade, or the 1/4” setting on a 3/8” blade, you will probably be in the 10,000 - 11,000 PSI range. If you go down two steps (use 1/4” setting on 1/2” blade) you will probably be around (or just under) 8,000 PSI.

I ran some 4” maple on a Starrett 1/2” blade today, using the EZtension 3/8” setting, and got very nice results.

I’m curious of other’s experiences using the EZtension?

[Mark Gibney]

Interesting stuff there Steven. I'll use this information with my EZtension gauge, thanks.

[John Kananis]

I'm probably going to need to run for cover after saying this but I've always tensioned my blades by plucking (while applying tension) until your hear a nice solid thud. Once the pitch goes past the "thud" and starts going higher, you've gone just too far. That said, I want to build the gauge in John's post.

[Curt Harms]

Kind of math intensive but the price is right, especially if you already own a digital caliper.

https://woodgears.ca/bandsaw/tension.html

[John TenEyck]

I'm probably going to need to run for cover after saying this but I've always tensioned my blades by plucking (while applying tension) until your hear a nice solid thud. Once the pitch goes past the "thud" and starts going higher, you've gone just too far. That said, I want to build the gauge in John's post.

Whatever works for you is good, but I wouldn't be willing to risk a carbide blade costing a couple hundred $'s using that method. Chances are the tension you think is correct will be too low, which will diminish performance and blade life. If you and your saw are the robust type, however, you could be applying too much tension. In that case, it will cut great, but both the saw bearings and blade may suffer a shorter life.

Not picking on you John, but I'm always surprised that people will spend countless hours trying to get their TS fence, and/or blade perfectly aligned, install router lifts with control to 0.001", etc, but not spend 10 minutes to properly tension a bandsaw blade. And you only have to do it once, after which you can use the onboard tension indicator to go back to that same tension.

Other folks recognize the importance of setting blade tension, but buy a commercial tension meter thinking it must do a better job than anything you could make yourself when the opposite is true. Commercial tension meters infer tension from bending deflection, whereas the shop-built gage I showed, and the one by Matthias Wandel, measure actual strain in the blade over a long span to give a more accurate measurement of blade tension.

Build yourself a tension gage and start off the New Year knowing what blade tension you are running at. You probably already own a dial gage or set of vernier calipers, so your cost is less than an hour of your time.


John

[John Kananis]

Hey John, happy holidays. I don't feel picked on at all but thanks for the consideration. To be fair, in the thirty years I've been working with bandsaws and in other various pro shops I've been in, checking blade tension with a dedicated gauge was kind of unheard of (in my experience). That said, we're talking mostly carbon steel blades here and I have no doubt the bi-metal and carbide blades would benefit so I'm changing with the times and I'll build the gauge. My pluck and thump method has worked great for me this far but...

Whatever works for you is good, but I wouldn't be willing to risk a carbide blade costing a couple hundred $'s using that method. Chances are the tension you think is correct will be too low, which will diminish performance and blade life. If you and your saw are the robust type, however, you could be applying too much tension. In that case, it will cut great, but both the saw bearings and blade may suffer a shorter life.

Not picking on you John, but I'm always surprised that people will spend countless hours trying to get their TS fence, and/or blade perfectly aligned, install router lifts with control to 0.001", etc, but not spend 10 minutes to properly tension a bandsaw blade. And you only have to do it once, after which you can use the onboard tension indicator to go back to that same tension.

Other folks recognize the importance of setting blade tension, but buy a commercial tension meter thinking it must do a better job than anything you could make yourself when the opposite is true. Commercial tension meters infer tension from bending deflection, whereas the shop-built gage I showed, and the one by Matthias Wandel, measure actual strain in the blade over a long span to give a more accurate measurement of blade tension.

Build yourself a tension gage and start off the New Year knowing what blade tension you are running at. You probably already own a dial gage or set of vernier calipers, so your cost is less than an hour of your time.


John

[Robert Hayward]

How would you correlate whatever value it records in to psi on a bandsaw blade? Makes more sense to me to make your own tension gage. Less than an hour of your time and for the price of a dial gauge.

https://sites.google.com/view/jteney...ter?authuser=1

John

I made one of these a couple years ago, I think that long. I used it to tensioned three different blades I normally use. Wrote the settings on a piece of paper and taped it to the inside of my bandsaw top wheel cover. My PM1500 has a tension indicator. Have not bothered with tension settings since. Just crank the tension wheel until I hit my proper mark and start cutting. I did not spend anything as I had a dial gauge on hand. Thanks John.

[John TenEyck]

Hey John, happy holidays. I don't feel picked on at all but thanks for the consideration. To be fair, in the thirty years I've been working with bandsaws and in other various pro shops I've been in, checking blade tension with a dedicated gauge was kind of unheard of (in my experience). That said, we're talking mostly carbon steel blades here and I have no doubt the bi-metal and carbide blades would benefit so I'm changing with the times and I'll build the gauge. My pluck and thump method has worked great for me this far but...

Good deal, John. After you have the tension gage built, tension a blade the way you normally do, then install the tension gage, zero the dial gage, and then let off the tension to measure the strain. The dial gage will stop moving when the tension equals zero. After you do the simple calculation, you will know exactly how much tension you have put on the blade. The next paragragh simplifies the calculation. Should you wish to do it from scratch, however, the formula to do so is:

Stress (tension) = E (Young's Modulus) x Strain, which leads to:

Tension (psi) = 30 x 10^6 (30,000,000 psi) x dial gage movement (inch) / gage length (distance between the clamps in inches)

I have a 12" gage length (distance between the clamps) on my gage. So every 0.001" the dial gage moves = 2500 psi of blade tension. If the dial gage moves 0.008", the tension = 20 ksi. Below is a table you can use for a gage of varying length between the clamps. If yours is not included, you can use a ratio from any of the ones I've listed since the relationship is linear.

Gage Length - inch Blade tension per 0.001" dial gage (or vernier) change - psi
12 2500
10 3000
8 3750
6 5000

A dial gage capable of measuring to 0.0001" will be more accurate than one that can only read to 0.001". For short gage lengths having a higher precision dial gage would lead to greater accuracy in measuring blade strain. For the 12" gage length I use a dial gage with 0.001" precision is good enough.

Also, keep in mind that blade width and thickness have no bearing on measured tension. 0.001" of dial gage movement over 12" of gage length will be 2500 psi whether the blade is 1/8" or 1" wide, or 0.025" or 0.042" thick. Spring force will change for different blade widths and thicknesses, but not tension. So you can measure any blade using the same process and the same calculation. It can't get much simpler.

John

[Steven Cok]

I like your design. I’ve got a dial indicator that I can use for this, maybe after the holidays…

I’m curious, John, what PSI values you think might be good for 1/4”, 3/8”, and 1/2” blades on a 14 inch bandsaw? No riser block, so nothing taller than 6” will be cut, and most work is simple cuts on furniture thickness hardwoods…

[John TenEyck]

I like your design. I’ve got a dial indicator that I can use for this, maybe after the holidays…

I’m curious, John, what PSI values you think might be good for 1/4”, 3/8”, and 1/2” blades on a 14 inch bandsaw? No riser block, so nothing taller than 6” will be cut, and most work is simple cuts on furniture thickness hardwoods…

18 to 20 ksi is a good number for most blades, and most any saw can put that much tension on a 1/4", even my little 14" cast iron Delta. But with a 1/2" blade my Delta can't comfortably apply more than about 12 ksi before the frame starts bending, and to go higher would risk damage to the blade tilt mechanism. Your input of "no riser block" suggests your saw is a Delta or clone. If so, you will be limited to around 12 ksi on 1/2" x 0.025" blades, and that's with an Iturra or similar high tension spring.

The limited tension capability of the cast iron Delta is one reason I most often have a 1/4" or 3/8" blade on it. With a 1/4" blade with 6 tpi running at about 18 ksi I can cut anything up to about 4" thick pretty efficiently considering it's only 1.5 hp. That 1/4" blade can do so many things; cuts pretty straight, great for cutting most curves, most anything except thick resawing and veneer slicing. I sliced a lot of veneer on my Delta using a 1/2" x 3 tpi blade, some up to 10" wide, so it can be done, but requires very careful setup and a good deal of patience because of how slowly it cuts with such a low power motor.

If you have a steel spine saw, then 18 - 20 ksi is a good range for nearly any blade, IMO. I run carbide blades at around 24 ksi, but I wouldn't put any of those except maybe a Resaw King on a 14" saw. I don't consider bi-metal blades any differently than carbon steel blades; 18 - 20 ksi for them, too.

Adequate tension gives you the best cut quality and greatest cutting efficiency that a particular blade is capable of, as well as maximum blade life. Reason enough to do it.

I hope this helps. Merry Christmas.

John