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/modesto-borrough-belt-tension-gauge-bt/7669110329.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/jteneyck-woodworker/current-projects/bandsaw-blade-tension-meter?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/jteneyck-woodworker/current-projects/bandsaw-blade-tension-meter?authuser=1

John

Thanks for writing that article John. Very informative.

[Johnny Barr]

Or this ...... https://www.eztension.com/buy-one-now/eztension-bandsaw-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-now/eztension-bandsaw-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/jteneyck-woodworker/current-projects/bandsaw-blade-tension-meter?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

[John Kananis]

John, thanks for that write up. If you don't mind a followup question, how does the length of the vertical arm of the gauge affect the calculation? Why does 12 inches work?

I have quality dial indicators (Mitutoyo) but resolution is either .01 mm or .001 inch. Can you recommend something decent? I don't normally need that kind of precision so not looking to break the bank but not into buying junk at all.

[John Kananis]

I'm surprised to hear you say this about bimetal. I find (without a gauge obviously) they need much more tension than carbon or silicon blades.

[Steven Cok]

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

Thaks John, good input.

[Steven O Smith]

John, I don't follow this part:
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.

When you remove the 0.02" spacer, the dial indicator must still be in contact with the lower piece. Then you adjust tension to find zero, moving the lower piece up and down via the alignment dowel. Why do you need the spacer? I'm missing something.

[John TenEyck]

The spacer does 2 things. It assures there is room for the upper and lower jaws to move in both directions. The gage length includes that 0.020" spacer, so the calculated tension would be slightly high without it. The error isn't large (< 0.2% for a 12" gage length) but I'd rather have it be correct.

You can use any spacer thickness you want, as long as it's more than 0.010".

John

[John TenEyck]

I'm surprised to hear you say this about bimetal. I find (without a gauge obviously) they need much more tension than carbon or silicon blades.

John, my response is attached. I wrote it as a reply but it wouldn't load. Fortunately, I was able to take a screen shot before losing it.

John

https://lh3.googleusercontent.com/pw/ABLVV86gsqrAc58J7sw6AMoTdLghzDOwbYUbSqpJR7kt6w4fFL e-3VBEktywQId6ki2CvZaMPddW-L8eyzpvVAHVHB4YiqhKmzeIaWeA9RPcR1BZ5HgYPVtUKSqWgrQ a_Ya1nhchMX_goUrf4E-DvwFXSM5YnQ=w1574-h885-s-no?authuser=1

[John Kananis]

Thanks, John. Could it be the band thickness of the bimetal blades? It's .035 compared to .025 of other blades.

[Steven O Smith]

Makes perfect sense now, thank you.

[Steven Cok]

Thanks, John. Could it be the band thickness of the bimetal blades? It's .035 compared to .025 of other blades.
Assuming your bandsaw gauge is similar to mine (measuring spring compression), it isn’t really measuring tension, it’s measuring the force that is applied to the blade. Tension is actually pounds per square inch, which is the force divided by the cross sectional area.

(Using made-up gauge numbers for the sake of discussion)…if your gauge reads “100” on a properly tensioned 0.25 blade, it would need to be cranked up to “140” to get the same tension on a 0.35 thick blade.

[John Kananis]

I see, this makes sense. Thank you, Steven.


Assuming your bandsaw gauge is similar to mine (measuring spring compression), it isn’t really measuring tension, it’s measuring the force that is applied to the blade. Tension is actually pounds per square inch, which is the force divided by the cross sectional area.

(Using made-up gauge numbers for the sake of discussion)…if your gauge reads “100” on a properly tensioned 0.25 blade, it would need to be cranked up to “140” to get the same tension on a 0.35 thick blade.

[John TenEyck]

John, thanks for that write up. If you don't mind a followup question, how does the length of the vertical arm of the gauge affect the calculation? Why does 12 inches work?

I have quality dial indicators (Mitutoyo) but resolution is either .01 mm or .001 inch. Can you recommend something decent? I don't normally need that kind of precision so not looking to break the bank but not into buying junk at all.


The equation I posted earlier shows why gage length is important:

Tension = Young's Modulus x Strain

Strain = dial gage movement / gage length, where gage length = the length of the long and short vertical arms of the gage (the distance between the clamps).

So if your dial gage moves 0.010" and you have a gage length of 12", then the strain = 0.010/12 = 0.000833 inch/inch

Tension (psi) = 30 x 10^6 (30,000,000 psi) x 0.000833 = 25,000 psi = 25 ksi

Any gage length works fine, as long as you know what it is. The longer the gage length, the less precise the dial gage needs to be to still give a good measure of strain. I created the table in an earlier post just to make it easier, so you don't have to calculate strain.

If your saw has enough resaw height to install a meter with at least 10" gage length the 0.001" dial gage you have will work fine. If your saw can only handle something 5 or 6 inches long, then a dial gage with 0.0005 or 0.0001" precision will give more accurate measurements. Here are a couple of options I found on Amazon:

https://www.amazon.com/AccusizeTools-0-0-05-0-0001-Indicator-P900-S097/dp/B0189Q1XYS/ref=sr_1_3?crid=20XE6092RMXQY&keywords=0.0001%2Bdial%2Bindicator&qid=1703527291&sprefix=0.0001%2Bdial%2B%2Caps%2C93&sr=8-3&th=1


https://www.amazon.com/AccusizeTools-0-0-05-0-0001-Indicator-P900-S097/dp/B01AVG7VPO/ref=sr_1_3?crid=20XE6092RMXQY&keywords=0.0001%2Bdial%2Bindicator&qid=1703527291&sprefix=0.0001%2Bdial%2B%2Caps%2C93&sr=8-3&th=1


John

[Steven Cok]

I’m throwing a gauge together right now. I think I can clamp the blade on the frame side close to the wheels, and get a gauge length of 18” instead of 6” or less on the cutting side. If I’m doing the math correctly, I should get 1,667 psi per 0.001”?

(30,000,000 X 0.001)/18 =1,666.67


edit to add: If I target 12,000 psi on the 1/2” blade (referencing earlier discussion), I would look for 12,000/1,667 = 0.0072” of stretch over my 18” gauge.

[Steven Cok]

While I’m letting glue dry I thought I’d run some other numbers on the spring force required, but I’m starting to confuse myself a little. Maybe someone can check me on this…

The blade I have on right now is 1/2” x 0.025. The blade width at the gullet is around 3/8”. I’m not sure how the varying width affects the strain in the blade, so I think I’ll run both min and max areas and assume the effective area is somewhere in that range.

I’ve got the Jet 14”, so based on John’s input I’ll use 12,000 psi as a target number.

Min area calculation
12,000 X 0.025 X 0.375 = 112.5 pounds

Max area calculation
12,000 X 0.025 X 0.5 = 150 pounds

Here’s my question: doesn’t the spring have to apply double the force calculated above because it is stretching both the left side and the right side strands? Force required would then be 225 to 300 pounds?

[John TenEyck]

I’m throwing a gauge together right now. I think I can clamp the blade on the frame side close to the wheels, and get a gauge length of 18” instead of 6” or less on the cutting side. If I’m doing the math correctly, I should get 1,667 psi per 0.001”?

(30,000,000 X 0.001)/18 =1,666.67

That's correct. Whichever side you clamp the gage onto, make sure to clamp to the band, avoid the teeth.

John

[Steven Cok]

Thanks. I drilled a relief hole to give room for the teeth set.

[Steven Cok]

Here’s my quick cobbled up version of an 18” gauge. I wasn’t happy with the way I set up the clamping, at least on the short floating arm. Any tweaking around near it, like trying to set zero on the indicator, and the arm would move slightly. When I left it alone it would stay in place and I could get repeatable results, so I’m not going to bother trying to improve it at this point.

I just replaced the stock spring with a Carter replacement, and I’ve been running a 1/2” blade. With the new spring I liked how it was running if I put the saw’s “tension” indicator at or just above the 1/2” mark. When I hooked up the dial indicator tension gauge and set the spring to the 1/2” setting I was getting a pretty consistent 0.009” of movement over the 18” gauge. That works out to 15,000 psi. When I cranked it up to the 3/4” setting I was getting around 0.012”, or about 20,000 psi. (I wasn’t comfortable with the way the saw felt at that tension, so I didn’t try running it there.)

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[John TenEyck]

Good stuff, Steve. If your saw is cast iron 15 ksi is probably as high as you should run it. As long as the upper blade guides aren't moving so far to the right that the one on the left side starts rubbing on the side of the blade it should be OK.

Glad the gage worked out for you. In the second photo it looks like the short arm is not 90 degrees to the long piece. If it stays that way and the dowel can travel freely in its mating hole in the end of the long piece then it will work as it should, but you might still want to set it square the next time.

And now you know what tension you have at the 1/2" mark with a 1/2" blade. You can do the same test when you install a 1/4" or 3/8" blade, too, and adjust the tension if needed to whatever value you want, and then you'll know where to set it for any of those blades in the future.

John