Bandsaw Blade Tension Question...Iturra...

[Derek Arita]

Somewhere I read a comment by someone saying that the Iturra tension gauge is inaccurate to the tune of about twice the actual readout. In other words, the actual tension may be twice what gauge is reading. Is this the consensus? I have had the gauge for a while and just recently broke it out, but I'm hesitant to use it now.

[David Kumm]

No. There was an article that tested some gauges and got a bad one and interpolated that all were inaccurate. The actual number is less important than the repeatibility and consistency. I had one that was inconsistent and sent it back to Louis who fixed it for free. I've owned a half dozen gauges, Iturra, Starrett, and Lenox. All read within 1000-2000 of each other. Keep in mind you are measuring very slight movement so the quality of the dial indicator is the only variable here. Dave

[Dan Hintz]

Mine seems to agree (for the most part) with the sticker Jet put on my 18"er (or the other way around, depending upon viewpoint).

[Sam Layton]

I have the Iturra, and have been very happy with it. However, I have nothing to compair it to. It seems to be very consistant.

Sam

[Mike Cutler]

Derek

No they're not that far out.
Some years ago I tested 3 Iturra's, a Starrett a Lenox tension and a Carter ETG, gauge for Mark Duginske. One of the Ittura's was actually broken and I had to repair it prior to testing, but that's a separate issue.
The gauges were calibrated against known NIST standards by performing two tests. The first was a Calibration check of the dial indicator itself, and the second was an Calibration of the dial indicator mounted in the tension assembly. Of the 3 Itturra's I tested the maximum deviation in the usable range ~ 4000psi. The Carter was calibrated utilizing a load deflection assembly.
Where the Itturra's I tested fell down was in the mechanical relationship of the dial indicator to the lever arm providing the input.

Force, or distance travelled, is translated using a curved bearing surface, the end of the dial indicator, acting against a lever arm. The three Itturra's I tested all had a misalignment of the bearing surface such that it was not centered on the lever arm, but was on the edge of the lever arm.the resultant was that instead of a linear equation of force/distance travelled, the curvature of the bearing surface itself was represented in the equation.This primarily affected the return to zero after a tension adjustment. If you use an Iturra I would recommend resetting the zero after each tension check. I have no idea if the Itturra's still have the same relationship of bearing to lever arm.
The full range of the Ittura's I tested was 540,000 psi. The "Area of Interest" range is 0-30,000 psi. So it is a very small part of the total overall range. Basically the device is a mechanical load cell being used in the bottom 5% of range.
The Lennox and Starrett both had individual issues that affected their overall accuracy, but they were statistically no better than the Ittura's.
The Carter utilizes a different technology and is the most repeatable and accurate of the tension gauges I tested.
The eye opener in the testing I performed was that I found that the OEM spring in my Jet 14" was only capable of developing ~ 9000 psi max. I changed it out to Cobra Coil.
I do not utilize an after market tension gauge of any type on my bandsaws. The manufacturer's indicator is sufficient for me.

As a warning;
Tension gauges are an aid. The real litmus test is that the bandsaw is performing properly and that there is space between the spring coils of the bandsaw tension assembly. No space= No Spring, and you no longer have a bandsaw. You are actually close to breaking it. Specifically the upper wheel yoke assembly.

Disclaimer for those that seem to require it.

I was not paid, nor compensated, for performing these tests for Mark. I specifically did not want that to remain objective during the test. I did the tests because I initially disagreed with Mark's position on a specific issue. It turned out he was right, and I learned quite a bit from him.
I have no dog in this hunt.

[Frederick Skelly]

Derek, I dont mean to hijack your thread, but if you wouldnt mind a quick aside, something Mike said caught my attention.

Mike - if you changed to an aftermarket spring, how do you know the manufacturer's indicator is still accurate? (Im not trying to be a wise guy.) I replaced the stock spring in my jet 12" with an aftermarket years ago. I think I remember the supplier (may have been Iturra) including a note saying to expect the original to be inaccurate now and suggesting I use flutter or other methods. So Ive ignored that indicator for several years. Id sure appreciate learning what you know here.

Thanks,
Fred

[Derek Arita]

Mike and all, thanks so much for good info. I hate to say it, but up until now, I've used my MM16 very little due to my lack of knowledge about band saws and my being lazy about going thru all of the adjustments to make it work properly. I finally had to learn a little about band saw set up due to a bench, then a chair project. It's about time I used this expensive saw.
What I had been doing was to simply tension the blade until I got a medium pitched "ping" when plucking it...very hi-tech. Since I had the Iturra gauge, I decided that might be a better way of determining proper blade tension. Since I didn't know a lot about how to use the gauge, I went online to do some research and that's where I read about Iturra's inaccuracy.
I'm glad to find out that it is a relatively accurate gauge, if it's working properly and it's being used properly. How will I know if mine is faulty or not?
Thanks again for the help.

[David Kumm]

Derek, the more you use the saw the more you will become familiar with the sweet spot for each blade. Because i was concerned about repeatability I used to line up two or three gauges in a row on the band and see how they all read. Once i determined they were relatively accurate I had a way to judge the saw at different tensions and pick what seemed to work the best. On my saws, if the blade backs into the rear bearing and spins it I know the tension is low with the 1" trimaster. At 25000-30000 the blade seldom encounters enough force to spin the bearing. If you talk to Lenox they would prefer their Trimasters NOT be run at that tension but it works best for me. For those with smaller saws, you need to be careful in just putting a stiffer spring on the machine. If the frame can not handle the tension the flex will exceed what the saw was designed for and everything will go goofy when you use the blade. Again, the gauge does help you sneak up on the tension that both the blade and the saw can handle.

I have also found you need to be careful when you use a gauge as it is easy to not preload it, to preload it too much, or to put it on with the blade under some tension and mess up the reading. While most of the dial movement comes right at the end, you can change the reading depending on how tight the blade is when the gauge is attached. When I tension i always release the tension back down until the gauge stops to see if it still zeroes out. If the dial goes below zero you need to reset. After you use it this all becomes intuitive but it takes a few attempts to learn to set it up for consistent readings. Dave

[Derek Arita]

Derek, the more you use the saw the more you will become familiar with the sweet spot for each blade. Because i was concerned about repeatability I used to line up two or three gauges in a row on the band and see how they all read. Once i determined they were relatively accurate I had a way to judge the saw at different tensions and pick what seemed to work the best. On my saws, if the blade backs into the rear bearing and spins it I know the tension is low with the 1" trimaster. At 25000-30000 the blade seldom encounters enough force to spin the bearing. If you talk to Lenox they would prefer their Trimasters NOT be run at that tension but it works best for me. For those with smaller saws, you need to be careful in just putting a stiffer spring on the machine. If the frame can not handle the tension the flex will exceed what the saw was designed for and everything will go goofy when you use the blade. Again, the gauge does help you sneak up on the tension that both the blade and the saw can handle.

I have also found you need to be careful when you use a gauge as it is easy to not preload it, to preload it too much, or to put it on with the blade under some tension and mess up the reading. While most of the dial movement comes right at the end, you can change the reading depending on how tight the blade is when the gauge is attached. When I tension i always release the tension back down until the gauge stops to see if it still zeroes out. If the dial goes below zero you need to reset. After you use it this all becomes intuitive but it takes a few attempts to learn to set it up for consistent readings. Dave

David, thanks. I was wondering how to determine the "0" point, but what you say makes sense and I'll give that a try. I have a 1/2" blade from a local shop, welded there. I'm running that at about 15K. I have a 1" Woodmaster CT coming and was wondering what I should run that at?

[David Kumm]

Derek, I forget what saw you run. Zero the dial and tension to 20K. Track the blade by hand for a couple of minutes to be sure it doesn't run against the guards and then run about an 8" hardwood and resaw. Then tension to 22K etc until the cut seems to not improve and stop. At that point the 8" maple or whatever should not push the blade back more than just slightly under moderate feed rate and you should be good to go. Check the saws gauge and note the reading. Use the tension gauge a few more times to be sure the saw gauge always reads the same and then you can put the iturra in the drawer until you need it again for verification. My saws don't have a built in gauge so the Starrett and lenox get used a lot. Dave

[Mike Cutler]

Derek, I dont mean to hijack your thread, but if you wouldnt mind a quick aside, something Mike said caught my attention.

Mike - if you changed to an aftermarket spring, how do you know the manufacturer's indicator is still accurate? (Im not trying to be a wise guy.) I replaced the stock spring in my jet 12" with an aftermarket years ago. I think I remember the supplier (may have been Iturra) including a note saying to expect the original to be inaccurate now and suggesting I use flutter or other methods. So Ive ignored that indicator for several years. Id sure appreciate learning what you know here.

Thanks,
Fred

Frederick

It's not that the OEM gauge is accurate, it's just sufficient. Without NIST traceability you have no accuracy. You can can have repeatability, or reliability, but not accuracy. The "Tick" marks on a 14" Delta/Delta clone are a good starting point.
All springs have to conform to Hook's Law. Springs can be linear and non linear rate devices, depending on the coil configuration.
The OEM coil on the Jet is shorter than a Cobra Coil, so for equal cross sectional coils, the Cobra will have a larger range. The Cobra coil configuration is a "D" cross section, which is slightly different that the OEM spring. Bottom line is that my Jet can tension a 1/2" blade properly now, and be closer to the actual 1/2" indication. All it ever sees is 1/4" and smaller though. My Rikon is for resaw and it has a 1" 2/3 varipitch which it can tension properly.

I really don't pay attention to anything other than the finished cut. It's either good, or it's not, regardless of what any tension device indicates. I adjust the blade from the that point.
I don't use the flutter method or anything like that either. Mostly because I don't buy into it. Steel is steel, and within a very narrow band it's modulus will be the same. If the flutter method works for one blade, it should work for them all. I guess though that if a person uses it, and many do with great success, that your blade will not be over tensioned, and that's a good thing.

Derek
If you've got an MM16, get that machine in use Big Guy!. That's way too nice a machine to be left idle ( Better than any machine I own.:o )
Grab some scrap wood, a cheap vernier and and pencil and get comfortable with it. Don't get hung up on checking and making all kinds of adjustments right off the bat. Run the wood through it, and go from there. I'm willing to bet, that "box stock", and right off the truck, that bandsaw was pretty close to performing properly, with the exception of putting the correct blade on it. Too many folks get too hung up on checking and overhauling a brand new bandsaw before they've ever used it. The wood will tell you what adjustments need to be made.

[Derek Arita]

Frederick

It's not that the OEM gauge is accurate, it's just sufficient. Without NIST traceability you have no accuracy. You can can have repeatability, or reliability, but not accuracy. The "Tick" marks on a 14" Delta/Delta clone are a good starting point.
All springs have to conform to Hook's Law. Springs can be linear and non linear rate devices, depending on the coil configuration.
The OEM coil on the Jet is shorter than a Cobra Coil, so for equal cross sectional coils, the Cobra will have a larger range. The Cobra coil configuration is a "D" cross section, which is slightly different that the OEM spring. Bottom line is that my Jet can tension a 1/2" blade properly now, and be closer to the actual 1/2" indication. All it ever sees is 1/4" and smaller though. My Rikon is for resaw and it has a 1" 2/3 varipitch which it can tension properly.

I really don't pay attention to anything other than the finished cut. It's either good, or it's not, regardless of what any tension device indicates. I adjust the blade from the that point.
I don't use the flutter method or anything like that either. Mostly because I don't buy into it. Steel is steel, and within a very narrow band it's modulus will be the same. If the flutter method works for one blade, it should work for them all. I guess though that if a person uses it, and many do with great success, that your blade will not be over tensioned, and that's a good thing.

Derek
If you've got an MM16, get that machine in use Big Guy!. That's way too nice a machine to be left idle ( Better than any machine I own.:o )
Grab some scrap wood, a cheap vernier and and pencil and get comfortable with it. Don't get hung up on checking and making all kinds of adjustments right off the bat. Run the wood through it, and go from there. I'm willing to bet, that "box stock", and right off the truck, that bandsaw was pretty close to performing properly, with the exception of putting the correct blade on it. Too many folks get too hung up on checking and overhauling a brand new bandsaw before they've ever used it. The wood will tell you what adjustments need to be made.
Thanks...good advice here too. I just avoided curves and resawing for so long, but now it's time. I had a 14" Jet as well and used it only occasionally, but recently I downsized, so the Jet had to go. I'm glad I kept the MM16, as it is so much more capable, not that the Jet wasn't a good machine in it's own right.

[Mike Cutler]

Derek

One of the biggest errors I see people make, and I make it too, is that we are inconsistent with our feed rate though the bandsaw.
Find a comfortable position and feed the material through the blade at a consistent rate. Avoid stopping the material during the cut and look at not only the front of the blade, but through the blade to the back as well.
You'd be surprised at jut how closely your motor skill will track your eye. ;)

[John TenEyck]

When I was really interested in resolving some tracking and resawing problems with my 14" Delta I made my own tension gage using a vernier caliper and a couple of little C-clamps. Knowing the cross section of your blade and the Young's Modulus of steel (approx. 29 x 10^6 psi) you can easily calculate blade stress (tension) vs. strain as you tighten the spring. It wasn't very hard to do and I found that with a 1/2" blade you really can't comfortably put more than about 12,000 psi on it, and that's with an Iturra spring. Many blade manufacturers tell you to run their bands at 18,000 psi, or more, but you cannot do it on these small CI saws without risk of serious damage. In the end, there's really no reason to. I found that a sharp blade with equal tooth set on both sides was the key to straight cutting and effective resawing. Of course, you have to get the blade to track straight, but you don't need a lot of tension with a really sharp blade. I can easily cut 10" maple, etc. into veneer with my saw at 10 - 12,000 psi. I'll bet dull blades, or ones that aren't set equally, cause more problems than about any other issue with bandsaws.

Your MM 16 is capable of high blade tension, but how effectively it cuts will have little to do with that. As such, I wouldn't spend money on a tension gauge.

John

[Myk Rian]

The flutter method has worked for me with every band saw and blade I have ever used.

[Mike Cutler]

The flutter method has worked for me with every band saw and blade I have ever used.

Thank you for that piece of info. I always thought that it should, and was nothing exclusive to the Timberwolf's.
I took a lot of heat for this position once.

John TenEcyk

Believe it or not, your initial thread, on your homemade tension gauge, was the basis for my testing methodology. I took your method and went backward to a traceable calibration method. Nice work. A very simple method, which you already did the math, for everyone on to emulate.