Bandsaw blade tension.

[keith micinski]

Everyone is always saying you got really max that saw out to get the blade tension you need, or that saw really isn't big enough to tension that blade. So my question is, What are the ramifications of low tension? The first thing I assume would obviously be poor cut quality. My assumption would be that the lowest tension you could run on a blade and still maintain good cut quality would be the ideal tension to run. Less wear and tear on everything involved in the process. Is this accurate? I bought a used g0555 and put a 3/4 wood slicer on it after going throu all of the setup and redoing everything according to the manual. I have very little experience with a band saw so obviously I'm guessing at what is good tension by using the deflection method. The thing cut an 1/8th inch strip 6" tall perfect with zero issues. Does that mean I have the blade tension set right? If I made it tighter would I gain anything or if I made it looser would I lose anything. I see so many people always talking about tracking problems and setting blade drift when all I did was square the fence up put some random tension on the blade and make a perfect cut.

[Ben Rivel]

If it ain't broke, don't fix it.

[Dave Stuve]

I'm a novice with bandsaws, but found this Fine Woodworking video on changing blades useful. He claims only medium tension is needed, not really high tension, and uses the deflection method (1/4" deflection with one finger.)

https://www.youtube.com/watch?v=LE9IrZGs3SM

[Erik Loza]

My rule of thumb has always been to apply only as much tension as needed to get the cut I want. This will vary from blade to blace and brand to brand. That being said, most of the "performance issues" I read about on SMC with bandsaws are directly related to inadequate blade tension: Wandering cut or deflecting cut, etc. If you don't have any of these issues, then I wouldn't worry about it.

Erik

[John K Jordan]

...The thing cut an 1/8th inch strip 6" tall perfect with zero issues. Does that mean I have the blade tension set right?...

To me that means you have the tension, guides, drift adjustment, blade sharpness, feed speed, and probably wheel alignment right. For further assurance maybe try resawing wider hard wood, maybe up to the capacity of the machine.

For peace of mind, you might invest in a bandsaw tension gauge. That way you can measure the tension on the blade you have, check it against the specs, and use it to get consistent tension on future blades. I use a Starrett but they are all about the same (simple frame, spring, clamps, and dial indicator) and some are quite a bit cheaper. Itura Design sells (or used to sell) several models.

JKJ

[lowell holmes]

I use the flutter method. I back off the tension until the blade flutters and then tighten the tension until the flutter disappears. I add 1/4 turn and lock it down to start sawing.
Watch this video.

https://www.youtube.com/watch?v=chyo9chuwJs

https://www.youtube.com/watch?v=z8zZuDosSy0

[Van Huskey]

Blade tension is a loaded question on hobby forums, partially because 99% of the people that respond don't actually know what tension they are running on a given blade. Most have found a way to approximate the tension and use what works for them and most don't use nor are interested in buying s strain gauge. You also get bitter disputes regarding tension within the group of people who are recognized as experts with smaller saws ie Duginski and Iturra.

Talking about tension is like having a discussion with 100 car guys about tire pressure and only 3 of them have and use a tire pressure gauge, there is little objective you can take home.

As to your questions, blade manufacturers set optimum tension ranges for their various blades, they don;t pull these numbers out of the air. Most of us do not have saws that will cause any high tension issues with anything but the most narrow blades but high tension will wear a blade out quicker. Low tension will not produce a perfectly vertical cut, even at optimum tension the cut is never perfectly vertical but the barreling will be at a minimum. Low tension also increases blade wear.

Just like a car tire one can experiment and find a pressure that works well enough for them but I find it simpler to simply test the strain and set it correctly. Most of the standard setup methods leave tension well below manufacturers recommendations.

[Ben Rivel]

Well, if you really wanna get it right, pick up a Starrett 682EMZ (LINK (http://www.starrett.com/metrology/product-detail?k=682EMZ)) bandsaw blade tension gauge and use it to set the blade to the manufacturers suggested tension. My guess though is once you see the price of "getting it right" youll just keep going how you have been as it has been working well for you. :)

[lowell holmes]

It does not cost anything to try the flutter method. Try it, you might like it.

[Van Huskey]

It does not cost anything to try the flutter method. Try it, you might like it.


It doesn't cost anything to use a caliper (as most of us have them) and a tiny bit of math and in most cases will be far more accurate to set tension than the flutter method. The flutter method generally results in the lowest tension of all the seat of the pants methods. Again, if someone is happy then they are happy but I honestly don't get the reluctance to actually measure the strain.

As to the Starrett strain gauge I prefer the Lenox since the scale over the normal woodworking range is much larger and it is generally cheaper than the Starrett as well. Mathias at woodgears built a pretty nice approximation of a standard blade strain gauge and runs only the cost of a little labor and a dial indicator.

[John K Jordan]

As to the Starrett strain gauge I prefer the Lenox since the scale over the normal woodworking range is much larger and it is generally cheaper than the Starrett as well. Mathias at woodgears built a pretty nice approximation of a standard blade strain gauge and runs only the cost of a little labor and a dial indicator.

My bandsaws got more predictable and my cuts better when I started using the tension blade. I have no idea if the price of the Starrett has gone up a lot since I got mine or the link you gave is high - I think I paid at least $100 less. Might check around.

The first thing I found was there was no way to bring up the larger blades I was trying to use on a 14" delta to the mfgrs recommended tension. I since switched to a smaller blade (1/2" 3tpi Lennox) for all my thick green turning blank processing and most other bandsawing as well, even on the much stouter 18" bandsaw I use now.

I also use the tension gauge to check my Woodmizer sawmill, and two metal-cutting bandsaws, one big horizontal saw and one portaband.

The gauge takes away all the guesswork. If I get a poor cut, I can start looking for other reasons than tension.

JKJ

[keith micinski]

So if it's not going to be dead nuts on then it sounds like there is some merit in maybe having a little extra tension as opposed to a little less.

[John TenEyck]

As Van said, it's cheap and pretty easy to measure blade tension. Flutter, schmutter - measure the tension and then you'll know. All you need is a set of 6" vernier calipers and two little c-clamps. A calculator and a little math get you an answer in a few minutes. Once you measure blade tension you'll learn where to set the tension scale for any particular blade you use and the max. blade width your saw can run (and likely find it's not as wide as the manufacturer claimed).

In a related issue, if you are using a 14" cast iron Delta or clone, those saws cannot put much tension on any blade wider than about 1/4". They will still cut OK but not anywhere as good as a larger saw would with the same blade. For example, my 14" Delta can comfortably manage only about 12K psi on a 1/2" blade. It cuts OK as long as you keep the feed rate slow enough not to belly the blade. Take that same blade and put it on my larger saw that can easily put 25K psi on it and it will cut straighter, several times faster, and last a lot longer.


John

[Jamie Buxton]

As Van said, it's cheap and pretty easy to measure blade tension. Flutter, schmutter - measure the tension and then you'll know. All you need is a set of 6" vernier calipers and two little c-clamps. A calculator and a little math get you an answer in a few minutes...

Want to detail out the method and the math? Or provide a link?

[Mike Cutler]

Keith
If the saw is doing what you need it to do, I'd be inclined to leave it alone.
There is however much merit to knowing what the blade tension is when it is functioning properly, so that it can be repeated.
I tested 5 bandsaw tension gauges for Mark Duginske a few years back, and did a cross comparison between them, and the installed tension gauge on a 14" Delta style clone.
I had two Iturra's,a Lennox, a Starrett, and a Carter.
The Iturra's Lenox and Starretts all work on the same basic principle. The Cartet is an electronic strain gauge.
Every gauge was cal,d to NIST traceable equipment.
The four mechanical gauges were nice, but all of them are being used in the bottom percentile of range.
The Carter measures in lbs. wheel force.
Of the five the Carter was the most repeatable, and most " sailor proof". The Carter is also designed for your saw, and is always in place.
If a person were to want to use a tension gauge. I would recommend the Carter for a 14" saw. The others would be better suited to band mills and Marvel metal saws, where the tension in psi is higher into the range of the instruments.
I personally do not use an after market tension gauge. The installed gauges have worked well enough for me.

[Mike Cutler]

Want to detail out the method and the math? Or provide a link?

Jamie
The vernier method is measuring the "stretch" of a blade when tensioned.
The value read from the vernier is then put into a formula utilizing Young's modulus for steel.2.9 E07 psi.
John Steven s did a really nice post detail on it here on the forum about 10 years ago.
I'm on my iPhone right now in a horse barn, and am working from memory.
I'll try to find the thread when I get to my real computer. Bigger screen😉

[Jamie Buxton]

Several of you have referred to the manufacturer's suggested tension. I cannot find that on either Lenox or Laguna's web sites; they're the most popular carbide blades in small shops. Can any of you point to a spec?

[John TenEyck]

Want to detail out the method and the math? Or provide a link?


Sure. Here's the setup:

https://lh3.googleusercontent.com/v2-EVQWQvHw4Fql5cqWIus8j6P-8s4VRzInKhiUh9ZAv9QgY0Dh_j_8iW56PZK4AOmdyOFzjFuTV8 TNib3JVBBB_zc-cF2QsrN01HHBGzUOSSXR_8P77ZyKBrFiCk6vKJxmAUyDGw1346 sLfZt3H9TvhfgAg6AOo7bWJ529bxx8AQI7QmlmZslOlmku3sIT 86cOl2IQvj_rf7xH2vb0DIskzYNfqpm4dLH9-72qxQMT8I_2SQWZ8wSBW-L6Ex6sAQMZ49zlQs-h2CyNqWZWQ_iBwmJXpZgRF9VXIrHVOwsSRGHj8favJsukggZCm yXcXZGexl17TVTgHueJ00_PEu24SIw6t1UGXKMXl8YD0dTa1WU W_TmQoTWtSuDHP8lCIFUulE-5JPNmyChUAL853GPdiyUBLMobsjOJ678XEBJtzcHsvjMeNOffU 5byIyoZmONW6lKhcjYr5-dd8qxSljMbOw9sJPr9SPe-pZlH3YAyPVZkCga3NquqvHHJHVmWMNwyW24pPE8QDgJ3qecr8G CXWeAPwL1NTKpcp9Nh5BITdobuVFaGdDEmgVjyhpqgso_3hwrk Xxnpnl1Kx8RwxIPOmXk75r3-YnmYWUuePDqatHVcwGRZH=w471-h628-no

Note the blade guides are removed or at least backed away from the blade. Clamp the vernier with about a 5" gage length so that each jaw is on the flat of the blade, between two teeth. On really narrow blades it's best to face the vernier towards the back of the saw in order to avoid the teeth altogether.

The basic calculation is Young's Modulus = Stress/Strain, where:

1) The Young's Modulus of steel is about 30 x 10^6 psi.
2) Stress, the value you are after - the tension in the blade in psi.
3) Strain = Deflection / gage length. The vernier measures deflection, and the gage length is the starting distance between the jaws under zero load.

So, you rewrite the equation as Stress = Young's Modulus x Strain = 30 X 10^6 x deflection/gage length

The gage length I started with was 4.768", so when I measured a deflection of 0.003" that was equal to a blade tension of 30 X 10^ x 0.003/4.768 = 18,876 psi.

My little Delta was more than maxed out with the 1/2" blade I was using. The Iturra spring was nearly fully compressed, the frame was distorted by nearly 0.010" and that pulled the upper guide completely out of alignment. The data showed that I can't really run more than about 12K psi on a 1/2" blade. But with a 1/4" blade I can run at nearly 25K psi w/o over stressing the saw. The 1/2" blade will still cut OK at 12K psi, but I have to run more slowly than I would if I could apply higher tension to avoid blade deflection.

I hope that helps. And I hope it shows you can easily measure blade tension for essentially no cost. I think I paid a couple of dollars for those two little c-clamps.

John

[Van Huskey]

Several of you have referred to the manufacturer's suggested tension. I cannot find that on either Lenox or Laguna's web sites; they're the most popular carbide blades in small shops. Can any of you point to a spec?

I can recount the numbers but just get 'em on the phone, the Lenox guys are VERY helpful either on the phone or in person at a show. The Laguna guys are less helpful because you generally talk to salesmen and they are either less forthcoming or simply don't know the answer.

To those looking for the cheap but effective approach besides the older threads here there is a good "how to" on woodgears https://woodgears.ca/bandsaw/tension.html

[John TenEyck]

Several of you have referred to the manufacturer's suggested tension. I cannot find that on either Lenox or Laguna's web sites; they're the most popular carbide blades in small shops. Can any of you point to a spec?

From the Lennox website:

LENOX blades are designed to handle up to 30 000PSI. Please consult your machine manual for proper setting on your machine. Over-tensioning blades can cause premature machine failure.

Note they say over tensioning can cause premature MACHINE failure, not pre-mature blade failure. My measurements on my 14" Delta showed how easily that could happen if I insisted on trying to run high tension on a 1/2" blade.

John

[Van Huskey]

Keith
If the saw is doing what you need it to do, I'd be inclined to leave it alone.
There is however much merit to knowing what the blade tension is when it is functioning properly, so that it can be repeated.
I tested 5 bandsaw tension gauges for Mark Duginske a few years back, and did a cross comparison between them, and the installed tension gauge on a 14" Delta style clone.
I had two Iturra's,a Lennox, a Starrett, and a Carter.
The Iturra's Lenox and Starretts all work on the same basic principle. The Cartet is an electronic strain gauge.
Every gauge was cal,d to NIST traceable equipment.
The four mechanical gauges were nice, but all of them are being used in the bottom percentile of range.
The Carter measures in lbs. wheel force.
Of the five the Carter was the most repeatable, and most " sailor proof". The Carter is also designed for your saw, and is always in place.
If a person were to want to use a tension gauge. I would recommend the Carter for a 14" saw. The others would be better suited to band mills and Marvel metal saws, where the tension in psi is higher into the range of the instruments.
I personally do not use an after market tension gauge. The installed gauges have worked well enough for me.

You are the named but unindicted co-conspirator in the Duginski camp. I do not mean that in a pejorative manner BTW. I have always wanted to be in the same place as you because I would love to pick your brain beyond what you wrote here years ago and what Mark recounted, here, there and in his book. Beyond your overall thoughts and what exactly your role was I have always been curious what your reply/opinion of the Louis Ittura's response to Mark's conclusions are/were.

Alas the load cell based Carter is out of production, I have a couple of them I picked up for 75% off on clearance. I would love to build one for my saws since they work in real time and allow one to monitor and adjust tension on the fly to compensate for increases in length due to temperature. The Carter version with the automatic power switch to cut off the saw when tension was lost due to a broken blade was very cool.

[Jamie Buxton]

From the Lennox website:

LENOX blades are designed to handle up to 30 000PSI. Please consult your machine manual for proper setting on your machine. Over-tensioning blades can cause premature machine failure.

Note they say over tensioning can cause premature MACHINE failure, not pre-mature blade failure. My measurements on my 14" Delta showed how easily that could happen if I insisted on trying to run high tension on a 1/2" blade.

John

Yes, that's the only comment on tension I could find on the Lenox web site. Notice that it only provides a maximum psi. It does not provide an ideal psi. In fact, Lenox is passing the buck to the saw manufacturer.

[John K Jordan]

My little Delta was more than maxed out with the 1/2" blade I was using. The Iturra spring was nearly fully compressed, the frame was distorted by nearly 0.010" and that pulled the upper guide completely out of alignment....

I actually bent the tension support bracket on my 14" delta by trying to tension blades that were too big. A new bracket and spring from Iturra and I was in business again and a little bit wiser.

JKJ

[John TenEyck]

Van, if you are motivated to do that there are plenty of miniature load cells available that could be placed between the spring and frame of the saw to provide a real time readout of load. But unless you are running a production saw I don't see what real benefit it would have. The spring's job is to provide load to the band; over small changes in length its force is pretty constant, dependent upon the spring constant. It would take a lot of expansion of the band for the load to fall off appreciably. Remember, the frame will heat up during use, too, and that will add tension. It might be an interesting exercise to see how the load changes during use, but I doubt it would lead to any meaningful operational changes for the hobbiest user.

For example, I measured the spring constant of the Iturra spring to be about 435 lbs/inch. Assuming no expansion/contraction of the frame, a change in blade length of 0.010" would result in a change in spring force of only 2 lbs., and that changes the tension in the blade by only about 100 psi.

John

[Van Huskey]

It might be an interesting exercise to see how the load changes during use, but I doubt it would lead to any meaningful operational changes for the hobbiest user.


John

A load cell based tension meter is on my to-do list and I agree it is of little real use or value to a hobbyist woodworker but I am as much a bandsaw hobbyist as a woodworker so it is really more about increasing my understanding of band dynamics than producing any objective increase in the quality of my work. To paraphrase Jay Z, I got 99 projects and a cell ain't first. In fact I am half-heartedly looking for a complete early art deco Delta 14" saw since I kinda want one in my collection and it would allow me to use the Carter gauge I have to facilitate gathering data. The math indicates tension would mainly be impacted significantly on a high speed bandmills with very long bands but I am still interested in the real world usage on small saws.

[Mike Cutler]

You are the named but unindicted co-conspirator in the Duginski camp. I do not mean that in a pejorative manner BTW. I have always wanted to be in the same place as you because I would love to pick your brain beyond what you wrote here years ago and what Mark recounted, here, there and in his book. Beyond your overall thoughts and what exactly your role was I have always been curious what your reply/opinion of the Louis Ittura's response to Mark's conclusions are/were.

Van

You're catching me a little off guard here???
I do not know of the response by Louis Iturra that you refer too???? I don't believe I've ever talked too, or met him. If you have a link, that would be great.
My role was to simply test the after market band saw tension gauges I was supplied, and correlate a comparison to the installed OEM bandsaw tension gauge on the back of the Delta 14" bandsaws and clones.
Marks position was that people were applying too much tension to the band saw blades using after market tension gauges, resulting in broken upper wheel yokes, by trying to achieve the "15,000" psi ideal value, and that the OEM tension indicator was sufficient. At least as far as the 14" Delta style clones are concerned.
Of the 4 mechanical gauges I tested one was broken and I had to repair it prior to testing. This gauge had been in use, as is, by a forum member here.
The Lennox I received was poorly machined and had some serious "stiction" issues that manifested themselves as hysteresis . Once I polished the poorly machined surfaces of the Lennox it worked fine.
The Starrett was the only after market gauge supplied that I did not have to repair prior to use. The two from Iterra had a wear dimple on the force arm created by the steel ball bearing it exerted force on. The curved surface of the bearing had, in fact, become the math of the tension indicator. Whether or not this is how they are made, or whether they were misused,I have no idea.
Each dial indicator was calibrated against known traceable standards, and then reset into the respective gauge. The tension gauges were then affixed to a length of 1/2" band saw blade and place in a test fixture I made. The actual force applied was measured by a traceable strain gauge, and the gauges tested in the increase and decrease force direction to quantify actual calibrated indicator readings and mechanical hysteresis.
Once this was completed. I then performed a cross cal check against the installed OEM Gauge stamped on the tension block on the back of my Jet 14" bandsaw with 6" riser. I tested blades from 1/4"-3/4", and then ran through the cal's again. Believe it or not, the OEM tension indicator is pretty darn close.
I did find that all of the mechanical gauges benefitted from being pre-loaded to ensure they weren't on the stops of the internal dial indicator mechanism when in use.
At the end of it all I found that the actual component that was probably having the most dramatic effect on over tensioning, was the OEM spring. I tested the spring in my bandsaw and found that it was only capable of maintaining it's properties to about 8600psi. I added a carter Cobra Coil and the value went to about 13,600psi.
The point being that in order to achieve the "15,000psi ideal value on my 14" Jet would mean that the spring was completely compressed and the entire tension system was now "solid. All of the force beyond what the spring was capable of maintaining was being transferred to the Yoke assembly, resulting in broken yokes. It would be very easy to lose sight of the spring/yoke, when focusing on the tension gauge. and not realize that everything had gone solid.
From my testing I determined that my Jet 14" bandsaw could only tension up to a 1/2" blade. A 3/4" blade, on my Jet, cannot be tensioned without completely compressing the spring, and transferring the additional forces to the upper yoke assembly.
I also have an 18" Rikon and used it as a test platform also. The results were similar enough.


I think the band saw has always been my favorite wood working machine simply because of the versatility it brings to the table. I'd give up my table saws before I'd give up my band saws.
Out of the box, the band saws I've been exposed to have pretty "rough". But some time spent going through them is well invested. Both of mine were pretty much ripped down to the bearings within days of buying them.

[Lee Schierer]

So, what tension range are we looking for for each blade size? I don't recall my blades coming with any specific numbers for tension.

[Mike Cutler]

So, what tension range are we looking for for each blade size? I don't recall my blades coming with any specific numbers for tension.

Lee
At the time I did all this, the "magic number" being bandied about was 15,000 psi. The wider the blade, the more force required to achieve this value. As blade cross section increases, so too would the force required.
Personally, I've never been a big believer in the 15,000 psi number. I don't use it, or tension gauges.

[Bill Adamsen]

John ... this was so incredibly helpful. Thank you!

[lowell holmes]

If you want to play with gadgets, by all means measure the tension. If you want to cut wood, the the flutter method. I've used the flutter method for 15 years.

I've never hand a blade break or fly off the wheel.

Try it, you might like it.

[mreza Salav]

Here is a simple jig I made to measure tension on my bandsaw blade, it works quite well. Now I know the number on my bandsaw gauge that I should use to get the proper tension on this blade.

350605

[John TenEyck]

So, what tension range are we looking for for each blade size? I don't recall my blades coming with any specific numbers for tension.

Lee, tension is independent of blade size. You would shoot to run all blades in the same range. Most blade manufacturers recommend at least 25K psi for optimum performance. My Grizzly 0636X can easily do that on a 1" blade. My 14" Delta can't manage it on anything larger than 1/4". That's why I recommended measuring tension on your machine, at least on the largest blade you would like to use. Then you'll know what tension your BS can apply. If it can handle 25K psi, great; if it can't, you can decide if what it can apply is OK for your needs or if you would be better off using a narrower and/or thinner blade.

Real data leads to informed decisions.

John

[Van Huskey]

General rule (which is consistent with most manufacturers suggestions) 15K psi for carbon, spring steel and "Swedish" steel blades. 30K psi for bi-metal and carbide blades.

If anyone actually wants a Lenox gauge Zoro has them normally for $270, good not great price. For two days 1/4-1/5 they have 20% off $250 and 25% odd $300 so if you add 30 bucks of stuff they normally have at a good price anyway (Wera screwdrivers for example) you can get the Lenox gauge for $202 and that is with free shipping, code is NEWGEAR

[Van Huskey]

Van

You're catching me a little off guard here???


Sorry, I assumed you had read the Iturra response to Mark's original article. The response is printed in his catalog and I will try to find a link and PM you, that will be in the next couple of days.

BTW thanks for taking the time to outline your process! One question I have which Louis (Iturra) also had is how did you recreate the same tension each time for the varying gauges? I have always assumed you used your traceable gauge in tandem with the gauge you were testing which SEEMS to be the case reading the above, Louis had a different idea which I would not think you would use.

In any event if you don't get the link in a couple of days, yell at me via PM.

The BS is my favorite woodworking machine partly because of the versatility but also in large part to the fact it requires a little art or voodoo to get it running at an optimum level.

[Jamie Buxton]

General rule (which is consistent with most manufacturers suggestions) 15K psi for carbon, spring steel and "Swedish" steel blades. 30K psi for bi-metal and carbide blades. ...

Why would a carbide-tipped blade want a different tension from a non-carbide blade? The carbide is a teensy addition to a mostly-steel blade.