Iturra's tension gauge.

[JC Bagley]

Over the holidays, I bought my first bandsaw (Grizzly 17" G0513X). :D I'm (still) having some trouble figuring out proper tension. The Grizzly built-in gauge doesn't have a reference that correlates to blade width. Instead, it's just indexed starting at 1 (1, 2, 3, 4, 5, 6, ...). So, last week I ordered Iturra's tension gauge, which came in this week. I've done two tension tests using a 1/4" carbon steel Grizzly blade and the 1/2" stock blade.

First, I used the flutter test (as described in the manual) to set the 1/4" blade to proper tension (I think). I put the Iturra tension gauge on and took a reading and it read 46,500 psi!!! :eek: I redo the flutter test and get about the same reading. This is about a 2.5 on the built-in scale. If I use the blade gauge to set the tension to 15,000 the blade feels very loose, very little tension. If I set the tension to 30,000 then the built-in scale barely reads 1. :confused:

Ok, so I try the 1/2" blade next. Flutter test puts me at 4.5 on the built-in scale, which reads 35,000 psi on the Iturra.

I expected both of these blades to "properly tension" somewhere around 15,000 psi. I'm not sure what to believe - flutter test or Iturra. If I'm going to use the flutter test as the definitive gauge, then I'll return the Iturra and get my money back.

There seems to be a lot of Iturra users here, so I thought I'd post and get some of your advice.

Thanks,
J. C.

[Pete Brown]

When you use the iturra, do you de-tension the blade, attach the iturra and then zero it out?

I have the same gauge, and I tension my lenox 1" carbide blade around 35000 PSI and it reads correctly (although a recent magazine article disagrees with that).

Pete

[Mike Weaver]

I haven't bought a gauge to use on my MM16 yet, but either an Iturra or Lenox will be my choice.

Just a question - what thickness blade are you using, and does that match the thickness for which the Iturra is calibrated?

Thanks, and definitely let us know how this turns out!
-Mike

[Pete Bradley]

The flutter method should get you there. Was it working once you'd set it with this method?

Most likely as you gain experience you'll find that you rarely look at the gauge.

I too suspect some sort of issue with how the gauge is being used to get a reading that high.

Pete

[Jim Becker]

I own the Iturra and found it very useful to learn where the tension needs to be for different blades on my MM16. Like every other bandsaw on the planet, the "on-board" gage is not even close. I'm not sure why you are getting a reading of 35K PSI...doesn't sound correct.

[JC Bagley]

Thanks for the replies so far.

I have checked the tension two ways. One way was to tension the blade (using flutter test while running), turn off the saw and attach the Iturra, zero out the Iturra, detension the blade and take a reading. The other way is to detension the blade first (using the quick-release lever), then attach the Iturra, zero it out, and tension the blade again. Both ways give the same reading. The band saw has a quick release lever so it's easy to take the readings with and without tension.

Each time I wanted to get a tension reading, I would take three or four readings just to reduce the likelyhood of error and to make sure the gauge would return to zero each time I threw the quick release tension lever.

The gauge is pretty easy to use, so I'm confident that I'm using it correctly. However, the flutter test is another matter. Maybe I'm doing that wrong.

My flutter test:
- Back off all upper and lower guide bearings (sides and back).
- Raise the blade guard all the way.
- Start the saw.
- Reduce tension until the blade turns into a blur (my definition of flutter).
- Slowly add tension 1/8 turn of the tension wheel at a time.
- Keep adding tension until the blade stops vibrating/blurring and turns into a straight line.
- Add a little more tension for good measure (1/8 turn of the wheel).

Normally I think of flutter as a sound, but, for band saws, I define it as a visual description of blade vibration.

Am I doing that correctly???

[Jim Dailey]

I have the Iturra tension gauge that I use on my MM20 & Delta 14" saws and I have been happy with the gauge.

However I was surprised at the findings in an article writen by Mark Duginske & Aaron Gesicki in this months Woodworkers journal tittled "Blade Tension". The findings of the article; tension gauges on saws are "quite accurate", original equipment springs provide "more than enough tension", and two of the three tested mechanical gauges tested (Iturra, Carter & Starrett) aren't "accurate enough to provide useable information". They wouldn't say which one was accurate......... They only recommended the Carter digital gauge.

Needless to say I was surprised!!!

jim

[Mike Cutler]

JC.

Try the dial indicator method in the following link.

http://www.sawmillcreek.org/showthread.php?t=22144

[Pete Brown]

Yeah, that's the article I was thinking of. The generalizations in that article were a bit sweeping for me. Also note that carbide didn't come into the picture, same with wider blades. Perhaps it was accurate for 3/8" blades on 14" saws. I don't know; I don't own one.

[Pete Bradley]

I'm still wondering -- how is the machine working in use? Tensioning this saw isn't rocket science. Assuming it runs fine with the flutter method, you're good to go. If it flutters in tall cuts, crank it up a hair. Developing experience with the saw will be far more valuable than experimenting with the tension gauge.

[edit] The following paragraph is incorrect. Band CS area would be critical to calculating force, not tensile stress. More coffee woulda helped. -Pete
Not sure how the Iturra gauge adjusts for band thickness, but thickness is critical to this measurement method. If you're running a thin band such as the ones from Suffolk, perhaps the high measurement is due to the gauge being set for a thicker band.

Pete

[Harold Beck]

The blade thickness doesn't come into the picture. Stress is force divided by area. Deflection is directly proportional to stress. If I remember correctly, and I don't have my reference books in front of me to look up the modulus of elasticity, steel stretches 0.001" for approximately 1000 psi of stress. The Iturra gauge is directly attached to the blade and senses the amount the blade stretches under the load. The gauge does assume that you are using a steel alloy blade for the correlation of stretch to stress.

Again if I remember correctly without reference books in front of me, the modulus of elasticity of steel varys less than 5% across most of the various carbon steel alloys.

HB

[Roy Wall]

The blade thickness doesn't come into the picture. Stress is force divided by area. Deflection is directly proportional to stress. If I remember correctly, and I don't have my reference books in front of me to look up the modulus of elasticity, steel stretches 0.001" for approximately 1000 psi of stress. The Iturra gauge is directly attached to the blade and senses the amount the blade stretches under the load. The gauge does assume that you are using a steel alloy blade for the correlation of stretch to stress.

Again if I remember correctly without reference books in front of me, the modulus of elasticity of steel varys less than 5% across most of the various carbon steel alloys.

HB

Harold,

Good points...

I do believe, however, the steel stretches 0.001" for every 5-6000 psi of tension. I.E. .005 = 25-28,000

[Dan Stuewe]

At risk of putting my foot in my mouth and showing how much I've forgotten since college...

E = stress / strain

strain = total elongation / total length

Therefore stress = E * total length/total elongation

E is pretty constant for steel of 30 Mpsi (30,000,000 psi)

We don't want to look at the entire length of a bandsaw blade (in fact it would be very difficult to define the length since both "ends" are wrapped around 1/4 of a wheel). So we'll use our gauge to measure the stretch over a portion of the blade (in fact the important portion of the blade, the portion that will be used to do what we want, cut wood). So, the gauge is attached to the blade and tension is applied. The gauge measures how much the blade between the two attach points stretches. So, we know E, distance between the two attach points at rest and the amount that section has stretched.

Assume the distance between the two attach points is 4”…

Stretch Stress
0.0001” 750 psi
0.0002” 1500 psi
0.0010” 7500 psi
0.0040” 30000 psi

For these tension gauges the markings on the dial must be adjusted for the distance between the two attach points. (If the attach points are actually 4.1” apart the actual stress would be approx 2.5% lower.) Now, if you want to know the force required to achieve that stress, then you’ll need to know the size of the blade. Hint, the force is much larger for blades with larger cross-sectional areas. (F = A*stress) don’t forget to double that since we only looked at one side of the blade.

What does this all mean?

Don’t ask me, I don’t own a bandsaw…yet. I think the best solution is the one that gives the best results, cuts in wood that require the least amount of time as possible with sandpaper.

[Pete Bradley]

The blade thickness doesn't come into the picture. Stress is force divided by area.
HB
You're right. Somehow I was thinking force rather than PSI. I edited my post to note the error.

Pete

[Wilbur Pan]

However I was surprised at the findings in an article writen by Mark Duginske & Aaron Gesicki in this months Woodworkers journal tittled "Blade Tension". The findings of the article; tension gauges on saws are "quite accurate", original equipment springs provide "more than enough tension", and two of the three tested mechanical gauges tested (Iturra, Carter & Starrett) aren't "accurate enough to provide useable information". They wouldn't say which one was accurate......... They only recommended the Carter digital gauge.
I just read that article. I was more excited about reading the article before I read it than afterwards. Basically, the conclusion is that bandsaws out of the box have sufficiently sturdy construction to apply 15,000 PSI of tension, and that the on-saw guides are accurate enough to get you to that point.

What the article doesn't address is whether 15,000 PSI is optimal for sawing purposes, or whether going to higher tensions will improve saw performance. The 15,000 PSI mark was chosen because of information provided by blade and bandsaw manufacturers. These are the same people that tell us that the motor really puts out 1.5 HP, honest.

[Ken Garlock]

That article in Woodworker Journal was a JOKE.:eek: A brass plated JOKE.

The fact that they would not list the results for the various gauges tells me that the entire article was a white wash with only the Carter product not hitting the bucket. If they would have read the directions on the Ittura gauge, they would have found that is is necessary to put a little initial tension on the gauge as indicated by the dial indicator. Then set the gauge to zero. This action will take the slack out of the linkage between the blade clamp and the dial indicator. Now you have a starting point at which to measure the tension. The discussion of setup of the gauges was minimal at best. The article did not explain how each gauge was attached to the blade and set to zero.

I was greatly surprised that the authors would have the guts to publish such garbage.

I find it difficult to believe that the Starrett gauge did not perform correctly. Starrett made its name on precision instruments and does not sell junk.

[Pete Brown]

The problem is, once something is in print, people point to it as authoratative.

I run into that in my industry all the time. I know many of the authors and know better than to take what they write as gospel :)

[Mark Duginske]

That article in the Feb. 2007 Woodworker’s Journal is based on a number of tests that I did for my new book THE NEW COMPLETE GUIDE TO BAND SAW, which is designed to update the BAND SAW HANDBOOK, published in 1989. No field of woodworking has more wrong information that the topic of blade tension. I acquired all of aftermarket tension gauges and tested them. The results were all over the board and to help me sore it out I hired Aaron Gesicki who has and under grade and Masters degree in metallurgical engineer with 30 years of experience with GM and Cat making engine parts. Along with research by an electrical engineer we will be presenting
a Scientific Paper and demonstration at a seminar this summer covering the relationship between blade tension, sharpeness and wheel alignment.

Here are some points.

1. This whole tension thing started with Jim Cummin's article in FWW which said that the spring weakened, the gauge was erroneous and Lennox gauge was correct. HE WAS WRONG ON ALL ACCOUNTS, and knowledgeable practitioners disregarded the article. Cummins assumed that the Lenox gauge was accurate not realizing the gauge was reading 15,000 psi in the 8,000 to 9,000 range. Which means that if you use that gauge you are overtensioning the saw by 50 percent.

2. However, author’s and merchants have continued to pass on the false information without doing any research or testing. This wrong information (that the gauge on the saw is erroneous) is now accepted as fact and this poor quality information keeps getting quoted over and over.

3.The Carter gauge is the most accurate for this application (a tired woodcutting band saw). The spring gauge in the saw is adequate and more accurate than the mechanical gauges. Of the mechanical gauges the Starrett was the most accurate in terms of psi reading. The Lennox was most precise (repeatable). The worst is Itura which has a calibration problem and often does not return to zero. With the faulty Itura gauge we got 15,000 psi readings as low as 8,000. Which means that if you use the Itura gauge you could be almost doubling the tension on your saw. No wonder parts are bending or being broken.

4.15,000 psi is the appropriate tension for wood.

Tension is only one of many ingredients in good band saw performance. Don’t make a religion out of it. To quote my friend
Toshio Odate, “Americans love numbers, they don’t know what they
mean but they love numbers” Acceptable tension is how much you need to keep the blade straight in the cut, period. Before you buy a solution try common sense. Use the saw gauge (which you can trust) as a base and experiment from there.

To respond to Ken Garlock- The Starrett gauge was the most accurate of the mechanical gauges and it is a fairly good solution for heavy duty tireless metal cutting saws without a gauge for which it was designed. One problem with using the mechanical gauges on tired (woodcutting) band saws is that the mechanical gauges are designed for untired metal cutting saws. The tires and the top wheel hinge on wood saw flex enough to effect the accuracy of the mechanical gauges for that particular application. The electronic gauge measures wheel load rather than blade load which is more appropriate for a woodcutting band saw.

If you ever wrote an article you would realize that there are space limitations so not every aspect can be discussed in detail.
Considering the fact that Aaron has designed and built a $200,000,000 foundry from scratch I think he knows how to use a tension gauge. Your comments show that you know a lot less than you think.

[Pete Brown]

Mark, did you talk to any of the blade manufacturers, like Lenox? I always understood that their carbide blades need to be up around 30-35k PSI.

When you tested the tension guages on the 14" bandsaws, did you find that they were accurate for all blade thicknesses, or just the one? That wasn't clear from that article.

Don't take offense to the posts here. Your article was very short for the topic, and made some very sweeping generalizations without much info to back it up. When you want to turn the world on its ear, you need to have a bit more info to back it up (which I assume you'll have in your book) :-)

One more question: how did you decide that the PSI was correct or incorrect on the indicators? What was your control? I can understand issues with repeatability, but not with figuring out the actual PSI.

In addition, I'm surprised the starrett and iturra differed much at all, I believe the design is basically the same, and even my cheapest dial indicators have decent repeatability. Did you contact either manufacturer?

Finally, how does this apply to larger saws and wider blades? Lots of folks here are running 16", 18", 20", 24" and larger saws which are designed to provide significantly more than 15K PSI tension.

Pete

[Wilbur Pan]

4.15,000 psi is the appropriate tension for wood.

I'd like to ask again, how is this number derived? I know you've stated that 15,000 PSI is what the manufacturers recommend. But is there other empirical data to back this up? For example, can you show that tensioning a blade to, say, 18,000 PSI does not impact the smoothness or straightness of the cut?

I do agree with all of the data you and Aaron Gesicki put forth in your article. For what it's worth, I also bought "The Band Saw Handbook", and have found that book to be one of the most useful woodworking books I have. My only issue with your article in Woodworker's Journal is your conclusion: "We've found no good technical reasons for overtensioning." The only conclusion I can draw from your data is that the tensioning mechanism and gauges that come with a bandsaw are accurate enough to tension it to 15,000 PSI -- not that 15,000 PSI is the optimal tension for bandsawing operations.

[Mac Cambra]

Mark,

How was the "real" measurement that was being used as the standard derived? Obviously there was a "right" answer that each of the gauges were being compared to.

I own the Itturra, I find it correlates well with the built in gauge on my MM16 (scale based on blade width) when I would tension non-carbide blade to 15k psi.

I am really hoping that I didn't throw $160 away for nothing......

Did you have more than one of each of the gauges, seems like if your article was based only on a single unit from each manufacturer you could only comment on that specific gauge not the design as a whole.

Thanks,

Mac

[JC Bagley]

Use the saw gauge (which you can trust) as a base and experiment from there.

The point of my original post is that the Grizzly built-in gauge has an integer index, not saw blade width. Once I know what the proper tension is, then I will be able to use the gauge to get back to that tension. The problem is that I don't know what proper tension is.


Isn't there a saying, "You have to have money to make money." It seems that the same thing is true with band saw tension. You have to know what proper tension is in order to set proper tension.

J. C.

[Pete Bradley]

Tension is only one of many ingredients in good band saw performance. Don’t make a religion out of it.

Mark,

Great to have you check in. Your book is a great resource and I'm looking forward to the update.

Along the lines of your comment above, I'd like to suggest that the Turley section on "beam strength" be put in the same perspective. One would have thought that the limitations of applying static beam theory to a band saw blade were obvious, but this section is frequently misunderstood to mean that loading up the biggest band the saw will take is a mandatory step to optimal resaw performance. I've seen beginners get numerous posts of "internet wisdom" along these lines; advice that will lead to sub-optimal performance in many cases since factors like dynamic effects, horsepower, and the tensioning ability of the machine may be equally critical.

Pete

[Pete Bradley]

The problem is that I don't know what proper tension is.
J. C.
JC,

Mark's post put it best: "Acceptable tension is how much you need to keep the blade straight in the cut, period." Using a band saw is nowhere near as complex as the internet might make it seem. I've never owned a tension gauge, a European band saw or a $200 band, yet I can resaw everything from logs to veneers. Duginske's book is a great resource, and a few weeks of experience with your new machine will give you far more knowledge and perspective than reading our posts. ;)

Pete

[Noah Levy]

Mark,

As an engineer myself, I just wanted to say that your books are definitely some of the best and most informative available, and I look forward to reading just about anything you write. It was obvious in the WWJ article that space was limited and you therefore weren’t able to present the data. Anyway, I just wanted to share my thoughts.

BTW, love the quote by Toshio Odate, “Americans love numbers, they don’t know what they mean but they love numbers”.

[Ken Garlock]

It would appear that testing protocol has changed considerably since I took the 'strength of materials' and 'mechanics of materials' courses some 40 years ago.

When I see a test of a product I like to see detail that exceeds the level presented in the article.

Validating the Carter gauge involved an "axillary metering gauge fixture;" can we conclude that it was a test fixture included with the gauge? If not, what was the instrument and is its calibration traceable back to NIST?

Were the gauges installed on the saw blade using the manufacturer's instructions? I will assume they were, as that would be a gross over site that I don't think your would make.

I accept the fact that your article represents your test, but it is missing critical detail. For example, had you used an electronic strain gauge attached to the blade to measure deformation and that gauge had been calibrated by xyz lab, then you would have firm reference from which to make evaluations. A set if stress-strain curves representing each gauge's value at selected stresses would be quite revealing. By using one test sample to measure other test samples only gives a comparison among the samples, and says nothing about actual values. In my opinion, your article, with the information given, doesn't settle anything, it just introduces another opinion.

As I was about to end this posting, I went back and reread your comments above. When I got to the following, I had to get up and take a walk.

"To respond to Ken Garlock- The Starrett gauge was the most accurate of the mechanical gauges and it is a fairly good solution for heavy duty tireless metal cutting saws without a gauge for which it was designed. One problem with using the mechanical gauges on tired (woodcutting) band saws is that the mechanical gauges are designed for untired metal cutting saws. The tires and the top wheel hinge on wood saw flex enough to effect the accuracy of the mechanical gauges for that particular application. The electronic gauge measures wheel load rather than blade load which is more appropriate for a woodcutting band saw."

Your comment about gauges and tires amazes me. If you have been able to find a method of violating simple physics, you better get to the patent office on Monday morning.

Let us think about this:
1. gauge is attached to a metal band.
2. metal band is supported by a wheel
3. wheel is supported by a spring and axel to the frame.

No where did I mention that composition of the wheel. The wheel could be made of plastic, ceramic, or goose down. All materials used in the wheel MUST, by laws of physics, transfer its forces to the next item in the chain of force transfer. The fact that there is a plastic tire on the wheel does not change that fact that the forces introduced by moving the wheel hub(applying tension) MUST be transfered to the blade. The tire may compress to some degree, but it is still transferring the force through its structure to the blade. The tire does not bleed off force to some undetermined force sink. The fact is that the gauge is measuring the deformation of the metal blade, the way that deformation is applied is irrelevant. It would be my guess that the tires for wood bandsaws are there to reduce noise.



Finally, my congratulations to Mr. Gesicki on his engineering accomplishments.

[Pete Bradley]

One problem with using the mechanical gauges on tired (woodcutting) band saws is that the mechanical gauges are designed for untired metal cutting saws. The tires and the top wheel hinge on wood saw flex enough to effect the accuracy of the mechanical gauges for that particular application.

I wondered about this also. The band just sees a stress exerted by the wheel, and the gauge measures the band strain to get stress. Assuming the gauge is used correctly, how would the tire make a difference?

Pete

[Pete Brown]

I wondered about this also. The band just sees a stress exerted by the wheel, and the gauge measures the band strain to get stress. Assuming the gauge is used correctly, how would the tire make a difference?

If Mark is talking about overtensioning on a 14" saw, I can see his point and how it would overstress the frame. Otherwise, not really.

Pete

[Mark Duginske]

I talked to Aaron and he straighten me out. I tried to call him and didn't get him. I should have talked to Aaron before I sent the note.

I am not an engineer so I'm not into "engineer talk". However, I know when a band saw is working. I also know that I didn't have to waste money on a gauge to get it to work.

Aaron and I and an electrical engineer are going to be doing more testing of the various factors that affect band saw performance. I won't make off the cuff comment until I talk to those guys.

Now I remember why I don't spend much time with chat groups.

[Pete Bradley]

Now I remember why I don't spend much time with chat groups.
I dunno. If someone caught an error or need for clarification before your book went to print, it's likely worth it.

Pete

[Jim Dailey]

Hi Mark,

I for one am very happy that you "did take the time" to respond to posts on SMC

As I said in my original post I was "surprised" at your findings. But I have an open mind & am willing to learn. Having both a Delta 14" & a MM20 I have a chunk of $$$ in band saws. To get the "most" out of these is why I bought your book, even though I had own bandsaws for years before buying it. That is also why I purchased Luis Iturra's gauge to get the most out of the saw. Or another way to say this is that thru these and other resources to make sure that the saws are properly setup wether it's a 1/4" blade on the Delta or a 1" Lennox carbide Trimaster on the MM20.

I for one will be looking for any additional information regarding proper setup of my saws.

jim

[Mark Duginske]

Thanks Ken G.- Aaron Gesicki already straintened me out. I tried to call him before I sent the note but didn't get him. I should have talked to him before I sent the note.

I'm not an engineer so I am not into "engineer talk". However If you watch my Taunton Video MASTERING YOUR BANDSAW you will see that I know how to get a band saw to work. I also didn't have to waste money on a gauge.

ARE you spelling my name incorrectly on purpose?

Now I remember why I don't spend much time with chat groups.

[Ken Garlock]

Your name was misspelled because I didn't copy it correctly from a previous post. I may be guilty of a lot of things such as spelling errs, but making a joke of someone's name is not one. I have had my turn at being called warlock, and other letter substitutions in both the G and L positions.

Anyway, I think it is about time to end this dialog and move on.

I sincerely wish you good luck with your new book.

[Mark Duginske]

This is an response to the post by Jim Dailey of 1-28-07

Jim

If you can use the gauge and get good results: fine. REMEMBER THAT THERE IS A VERY WIDE RANGE OF USABLE TENSION SETTINGS. USEABLE TENSION IS NOT THE DISTANCE BETWEEN
THE TWO 49 YARD LINES IT IS THE WHOLE MIDDLE OF THE FOOT BALL BAND FIELD. I have a 14" Delta and a 20" Italian saw and I use the tension gauge on both at the standard settings. I know that this goes agains everything written by Ittura, Bird and White. However, I did two Taunton videos, the Minmax video, the original English version Laguna and Aggazani manuals and have use probably used 100 different saws for demonstrations and seminars. I do a seminar where I change and track and tension 4 different blade in an hour. I always use the standard guage have have to "fine tune" it about 5 percent of the time.

I'm a fourth generation woodworker. Both my father and grandfather had sideline businesses making patterns. I grew up in a shop with 3 different 14" Deltas and much bigger saws, all set at the gauge mark. That 14" Delta saw has been the standard of the industry for 75 year (often working 24 hours a day during WW2 in pattern shops).

It astounds me that anyone who has used that 14" Delta saw a lot could believe Jim Cummins article about 20 years ago in Fine Woodworking that said the gauge is off, the spring is week and doesn't provide enough blade tension. That article is the seed for the mistrust of tension gauges. The gauge that Cummins used was the Lenox. When Aaron tested that gauges it registered 10,000 psi while Carter electronic ( which is modern technology) measured the equivalent of 15,000 psi (292 pound of wheel load).

I got another Lenox gauge and it tested the same. Cummins, when writing the article, assume the Lenox gauge was right and the Delta was wrong. However it is just the opposite. As for mechanical gauges. there is a very wide range of “functional tension” so even if actual gauge reading is off you can still have adequate tension. The Starrett testing in the 13,000 range and the Iturra was all over the board from 8,000 to 12,000 psi.

What surprised me was the differncees between the three different
mechanical gauge. I don’t think the mechanical gauges are
applicable to woodworking. Would you pay $200 for a new gas gauge in your car?

[Jim Dailey]

Mark,

"Thank You" again for taking the time to post & share you insights.

I will be looking forward to reading you new book. Any more surprises... No don't tell me... I hate when the spoil the ending. ;)

jim

[lou sansone]

hi ken and others



"No where did I mention that composition of the wheel. The wheel could be made of plastic, ceramic, or goose down. All materials used in the wheel MUST, by laws of physics, transfer its forces to the next item in the chain of force transfer. The fact that there is a plastic tire on the wheel does not change that fact that the forces introduced by moving the wheel hub(applying tension) MUST be transfered to the blade. The tire may compress to some degree, but it is still transferring the force through its structure to the blade. The tire does not bleed off force to some undetermined force sink. The fact is that the gauge is measuring the deformation of the metal blade, the way that deformation is applied is irrelevant. It would be my guess that the tires for wood bandsaws are there to reduce noise."

ken I believe that in a perfect world you would be correct, but one of the problems with this linkage is the very real fact that the wheels and tires are not perfectly concentric. This "eccentricity" of the band saw tires might cause the blade tension to vary slightly( think about if for a moment - the tension in the blade is a function of the overall path that the blade is traversing, if the wheel is eccentric, then the path length will change and hence the tension as well), even with the fact that there is a spring backing up the upper wheel travel. With larger band saws there is a fair amount of mass to have to rapidly move and I think we would have to do some pretty detailed vibration analysis to ensure that the spring was able to remove even the highest frequency eccentricity components ( one of the F=MA things )

In the past I have also posted about band saw tension, and here are some of those thoughts


http://www.sawmillcreek.org/showthread.php?t=29085&highlight=band+blade+tension


Lou

[Mark Duginske]

When I looked at this tread this morning there was a post by Lou
Sansone refering to a previous post.

I've only been on SMC for a week or so but I read the previous post and it is one of the best things have I read here.

As regard's to Ken Garlock comments in that material about the Iturra catoalog I think the ration should be reversed. I think that it is 20% education and 80% sales.

lou, keep writing, from what I see you and Mark Singer make the most sense.

Lou's comment, "I have yet to have anyone who believes in tension gauges
give me a good engineer reason for using them." is to the point. Considering the descrepency between the results of the mechanical gauges
that comment is especially true.

Mark Duginske

[lou sansone]

Hi guys

for those who did not look all the way through the link to the previous post, I have posted the "end of the story "


"ok guys I finally figured it out on this band saw tension thing..

it turns out that many steels tend to yield at about 1/3 of 1% strain. so it looks like band saw blade mfgs simply play it real safe with the blade tension in the 15kpsi to 30kpsi range ( 1/20 to 1/10 of 1% strain ). this gives the blade a decent amount of tension, but pretty far away from actually yielding the steel for plastic deformation.

So there is actually a real engineering reason for the recommendation, but I believe that the recommnedation is "caveman like" because it still does not remove the very real possibility that the blade will be accidentally tensioned at the fundamental resonance of the blade. This would cause the worse possible cut.

Lou

"

lou

[Mike Cutler]

Interesting topic of conversation. For the sake of argument/clarification I feel compelled to respond.

Accuracy.- The accuracy of any device is established against a known standard. In Ken Garlock's post he made reference to NIST standards. NIST is the National Institute of Standards and Technology. NIST is the origin of all calibrated standards and instruments. If your device, in this case a bandsaw tension gauge, cannot be traced back to known standard that is traceable to NIST . That instrument has no quality attributes. In other words, to assign an accuracy spec to it would be erroneous.

In Mark's post, and I am not singling Mark out here, reference was made of correlating accuracy to repeatability. If I have an instrument that gives me the same indication/response in the exact same configuration and use. That is a function of the instruments repeatability, not accuracy. UNLESS the instrument has been certified to NIST standards.
The instrument that Mark obtained the most repetetive results from tells me, that instrument has the least amount of Mechanical Hysterisis, in otherwords the mechanical properties of the instrument do no deviate or change with use. It was also the higher quality instrument that they had available to them.

There is another term that often gets misconstrued as accuracy, and that is resolution.
Resolution is simply the graduations and "readability" of the device in hand.
If I have tape measure, and it reads out to the 64th of an inch. That tape measure is not accurate to a 64th, it is only resolved to a 64th.
As an example, I have a tape rule that is ~ 1/16" off.( Using a 6' Starret metal rule that lost it's NIST traceability due to administrative requirements). If I were to measure out, and mark a board 12 and 21/64", that board in my case is actually 12 and 17/64ths.
Another reference was made to using the device on new metal versus tired metal. There is validity to this statment. However, the strain gauge doesn't know what it is hooked up to, or the material composition. Steel, brass,aluminum, titanium etc. Old metal, new metal or kite string. Is the metal hot , or cold. How has the temperature effected the ductile properties .It just provides an indication of mechanical distortion of the test device that can be transmitted to a force indication. It is up to the user to apply the instrument in the correct application.
These tension gauges are not new. They have been in use in industry for well over a century and a half,and have not changed in principal. We have added some bells and whistles, like digital readouts. Some of the more sophisticated models are in actuality a variable capacitor that has the capacitance, or dielectric changed based on the movement and distortion of two metal discs. Still though, it is the know distortion of metal that is the basis.
There are many points that I disagree with with respect to the testing methodologies that have been applied as stated throughout the context of this thread. (I am going to assume that the engineering people that have helped Mark to date are fully aware of standards and testing methodolgy). They are however, academic in nature,and would be way outside any relevant, or usable info.
In the end Mark has the correct answer, in my opinion. Adjust the tension using the supplied indicator until you get the desired result, and don't go any further, regardless of what the tension gauge or the flutter method indicates.

[Phil Thien]

In Mark's post, and I am not singling Mark out here, reference was made of correlating accuracy to repeatability.

I'm not a metrologist, but I think Mark's implication was correct. The way I read it, was that none of the gauges except for one offered repeatability. So he implied those were not accurate.

This is correct. Repeatability doesn't guarantee accuracy, but a lack of repeatability certainly indicates a lack of accuracy.

[Mark Duginske]

I started a new thread titled:

Carter, Iturra, Lenox, Starrett Comparison

Mike Cutler: thanks for your comments and I hope you give us some suggestions for future test on the new thread.

I'm not saying that I know everything about band saws but after first starting to spend time on SMC in the last week I'm amazed at the amount of biased information there is on band saws and tension in particular. My impression is that there are a lot of people who have wasted a lot of money on tensioning products of very questionable quality or value. There certainly is a time to spend good money on a quality product. But there is also a time to use common sense. My goal as a writer is to help people use their common sense before their credit card.

[Richard Butler]

I just checked my 1980's Delta bandsaw and it seems that the spring gauge is pretty close to 15k psi for any given blade using the dial caliper method. I could not achieve 15k using a 1/2" blade but I knew that I could not before I started. This is one time where the forum saved me money.

[Dennis Peacock]

I'm not saying that I know everything about band saws but after first starting to spend time on SMC in the last week I'm amazed at the amount of biased information there is on band saws and tension in particular. My impression is that there are a lot of people who have wasted a lot of money on tensioning products of very questionable quality or value. There certainly is a time to spend good money on a quality product. But there is also a time to use common sense. My goal as a writer is to help people use their common sense before their credit card.

Mark,

First of all, welcome to SMC. I am a reader of your books, articles, and a watcher of your video's. you have taught me a lot and The Bandsaw Book of mine has a lot of "dirty finger prints over it".

Maybe it's just me, but buying a tension guage appears to be a non-necessary item as I use the sound and feel of a blade to tension it. I've been doing this for years now and have never had a problem. So I guess I'll keep saving my money for something else. ;)

[Mark Duginske]

Thanks for the note. People can spend their money the way they want but certainly the discrepancies of the mechanical gauges doesn't encourage a purchase of that kind of gauge. However
I have to say that the electronic Carter is a neat item and may be very useful in some situations where you would have inexperienced users changing blades, for example a school or a shop.