Damaged Band Saws from Overtensioning

[John Shuk]

Jack,
I use a strand dynomometer. It is alot more accurate for tensioning.

[Mark Duginske]

My take on the discussions here are:

Aftermarket tension gauges are not accurate/repeatable
The clamped on dial caliper method is not accurate
The flutter method is not accurate
The Built in gauge on the bandsaw is accurate enough

My old (late 1940's) bandsaw does not have a built in gauge. What should I use to tension my saw? The saw also does not have a de-tension lever either, so I must manually de-tension when not in use. This requires re-tensioning every time I use it.
Is there an aftermarket gauge, or some other method that I can use to properly tension blades?

Jeff

There are a lot of theoretical ways to tension the saw. As noted above the methods other that the gauge are questionable. I would use a new high quality blade and experiment. For starters I would get a cheap ruler and
stick it on the saw by the spring the same way that the gauge is applied.
Start by compressing the spring half way. That is a good stating point.
From that point experiment with the tension up or down. Make some notes for further reference. The sharper the blade the less tension is needed.

Good luck.....

[Jeff Clow]

There are a lot of theoretical ways to tension the saw. As noted above the methods other that the gauge are questionable. I would use a new high quality blade and experiment. For starters I would get a cheap ruler and
stick it on the saw by the spring the same way that the gauge is applied.
Start by compressing the spring half way. That is a good stating point.
From that point experiment with the tension up or down. Make some notes for further reference. The sharper the blade the less tension is needed.

Good luck.....

I understand that this would be making my own gauge for this saw. Good as far as that goes, but I'm missing something here....What would I make notes of? I still don't see any way to accurately measure the tension. If I could borrow an accurate gauge (there must be such a beast), I can see how this would work to calibrate the scale. But lacking an accurate gauge, the aftermarket ones still sound better than nothing in this instance.

Jeff

[John Shuk]

Mark,
What do you think of the flutter test suggested by Suffolk Machinery for Timberwolf blades?

[Mark Duginske]

I understand that this would be making my own gauge for this saw. Good as far as that goes, but I'm missing something here....What would I make notes of? I still don't see any way to accurately measure the tension. If I could borrow an accurate gauge (there must be such a beast), I can see how this would work to calibrate the scale. But lacking an accurate gauge, the aftermarket ones still sound better than nothing in this instance.

Jeff

Tension is only one ingredient like a soup. Think of the tension as one of 8 factors affecting band saw performance. I think that blade choice and
blade sharpness are more important that tension. If a blade is sharp it requires only moderate tension. What you are trying to establish is a "baseline" or stating point. Use a new 3tpi 1/2 blade. Compressing the spring half way is a good starting point, then note the number on the scale. Use scrap for the test. Does it cut 3/4 material at that setting? Does it cut 2" and then 4" and then 6".

If you start to have trouble cutting the material straight increase the tension and experiment some more.

[Mark Duginske]

Mark,
What do you think of the flutter test suggested by Suffolk Machinery for Timberwolf blades?

Some people use that thest with good result and if it work for them that is great. I have tried it and have not had particularly good results. To quote one of my previous post:

“No field of woodworking has more misinformation than the band saw as it relates to tension and the standard tension mechanism. Although the feeler gauge and caliper (AND THE FLUTTER METHOD) of measuring tension is theoretically valid the actual usefulness of this technique is doubtful. How many of you measure tire pressure to know how much fuel is in your tank? Theoretically you could measure either your car weight or the tire pressure to determine the amount of gas in the tank. Why not use the gas gauge?

90 percent of the time you can use the gauge on your saw with good results. For cutting thick material or if the blade is dulling
go to the next higher setting. Just like the gas gauge in your car
it is a “good enough” device.”

[Alan Schaffter]

No one answered my questions above.

[Mark Duginske]

Mark can you or someone else address the below issues-

I read this thread and the one a few months back, and no where do I recall seeing a discussion about how desired blade tension figures (for sawing wood) are determined and how do we know they are correct, assuming there is or will be a bandsaw gauge to measure them.

Answer from Mark:
When I talked Starrett and Lenox they said that the 15.000 psi rating for woodworking is an international standard by an industry group. Both of them use the same 15,000 psi number for wood but neither tech person could explain where the number came from. Chuck Olson from Olson Saw doesn't use a psi number. They (Olson Saw) have a testing machine and test welds up to several multiple of the 15,000 to test if there computerized machine is still "doing its thing". As far as giving a psi number it just is not "relavent" according to chuck Olson.

Are these numbers theoretical or were they determined by testing and experimentation by the blade manufacturers? To me, an accurate tension gauge is only half the problem.

Answer from Mark:
As I said, these 15,000 psi numbers are established by a trade group. If you look at the Feb 2007 Woodworker's Journal article that Aaron Gesicki and I did for a 1/2" 3tpi blade that blade load at is 146 lbs and the Wheel load is 292 lbs. When the blade was tensioned to read 292 (wheel load pounds) on the Carter Electronic gauge (Carter ETG) the standard saw scale measure was adjusted to the half inch blade mark. So there is a correlation between the saw scale and the Carter Electronic. Mike Cutler will be giving us more details as to the accuracy of the Carter ETG. The Starrett Gauge averaged in the 12,000psi range , the Lennox
in the 11 to 12 range and the Iturra was all over the board and some of the Ittura reading were quite low which would result in overtensioning.

I realize, it would be nice to have a tension gauge to help prevent bandsaw damage from over-tensioning, but can we trust the tension numbers given for these blades?

Answer from Mark:
These are two different questions: The most important factor concerning overtensioning in not to compress the spring completely. At other places in the post I state that I use the gauge and that I set it one setting higher when resawing or when the blade dulls.

Do all blade manufactures provide recommended tension figures ?

Answer from Mark:
Some manufactures such as Lenox and Starret do provide a 15,000 tension number but others don't. Olson recommends using the saw gauge rather than a psi number which is much less confusing to the "laymen"

I thought some like Timber Wolf recommend the "flutter test" As a blade is used won't the tension need to be adjusted to account for blade elongation and dullness? And what about adjusting blade tension for differences in material being cut? If so, by how much?

Answer from Mark:
The "flutter test is fairly simple but I prefer the saw gauge. The tensioned should be increased (I increase the 14" saw from 1/2" to 3/4"" for thicker material or as the blade dulls.

So what is the answer to proper blade tensioning?

Answer from Mark:
The proper blade tension is the one that works without hurting the saw.

Might there be another whole methodology, simple or complex, we have not even touched on?

Answer from Mark:
Of course there are a lot of different methods and the latest is the Carter Electronic ETG.

[Alex Shanku]

I dont understand how you can take a semi-scientific approach to testing aftermarket tension gauges, yet when asked what to do when the saw in question has no built in gauge you tell him to compress the spring halfway and start from there.


Why is the flutter method not better than compressing various sized/strength springs halfway?

Also, as one poster mentioned, why does this topic receive so much debate. Ive never had a problem with centering the blade, cranking the tension knob until its pretty tight, and cutting away. Am I the only one who sees this as a non-issue?

Alex

[Steve Clardy]

I dont understand how you can take a semi-scientific approach to testing aftermarket tension gauges, yet when asked what to do when the saw in question has no built in gauge you tell him to compress the spring halfway and start from there.


Why is the flutter method not better than compressing various sized/strength springs halfway?

Also, as one poster mentioned, why does this topic receive so much debate. Ive never had a problem with centering the blade, cranking the tension knob until its pretty tight, and cutting away. Am I the only one who sees this as a non-issue?

Alex

Nope. I think its a non issue also. Just my .02

[Gary Keedwell]

Me three

Gary K.

[Mark Duginske]

Also, as one poster mentioned, why does this topic receive so much debate. I've never had a problem with centering the blade, cranking the tension knob until its pretty tight, and cutting away. Am I the only one who sees this as a non-issue?

Alex[/quote]

As one has more experience and if one has a higher quality saw one learns to intuitively adjust the band saw. No doubt that experience, comfort with machines and hand-eye-coordination play a part. IF YOU GET GOOD PERFORMANCE-GREAT. I've had students who were professional athletes,
Surgeons and other highly trained individuals who were getting into woodworking and did not have the time to develop the "heuristic" skill of
using the band saw. I do encourage people to "learn" the skill rather than buy some gadget that often doesn't work.

Just because it is easy for you it doesn't mean that it is as easy for everyone else.

[Gary Keedwell]

Just because it is easy for you it doesn't mean that it is as easy for everyone else.[/quote]


I think that it does generate more debate then is necessary. There is a learning curve but no more then there is in jointing a long board on a jointer.

Gary K.

[Steve Clardy]

Also, as one poster mentioned, why does this topic receive so much debate. I've never had a problem with centering the blade, cranking the tension knob until its pretty tight, and cutting away. Am I the only one who sees this as a non-issue?

Alex

As one has more experience and if one has a higher quality saw one learns to intuitively adjust the band saw. No doubt that experience, comfort with machines and hand-eye-coordination play a part. IF YOU GET GOOD PERFORMANCE-GREAT. I've had students who were professional athletes,
Surgeons and other highly trained individuals who were getting into woodworking and did not have the time to develop the "heuristic" skill of
using the band saw. I do encourage people to "learn" the skill rather than buy some gadget that often doesn't work.

Just because it is easy for you it doesn't mean that it is as easy for everyone else.[/quote]


True.
I don't consider a bandsaw my first go-to machine.
Its far down the line of use in my shop.
So I do not put a lot of extra though/thinking into that machine. It performs well, does what I expect from it when I use it.

[Mark Duginske]

I dont understand how you can take a semi-scientific approach to testing aftermarket tension gauges, yet when asked what to do when the saw in question has no built in gauge you tell him to compress the spring halfway and start from there.

Alex

On most saws (but not all) the setting for the 1/2" blade usually correlates with the spring (that the manufacturer chooses) being half way compressed. On most saws, especially with a sharp blade one will get acceptable performance with the spring half way compressed and not run the risk of compressing the it completely and thus negating the "shock absorber" aspect of the standard spring. He has to start somewhere and that is a good place to start experimenting.

People who get good performance (or achieve a certain level of success) take it for granted. The surgeon or professional may or may not get good performance with their band saw but they may get better performance out of their bank account than the average woodworker. That is a skill to.

Everyone is different and has spent time learning different things.