The Bottom Line about Sawing Straight - Part 3

by Tim Cook

Tim Cook

 

In this final article dealing with sawing straight I’m going to address an issue that has been one that has created a large amount of discussion among sawyers. Adjusting blade curvature to optimize performance and cure blade ailments have been described by most as a lifesaver to their sawing frustrations while a small minority brush it off as mere blade ‘voodoo’ as one writer so bluntly put it. Then there are those who simply say it doesn’t matter.

However, one universal truth has continued to remain constant in my dealing with the naysayers and that is that they are unwilling to apply these truths to their own operation or even to put them to the test. The fact is, we are dealing with testable and repeatable results (science not opinions). So I will offer you a little ‘science’ in this article as well as tell you how it can increase your blade efficiency in sawing and in prolonging the life of your blades.

I must begin by first establishing some of my qualifications on this subject:

  • 35yrs. experience in hammering and tensioning saw steel. Including circle saw blades and wide bandsaw blades up to 12” in width
  • Personally performing more than 5000 experiments concerning narrow bandsaw blade flatness and its impact on performance and blade longevity
  • Introduced the first band roller to the narrow kerf industry
  • I have been rolling narrow bands for 21 years

 

It has been known for years that in the wide band industry that rolling the body was a necessity. Yet it was understood and taught that narrow bands never needed rolling. However, I learned over 21 years ago that they did need to be flattened and it did matter. So I built band rollers and started teaching the process. You can just imagine the reaction from those that didn’t understand. At the same time many more embraced this teaching and taught others as well, and have been sawing at peak performance ever since.

Technology and innovation will always continue to progress and those who want to ignore innovation will continue to get the same results year after year.

The first important fact to understand is that blade curvature is real.  We call this physical change Anti-Clastic-Curvature .

  1. Anti - because as the blade starts to make an arc, the curvature of the body does the opposite of what one would expect it to do (more on this later).
  2. Clastic -  simply means stretching / bending
  3. Curvature - describes something taking on a curving shape.

 

All bands going around a band wheel will be changing in flatness or curvature whether they are sawing or not. The shape that they form in the body is Anti-Clastic Curvature.  There are no exemptions; not belted wheels, not rubber wheels, and not steel wheels will prevent this.  There are ways however in which to minimize this effect on the blade. I will discuss later.

When a band saw blade is tensioned onto a band wheel would you say that the body of that blade as it goes around the band wheel would ‘cup’ itself around the wheel?  In other words would it take the shape of the band wheel crown or curve away from the band wheel opposite of the crown with the outer edges being raised up?  Here is a test that you can perform: take a good bandsaw blade and bow it into a 12 inch circle and put a straight edge razor on the width of the band on top of the circle. What you will see is a dish or a smile of light. The outer edges will rise up and the middle will go down.  Just the opposite of what we would think it would do.  It will always do this. Now turn the blade inside out and repeat the test and you will see the same dish or smile of light on the topside of the blade body.

So now that you understand what the blade body is doing as it comes around the band wheels it should make sense that as a blade makes thousands of these rotations that it begins to conform to this shape. In turn, over time this causes blades to teeter on the guides and the end result is a diving blade.

Here are a couple of things that will help slow the process.

  1. True band wheels – wheels that are true on the outside and balanced to run smooth at full rpm. When wheels are untrue there is a ‘shock’ or ‘bump’ against the blade on every rotation on both wheels.  These shocks multiply the effects of anti-clastic curvature
  2. Use the largest band wheel possible – This may be limited to 19” for you but that just means you will need to change blades sooner compared to if you were running 26” or even 30” band wheels.

In the end, the problem is corrected by rolling the blade flat. It works every time.

I am often asked by those who are new to sawing and looking for good answers, “How do I know who is correct or what theory is correct?”  My answer is this:  When you read behind the non-believers they will qualify themselves by saying they have never used a roller for keeping their blades flat so therefore nobody needs to use one. Then they will proclaim they don’t have blade curvature issues. I will tell you again there are no exemptions.

We are seeing major blade manufacturers willing to admit the impact that blade body flatness has on sawing performance even to go so far as to market this technology using a different term than anti-clastic curvature. Then there are those who will continue to hold on to old technology while claiming to be in the forefront of it by publically denying the effects of blade body rolling to their customers saying it is something only needed when running all steel wheels. Really? Would anyone like to put that claim to the test?  I have many, many times and it’s simply false. Someone either doesn’t know what they’re talking about or they’re lying.  But I digress; maybe they just don’t get it.

Here’s the bottom line: If you desire to saw at peak performance you must keep the blade flat.  If not, you simply are not sawing at peak performance even if you think you are.  So needless to say there are believers and non believers.  All I can say is step back non-believers because you will get run over by those sawing faster.