The Bandsaw Myth, Take 2

[Bill Space]

Please bear with me, I did not want to derail that other thread where I asked for references regarding bandsaw wheel relative positioning.


I think Van Huskey’s response to that thread merits a separate discussion. Here is that response:


Take a couple of seconds to think about the issue of coplanar as it relates to bandsaw wheels.


If the proper operating state for bandsaw wheels is supposed to be exactly coplanar then why do bandsaws have a mechanism to adjust the plane relationship between the wheels which you are supposed to use each time to put on a new blade? The word "tracking" would not be in the lexicon of bandsaws if coplanar was the proper way to orient the wheels. They would be adjusted to coplanar and never moved.


So why does the coplanar "myth" exist? It exists because the wheels of a bandsaw have to be within a certain tolerance of coplanar to operate. This will vary with the width of the tire, the width of the blade and distance between the wheels. Consider the venerable Delta 14" saw, you can't have one wheel offset by 3" and have it function nor can you have one wheel canted 45* in relation to the other. So "everyone" talks about coplanar because you need to have the wheels near coplanar.


So why is it that truly coplanar is bad. If the wheels are perfectly coplanar then the blade is very twitchy and tracking it is a huge pain, this is where the smallest adjustments to tracking have the largest impact on blade position*. The offset doesn't need to be much at all, probably lower than most peoples tolerance of what they call coplanar. Keep in mind the methods I have seen on how to check and adjust to coplanar all use the incorrect reference surface. The rim of the wheel is NOT the proper reference surface, the actual top of the crown is the proper reference.


The reason I hate the coplanar mantra is far more people have screwed up their saw by futzing with the lower wheel. I have only seen one bandsaw so far out of coplanar that it would not track blades correctly. It was a PM140 that had the upper shaft so beat up the upper wheel would not seat and was sitting about an inch forward of its proper position.


One doesn't need a higher authority to understand the sole function of the tracking mechanism on a bandsaw is to adjust the wheels in relation to coplanar.


The first thing that struck me is that perhaps what Van is referring to as exactly coplaner, and what many refer to as coplaner are not the same thing. As Van says, truly coplaner refers to the position of the crowns on the tires, not the edges of the wheels. Van states that when the crowns are truly coplaner, the blade becomes jumpy; but actually this could be caused by approximately equal but opposite (and probably slightly varying)forces being applied to the blade by crowns that are close to being coplaner, but are not.


I am pretty sure Van would agree that there is no easy way to determine if the tire crowns are truly coplaner or just very close.


So anyway, I think when one strives to make his bandsaw wheels coplaner, without realizing it he may just be making his wheels close to being coplaner. And as Van says above, and which I can buy into, a bit of offset may result in stability.


Now carrying these thoughts a bit further. The crown on the wheel exerts a force on the blade to keep it running on the crown. If the wheels are offset with respect to crown position, the blade will experience a force on it, with each crown trying to pull the blade towards itself. If the crowns are close to being coplaner, the forces felt by the blade will be minimal. And the blade will be stable. The more the crowns are offset, the greater the bending force the blade will feel. Or so it appears to me anyway.


So an argument can be made that since it is very difficult to determine if tire crowns are coplaner, as a practical matter one should make an attempt to get the tire crowns close to coplaner, but not exactly coplaner, because exactly coplaner is too hard of a target to hit. And may be undesirable anyway.


On the other hand, another (complementary)argument can be made that if the wheels(crowns) are too far offset, the forces on the blade caused by the crowns might lead to premature blade failure, so significantly offset wheels (crowns) should be avoided.


So, at the end of the day, it seems to me that when we strive to make our bandsaw wheels coplaner, in reality we are just making them very close to being truly coplaner, but they are actually not coplaner in the truest sense of the word (except for that rare case when one hits the target without knowing).


I would carry this thought one step further. If someone is satisfied to run his bandsaw with the wheels significantly offset this may work just fine, but it could lead to premature blade failure due to stresses imparted into the blade by the opposing actions of the tire crowns.


As a final comment, although Van states it, I am not sure we are supposed to use the top wheel tilt function each time we change a blade. My guess it is there as a fine tuning mechanism to compensate for undefined variability. But that is my gut speaking...


I have experience in a past life troubleshooting relatively complex control systems but bandsaws are new to me so this is a learning exercise on my part.


All thoughts are helpful and greatly appreciated.


Bill

[Van Huskey]

I think you have nailed my position, with a couple of small differences.

1. the slightly opposing forces when blades are run (slightly) on the opposite sides of the top and bottom crowns is a good thing. It is actually MORE stable in this arrangement than running at the top of both crowns because it takes more force against the blade to move it. One could call it a level of preload.

2. It is indeed possible to change blades and not need to touch tracking but I find it is rare and my ritual always has me moving the tracking back and forth a little which in my mind settles the blade, that is likely more "ritual" oriented than necessary.

My entire issue with "coplanar" is the way it is discussed often leads people to think it is a natural part of setting up/dialing in a bandsaw. This is rarely the case. Adjusting the lower wheel should always be a LAST resort because it is what I refer to as a muddy downhill road. It is very easy to go down but things get really hard when you need to turn around and go back. As I mentioned in the other thread I have only encountered 1 bandsaw (out of well over 50) that required dealing with the general coplanar issue and that was a damaged saw that I could see with my eyes very easily that the upper wheel was not where it should be.

Bottom line is exhaust every other option prior to touching the lower wheel adjustments unless it is obviously very out of whack. Bandsaws are simple beasts but they have a set of variables other woodworking machines seen in a hobby or small shop setting don't have. The flexible tooling and the variability in the tolerances of that tooling often give rise to a complicated setup on an otherwise simple machine.

Another thing to note that is part of bandsaw fatigue/frustration is there is no ultimate higher authority to look to. Buy all the books and videos and watch a few hundred videos on youtube and you will see there is very little consensus. Duginski, Bird, Johnson, Iturra, Snodgrass et al disagree on many large issues. Honestly, most people do fine without worrying about the theoretical but if you are interested then read and watch everything you can get your hands on but most importantly get out in your "lab" and experiment. In the end, you may not discover the "bandsaw theory of everything" but you will have a better understanding of your saw and you will find a method and "belief" system that will work for you.

[johnny means]

Most of the misinformation of there is out there because it seems intuitive to someone. Bandsaw wheels should be coplanar because wheels should be aligned, right? WorkS for cars.

[Van Huskey]

Most of the misinformation of there is out there because it seems intuitive to someone. Bandsaw wheels should be coplanar because wheels should be aligned, right? WorkS for cars.

Excellent example. For anyone reading this and thinking yeah but my car wheels are coplanar lookup caster, camber and toe-in. A car with coplanar wheels would be basically undrivable, especially at highway or higher speeds.

[Frank Pratt]

These 2 threads are very good. I wish I'd had learned more about this stuff before I got my bandsaw. And @Van Huskey, thanks much for sharing your bandsaw knowledge with the rest of us.

[Bill Space]

Van,

I did not mean to dispute the small differences you listed. Thanks for pointing them out. I take no exception to them.

I am feeling more comfortable with the “independent” conclusions I reached.

With my 20” Davis and Wells bandsaw the blade tracking was terrible when I bought it. The tires were flat. I crowned them and the world changed. I bet I could have left it at that. But getting the wheels close to coplaner was not a big deal and I am glad I did it.

I love the opportunity this forum offers us to increase our understanding of all things related to woodworking!

Bill

[Van Huskey]

I think you did a really good job at summarizing my opinions, probably better than I would have done. I type stream of consciousness at about 120 wpm so it usually takes multiple edits to get it worthy at work, here I just vomit it out. I just wanted to clarify a couple of things.

Doing and finding your own "truth" is more beneficial than just picking someone's opinion and running with it. Even if you come to the same conclusion you will almost certainly learn something new or develop/hone new skills. My bandsaw opinions have been in flux for 30 years and while I found methods that worked for me years ago it is just a machine I am fascinated with. I am like the poor guy that tries every new sharpening method and has enough stones to pave a patio even though his chisels were razor sharp decades ago.

[Bob Vaughan]

Flat bands track on crowned pulleys. That's physics and we can't change that. A band saw blade is a flat band so the bandsaw's wheel needs to have a crown for it to track in the middle of the wheel. The compulsory coplanar myth was started a long time ago by someone that didn't understand this.

Sanding belts run on crowned pulleys. So do flat drive belts. Coplaner may be nice but it isn't mandatory for tracking. There are many cases of pulleys and flat bands were close is good enough.


coplaner.jpg

[Zac wingert]

I hope that one day I will read something like this and understand.

[Edwin Santos]

These 2 threads are very good. I wish I'd had learned more about this stuff before I got my bandsaw.

Why do you say that? Are you unhappy with your bandsaw?

[Frank Pratt]

Why do you say that? Are you unhappy with your bandsaw?

Mainly that the wheels were horrendously out of whack when I bought it & had the idea that they had to be coplanar. Just made so much work & frustration for myself. I am happy with it now that I have got it fairly well tuned. I do find the guides to be a bit of a pain to adjust though. Gonna upgrade them at some point.

[Chris Fournier]

I would never fiddle with the lower drive wheel unless I identified a problem with it. I used the co-planar technique with my Delta 14" over 20 years ago because I read it in a book and wanted to use the best set up that I could understand. It was a relatively weak framed saw for the .75" blades that I used for resawing and perhaps the co-planar method had some benefits. With my heavier 18" Euro saw I simply set up the blade for tracking using the top wheel adjustment. If it works, I saw, if it doesn't I re-adjust. Why it works may be interesting as a conversation but it doesn't change the functionality one bit. I really like using a bandsaw and part of my admiration for it is the somewhat finicky nature of the beast. When it's perfect it is so satisfying for primary breakout, when it's fussy it challenges all I have to get good results.

I personally believe that the blade is the greatest variable in the okay to perfect continuum.

[Nick Decker]

The manual for my Rikon 14" 10-326 does have a couple of pages devoted to aligning the bottom wheel position, with a warning that you should call Rikon tech if you don't fully understand the procedure. What it describes, though, is adjusting the tilt of the axle that the bottom wheel rotates on. So, once you get the top wheel tracking correctly, you tighten and loosen various nuts to get the blade to track correctly (centered) on the bottom wheel. You do this, probably several times, until this procedure gets everything lined up.

You also, of course, lose the factory setting. In my case, the factory setting resulted in the blade tracking a bit off center on the bottom wheel but the saw cuts just fine. I've never had a blade break or come off of the wheels. If it ain't broke...

[marty fretheim]

How does all this come into play on non-crowned wheels? If I understand the theory as Van states it, the center of the blade would be somewhat on opposing sides of the crown on either wheel. The opposing forces cause the blade to want to remain in place. The theory seems to fall apart with flat wheels. At least in my tiny brain.
Maybe that's where ability to properly tension a blade comes into play.

Marty

[Bill Space]

Flat wheels are different than crowned wheels. I posted a link in "the other" thread to a thesis that addresses this.

The short of it is that on flat wheels the blade runs on the edge of the wheel/tire, and the edge of the wheel, with the blade overhanging, acts on the blade in a fashion similar to what the crown on a crowned wheel does.

Do not have the link handy where I am at the moment...sorry...the title of that thread is "Bandsaw wheel alignment: Cite your references". You can find the link there if you are interested.

Bill