Bill Space
12-08-2018, 8:08 PM
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
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