ian maybury
01-10-2011, 8:42 AM
These damn band saws are addictive!!!!! I've posted before about how I think maybe the ability of a carbide tipped band saw blade to cut/plane a little off the side of its teeth may be a factor in both it's improved ability to cut a true line, and at the same time deliver a good finish.
Van and others I think have posted on not just of the benefits of the additional beam strength delivered by a wider blade when re-sawing, but also of the downside this brings in terms of the need this brings for a saw capable of applying much increased blade tension.
The situation (it struck me while hand sawing some wood blocks I needed when building a rack over the weekend because my machines are not up and running yet) is not even as straightforward as the above.
One further problem with wider blades it seems to me is that once one gets deflected off track, the effect of the deep back is going to be to keep it on that line - making it much harder to get it back once the deviation exceeds the clearance available in the width of the kerf. You see the effect with a handsaw where getting a straight start is all important to sawing to a line.
Another is that since the the blade is flat and cuts off its leading edge the effect of too much thrust loading will eventually be to produce twisting - which will also take the blade off line. But this will presumably be influenced by the effectiveness of the guides too.
The positive of the wide blade is of course that (provided the kerf isn't providing much clearance) the back of it will tend to be guided by the already completed part of the cut - although this isn't a self correcting system of guidance as such.
I wonder if it's possible that (if we were dealing in ideals) that the optimum band saw re-saw blade might be a circular section blade of very high tensile strength cutting equally off all sides - combined with a saw frame/chassis capable of applying so much tension that beam strength in the blade was unnecessary to take thrust loads. That way it would rely entirely on the fence or whatever for guidance, and be completely non-directional. (it'd be hard to guide to a line by hand though)
It seems to me that blade tension is probably one variable where there's a fairly clear 'more is better' situation (frame strength is probably another) - at least until it starts to produce side effects like blade breakage, frame twisting or undesirable vibration harmonics or whatever.
The ideal is not going to arrive any day soon I guess, but maybe it does suggest that the optimum re-saw blade is one that is just wide enough to be strong enough to handle the maximum tension the saw can apply, and also add enough additional beam strength to get the job done without the blade deflecting/twisting under the thrust loading.
Kerf clearance and side cutting ability (a little like a circular saw blade) is an interesting variable too, in that there's potentially arguments for both less and more.
What this really brings out for me is that a band saw to work well has to be designed and set up so that it's sitting in a 'sweet spot' where all of these multiple variables (and many more - including stuff like depth of cut, feed force etc) line up. Also that it's so easy by changing or blunting a blade or something to slip out of this zone.
The zone becomes very narrow indeed on badly designed, flimsy or under specified saws I guess. We tend to lose interest once we have something that gets our job done, but I wonder how well optimised even larger professional saws and blades truly are? What might it take to get to a point and shoot band saw that once set up would stay that way, and not need to be cajoled into behaving itself for every job?
:o Pardon me if this is all to esoteric, please just ignore it if that's the case....
ian
Van and others I think have posted on not just of the benefits of the additional beam strength delivered by a wider blade when re-sawing, but also of the downside this brings in terms of the need this brings for a saw capable of applying much increased blade tension.
The situation (it struck me while hand sawing some wood blocks I needed when building a rack over the weekend because my machines are not up and running yet) is not even as straightforward as the above.
One further problem with wider blades it seems to me is that once one gets deflected off track, the effect of the deep back is going to be to keep it on that line - making it much harder to get it back once the deviation exceeds the clearance available in the width of the kerf. You see the effect with a handsaw where getting a straight start is all important to sawing to a line.
Another is that since the the blade is flat and cuts off its leading edge the effect of too much thrust loading will eventually be to produce twisting - which will also take the blade off line. But this will presumably be influenced by the effectiveness of the guides too.
The positive of the wide blade is of course that (provided the kerf isn't providing much clearance) the back of it will tend to be guided by the already completed part of the cut - although this isn't a self correcting system of guidance as such.
I wonder if it's possible that (if we were dealing in ideals) that the optimum band saw re-saw blade might be a circular section blade of very high tensile strength cutting equally off all sides - combined with a saw frame/chassis capable of applying so much tension that beam strength in the blade was unnecessary to take thrust loads. That way it would rely entirely on the fence or whatever for guidance, and be completely non-directional. (it'd be hard to guide to a line by hand though)
It seems to me that blade tension is probably one variable where there's a fairly clear 'more is better' situation (frame strength is probably another) - at least until it starts to produce side effects like blade breakage, frame twisting or undesirable vibration harmonics or whatever.
The ideal is not going to arrive any day soon I guess, but maybe it does suggest that the optimum re-saw blade is one that is just wide enough to be strong enough to handle the maximum tension the saw can apply, and also add enough additional beam strength to get the job done without the blade deflecting/twisting under the thrust loading.
Kerf clearance and side cutting ability (a little like a circular saw blade) is an interesting variable too, in that there's potentially arguments for both less and more.
What this really brings out for me is that a band saw to work well has to be designed and set up so that it's sitting in a 'sweet spot' where all of these multiple variables (and many more - including stuff like depth of cut, feed force etc) line up. Also that it's so easy by changing or blunting a blade or something to slip out of this zone.
The zone becomes very narrow indeed on badly designed, flimsy or under specified saws I guess. We tend to lose interest once we have something that gets our job done, but I wonder how well optimised even larger professional saws and blades truly are? What might it take to get to a point and shoot band saw that once set up would stay that way, and not need to be cajoled into behaving itself for every job?
:o Pardon me if this is all to esoteric, please just ignore it if that's the case....
ian