Why no 3-wheel bandsaws?

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A simple question: why aren't bandsaws more commonly made with three wheels instead of two? Sure, I've seen custom jobs made that way, and the fact that 2 is more simple than 3 is obvious, but the tradeoff for cutoff and height capacity seems worth it, but I don't know of any popular manufacturers making them.
There must be a good reason...anyone know?
Curiously, H
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Hylourgos wrote:

ISTM it's harder to get three wheels in the same identical plane as two. I think that's the primary issue.
-- Mark
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Mark Jerde said:

Blade fatigue is the big reason-in addition to manufacturing expense.
Greg G.
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Greg G. wrote:

Why would there be blade fatigue if you used the same diameter wheels? All the 3-wheel bandsaws I've seen use smaller wheels but ISTM this is a decision, not a requirement.
-- Mark
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good question. I just checked in "Bandsaw Handbook" by Mark Duginske. He said that early 3 wheelers had small diameter wheels that stressed the blades. He mentions that even with larger wheels the blade life is shorter. No explanation of this phenomenom is given.
dave
Mark Jerde wrote:

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Bay Area Dave wrote:

I made it to 2/3 rd's of a Mechanical Engineering degree before switching to Computer Science. The only possible explaination I can think of in 4 minutes of cerebration is that the number of bends per blade revolution is significant. Suppose you had two bandsaws, each with 15" wheels. One has two wheels, the other 3. The two wheels model would subject the blade to two bends per revolution. The three wheeled bandsaw would have 3 bends per rev of the blade. Maybe it is not so much how long the blade is curved around the wheel but how many times you change its straightness. The answer is beyond my knowledge one way or the other.
-- Mark
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DINGDINGDINGDING!!!! We Have a Winner, Folks!
That is exactly why the three wheel BS blade break faster. The fatigue is created from the flexing of the blade BOTH onto and off off the wheel, therefore you are absolutely correct that the blade on a 2 wheeler will have 150% the life of the 3...all other things being equal, of course.
Mike
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Mark Jerde said:

Every time you bend the blade around a wheel, it results in fatigue. Eventually, the constant bending and straightening of the blade results in breakage.
Greg G.
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Greg G. writes:

If the wheels are the same size and distance apart, and the motor RPM the same, the blade is subject to the exact same bend/straight cycling, so there should be no more fatigue than with only two wheels. In fact, there may be less because the blade is bent for a shorter time each time it bends (120 degrees around instead of 180).
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180 x 2 = 360 120 x 3 = 360 However, it is still flexed 3 times per revolution rather than only two. It is probably the more total flexes rather than the amount it is flexed each time. Perhaps a metallurgist can be more detailed in this. Ed
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But with the conditons above one complete blade revolution takes longer because the third wheel in that configuration requires a longer blade,
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At the same RPM, each "revolution" takes 1.5 times as long. The number of flexes *per minute* is the same, for a given linear FPM speed of the blade.
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No, it's subject to 3/2 as much.
It's bending the blade to fit the wheel, or straightening it afterwards that represents the stress cycling, not just the total bending angle (which is always going to be 360)
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If it's bending the same number of times each minute, how is that 3/2 the stress then?
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It isn't.
It's 3/2 the bending per cycle, but the bending per minute depends on the band length (and the speed). A large bandsaw always gets better band life, simply because it's spreading the load between more band.
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And if you read my original email, you'll note that I specified that the distance between the wheels remained constant, as did the motor RPM and wheel diameter.
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But how can the distance between the wheels remain constant in switching between a 2 and 3 wheeled machine ?
A tricycle is either going to have tiny wheels (band breakers) or it's going to have the same wheels, same spacing and an extra long band (long band, long life). Presumably there's a point somewhere in the middle where band life is equal for the same cut performance, but you'd have to estimate the increase in fatigue with decreasing radius to calculate it.
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On Thu, 15 Jan 2004 01:55:58 +0000, Andy Dingley

cheap benchtop 3 wheel bandsaws aside, big 3 wheel saws generally have 2 wheels top and bottom and a third bigger wheel somewhere way back there to open up the width. it makes for a large expensive saw usually requiring a pretty specialized process to justify it.     Bridger
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Well, anytime you run something across three items versus two there is more friction, thus more blade wear and fatigue. Make sense?
Jim

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On 13 Jan 2004 20:36:15 -0800, snipped-for-privacy@sewanee.edu (Hylourgos) brought forth from the murky depths:

From what I've heard, the blades break every dozen revolutions or so due to the small wheels and tight radius. It stresses the metal too much for longevity.
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