A comment I get repeatedly on the first
video
about making the
wheels for my big bandsaw
is "why a bigger bandsaw". I thought this was self explanatory - bigger
is better!
Why bigger wheels are better
More elbow room
A bandsaw has a post on the left side, which is as far from the blade
as the wheels are in diameter. So a 14" bandsaw will have 14" of space
between the blade and the post where the blade goes back up
(minus a few millimeters for the blade guard).
This means the maximum width piece I could cut through the middle is twice
that wide. When cutting out complicated shapes in larger pieces of wood,
hitting the post, even with smaller pieces is not unusual. You can often work
around it by flipping the piece over or strategising over which order
to make the cuts, but having the post further away always makes it easier.
Bigger is better.
Longer blade life, less metal fatigue
If you take a typical bandsaw blade, you can bend it to a fairly tight
radius and it will spring back to its original shape. So having fairly
small wheels, say 8" (20 cm) in diameter, would seem adequate for most bandsaw
blades. I could bend the blade to an 8" diameter hundreds of times and not
run into problems. But if I bend it to that radius hundreds of thousands
of times, It will break from a problem known as
"metal fatigue".
The smaller the wheels, the tighter the bend that the blade needs to make.
Generally speaking, most general purpose bandsaw blades are about 0.026"
thick (.65 mm), so a 14" (35 cm) diameter is large enough to avoid this problem.
9" bench top bandsaws have to use thinner (flimsier) blades.
For thicker blades, such as used on Wood-Mizer saw mills, 14" would be too
small. My friend Kurt, who runs
a Wood-Mizer sawmill, says that blades cracking (from metal fatigue) limits
blade life to about 10 hours run time before they break. The blades could
be re-welded, but after 10 hours, it will soon break somewhere else, so no
point in welding it. Wood-Mizer's wheels are just under 50 cm in diameter.
3-wheeled bandsaws
More elbow room
A way to get extra "elbow room" without making a very large bandsaw is
to make a bandsaw with three wheels. The third wheel pulls the blade
way off to the side, making for a "throat depth" that is larger than the
wheel diameter. This would allow you to build a bandsaw with a 20-inch (50 cm)
throat depth that could still be used on a bench top.
Moving it around
But you also need a lot of room around a bandsaw. I keep my bandsaw pushed
against the wall, but it's on wheels. When I run out of room around the saw,
I just pull it out from the wall to make the cut. Now imagine a bench top 3-wheeled
bandsaw. If you run out of room, you have to pick it up and move it somewhere
else to get the extra space.
Less space efficient
Of course, you could always put the 3-wheeled bandsaw on its own stand on
the floor, so you could pull it out. But if the saw is floor standing, then
you have lots of vertical room, so you could just have two larger wheels.
But worse yet, the three-wheeled bandsaw typically needs at least the width
of the wheel of additional room on the left for the third wheel. So a 20"
three-wheeled bandsaw will be wider than a 20" two-wheeled bandsaw, even though
the 20" two-wheeler will be much taller. So in terms of footprint, a conventional
large 2-wheeled bandsaw makes better use of space. Granted, the 3-wheeler may have
a smaller table and save room that way, but you could always put a too-small
table on a larger bandsaw and achieve the same effect.
More complicated
Three wheels instead of two means more wheels need to be built.
And the three wheels need to be aligned with
each other. If the blade doesn't track right, it's much harder to figure out
what's wrong on a 3-wheeler than a 2-wheeled bandsaw.
On a 3-wheled bandsaw, the forces on the wheels are diagonal because the blade
doesnt pull vertically on the wheels. So the wheel mounts need to be either
at the appropriate angle for the force applied, or be sturdy against side
forces as well, whereas on a 2-wheeled bandsaws, fordces applied to
the wheels is straight up and down.
Three-wheeled bandsaws were popular in the 1970s. It seemed like a good idea
at the time. But, I imagine manufacturers got fed up with custmers complaining
about their 3-wheeled machines. They break blades far more often, are
more finicky, and more complicated to produce. Blade changes are also harder.
So I don't know of any general purposes 3-wheeled bandsaws for sale anymore.
There are however some specialty applications for three wheeled
bandsaws still out there, such as this
articulated bandsaw or this Falberg bandsaw
More bad bandsaw ideas
Answering some further suggestions that keep coming up....
A four wheeled bandsaw would eliminate the extra width needed for the third wheel, because
the blade would no longer have to move at a diagonal. But now you have four wheels
instead of three, introducing even more complexity. That said, this is perhaps the least
dumb idea that keeps popping up. At least this type of saw would only be about as bad
as a three wheeled bandsaw.
How about adding some small idlers to deflect the blade
You could add two small idler wheels to deflect the blade further left, giving extra
throat depth without making the wheels bigger. Except, when you add small wheels,
the blade has to bend to the radius of the small wheels. Small wheels are a problem.
any small wheel is a problem, even if it deflects the blade by just 10 degrees,
the blade still has to bend to the radius of the blade. The only exception is wheels
as blade guides - because these generally don't deflect the blade.
How about a Teflon guide in the shape of an arc or semi-circle to deflect the blade
This would eliminate a third wheel, or the wheels altogether. But with the amount of
tension on a blade, Teflon would not be slippery enough. In addition, the teeth would
dig into the Teflon. Also, the Teflon would get hot. There's a reason Teflon isn't
used for bandsaw guide blocks.
How about a semicircle of small wheels?
Maybe an arc of 20 small wheels to gently deflect the blade instead of a big wheel?
That might work if the blade was very thick and there were a LOT of rollers, and
blade tension relatively low, so that the blade never actually bends to the
curvature of the rollers.
But to actually use a saw, the blade tension needs to be high enough that any regular
saw blade would bend to the rollers. In addition, all those rollers would be very
difficult to align, would have to turn very fast (and wear out quickly), and would be
very noisy. The fallacy this idea tends to be based on is that if the wheel
only deflects the blade by a small angle, it won't cause as much wear. But the blade
needs to bend to each wheel and unbend again. Whether it goes around the roller 180
degrees or 10 degrees doesn't matter much. If it did matter, wrapping the blade in
a coil and spinning the coil (without unwrapping the blade) would also cause it to
wear out! At any rate, the semicircle of small wheels is an incredibly dumb idea.
Don't agree with me? Do the experiment, like
John Heisz did.
What it comes down to...
There are reasons that bandsaws are built the way they are,
and those reasons are based on physical limitations and not the lack of imagination
of bandsaw builders. So if you have a brilliant idea for how to build a better
bandsaw (and I haven't shot it down here yet), don't try to prove your idea by
arguing with me. Just try it out by building it. Don't have the ability to build
it? You might want to consider the possibility that those who do have the
ability to build it might have a better understanding of the problem than you do.
The physics of bandsaw resawing
Making the wheels
Cheap 8" bandsaw
Mikiono's bandsaw
Pekka's bandsaw