Cutting stuff from boards on the bandsaw is pretty easy.
But, if you want to do any resawing.
Or you're cutting through very large depth of wood
a large chunk of wood. It gets dramatically more difficult.
Some people think it's just a matter of
how far you can move the blade guides up.
But, I'll show you some of the physics involved.
And why it's so hard to re-saw.
So, I made this wooden model of a bandsaw blade
to show how it works. And, because the
wooden blade won't actually cut anything
I'm just using sawdust to pretend to be my board.
So, as the bandsaw blade moves past the board
each tooth cuts away a little bit of the
board and carries away the sawdust.
And as long as the board isn't too thick
that works just fine.
Now if we have a board that's really,
really thick because we're resawing.
And we're cutting along with that same blade.
What happens is the space between the teeth
is just not enough to hold all the sawdust
that the teeth cut away.
And so, thing's get really clogged
up and we get some of this sawdust
ending up next to the blade.
And there's just too much in front for them to really cut.
So, the solution, you would think
would be to cut a little bit slower.
But the problem is, as we cut very, very slowly
the teeth need to be really, really
pointy for that point of the tooth
to still be able to bite into the wood.
And as we cut with the saw blade the tips of
the teeth actually become a little bit round.
And the slower we feed if we feed really, really slow
that round actually just kind of
rubs against the edge of the wood
instead of actually biting into it.
So, if you want to resaw with a blade with a high tooth count.
It has to be really, really sharp.
A better solution
is to just use a bandsaw blade that has a lot fewer teeth.
So, here's a blade with half as many teeth.
And now, for the same amount of engagement for each tooth
we have enough space between the teeth
to actually carry away the sawdust.
Plus with only half as many teeth engaging in there
we don't need quite as much power.
Because again, each tooth needs to have a minimum amount of bite
for it to really cut away.
Now, as the wood gets really thick
imagine we're cutting through
a 30 centimeter or 1 foot thick piece of wood.
We still have an awful lot of teeth in the wood
And, with each tooth requiring a minimum bite.
That ends up being quite a bit of power.
But, there's more problems than that.
As we have a lot of teeth in the wood
each tooth also needs a certain amount of thrust into the wood.
So, we have to push that board quite hard.
And so, with a really deep piece of wood
we have a lot of force pushing against the blade, like that.
And it will want to, kind of bend away from the wood.
And that, in turn, causes more problems.
So, here I've got another model of this.
So, pretend this strip of cardboard is the blade.
And it's being held in place by the upper
blade guide and a lower blade guide.
And, as I push the wood against it
it just tends to... it'll want to move out of the way.
And what will happen is it will typically buckle sideways
in one direction or the other
to get out of the way because we're
pushing the wood really hard
because we have all these teeth that
need to engage at the same time.
So, as it buckles, it tends to twist sideways
because that's the easiest way for it to go, like that.
And, of course, as the blade is twisted sideways
it will really wander.
Now the antidote to this is more beam strength in the blade.
A wider blade helps but also just if we pull on this blade
from both directions really really hard.
That will prevent that from happening, in fact
the blade tends to buckle once the front
edge no longer has tension on it.
So, we apply tension. And then pushing on here
causes tension in the back and compression in the front.
And as that compression that we're added from this
balances out the tension that we gave the blade to begin with.
Once there isn't any tension on the front edge anymore
that's when it tends to twist sideways.
Now you've probably experienced this insufficient
beam strength problem in a hacksaw because
the blade on here is, in some ways, similar.
So, if I want to cut through here, if I just
apply a light amount of pressure, I'm ok.
But, if I want to really bear down on this
the blade tends to want to twist
sideways and I don't get a straight cut
so it keeps doing this. And If I just
increase the tension on the hacksaw
so the blade is really taut
it's beam strength goes up a lot. And now...
it does it a lot less. And let's give it some more tension.
And now I've got much better control over that blade
because it doesn't want to just buckle
over every time I push down on it.
So, for intricate work I would use a narrow blade, like that.
And this one's got about 10 teeth per inch or
about 2 and a half millimeters between the teeth.
And for a bit heavier work there's a blade like this.
You can do a little bit of resawing with this blade.
It's got about 4 teeth per inch.
About 6 millimeters per tooth.
And it's also a bit wider. About 12 millimeters wide.
And for resawing you end up with
some of these really heavy blades.
And this blade is 2 teeth per inch or about 12 millimeters
per tooth. And it's 3/4 of and inch wide.
Or about 19 millimeters and it’s also a bit thicker material.
Now a problem with a thicker material is
as you bend it around tight radius'
that material tends to die from metal fatigue.
So, you need bigger wheels on the bandsaw, as well
for using blades like this. This one is
just barely ok with a 14 inch bandsaw.
Or, at least, I haven't broken it
yet running it on my 14 inch saw.
I really should use something bigger for a blade this heavy.
So, if you want to do resawing and you
don't want your blade
to drift too much
you need a wide blade and you need
to put lots of tension on it.
So that it has lots of beam strength.
It also helps to make the blade really, really sharp.
And, what's also important is to have lots of power on your saw.
Because as you have a lot of teeth engaging2
that takes a lot of force to run it through.
So, if you really want to do a lot of resawing
the solution isn't so much to put a riser
block on a little 14 inch bandsaw.
Because that only makes your blade guides further apart.
But, in terms of more tension and more power
you just need a bigger saw.