When you’re resawing by hand, there is a big consideration in determining how difficult it’s going to be: Under how much stress is the wood? There are two big factors that I’ve noticed:
- The cut of the wood
- Moisture content
Let’s start with the moisture content, because that’s perhaps a little easier to understand. Green wood is usually under a lot less internal stress than dry stuff because that’s more or less its natural state before being cut down. As R. Bruce Hoadley’s book explained, you can cut slices off of a fresh log and it won’t crack apart until it starts to lose moisture. Sure, there might be pitch, resin, sap, or whatever else inside to make it more difficult to cut, but it does mean that the wood will be less likely to close up on you.
Because I rarely get the chance to work with green wood, the cut of dry wood is what causes me the most grief. Dry wood is always under stress of some sort; it’s unavoidable because you’ve taken away the water that was maintaining equilibrium when it was (probably) a stable, living organism. What you want is another state of equilibrium where the lignin is strong enough to hold everything together without cracking. Quartersawn wood is great because it’s under the least stress–because it’s got a consistent density pattern across the cut, it dries evenly and doesn’t tend to cup. Just a little more shrinkage at one end is pretty easy to handle.
Well, that’s nice, except that quartersawn wood is more expensive and it’s a lot harder to find than flatsawn stuff (not to mention that the figure may not be what you’re looking for). So this is the sort of thing I usually end up with:
This is a cross-section the 8/4 stock for the new nightstands that I wrote about earlier. The wood on the bottom that’s closest to the pith (center) is under a lot of stress. You can see a minor check here–this was due to that knot and its proximity to the end of the board.
You can see that this board was fed through a planer a little after drying because the cross-section across the cut is flat. But below is what happens when you resaw it:
That pencil line (and the sawcut) was straight when I started, but as I got further into the cut, the stress along that cross-section was relieved slightly, and this cupping was the new state of equilibrium.
The problem is that this stress relief is a major pain in the tuchus when you’re resawing dry flatsawn stock by hand. Basically, some part of the wood inevitably closes up around your saw as you are sawing, and you find your saw incredibly hard to push or pull through the cut, especially if you’re using a deep-bladed affair such as a Disston handsaw. It’s less severe with a frame saw, but it’s still there.
To work around it, break out your wedges and keep tapping them in as you’re working:
They’ll keep the kerf from closing in around you and it will be easier to saw. You really want to put them in as soon as you can, because the easier you saw, the straighter your cut will be. If your blade is pinched by the wood, it is being bowed out of a straight line, and your cut will wander.
Wedges are easy, except for one minor detail. You mostly want to be working like a bandsaw, perpendicular to the grain. However, when working with a fairly thin blade such as this, you need to be able to establish a shallow kerf in both sides so that your blade can track inside. To get these small kerfs, you need to tilt the saw at a diagonal, and this is precisely where the wedges and/or stress-relieved wood will get in your way. If you pop out a wedge or if you’re not able to drive them in deep enough, the wood will close up around your blade.
So what you often end up doing is tilting the saw just a little and establishing a small kerf until you can get deeper.
A bandsaw arguably does this better, because it always cuts perpendicular to the grain because you’ve got a fence, and the blade will always be cutting next to some (hopefully) straight wood. But that’s not to say that the wood isn’t under stress and isn’t closing around the wood–it is, and that’s why you’ll hear a POP at the end of a particularly nasty cut. You need a fairly beefy bandsaw to resaw wide flatsawn stock. You can cheat a little with wedges by turning the machine off in mid-cut, banging some wedges in, and resuming, but this is to be avoided if at all posssible…
As far as the current project goes, I’ve chosen to cut the thinner slice from the more stressed parts of the wood, the “pith” side. The result is that the thicker slice, having a more consistent density, mostly retains its straight profile, but the thin slice (shown above) cups like crazy. My plan is to make those thin slices into panels, where I can use their more interesting figure to my advantage, and not care about their increased instability, because they will be flexible and slide in grooves.
That said, here is what became of that 8/4 piece of cherry in an intermediate state (the chunk on the right is what remained at the end and I probably won’t use it):
It’s hard to believe how large that board used to seem, and now it’s so much more compact. The crazy thing is though it’s not much different in volume (I was actually efficient at slicing this for a change), it seems like it’s a reasonable weight now, whereas before, it was really unwieldy. Of course, there will be a significant change in volume when I whittle those panels down to desired thickness.
Eh, whatever. What it boils down to is that I’ve got my new project frames right there! There are a few more notes I have for how I chose to cut this, but I’ll save them for a later post.