Getting grain direction right while shaping curves can be a struggle.
Go the wrong way and you'll get nothing but tearout — with hand or power tools alike.
But a simple rule can help you go from tearout-ridden disasters to ultra-smooth curves in no time.
That rule? Always cut downhill.
Now, what does cutting "downhill" mean? Simply put, ensuring your cutting direction goes from the apex of a curve toward the bottom.
When shaping a concave curve, start your cut from the top of the "hill", moving towards the "valley." Stop in the middle and repeat from the other side.
When it comes to convex curves, the same principle applies. Work from the apex down.
(If you really want to drive this point home, shape the edges of a circular board with hand tools. You'll figure it out in no time.)
Quick disclaimer. This "rule" is dependent on how the grain runs in a board. The straighter the grain, the more true it will be.
Think about the "petting the cat" principle of grain direction. In straight-grained boards, curves are going to have a massive effect on how the "fur" lays. But on boards with truly wild grain direction, the downhill "rule" might not be as effective.
Remember, woodworking is an art that takes practice. So, don't get discouraged if your first few attempts at curve shaping aren't perfect.
With time, patience, and this little tip, you'll be creating beautiful and smooth curved wood components in no time.