Sanding blocks with a curved face can be very effective for smoothing and, with coarse grits in the right circumstances, even shaping curved surfaces in furniture making. I use spokeshaves, specialty planes, rasps, and scrapers to shape and smooth curved surfaces, but not to the exclusion of the humble sanding block.

They can be made quickly and easily with the bandsaw or bowsaw. For working concave surfaces, the curve of the block should be slightly steeper than the steepest part of the curve of the work piece. For convex work, a flat block is adequate for working shallow curves. For working steeper convex curves, the block’s curve should be slightly shallower than that of the work.

The top of the block should be shaped friendly to the hand using saws and rasps. I like to steeply cut down the corner of the block near the base of my right thumb, as well as the diagonally opposite corner.

The backing surface for the sandpaper should be have some type of firm cushioning, similar to a random orbit sander. For most broad surfaces, I like the high-friction cushion material available in with a pressure-sensitive adhesive backing from Lee Valley. PSA-backed 1/16″-thick sheet cork is firmer and thus good for narrower, smaller scale, or more detailed work.

Cutting regular sandpaper sheets and wrapping them around these sanding blocks is particularly annoying because of the curved surface. I much prefer using PSA-backed sandpaper that comes in large rolls, such as that available from Klingspor. It is quick, effective, and wastes less sandpaper, especially if the block is made to the width of the sandpaper roll. It is also reduces hand fatigue because there is no need to grip the paper to the block.

A gum rubber block is usually associated with cleaning retained sanding dust from the sandpaper on power sanders, but it also works quite well on these sanding blocks, especially when doing heavy work.

As with any sanding, it is important to remember that only the coarsest grit – the first one in the sequence – should do any required  shaping. (Though most or all of the shaping will have already been done with other tools.) All the subsequent grits simply remove the scratches made by the previous grit until the surface is smoothed to your satisfaction.

In time, one accumulates a small collection of these curved sanding blocks, so some will coincidentally be just right for future projects. This is simple, effective woodworking – one more tool for working with curves.