Smoothing Plane: The No. 4 Complete Guide

Last reviewed on 2026-04-24

The smoothing plane is the last plane to touch a surface before finish goes on. Where a jack plane flattens and a jointer trues, the smoother's job is narrower and more demanding: to leave a surface clean enough that sanding is either unnecessary or reduced to a single fine grit. The Stanley No. 4, at 9 inches long with a 2-inch iron, is the most common smoother ever made and the default choice for most work.

What Makes It a Smoother

Smoothing planes are short — 7 to 10 inches — and that is deliberate. A short sole follows the existing surface instead of spanning it, which is exactly the right behavior at this stage: the board has already been flattened, and the smoother's task is to refine every square inch without reintroducing a crown or a dip. Combined with a tight mouth and a chipbreaker set close to the edge, the short sole makes it possible to take shavings measured in thousandths of an inch.

The common smoothing sizes in the Stanley catalog are:

Sharpening and Setup for Smoothing

Smoothing is the most demanding configuration a bench plane can be asked to produce. The iron needs to be genuinely sharp — shave-arm-hair sharp — with a straight edge that is relieved at the corners. Procedure:

  1. Flatten the back of the iron to a mirror finish for at least the first half inch.
  2. Grind the primary bevel at 25°, then hone a secondary bevel at 30° on a fine stone.
  3. Relieve the corners of the iron with a few extra strokes on each corner of the hone, so they don't leave track lines.
  4. Set the chipbreaker within 0.5 mm of the edge. On difficult figured wood, as close as 0.1–0.2 mm.
  5. Close the mouth by advancing the frog until the opening is roughly the thickness of a business card.
  6. Advance the iron until it just begins to take a shaving, then back off a hair. The shaving should be continuous, thin enough to read through, and leave a surface that reflects light evenly.

Working Technique

On straight grain, plane downhill with the fibers — shavings come off cleanly and the surface feels polished under the hand. On figured or reversing grain, no direction is safe; here the close-set chipbreaker does the work. Take overlapping passes across the full width, moving slightly sideways between passes so the smoother reads the whole surface rather than leaving tracks.

Pressure shifts through the stroke: more on the front knob as you start the cut, balanced in the middle, more on the rear tote as you finish. This keeps the plane from rocking and producing dips at the ends.

When Smoothing Beats Sanding

A well-tuned smoother leaves a surface that reflects light like burnished metal, with pores intact and fibers cut rather than abraded. Sanding to 220 grit tears fibers and embeds grit into the surface; a smoother leaves none of that. Many furniture makers finish directly off the plane for this reason — oil, wax, or shellac goes on a planed surface without any sanding at all. Sanding is still useful for end grain, for blending a repaired area, or where the grain is too wild for any plane to handle cleanly.

Buying a Smoothing Plane

Vintage Stanley No. 4s from the 1940s–1960s are the standard recommendation. Plentiful on the used market, well-made castings, affordable to acquire and restore. Post-1970 Stanleys are hit-and-miss; inspect carefully. Modern premium smoothers from Lie-Nielsen, Veritas, and Clifton start well above the cost of a restored vintage plane, but they arrive with thick irons, heavy castings, and precise machining and require no tuning.

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