What is a smoothing plane?
What it's used for
The smoothing plane is typically the last plane used on the wood's surface. When used properly, the finish it gives is far superior to that made by sandpaper, which can scratch and dull the fibre of the wood.
Standard and low-angle
There are standard and low angle metal versions of the smoothing plane, with irons pitched at 45 degrees bevel down and 12 degrees bevel up respectively.
Wooden smoothers usually have their irons pitched at 45 degrees.
The length of a smoothing plane is between 140mm (5½”) and 254mm (10”).
Smoothing plane irons can be 32mm (1¼"), 41mm (1 5/8"), 44mm (1¾") or 50mm (2") wide.
Choice of size depends on how big your workpieces are likely to be – small if you only make smallish models, bigger if you make larger items. If the size of your workpieces varies, it's best to go for a larger plane that fits most circumstances.
Shape of the cutting edge
The usual shape for a smoothing plane's cutting edge is crowned (slightly cambered). With the middle of the cutting edge projecting slightly through the mouth but the edges kept slightly retracted, the smoothing plane iron has no sharp edges to leave unsightly tracks in the wood's surface.
This does result in very slight curves in the wood, but with the overlapping of cuts, they are not noticeable.
Stanley/Bailey model numbers for metal smoothing plane designs which are still sold today by Stanley and other manufacturers are the No. 1 (the smallest) and No. 4½ (the biggest) with the No. 2, No. 3 and No. 4 in between.