2 Roughing Plane
This plane is probably the oldest type of plane. The single iron (roughing) plane is used for smoothing (finishing) of a surface previously worked with a scrub plane (or with a hatchet or an adze) in the coarse. It has a single iron, the cutting edge is straight, only the corners are slightly rounded, because sharp-edged corners would leave traces on the wood surface. Sometimes the cutting angle was slightly cambered, the the plane was called a coarse roughing plane. The cutting angle is about 45 degrees, the length is about 220 - 300 mm. With a very sharp iron, a flawlessly smooth surface can be created with this tool, provided that the wood's grain is straight. And that was his job for at least 2,000 years.
In the first half of the 18th century the double iron with cap iron was developed. A plane with double iron leaves fewer tear outs on the surface, it can remove finer shavings than a plane with single iron, especially on knotty or flat sawn wood it is clearly superior. The craftsmen recognized these advantages very quickly, the double iron spread throughout Europe within a few decades.
One might think that the single iron (roughing) plane had lost its meaning and would have disappeared. In England (and also America) this has largely happened, but not in continental Europe. Here, the single iron plane was still used for all tasks where the surface quality was not decisive. For example, for the preparation of stock or dimension individual parts. Because the single iron had one advantage over a double iron: a single iron is sharpened faster and easier adjusted correctly again than a double iron. The roughing plane with double iron simply became a new type of plane: the double (smoothing) plane.
The roughing plane was number 2 right from the start. In addition, everything that has already been said about the scrub plane and the catalog numbers also applies to the roughing plane.
Catalog images of roughing planes by Weiss & Sohn
Model development based on the iron widths
Basically, the blade of the roughing plane is wider than that of the scrub plane. Until around 1870, however, there was an overlap (at least at Weiss & Sohn): Both types of planes had models with 33 mm wide blades, which differed only in the bevel of the blade.
The following technical drawing is a processed scan of an original drawing by Johann Weiss & Sohn from 1949. The original is unfortunately a bit pale and not made on white paper, so the quality of the scan is not particularly good, but at least the dimensions are quite legible. (Click PDF icon for free download)