Making Plow and Skated Planes
by Bill Clark & Larry Williams
For years we weren't able to produce plow or other skated planes. It wasn't that the planes themselves presented overwhelming problems, it was properly producing the irons or blades. Others do make these planes but they fit them with old irons. You'll find at least one maker of plow planes on the Internet but those planes are intended more for collectors than users and each is provided with a single old iron.
A proper iron for a skated plane is tapered and has a skate registration groove on its back that matches the taper. That part is easy. The difficulty lies in that, at a couple inches from the cutting edge, the taper on the back of the iron transitions to a slow section of an elliptical arc. For the irons to be truly interchangeable, machining of the taper, registration groove and the arc have to be exactly the same from iron to iron.
It's important to understand that the skate becomes the plane bed in skated planes. The skate must properly support irons ranging in width from 1/8" to 5/8". The skate must be thin enough to allow clearance for a narrow 1/8 cut but also offer support for the wider irons and prevent racking and the accompanying chatter. The support for wider irons comes from mating angles or tapers that function much like the Morse or Jacobs tapers most woodworkers are familiar with. Fitting that taper for the full length of the bed of the skate with hand tools would represent great difficulty and the mated sections are necessary only near the back of the cutting edge. By curving the back of the blade to the necessary thick portion at the end of the blade, the plane maker reduced making these mating surfaces to an accomplishable and repeatable task.
An old iron on top and two new irons below. The two new irons have been through rough machining of the sneck (tab at the tang end), taper, arc and the registration groove.
We believe old irons were drop forged to their shape. To do this the old way would have required we put in a forge, drop hammer and have dies for the drop hammer custom made. The forge and drop hammer would have required a separate building to house them and represented a large investment which the planes simply couldn't return in a reasonable time.
Another solution would be CNC machining, requiring a computer controlled milling machine. A three axis CNC machine will easily handle the job but also represents a significant investment. If we were to invest in CNC, we have other tasks that could help off-set the investment but some would require five axis CNC machining. The return on a five axis CNC milling machine would be better than the drop forge approach but would still represent serious return on investment issues for our small company.
We had to figure out a different way to machine an accurately repeatable long taper that transitions to an elliptical curve. Through that curve, the registration groove must follow the original taper. We've now solved that problem with a relatively simple solution but we're sure not going to explain the process or the fixtures involved. This is one process we developed and won't give away.
Three completed and heat treated Clark & Williams plow irons with the bottom one showing the machined arc.
Shortly after figuring out our solution, the Cabinet Shop at Colonial Williamsburg requested a reproduction of an 18th Century British plow plane. This provided the impetus to build, rebuild, adjust and tune the required fixtures for the irons.
The Clark & Williams copy of an 18th Century British plow for Colonial Williamsburg.
When we build plane for Colonial Williamsburg, we're often copying old planes from their collections. These may or may not be planes we'd like to add to our offerings. This British plow, probably from the last half of the 18th Century, is a wonderful tool but we have some other features in mind for the plows we will normally make and sell. There's still development work to be done before we offer a plow plane. However, skated match planes are soon to come.
The old plane which was the source for this plane did have some interesting features. One was that it appeared, from the photographs we had, to have a depth stop placed so that the front arm wedge also served as a depth stop lock. We didn't have the plane to take apart and inspect so we just assumed that was the case. Our copy was made so that the depth stop was tightly friction fit but was also locked by the arm wedge.
The right side or skate side of the new Colonial Williamsburg plow plane with a 1/8" wide iron installed.
This plane's body is only 7" long. One of the striking things about this plane and probably plows in general is how many things pass through the body and how close together they are. There isn't a lot of wood structure left after making all the holes. There are a lot of things crammed into a pretty small package when it comes to plow planes, especially the compact early British plows.