Defining the ubiquitous block plane

What is the one thing that differentiates the block plane from other planes? Apart from its short length, there is one distinguishing characteristic – they usually have bevel-up blades. So what other characteristics make up a block plane?

1. The blade is bevel up.
This means that the bevel on the planes iron faces up. For the block plane, the angle of the cutting edge to the wood equals the bedding angle plus the blades bevel angle. This concept was also used on planes like the Stanley No.62 and Sargent No.514, and has been adapted for a whole line of “low-angle” and “bevel-up” bench planes fro contemporary tool makers Veritas and Lie Nielsen.

2. There is no cap iron.
The cap iron has two purposes – it supports the cutting iron, making it more rigid, and it helps break and curl the shavings being produced. Due to the low bedding angle, bevel-up blades, and its use on end-grain, there is less need for a cap iron. Ideally the blade in a block plane should be quite thick, to reduce vibration and chatter.

3. The bedding angle of the blade is between 12º and 20°.
This allows for the pitch of the blade to be changed by changing the blade itself. In many older block planes, the bevel angle of the blade is a standard 25°, which could be modified by means of a secondary bevel. Manufacturers such as Veritas also provide blades with bevel angles of 38° and 50° cutting edges. With a 12° bedding angle, this provides pitches of 37°, 50°, and 62°. The 20° bedding angle, provides pitches of 45°, 58°, and 70° respectively. A standard cutting angle of 45° or greater is ideal for using a block plane for long grain, where the fibre will be cut rather than lifted or torn. It requires more effort to push through the wood, but it breaks the chip quite aggressively for a clean cut. Conversely, a low cutting angle reduces friction, and requires less energy to use on end grain, where it slices through the vertical fibres. A block plane with a low cutting angle has problems with high-figured, or difficult grain, because the low angle achieves a knife-like cut, that can lift and tear.

4. The multitude of blade adjustment mechanisms.
On a good block plane it is possible to adjust the depth of cut, lateral adjustment, and size of the mouth. Some of these evolved out of need – a 12° bedding angle required a screw-like blade depth adjustment mechanism due to lack of space.

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The story behind these characteristics?
So, block planes were originally designed for making and re-finishing butchers blocks. Butchers blocks are often made of hardwood such as maple, with the end-grain oriented upwards. Working with these blocks required a lower pitch plane, as a smoothing plane had a blade pitch which would cause the fibre to split. Lowering the bedding angle of the plane resulted in a need for a more acute edge on the blade. It was impossible to lower the bedding angle to a workable pitch without the resulting angle on the blade being far too weak. Subsequently the only feasible way of lowering the bedding angle was to reverse the blade, resulting in a bevel-up blade. This also meant that there was no real need for a cap iron on a block plane.

Therefore the necessity for a low bedding angle induced the need for the blade to be bevel-up, which in turn meant that the cap-iron was superfluous.

Here are some of the general characteristics of a block plane:

plane body: cast iron, pressed steel, aluminum
throat: adjustable or non-adjustable
length: 3½, 5½, 6, 6½, 7
blade width: 1", 1-3/8", 1-5/8"
bedding angle: 12-20º
blade bevel: 25º (standard), up
trimmings: Japanned or nickel plated
front knob: hardwood or metal (brass)
levercap: cam, knuckle, screw-cap
adjustments: throat (mouth size), blade-depth, blade-lateral

 

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