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3 October 2014

Anatomy of a Block Plane

Block Planes, disassembled, explained, and reassembled, ready to make shavings

Let my demystify the anatomy of these popular 'apron' planes.

The video shows all the main points:

Record No.60½

The 60½ is a low-angle block plane, where the bed angle is 12 degrees. It has an adjustable mouth, and blade advancement mechanism. It has the main features of all metal block planes:

  • Palm sized (the No.60½ is 6½" (165.1mm) in length, 2-1/8" (53.97mm) wide)
  • Bevel Up - that is, the iron is used with it's bevel upper most
  • Fixed bed - the iron rests on a slope milled directly on body casting (standard bed angle of around 21 degrees, low-angle around 12 degrees)
  • Lever cap shaped to fit the palm comfortably, and tightened with either a lever, knurled knob, or spin wheel.
And the additional features that can be found on some models:
  • Advancement mechanism for the iron - usually engaging in a slot on the blade iron

  • Adjustable mouth - locked by front knob, and moved with the lever below the knob

Some block planes also have:
  • Mechanical means of lateral adjustment for the iron
  • Skewed blade
  • Fence
Main considerations for good performance:
  • A flat sole
    Prepared, with an iron installed and set at working tension, by lapping on a surface plate, hand scraping, or sanding on top of a flat reference surface.
    If the plane has an adjustable mouth, then it is essential that the contact tracks are parallel to the sole. Otherwise adjusting the mouth will throw the sole out of flat.
  • Well prepared blade
    Since the blade is installed bevel up, the bevel angle will directly affect the angle of attack during a cut, and therefore you can tailor the angle to suit the work in hand. In practice, you would have two or three blades ground at different angles, and install the appropriate one for each task.
  • Squared sides
    Prepared in the same way as the sole, but using an engineer's try square and uneven pressure to correct inaccuracies.
  • All sharp corners eased - to prevent injury to either work or user
In Use:
Although the block plane is a comfortable grip in one hand, best results are usually achieved by using both. In many instances, skewing the plane will yeild a smoother cut, as this lowers the effective angle of attack and reduces the width of cut. Wrapping the thumb and/or fingers under the plane can provide a 'fence' or stabaliser to lock in an angle when making chamfers. If chamfering the end grain of a component, skew the plane to avoid the mouth droping over the edge and the iron digging in deep.