midfeather

A midfeather is a vertical or near-vertical timber support placed at or near the centerline of a tunnel to carry weight from the roof above. In hard-rock mining, where tunnels are driven through stone, the weight of unsupported rock above the working section creates immediate collapse risk. The midfeather, typically a squared timber pole 6 to 12 inches in diameter, stands on the tunnel floor and bears directly against the roof, transferring load downward through its length and then into the ground.

The term appears most often in older mining records from the 19th and early 20th centuries, particularly in metal mining in Britain and North America. A midfeather worked alongside side props and lagging (timber boards) to create a temporary or semi-permanent roof support system. Where a tunnel cross-section was wide, miners would place one midfeather down the centerline and additional props along the sides. The arrangement allowed work to proceed in the heading while the tunnel was being lined with stone or brick.

Why "midfeather"

The origin of the name is obscure but likely reflects the timber's position in the middle of the span and its function as a feather or wedge holding up weight, much as a feather might steady something balanced on edge. Regional variants included centre prop, crown post, and simply middle post. The term is now rarely used; modern tunneling relies on rockbolts, shotcrete, and steel sets rather than timber temporary support.

A midfeather was set under compression from above and had to resist both vertical crushing and lateral movement as surrounding rock shifted. Timber props would often crack, split, or fail if the rock load increased unexpectedly or if water-logged timber lost strength. Miners watched for signs of crushing or bending and replaced faulty props regularly. In wet headings, the life of a timber prop could be as short as a few weeks.

The work of placing and managing midfeathers fell to the timbering crew, distinct from the face miners who broke rock. This specialization reflected the critical safety role these props played; poor timbering was a direct cause of falls and entrapments. The expense and labor of timber support was a significant part of tunneling cost, driving early experiments with steel props and, later, the shift toward rock bolting and reinforced shotcrete.