TO REAM

To ream is to enlarge, regularize or bring an existing hole to size using a Reamer, a conical or cylindrical cutting tool with longitudinal edges. In watchmaking, the operation is delicate because it involves very small drillings: holes for jewels, pins, Screws or pivots in a Main plate, a Bridge or a component of External parts (case, dial, hands). Unlike drilling, which creates the hole, reaming starts from a pre-hole to refine its diameter, correct a slight roundness defect or To trim (deburr) the wall, removing only a thin layer of material. The reamer is operated by hand (in a handle or tool holder) or by machine, at low speed, to avoid tearing the material or making the hole oval. The desired result is a reaming clean, cylindrical and to the correct size, able to receive without excessive play or undue tightness the part intended to fit into it. The operation is one of the fitting tasks specific to Établissage.