定義

• Bevel.  The angle of the slope between two surfaces, as the two sides of a medallic
  item, forming the edge; or the angle of the riser, the side of relief or lettering from the background to the top of relief. The bevel of relief, which allows a piece to be diestruck or cast in a mold, is also called draft or taper. Except for very low relief (stiacciato) all other relief must rise from its background (table). The angle of relief on the sides of this design is critical, and this is true for both devices as well as lettering. This angle must be such in the model that dies can be cut or engraved with this design, that pieces can be struck with the design, that the die can withdraw from the struck piece, and the struck piece can be ejected.
  For certain cast procedures – like electroform casting – it is also necessary for the pattern to have a minimum bevel so the cast can be easily removed from the mold.
  All this implies that there can be no undercuts and no nearly perpendicular relief. Obviously undercuts and too steep of relief should not be made in the model or pattern thus none will therefore exist in the galvano, hub, die or mold, or in the final struck or cast piece.
  For technical reasons this minimum angle requirement is different for different die making procedures. The minimum bevel or taper required for handcut dies is 5°; for galvano casting the minimum bevel is 10°; for dies cut on a die-engraving pantograph the minimum draft or taper permitted is 15°.
  The necessary reason for the higher minimum for the pantograph is that the stylus cannot trace steep relief and the cutting point cannot cut such relief (see pantograph). For this reason handcut dies, or dies made from puncheons, can have a steeper pitched relief – particularly for lettering – than dies made from oversize models that are reduced on a die-engraving pantograph. Such steep relief, however, does increase stress in diework and is often the cause of diebreaks.
  A bevel of only 21/2° – called a holding taper – is such that no piece can be
  released from the die, it freezes on the die once it is struck. Therefore no coining or striking dies can have a relief with less than 21/2° draft.  In effect any draft of less than 21/2° is the same as an undercut – impossible to reproduce in diestruck work. Perpendicular relief is called standing taper.  See undercut, undercutting.

  excerpted with permission from

  An Encyclopedia of Coin and Medal Technology

  For Artists, Makers, Collectors and Curators

  COMPILED AND WRITTEN BY D. WAYNE JOHNSON

  Roger W. Burdette, Editor

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