| 摘要 |
Rigid foam material, for example, expanded polystyrene foam, is drilled using a bit that forms an annular slit in the foam material and compresses the block temporarily around the slit. This frees the core for ready removal. The drill bit has a cutting ring at the leading end with an inside cutting edge and an annular bevel leading from the cutting edge to the outside surface of the cutting ring. The cutting ring is mounted on the leading end of a tube with an inside diameter greater than the inside diameter of the cutting ring in order to clear the core and an outside diameter less than the outside diameter of the cutting ring in order to clear the surrounding foam material. |
