- Ground Instruments
- In a sense all instruments are ground. When a cylindrical wire is ground into an obelisk shape (think Washington Monument) and then twisted the corners become helical spirals. But if a cylindrical wire is ground by applying a knife edged grind stone to the surface as the wire is both rotated and moved linearly, then a helical spiral is acheived without twisting the wire. It is this type of file that is usually referred to as "ground" rather than twisted.
- Examples of Ground Instruments
- Single Helix Type - If, using the explanation above, only one groove is ground then a single helical spiral is created. But envision what would result if after grinding the first groove, a second groove was started, half way between each groove originally cut. The file would have the same helical angle but a double flute. Generally double helical spiral instruments have to have a much steeper helical angle.
- Double Helix Type
- Dynatrak
- S-File
- Burns Unifile
- Trio Cut