Machining condition-determining device and cutting tool selection apparatus

A cutting tool selecting apparatus selecting a cutting tool to be used in a machine tool performing a machining with a plurality of cutting tools, comprising:

• a setter setting a cutting speed of the cutting tool;
• a first storage storing therein a maximum output value of a drive motor rotating a shaft holding the cutting tool and a number of revolutions of the drive motor corresponding to the maximum output value;
• a number-of-revolutions determiner obtaining a steady-state value of the maximum output value of the drive motor stored in the first storage and determining a number of revolutions of the drive motor corresponding to the obtained steady-state value of the maximum output value;
• a tool-diameter determiner calculating a tool diameter of the cutting tool based on the cutting speed set by the setter and the number of revolutions of the drive motor determined by the number-of-revolutions determiner;
• a second storage having previously stored therein a tool diameter of each of the plurality of cutting tools;
• and
• a tool selector comparing the tool diameter calculated by the tool-diameter determiner with the tool diameters stored in the second storage, in a case where any of the tool diameters stored in the second storage is coincident with the tool diameter calculated by the tool-diameter determiner, the tool selector selecting the cutting tool having the coincident tool diameter, and in a case where none of the tool diameters stored in the second storage is coincident with the tool diameter calculated by the tool-diameter determiner, the tool selector selecting the cutting tool having a tool diameter closest to the tool diameter calculated by the tool-diameter determiner.