Numerical controller of machine tool for drilling

A numerical controller that includes a feed shaft configured to move a rotary tool and a spindle configured to rotatably drive the rotary tool to perform drilling work for forming a hole in a workpiece using to rotary tool, the numerical controller comprising:

• a specified arbitrary area setting unit configured to set a specified arbitrary area including a contact position where the workpiece and the rotary tool come in contact with each other for the first time, above and below the contact position in the machining direction of the rotary tool;
• an updating unit configured to update a current position of the feed shaft configured to move the rotary tool;
• a speed changing unit configured to accelerate a feed speed of the feed shaft and a spindle rotation speed of the spindle in accordance with the current position of the rotary tool when the current position of the rotary tool is in the specified arbitrary area;
• an instructing unit configured to instruct:
• a hole bottom position being the position where drilling ends,
• a drilling instruction start position,
• a reference feed speed as a feed speed during drilling after an end position of the specified arbitrary area,
• a reference spindle rotation speed as a spindle rotation speed during drilling after the end position of the specified arbitrary area,
• a specified arbitrary area start position,
• a specified arbitrary area end position,
• a specified arbitrary feed speed ratio of the feed speed of the feed shaft from the drilling instruction start position to the specified arbitrary area start position with respect to the reference feed speed, and
• a specified arbitrary spindle rotation speed ratio of the spindle rotation speed of the spindle from the drilling instruction start position to the specified arbitrary area start position with respect to the reference spindle rotation speed;
• and
• a speed ratio calculating unit configured to, in the specified arbitrary area, calculate a feed speed ratio of the feed shaft of the rotary tool in the current position from the specified arbitrary feed speed ratio and calculate a spindle rotation speed ratio of the spindle from the specified arbitrary spindle rotation speed ratio, wherein
• the speed changing unit is further configured to calculate the feed speed and the spindle rotation speed in the current position from the feed speed ratio and the spindle rotation speed ratio, and wherein
• the reference feed speed is larger than the feed speed of the feed shaft from the drilling instruction start position to the specified arbitrary area start position, and the reference spindle rotation speed is larger than the spindle rotation speed of the spindle from the drilling instruction start position to the specified arbitrary area start position.