Glass drilling machine with cooling fluid back pressure control system

A machine for drilling a hole in a sheet of a relatively brittle planar material, said machine comprising:

• support means for positioning the sheet at a drilling location;
• first rotary drilling means for drilling a first hole into the sheet from one side of the sheet, the first hole extending partly through the thickness of the sheet;
• second rotary drilling means for drilling a second hole into the sheet from the other side of the sheet, the second hole being substantially aligned with the first hole and forming a complete hole with the first hole, the complete hole extending through the sheet;
• a first arm having a first end and a second end, said first rotary drilling means being secured to said first arm at a location adjacent said first end of said first arm;
• means mounting said first arm for movement relative to said support means in a plane extending generally transversely through the drilling location, whereby said first rotary drilling means can be moved toward and away from the drilling location;
• a second arm having a first end and a second end, said second rotary drilling means being secured to said arm at a location adjacent said first end of said second arm;
• means mounting said second arm for movement relative to said support means and to said first arm in a plane extending generally transversely through said drilling location, whereby said second rotary drilling means can be moved toward and away from the drilling location;
• first motion means comprising a first stepping motor for moving said first arm in said plane extending generally transversely through said drilling location toward and away from said drilling location;
• second motion means comprising a second stepping motor for moving said second arm in said plane extending generally transversely through said drilling location toward and away from said drilling location;
• first cooling fluid supply means for supplying cooling fluid to said first rotary drilling means during the drilling of the first hole;
• second cooling fluid supply means for supplying cooling fluid to said second rotary drilling means during the drilling of the second hole;
• and
• means responsive to cooling fluid back pressure in one of said first cooling fluid supply means and said second cooling fluid supply means for controlling the operation of one of said first stepping motor and said second stepping motor to increase the motion of the one of said first arm and said second arm which is operated by said one of said first stepping motor and said second stepping motor in the event that the first hole and the second hole do not form a complete hole, as evidenced by the failure of the cooling fluid back pressure to fall suddenly and appreciably at the end of a drilling cycle.