G70 Bolt Hole Circle – CNC Mill Programming

Want to drill or tap in a circle, but you only know the radius of the circle and number of the holes.

G70 Bolt Hole Circle

G70 Bolt Hole Circle

Then don’t worry G70 Bolt Hole Circle will do all the mathematics itself for you.

The G70 Bolt Hole Circle cycle works with G73, G74, G76, G77 and G81 – G89.

G70 belongs to Group zero and thus is non-modal.

G70 Bolt Hole Circle Format

G70 I J L

I = Radius of the bolt hole circle (+CCW / – CW).
J = Starting angle of first hole ( 0 to 360° CCW from horizontal at the 3 o’clock position).
L = Number of evenly spaced holes around bolt hole circle.

For a G70 to work correctly, a canned cycle must be active so that at each position a drill or tap function is performed.
The tool must be positioned at the center of the circle either in a previous block or in the G70 block.

Skip Drilling at Center of Circle

On the drill or tap canned cycle, an L0 will not perform the cycle at the start location and an L1 will.
As the below cnc program code will do 6 (bolt hole circle)BHC see N6 G70 L6,
but will skip the hole in the center see N5 G81 L0

N5 G81 G99 Z-0.45 R0.1 F8. L0
N6 G70 I1.25 J10. L6