Find the X Y coordinates of holes on a pitch circle from the PCD, number of holes and start angle, with drilling blocks as X Y or polar coordinates (G16), and open them in the backplot.

Drilling blocks

How it is calculated

Hole k (counting from 0) is at angle θk from the +X axis, counterclockwise positive. With the centre at (Xc, Yc) and the pitch circle diameter PCD,

\theta_k = \theta_0 + k\,\Delta\theta \qquad X_k = X_c + \tfrac{PCD}{2}\cos\theta_k \qquad Y_k = Y_c + \tfrac{PCD}{2}\sin\theta_k

For holes spaced equally round the circle Δθ = 360° ÷ the number of holes; clockwise makes Δθ negative. The straight distance between neighbouring holes is $PCD \cdot \sin(\Delta\theta / 2)$ , which you can measure across two holes with a caliper (add one hole diameter when measuring outside to outside, or subtract one when measuring inside to inside).

Drawings often give the first hole as an angle from the vertical or from a datum. Convert it to an angle from +X first: a hole at 12 o'clock is 90°, and a hole 15° to the right of 12 o'clock is 75°.

Coordinates are rounded to 0.001 mm. The X Y form runs on any control. The G16 form writes the radius as X and the angle as Y, as polar coordinates do. G16 measures the radius from the work zero, so a circle away from the zero is first moved there with G52, and both are cancelled when the holes are done. G16 is a control option; check the machine has it before use. Both forms retract to the R level between holes (G99) and to the initial level after the last (G98).

The backplot button opens the blocks, in the form chosen, in a short program with a header and a safe height, so they can be checked against the drawing.

To check one hole by hand, Rec(r, θ) on the scientific calculator gives its X and Y from the radius and angle, and Pol(x, y) does the reverse for a hole measured on the machine.

Bolt circle (PCD) holes

Drilling blocks

How it is calculated