When drilling fixtures, the size and straightness of the hole is very important. The holes must be straight, without a taper and must be aligned to each other when the plates are stacked together.
Drill A: A center or spot drill bit is used to start the hole, ensuring straight holes for subsequent drilling.
Drills B and C: Carbide circuit board drill finishes the hole. An extended flute (Drill C) can be used for thicker plates. Peck drilling on smaller diameters will also help achieve straighter holes.
Drill D: Used for Engineering Change Orders (ECOs) or when plates cannot be taken apart. After steps 1 & 2, a conventional high speed steel drill bit (Drill D) is used to finish the hole. This drill type has along flute length to accommodate thicker plate(s).
Check Hole Sizes: Pin gauge tools, or Go-No/Go Gauges are used to test if the hole is sized correctly. The holes must be checked with both ends of the gauge to ensure the hole falls within the correct tolerance.
The NO/GO (RED) end of the gauge should not enter into the hole. If the NO/GO enters, the hole is oversized and the plate may need to be redrilled. The GO (GREEN) end of the gauge should go into the hole. If the GO end does not fit, the hole is undersized and must be resized.