Deep HolesDeep Holes in Drilling
Deep, small diameter holes should be avoided as they are difficult to machine. Small diameter drills tend to wander and are prone to breaking. Chip removal also becomes difficult while drilling deep holes. Therefore it is recommended that the hole diameter to depth ratio should be less than 3.
Entry/Exit Surface for HolesEntry Exit Surface for Holes
Drills should enter and exit surfaces that are perpendicular to the centerline of the hole. If the drill tip contacts the non-planer surface, then tip will wander as its axis is not perpendicular. Also exit burrs will be uneven around the circumference of the exit hole, which can make burr removal difficult.
Holes with Flat BottomHoles with Flat Bottoms in Drilling Operation
Blind holes should not have a flat bottom. Flat bottomed holes cause problems with subsequent operations (for example: reaming). A standard twist drill creates a hole with a conical bottom.
Holes Intersecting CavitiesHoles Intersecting Cavities in drilling
Holes should not intersect a cavity. If an intersection is unavoidable, at a minimum, the center-line of the hole should be outside the cavity. During machining, the drill follows the path of least resistance when it intersects a cavity. There is a good chance that the drill will wander when it re-enters the material.
Partial HolesPartial Holes design guideline
Avoid partial holes as there are high chances that drill will wander if a large portion of the hole is outside the material. The problem can become even more severe if the axis of hole is on or near the edge of the material. If partial hole is unavoidable, then ensure that at least 75% of hole area should be within the material.
Standard Hole Sizes in drilling
Specify standard hole sizes as they can be created using a standard drill. Unusual hole sizes are not recommended as they require custom tools and increase the cost of manufacturing through purchasing and inventory. Reducing variations in holes size will further reduce assembly accessories like fasteners, pin, rivets, etc