Drilling Holes on Curved Surfaces

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Application of ADF carbide flat drill in automotive drive shaft production

Yunjie Gu | OSG Shanghai

The drilling of holes on curved surfaces on drive shaft components has always been a challenge for manufacturers and cutting tool makers. The crux of the problem is to achieve consistent long tool life while ensuring hole dimensional stability. This article evaluates some of the key factors that affect the stability of hole diameter and tool life and to provide an optimum tooling solution for tackling these challenges.

Reasons that may affect hole dimensional stability:

  1. If the tool swings upon contacting the work material, which would result in a larger hole diameter as illustrated in figure 1.
  2. If burrs occur at the hole exit when processing a through-hole on the curved surface of a shaft part, which would enlarge the hole diameter as depicted in figure 1.

Figure 1. Drilling of a through-hole on curved surface and enlargement of hole diameter.

Reasons that may affect the stability of tool life:

  1. If the tool swings upon contact with the work material, the cutting edge will easily collapse, and the chisel will wear faster, as depicted in figure 2.
  2. When processing through-holes on curved surfaces of shaft parts, the cutting edge corner of the tool is prone to chipping as illustrated in figure 2.

Figure 2. Chipping of the drill cutting edge.

In order to solve the above problems, the following two traditional processing methods are generally adopted:

  1. The use of an additional tool, usually an end mill, to countersink a plane, and then use a drill for the hole processing. However, this method is not a trouble-free solution. If the diameter of the counterbore is too large, the workpiece will be scrapped. On the other hand, if the diameter of the counterbore is too small, it is necessary to expand the hole during the drilling process, which will affect tool life since the edge of the drill will come in contact with the work material as illustrated in figure 3.
  2. A chamfering drill is used to make a start hole, followed by the use of a drill for the hole processing. However, this method also has flaws. Regardless of the chamfer angle of the chamfering tool, the drill’s cutting edge will contact the surface processed by the chamfering tool, which will reduce the life of the drill.

Figure 3. Chipping of the drill caused by an insufficient counterbore size.

To resolve these obstacles, OSG has developed the ADF carbide flat drill, a series that combines two operations in one for the drilling of inclined surfaces and counterboring applications.

ADF Carbide Flat Drill

The ADF was developed with an “all-purpose” concept for superior versatility, reliability and quality for flat-bottom holes. Machining a flat hole traditionally required the use of an end mill and a drill. For the processing of thin plate shaft parts, the ADF enables one-step drilling, thereby simplifying machining time and tool management. The drill’s balanced point form improves precision and minimizes the shifting of the hole position. Its sharp cutting edge results in low cutting force to minimize burrs even in thin plates. With a wide chip room geometry, trouble-free chip evacuation can be achieved. Furthermore, with the addition of OSG’s proprietary EgiAs coating, tool life can be prolonged with excellent heat and wear resistance.

The ADFO is the oil hole type offering from OSG’s ADF multi-purpose flat drill series for inclined surfaces and counterboring applications. With the additional oil hole configuration, the ADFO is designed to excel in stainless steel applications.

For the processing of deep holes, the ADF can play the role of a guide drill, completely replacing end mills and chamfering drills. As a pilot drill, OSG recommends using an ADF drill that is 0.03 mm larger than the subsequent drill. In this case, contact with the hole wall during processing with the subsequent drill is minimized, thus significantly improving the machining accuracy and stability.

Figure 4. Reduction of burrs when processing curved exit surface. The hole on the left is processed by the ADF flat drill, which exhibits minimal burrs; whereas the hole on the right is processed by a twist drill and exhibits burrs upon the exit of the hole.

From left, a hole processed by the ADF flat drill and a hole processed by a twist drill.

The ADF series is not only ideal for flat-bottom hole applications, it is also compatible with a wide range of hole shapes such as inclined surfaces, curved surfaces, counterboring, half-holes, thin plates, and more. In order to better accommodate manufacturers’ various processing needs, the ADF series is available in an abundant lineup including the ADF-2D, a general-purpose type that can be used for a wide range of machining; the ADFLS-2D, which can be used for machining with long overhang length; the ADFO-3D, which include oil holes that can be effectively used in stainless steel applications; and the ADF-NC and ADFO-NC, which are compatible with small automatic lathes.

For more information on the ADF carbide flat drill series