|Hints for Resharpening
A Sharp, Correctly ground Drill, will produce more holes, with greater accuracy and finish, more quickly and therefore at low cost.
As point grinding is one of the most major factor in achieving economical and satisfying results, the use of a point strongly recommended. without their use, even the most skilled operator will have difficulty in maintaining the correct Drill Point consistently.
The following three main factor require careful attention when Resharpening.
Lip Clearance : Standard ITM Drills, supplied for general use, incorporate 80 to 120 clearance. The resultant chisel edge angle, as illustrated, is approximately 130 to the cutting edge. If the Lip clearance is excessive, the strength of the Cutters edge is reduced and may result in fracture on the cutting edge. Modification of the Lip Clearance angle is beneficial when Cutters certain materials and recommendations are shown in the table.
- Lip Clearance
- Lips(cutting Edges)
- Point Thinning.
Lips (Cutting Edges): Standard ITM Drills have an included Point angle of 118 degrees. This has been found most suitable for a general propose and should be maintained, ensuring at the same time that the angle is equal on both sides of the center line, so that the length of the lips will also be the same.
If the angles are unequal, the lips will be different lengths. All the work then be done by one cutting edge only resulting in oversize holes been produced and a shorter life for the Drill.
Point Thinning : All ITM Drills are made with a web which increases in thickness towards the shank. When Shortened by repeated grinding, therefore, it is necessary to thin the web at the point in order to maintain the original point thickness.
An equal amount should be ground from each web to ensure it been kept central. The Web thickness at the point can, as a general rule, be taken as been approximately one-eight of the Drill Diameter.