(continued)

Wrong Drilling and Chamfering Correct

Drill into the solid fi rst, then chamfer.

Wrong Drilling on Inclined or Rounded Surfaces Correct

When drilling on inclined or curved surfaces, use a lower feed than the standard value. The reduction of feed required is dependent on the inclination angle of the workpiece surface and the drill type (see table). 100% feed >1°

chamfer tool

reduced feed

reduced feed (% of standard value) 100% feed inclination 5 x D

_ 3 x D Long <5 x D

no premachine premachine

100%80%premachine
80–50%80–50%premachine
65%50%premachine
50%premachinepremachine
[30%premachinepremachine

Premachining is usually done with an end mill operation.

Wrong Drilling on Turning Machines Hole Depths Greater than 3 x D

When drilling on turning machines, the drill must be on Hole depths that are deeper than three times the centre. The tolerance range of the centre position should drill diameter may require a speed reduction. A not exceed ±0.025mm. On bar-turning lathes, do not drill 15% lower speed is suggested. 0,025mm into centre stub or bur. Cut-off tools must be mounted precisely to eliminate centre stub or bur. Do not drill into pre-existing holes.