Pilot Hole - First drill the hole in wood or plastic to locate or guide a screw and expand the size according to the tap. Without a pilot hole, the screw may get too tight and either broke the material or snap the screw completely.
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Countersink - Install the chamfer drill on the bench drill. If you need to chamfer 16mm hole, you can choose 15-20mm chamfering device. Add water or cutting oil to cool when chamfering.
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Clearance Hole - Finally screw on until flush with the horizontal. This bits should use the bench drill , it is easy to shake and it will affect the chamfering effect if you use the hand drill.
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