Milwaukee Metal Countersink, HSS-Co, 8.3 mm, 90°, 4932493970

Milwaukee 4932493970 Metal Countersink, HSS-Co, 8.3 mm, 90°

Milwaukee 4932493970 is a conical countersink for metal, 8.3 mm in diameter with a 90° included angle. The material is HSS-Co - cobalt high-speed steel. It has three flutes and a plain cylindrical shank.

What a countersink does

After drilling in metal the edge of the hole is left burred and sharp. The countersink takes that off in one pass. Its second and more common job is to cut a seat for a countersunk screw head, so the head sits flush with the surface. The 90° cone matches metric countersunk screws such as those to DIN 7991.

Why HSS-Co rather than plain HSS

Cobalt in the alloy raises the heat resistance of the cutting edge. Countersinking is a low-speed operation with a large contact area - exactly the conditions in which the tip gets hot. Plain HSS starts to lose hardness around 550 °C; HSS-Co holds on longer, which makes a real difference in stainless steel, cast iron and alloy steels. In soft material you barely notice the difference - the advantage shows up where it is needed.

Three flutes

The countersink has three cutting edges. That is the standard arrangement for a clear reason: with an odd number of edges the tool does not fall into resonance and does not leave the polygonal marks a two-edge tool produces. The result is a round, smooth seat.

Working with it properly

Countersinking is a low-speed, steady-pressure operation. The commonest mistake is the opposite - high speed, at which the countersink starts to chatter and leaves a wavy surface. In steel, work with cutting oil, which besides cooling stops swarf welding onto the cutting edge.

Technical specifications

Questions and Answers