HSS Straight Shank Twist Drill (14.0mmx1pc)

Drill a pilot hole first.

The reason is in the shape of the bit. The two cutting edges of a twist drill meet at the centre in a short flat called the chisel edge, and that flat does not cut. It extrudes and pushes the metal aside. On a 3mm bit the chisel edge is tiny and the effect is negligible. On a 14mm bit it is several millimetres wide, and it sits exactly where the bit is turning most slowly, which is the worst possible combination. So a large bit started in solid steel spends most of its effort not cutting at all, just pushing, which means enormous feed pressure, a great deal of heat, and a hole that fights you all the way.

Drill a smaller hole first, say five or six millimetres, and the chisel edge has nothing to push against because that material is already gone. The big bit then works only with its cutting lips, which are the parts designed to cut. The hole goes in with a fraction of the pressure, far less heat, and considerably more accuracy. Two operations take less time than one done badly, and the bit lasts several times as long.

This is standard practice in any machine shop and is almost unknown on site, which is why large bits get destroyed.

Fourteen millimetre holes in steel are for bolt clearance, bracket and base plate fixings, fabrication and structural work, and repairs to plant and machinery.

The spec's mention of a carbide tip and percussion drilling belongs to a masonry bit and does not apply. This is an M35 cobalt high speed steel twist drill, suited to steel, stainless and alloy steels.

Buyers are fabricators and welders, engineering shops, plant and machinery maintenance, and hardware dealers supplying industry.

Message 94 77 111 8880 and tell us the material and thickness. Island-wide delivery.