HSS Straight Shank Twist Drill (20.0mmx1pc)

Cutting fluid is the part most often skipped and it matters most here. A cutting fluid does two jobs at once: it carries heat away from the cutting edge, and it lubricates the interface so less heat is generated in the first place. On a 20mm hole in steel, the cutting edges are travelling a long way per revolution and are in continuous contact, so heat builds fast. Without fluid the tip reaches the temperature at which high speed steel softens, and once that has happened the bit is finished and no amount of care afterwards recovers it. A drop every few seconds is enough; it does not need to be flooded.

Cobalt steel helps, because it holds its hardness to a higher temperature than plain high speed steel, but it comes with a trade worth knowing. The same alloying that makes it hold an edge makes it less forgiving. It chips rather than blunts if the bit is allowed to chatter, if the workpiece moves, or if the drill is rocked in the hole. So a cobalt bit wants firm clamping, a steady machine and no side pressure.

Pilot the hole first, run slow, feed firmly, keep it wet, and this bit will do a great deal of work. Rush it and it will be scrap in a minute.

For holes larger than this in steel, the answer is usually a step drill in thin material or a hole saw in plate rather than a bigger twist drill, both of which we stock.

Twenty millimetre holes serve large bolt clearance, structural and plant fixings and heavy fabrication.

M35 cobalt high speed steel; the spec's carbide tip and percussion drilling lines belong to a masonry product and do not apply.

Buyers are structural and general fabricators, engineering shops, plant and heavy vehicle maintenance and industrial dealers.

Ask on 94 77 111 8880 about cutting fluid and the alternatives for larger holes. We deliver island-wide.