How to drill stainless steel
For many drilling stainless steel can be a daunting task. However it can be done easily and efficiently if you follow some simple steps which all amount to keeping the drilling surface temperature as low as possible.
1. Reduce drilling speed
Many people have a tendency to drill at as high a speed as possible assuming that the faster the drill bit is turning the quicker it will drill the hole. Unfortunately this is a big mistake, particularly when drilling stainless steel. Despite what many believe stainless steel is not the hardest of metals in its natural form. As pointed out by Chip Lawson in his piece ‘Know How: Drilling Stainless Steel’, stainless steel will ‘work harden’ fairly quickly when heated, and one sure way to increase heat is to drill fast. Once the stainless steel is work hardened it will become very difficult to drill.
There are many drill speed charts available quoting revolutions per minute, in reality not too many people will be able to relate to these figures. Our advice would be to drill at as slow a speed as your power drill will allow.
2. Reduce pressure
Another misconception is that maximum pressure will result in maximum results. Unfortunately excessive pressure will have the same effect as drilling at a high speed, it will cause unwanted heat build up. The best approach is to start off with a light pressure increasing slowly until you achieve nice spiral cuts coming from the cutting face. Once achieved do not exceed required pressure.
It may seem obvious to some that when two metal surfaces are are moving against each other under pressure that lubrication is necessary. However many will drill metal without any form of lubrication. Lubrication will reduce the friction and assist in controlling temperature build up. There are many types of drilling lubricant available including oils, sprays and pastes. Our advice would be to use one rather than not using any.
4. Take a break
Even with a slow speed, reduced pressure and good lubrication heat build up is inevitable when drilling metal. It is important therefore to stop drilling from time to time to allow the drill bit to cool down. We would recommend you do not drill for longer that 30 seconds without taking a break. As Allfasteners say in their article ‘Drilling Stainless Steel the Right Way’ drill the material on short bursts. The larger the drill bit size the faster the heat build up will be so this time should be reduced for larger drill bit sizes.
Which drill bits for stainless steel?
The best drill bits for drilling stainless steel according to most experts would be cobalt drill bits.
Cobalt drill bits are ideal for drilling harder metals and are perfect for use in either a hand drill or a drill press. 135º split point or self-catering drill bits are preferable as they begin to drill faster especially in harder metals and stainless steel (W.W. Grainger (2014)).
TTP HARD drills specialise in cobalt drill bits designed for drilling harder metals including stainless steel.
For further reading please see ‘Speeds and feeds for drilling and reaming stainless steels’ by the British Stainless Steel Association
C. Lawson (2017) Know How: Drilling Stainless Steel available at https://www.sailmagazine.com/diy/know-drilling-stainless-steel
W.W. Grainger (2014) : Which drill bit does the job? available at https://www.grainger.com/content/supplylink-greenfield-metalworking-drill-bit
Allfasteners.com.au : Drilling Stainless Steel the Right Way available at https://www.allfasteners.com.au/news-articles/drilling-stainless-steel-the-right-way