Cobalt drill bits can be an absolute lifesaver for some jobs, bit an expensive boondoggle for others. In this article we’ll explore why you should be using cobalt drill bits for the right jobs, and when to use a cheaper alternative.
What are cobalt drill bits, anyway?
Cobalt drill bits are a subset of HSS (high speed steel) drill bits. They are made of steel which has a substantial percentage of the element cobalt in it. Unlike many other kinds of HSS drill bits, cobalt drills do not use a special coating the strength and heat resistance comes form the steel of the bit itself.
25pc Cobalt Drill Bit Set | Split Point | Rustung
What is the Difference between M35 Cobalt Drill Bits and M42 Cobalt Drill Bits?
There are many types of cobalt drill bits, but the most common are M42 cobalt drill bits (composed of 8% cobalt) and M35 cobalt drill bits (5% cobalt). The higher the percentage of cobalt in the steel of a drill but, the harder the cobalt drill bit will be. As cobalt drill bits get harder, though, they become more brittle as well.
An M35 cobalt drill bit at 5% cobalt will work for most common metal drilling purposes. It is stronger than most other HSS drill bits already, but it is not fantastically brittle. It can be used in a hand drill with few problems, for example.
By comparison, M42 (8% cobalt) drill bits will cut the hardest of metals – stainless steel and titanium for example – with relative ease. They are quite brittle though, especially when exposed to twisting or sideways stress. For that reason, M42 cobalt drill bits are usually reserved for pedestal drills.
When Should I Use Cobalt Drill Bits?
First off, only ever use cobalt drill bits on metals. They are specifically designed for this. Not only do cobalt drill bits have a very high melting temperature, they are incredibly hard. Both characteristics come together to create a drill but that can get fantastically hot while drilling into a large piece of hardened steel and not melt, shatter or oxidise away (yes, steel drill bits can burn).
Can a cobalt drill bit cut into wood? Yes, certainly. Like a hot knife through butter. But that would be an incredible amount of overkill. Any drill bit, no matter how cheap, can drill into most kinds of wood. Use something cheap, and less brittle. You’ll save a lot of money in the long run. The same goes for plastics and even harder materials like concrete or stone. Cobalt drill bits would be expensive overkill.
Can I re-sharpen dulled cobalt drill bits?
Yes, if you are very careful. Most cobalt drill bits will work in a drill bit sharpener. You may even be able to sharpen one by hand with a grinding disc… but be very careful. They are brittle, remember.