CROBALT has been manufactured in the USA for many years and is a cast alloy made from 50% Cobalt, with the other 50% being Tungsten, Chromium, their carbides and some other additives. It is available in a multitude of different sizes and shapes, including square, round, rectangular, and several shapes of parting tool blades to suit different manufacturers’ holders.
At present we only have the 1/4" square available on the Eccentric Engineering website but we are testing out the Crobalt bevel type parting blade for possible use in the BTF parting tool.

Advantages of Crobalt

It has many advantages over brazed and indexable carbide tools. Carbide tools  work best on large rigid lathes with plenty of horsepower, they tend to bulldoze the material off. HSS and cast alloy can take a sharper cutting edge as they are less brittle, this means they can take a bigger cut with less stress on the smaller type lathes.

One piece of Crobalt will outlast an indexable tip many times over. Cast Alloy is ideally suited for turning tougher materials such as various grades of stainless, cast iron, high carbon steels, and high tensile steels, but unlike carbide where you would need another grade of tip it is also fine on non ferrous materials such as titanium,  aluminium, and also brass and bronze if a small flat is honed on the top of the point of the tool bit.
Less pressure on the cutting tip than carbide due to the increased clearance angles, means less deflection on slender work pieces and less stress on the lathe under heavy cutting.

Both HSS and Crobalt are better than Carbide when taking very light finishing cuts. Because of the slightly blunt edge on most carbide tips, the tool tends to rub on the surface rather than cut cleanly.

Compared with HSS, higher operating speeds and feeds are possible.

Shortcomings of Cast Alloy cutting tools

Crobalt and other cast alloys are more prone to thermal shock than HSS. After grinding Crobalt it should be left to air cool, don't quench the tool bit in water as this can cause microscopic cracks in the cutting edge. When turning you should either flood the cutting edge with coolant or use none at all. Don't drip coolant onto the workpiece or use a brush as this too may cause cracking.
All cast alloys contain large amounts of cobalt which can cause health problems if large quantites are inhaled. When grinding the angle on a new tool bit it is advisable to wear a dust mask or use adequate ventilation.

For turning very hard materials such as heat treated steel, Tungsten Carbide is the tool bit of choice. Crobalt is easier to chip than HSS when used in thin sections, so for threadcutting with a Diamond Tool Holder it is better to use CoHSS or HSS bits.


Sharpening Crobalt Tool Bits

Crobalt is best sharpened with a normal Aluminium Oxide wheel, it does not need a green silicon carbide grinding wheel. After grinding, allow the tool bit to air cool. Do not quench in water as this can cause cracking on the cutting edge.

For increased tool life and better surface finish on both Crobalt and HSS it is recommended to put a small radius down the front corner, using an oilstone or diamond impregnated sharpener.

For more information see Eccentric Engineering website.


By Gary Sneesby