How are hacking knives manufactured?

29th February 2020

How are hacking knives manufactured?

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		The blade and tang of a hacking knife are forged from steel, before the handle is either moulded or riveted to the tang.

		What is forging?
		Forging is a manufacturing process that makes the finished product stronger than a cast or machined part, by altering the direction of crystals within the metal. Forging compresses the metal into the desired shape. This can be achieved by either drop forging using a hammer and mould (die) or roll-forging – passing the metal through two or more rotating rollers.

		What is heat treating and tempering?
		Heat treating and tempering are manufacturing processes used to alter the physical properties of metal and other materials. Heat treating involves heating the metal up to a very high temperature and then quenching (rapidly cooling) it. This increases the hardness of the metal, but will also make it more brittle.

		Tempering is performed after heat treating, and also involves heating the metal, but to a lower temperature than heat treating, then letting it cool slowly. Tempering will decrease the hardness and brittleness of the metal, and at the same time increase its toughness.

		Some hacking knives will only have the bevelled cutting edge of the blade heat treated. This gives them the increased hardness on their bevel but leaves the rest of the blade less brittle, and so less likely to break when struck with a hammer.

		How is the bevel put on the blade?
		The bevel of a hacking knife is ground onto it, to give the blade its cutting edge.

		Grinding is the process of using a bonded grinding wheel made of abrasive particles to remove material from a workpiece. The grinding wheel is a wheel that is spun at high speed, and the workpiece is passed across the side face or circumference surface.

		What is injection moulding?
		Injection moulding is the manufacturing method used to make plastic handles for hacking knives. It involves raw plastic beads being fed from a hopper into a heated barrel chamber. This melts the plastic, which is then pushed though the barrel by a screw mechanism and into the cavity within the mould.

		The molten plastic solidifies within the mould cavity, around the tang of the hacking knife. When the two halves of the mould are separated, the finished part is revealed. Injection moulding can be used to make a wide range of products such as plastic toys and mobile phone covers as it’s a very quick and cost-effective way of manufacturing high volume products.

		Hacking knife handles that have a rubberised grip undergo a second injection process, in which a TPR (thermoplastic rubber) is injected around the original plastic handle.

		What are rivets and how do they work?
		A rivet is a type of fastener like a screw or bolt that is used to hold two or more objects together. Unlike screws and bolts which can be undone then re-tightened, a rivet is intended to be a permanent fixing.

		How do rivets work? Rivets are placed through holes in the scales and tang of a hacking knife. Then the end of the rivet is squashed in a press, preventing the removal of the rivet from the hole. This clamps the scales to the tang of the hacking knife to form the handle.

		Some hacking knives with wooden handles have tapered holes through the scales of the handle, so the rivet heads sit flush or countersunk. This makes the handle more comfortable.