How are engineer’s scribers made?

29th February 2020


How are engineer’s scribers made?


	Shop for Engineer’s Scribers


		Materials
		Scriber tip There are four types of material used to make engineers’ scribers tips: hardened steel, tool steel, tungsten carbide and steel with a diamond mounted tip. Scriber body The body of an engineer’s scriber can be made of several materials, the most common being steel or aluminium. Scribers with a steel body are nickel plated to help protect them from corrosion, while aluminium scriber bodies may be anodised, although this is done mainly for aesthetics. Some less expensive scribers have a plastic body made of PVC.

		Heat treatment
		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 in doing so will also make it more brittle.

		Tempering
		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 decreases the hardness and brittleness of the metal whilst increasing its toughness. By controlling the temperature the metal is heated to during tempering, it’s possible to alter the final balance between the hardness and toughness of the metal.

		Why is heat treating and tempering important to engineers’ scribers? Engineer’s scriber tips are heat treated to harden them. This hardening is needed to make the tip harder than the workpiece on which it is being used, enabling the tip to score a line. Scribers are lightly tempered to remove some of the brittleness imparted during the hardening process in order to prevent them breaking during use.

		Nickel plating
		Nickel plating is when a material (usually steel) is coated with a layer of nickel. This can be done for several reasons, such as corrosion protection, wear resistance and appearance.

		Electroplating Nickel plating is most commonly carried out by a process called electroplating, sometimes referred to as electrochemical plating. This is done by placing the workpiece in an electrolyte solution where it is then referred to as the cathode along with a nickel bar which is then referred to as the anode.

		A direct current is applied to the anode and the cathode, causing the anode to be positively charged and the cathode negatively charged. Nickel ions in the electrolyte are attracted to the cathode and deposited on the surface of the workpiece. These ions in the electrolyte are replaced by ions from the nickel anode, causing the nickel anode to dissolve in the electrolyte.

		Electroless plating Electroless plating does not require the use of electrical current. Instead, the workpiece is placed in an aqueous solution containing nickel ions, and a reducing agent (usually sodium hypophosphite) is added to the solution.

		The workpiece surface acts as a catalyst for the reaction, causing nickel ions in the solution to be deposited on the workpiece. The aqueous solution containing the nickel ions may be heated to around 90°C in order to speed up the reaction.

		What are the advantages and disadvantages of each plating process? Electroless plating produces a much more even and consistent layer of nickel than electroplating, particularly on recesses, holes and workpiece edges. Electroless plating does not require the workpiece to be connected to a current, so, many small workpieces can be plated easily at the same time, in the aqueous solution. Electroplating however, is often a cheaper way of plating material.

		Anodising
		Anodising is when a metal (usually aluminium or magnesium) is coated with a stable oxide layer via a process of electrolysis. Anodising can be used for corrosion protection but is more commonly used for decorative purposes.

		How is anodising carried out? Anodising is carried out by a process called electrolysis. This involves placing the workpiece in an acid electrolyte where it becomes the anode when it is connected to a positive terminal of a DC current supply. A metal cathode is placed into the acid electrolyte and connected to the negative terminal of the DC current supply.

		The flow of current causes hydrogen gas to be released at the negatively charged cathode, and oxygen on the positively charged anode workpiece, which then forms a layer of aluminium oxide on the workpiece. The aluminium oxide layer, however, is filled with small pores that could still allow corrosion. These pores are then filled with coloured dyes and corrosion inhibitors, which is what gives anodised parts their wide range of colours.

		Which material is the best?
		PVC-bodied scribers will not rust, but the tips of these scribers usually can’t be replaced so they are not suitable for anyone who intends to frequently use a scriber. Steel bodied scribers can rust if they are not nickel plated, which can cause problems with chucks, making them seize up, so changing the tips can become very difficult. Aluminium scribers have none of the drawbacks of steel or PVC but some people find them a bit light and prefer a scriber with more weight to it. This is of course purely a personal preference.