A knurling tool is used with a lathe to emboss metal pipes and shafts with raised grooves that act as hand grips or better traction. Knurls come in different sizes and patterns, with diamond being the most common for grips. The lathe must hold the metal straight, and the machinist should use machine oil. Knurling is best for softer metals, and apprentices often set up the lathe for repetitive tasks.
A knurling tool is used in conjunction with a lathe to emboss the ends of metal pipes and shafts. The raised grooves can act as hand grips for the user or better traction for rubber or plastic covers. The knurl itself consists of multiple rotating cutters which are held against the metal shaft as it spins on the lathe at a relatively low speed (500 rpm on average). Turning is a method by which cylindrical pieces of metal or wood are turned into position by a variable speed electric motor. As the piece spins, various cutting tools can be placed against it to remove material or cut shapes. A knurling tool falls somewhere between an engraver and an embosser.
There are generally three shapes generated by most knurling tools: straight lines, diagonal lines, and a diamond pattern. Knurling tools come in a variety of sizes and cutting patterns, depending on the purpose of the workpiece. The diamond pattern is most common with grips because it creates maximum traction between the user’s hand and the shaft. Diagonal and straight knurls are generally used to give extra pull to an outside handle or other connective piece.
To create a knurling, the lathe must hold the piece of metal perfectly straight, a condition machinists call true. When the lathe starts turning, a special holder for the knurl is attached to the worktable. The knurl itself is clamped into the holder and carefully directed towards the workpiece with a small crank. Since knurling is an abrasive process, the machinist should use a generous amount of machine oil on the turning shaft.
A knurl rarely leaves a complete imprint the first time it is pressed against the shaft. Machinists usually make several passes with the knurling tool, allowing individual cutters to make small bites into the metal.
A knurling tool is best suited for softer metals such as aluminum or standard grade steel. Hard metals such as titanium would most likely mar the tool before any embossing can take place. In commercial tool and die shops, it is not uncommon to see apprentices and workers setting up the knurling lathe. Knurling arbor for screwdrivers and other hand tools can be very repetitive and time consuming, making it an ideal task for workers with little seniority. But successfully performing a knurling operation can lead to more advanced lathe work with more interesting cutting techniques.
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