Parting off is one of the most demanding operations performed on a metal lathe. Unlike turning or facing, where the tool engages the workpiece across a relatively wide surface with the cut forces distributed, a parting tool engages on a very narrow width, directing all of the cutting force into a thin blade that must remain stable, straight, and vibration-free while cutting progressively deeper into a rotating workpiece until the piece separates cleanly from the stock. When the parting tool works correctly, it is fast, clean, and precise. When it does not, it digs in, chatters, breaks the blade, or leaves a rough parted face that requires secondary finishing.
The difference between good parting results and poor ones comes down almost entirely to the quality of the parting tool, the rigidity of its mounting, and the correct selection of tool width relative to the workpiece diameter. Buyohlic's parting and cut-off tools are selected specifically for reliable parting performance on the range of machines and materials common in US machine shops.
Parting Tool Types
HSS parting blades are the traditional choice for manual lathe parting operations. They are ground to a narrow width, typically 0.047 inch (1.2mm) to 0.094 inch (2.4mm), which minimizes the width of material removed and reduces the cutting force required. HSS blades can be resharpened when worn, which makes them economical for shops that part frequently. They are most effective at lower cutting speeds with appropriate feed rates and cutting oil.
Carbide insert parting tools use replaceable insert cartridges mounted in a rigid holder. They run at higher cutting speeds than HSS blades, produce better surface finish on harder materials, and the insert replacement is faster than regrinding an HSS blade. For CNC lathes and production turning centers, carbide insert parting systems are the standard. Buyohlic offers both T-style and A-style parting insert holders compatible with common insert sizes.
Parting tool holders are the mounting hardware that holds the parting blade or insert in the quick change tool post or turret. A good parting holder provides maximum rigidity with minimum overhang of the blade beyond the holder body. Excess blade overhang is the primary cause of parting tool chatter and breakage.
Parting Tool Selection Guide
- For small diameters under 1 inch: 1.5mm or 2mm HSS blade in a narrow holder with minimal overhang
- For medium diameters 1 to 3 inches: 3mm HSS or carbide insert system with good rigidity at the tool post
- For large diameters above 3 inches: Wider blade or reinforced carbide insert system with full support along the blade back
- For production CNC turning: Indexable carbide insert parting system with quick-change turret mounting
For complete lathe tooling, pair parting tools with turning tool holders and quick change tool posts. See our full lathe accessories collection.
Frequently Asked Questions - Parting Tools
Chatter in parting operations is almost always caused by one or more of these factors: too much blade overhang beyond the holder, the tool not set exactly at center height, insufficient spindle speed for the material, or not using cutting oil. Start by minimizing blade overhang to the minimum needed to reach the center of the workpiece. Ensure the cutting edge is exactly at center height. Apply cutting oil liberally throughout the cut. Increase or decrease spindle speed in 20 percent increments until the chatter frequency shifts away from a resonant point.
A starting point for parting mild steel is approximately one-third of the RPM you would use for turning the same diameter. For a 1-inch diameter mild steel workpiece, where you might turn at 600 RPM, start parting at around 200 RPM and increase gradually. Use cutting oil throughout the parting cut. Harder steels require even lower speeds. Aluminum and brass can be parted at higher speeds but still benefit from reduced RPM compared to turning.
Parting and cut-off refer to the same lathe operation: feeding a narrow tool into the workpiece radially until the piece separates from the stock. "Parting" is the more common term in precision machining contexts, while "cut-off" is used more in production turning. The tools and technique are identical regardless of which term is used.
Standard parting tools work on aluminum but perform best with a few adjustments. Aluminum's softness and tendency to form built-up edge means that a very sharp cutting edge, high spindle speed, and either no oil (for clean parts that cannot have oil contamination) or cutting oil applied constantly give the best results. Carbide insert parting tools with sharp polished inserts perform well on aluminum in production settings.
Narrow blades of 1.5mm to 2mm minimize material waste and reduce cutting force, but are more susceptible to lateral deflection on deep cuts. Wider blades of 3mm to 4mm are more stable on larger diameters. For most manual lathe use on common part sizes under 2 inches diameter, a 2mm to 3mm blade covers the majority of needs. Stock a narrow blade for small precise parts and a wider blade for larger diameter stock.
