Carbon and alloy steels do not have one safe turning speed or feed. The workpiece grade and hardness, insert geometry, machine rigidity, cut continuity, coolant and required tool life all affect the result. This reference keeps its figures tied to Tungaloy’s SH725 turning-grade data for carbon and alloy steel (ISO P), rather than combining unlike tool recommendations into a misleading universal chart.

Turning Speeds and Feeds for Carbon and Alloy Steel

Read the recommendation as a range

The cutting-speed range in the table is 10–200 m/min, and the feed ranges vary with chipbreaker and the insert nose-radius class. The source also pairs each chipbreaker with a depth-of-cut band. These values belong to the SH725 grade and the listed Tungaloy turning application; they are not guaranteed settings for every steel or turning tool. Check the current tool catalog before selecting an insert or programming a production run.

The nose-radius column is particularly important. A larger radius can support a heavier feed in an appropriate setup, but it also changes cutting force, surface texture and the risk of chatter. The chart’s values are related to specific insert geometries and chipbreakers, so do not select the maximum feed solely from the radius. Compare the actual insert’s catalog number and chipbreaker to the recommendation first.

Set cutting speed and spindle speed correctly

Cutting speed describes how quickly the workpiece surface passes the cutting edge. The lathe control needs spindle speed, which changes with workpiece diameter. For metric units, spindle speed in revolutions per minute is n = 1000Vc/(πD), where Vc is cutting speed in m/min and D is the cutting diameter in mm. For example, at 100 m/min on a 50 mm diameter, the calculated speed is about 637 rpm. Use the machine’s constant-surface-speed function only when the setup and chucking permit it, and set an appropriate maximum rpm near the center.

Feed per revolution is not the same as feed per minute. When feed is specified in mm/rev, the resulting linear feed rate is feed per revolution multiplied by rpm. The depth-of-cut range is radial; the corresponding diameter reduction is twice the radial depth in a straight external turning pass. These distinctions prevent unit errors when entering the values into a CNC program or calculating cycle time.

Apply the values to a real steel grade

“Carbon steel” covers many grades, from easy-cutting low-carbon stock to higher-carbon steels, while alloy steels can vary widely in hardenability and strength. Heat treatment, scale, inclusions and supplier condition can make a nominal grade machine differently from another lot. Use the grade certificate and the workpiece supplier’s data to establish the material condition. If the stock is hardened, interrupted, scaled or significantly different from the source’s assumed condition, ask the cutting-tool supplier for conditions that match it.

Start at a conservative point inside the applicable manufacturer window. Secure the workpiece with adequate support, verify insert seating and tool overhang, and make a short trial pass. Listen for chatter, inspect the chip form and finished surface, and check the insert for flank wear, chipping or built-up edge. Change one parameter at a time so the effect can be identified. If the machine lacks rigidity or the part is slender, reduce the load and correct the setup before raising speed or feed.

Limits of the chart

The published table is for SH725 and its specified chipbreakers. It is not a material-property table, an ISO P standard, or a guarantee of tool life. Cutting speed, feed and depth of cut interact, and the best combination depends on the cutting edge, workholding, power, coolant delivery and finish requirement. Use the current insert-specific catalog and validate the final process on the actual machine, part and material lot.

Sources

Recommendations summarized from Tungaloy’s SH725 turning grade page, which provides material-group cutting conditions and chipbreaker/nose-radius feed ranges. Use the manufacturer’s current catalog and product data for the selected insert.