All the Parameters of Mechanical Turning

Mechanical turning (different from milling) is one of the most widely used precision machining operations with interesting results, provided that the fundamental parameters are respected. That is, the tool feed rate (from which the spindle rotation speed is derived) together with feed and axial and radial depth. That is, in relation to the axis of the workpiece and its radius.

These elements, together, represent the essential parameters for good mechanical turning and if you want to get the most out of finishing operations, you need to know the details of these indicators. Otherwise, the workpiece machined under the lathe will never have the required qualities. Want to go deeper? Well, here are all the fundamental parameters of mechanical turning.

Cutting Speed (VC)

Let's start the list of key parameters of turning in the mechanical workshop with the basics: cutting speed. This is the recording of the dynamic movement with which the cutting edge moves relative to the workpiece. This technical element is measured in meters per minute (m/min). The cutting speed on a turning tool depends on the diameter of the workpiece and the speed of the tool.

This is why we can say that a closely related metric is spindle speed. Not by chance, the formula for calculating cutting speed is VC = π × D × n / 1000, where the letter n stands precisely for spindle speed. Cutting speed in turning is one of the most important and incisive parameters for the quality of the result: increasing it, the temperature in the zone rises drastically.

This can cause wear from diffusion and plastic deformation. On the other hand, too low speeds give non-optimal finishes due to irregular chips. The optimal point is a dedicated window for each material. To find out what values to maintain, machine shop tables can be consulted that provide average values considering the factors on which the choice depends.

Depth of Cut (AP)

Another technical parameter of turning that you need to keep under control because it defines how much material is removed in each cut of the cutting edge, measured radially in millimeters. What is the fundamental mistake? Incorrectly thinking that making deeper cuts is more productive. This is not so because, beyond a certain threshold, vibrations force you to slow down, eliminating the advantage.

Let's remember with care and precision that affecting the depths of cut fundamentally alters the balances, causing vibrations in more slender pieces that can undermine all the effort related to the quality of the machining.

To read: how to choose brazed tools for turning

Feed (F)

Another fundamental parameter of precision turning in mechanical machining is feed. By this term we mean the movement of the tool per revolution of the workpiece, measured in mm/revolution. This parameter significantly influences surface roughness and, more generally, the productivity of the lathe operating in your mechanical shop.

In the table below, we have a definition of the limits for feed values in relation to material quality and type of machining, using HSS tools like those you find in the Krino catalog (find it here for download).

In practical terms, feed determines waves on the turned surface and increasing the parameter directly affects the presence of grooves. The theoretical roughness Ra is calculated with the formula Ra = F²/(8×r), where r is the nose radius of the tool.

That is, one of the geometric parameters of the turning tool. With respect to cutting edge wear, it seems odd but low speeds can be harmful because the blade slides and cannot cut, creating wear through an abrasion process.

This is a very particular topic: feeds that are too low (< 0.05 mm/revolution) often worsen the finish due to vibrations and also damage the tools, so you must be very experienced to choose the solutions appropriate for individual metals.