CNC Knowledge: Do you know the structure of CNC turning and milling compound machine tools?

I am often asked to explain something related to machining with power tools on lathes, or what is commonly referred to in the industry as “mill-turn machining.” Even people with CNC turning experience can get a little confused sometimes, especially in the world of molds and when you need to use an additional Y axis.

In this article, the basics of machining with power tools and the use of the optional Y axis are presented.

What is a milling-turning machine?

Milling lathes can range from simpler 3-axis lathes (X, Z and C) to more advanced 6-axis machines where the spindle becomes a separate axis for milling operations and adds linear Y, W and programmable axes. Counter-spindle or counter-spindle. On machine tools equipped with a counter spindle, the W axis is used to position the counter spindle for machining.

In the image above you will notice that the Y axis is actually designed using a narrow angle “wedge”, but even on a machine with this configuration the Y axis still moves in a movement perpendicular to the X axis.

A common mystery surrounding mill-turn technology is knowing when a Y-axis is needed and when a specific feature can be machined on a simpler 3-axis machine using only the C-axis. Basically, the Y-axis is not necessary only if the tool is to be pulled from the centerline of the workpiece. However, in most cases it is usually sufficient to machine the feature around the circumference of the part. In most cases, surface characterization of a part can usually be accomplished using only the C axis.

The part shown below is a good example of functionality that can be created by simply adding a C-axis. Even though the hole shown in the drawing is not on the centerline of the part, the C-axis can be positioned to allow the X axis to move into position and machine the feature.

The part shown below has features that require a Y axis. Likewise, the Y axis is the axis perpendicular to the X axis and can be used to move the tool up or down, at -above or below center. Technically, the flat surfaces of the brass part can be machined only with the C axis, but since they are in the middle of the part, the Y axis is better suited for this function. However, the rounded edge of the end yoke of the part definitely requires a Y axis to delineate the feature. In the second part, the flat surface must be milled, with the part oriented, as shown in the image above. You can easily see that the cutter needs to be raised above the center to cut this particular profile.

This video shows how using the Y axis can make machining flat surfaces easier. Although the tool in the video is oriented along the Z axis, the concept is the same if the tool is oriented perpendicular to the part, which is useful on the brass part shown above.