PREVENT CHATTER ON YOUR CNC LATHE WITH OKUMA’S HSSC AND VSST EXECUTIVE SUMMARY Eliminating harmonics, which can produce tool chatter or poor surface finish, is critical for maximizing productivity. If you have an Okuma horizontal or vertical CNC lathe with a P200 or newer control (also available on the P100 control as an option), you have tools that help prevent chatter by allowing for RPM changes. Harmonic Spindle Speed Control (HSSC) and Variable Spindle Speed Threading (VSST) are functions available with Okuma’s THINC®OSP CNC control that are highly effective harmonics problem solvers. HSSC and VSST are particularly useful when machining parts with high L/D ratios, thin-walled parts, or thin-walled parts with threads. HARMONIC SPINDLE SPEED CONTROL (HSSC) The concept of Harmonic Spindle Speed Control (HSSC) is not new, but historically this has been a manual process. Basically this function constantly changes the RPM of a lathe spindle in order to prevent the build up of harmonics or vibration (chatter) during a cutting operation. To implement HSSC, the machinist of the past would manually use the spindle speed control knob, turning it up and down, varying the RPM. Now you can use the HSSC function that is built into Okuma’s control to constantly change the RPM of a CNC lathe spindle in order to prevent harmonics or chatter (see Figure 1). With this function, the OSP control (with the addition of a few lines of NC code) automatically adjusts the following variables according to pre-set parameters or parameters that are programmed to suit your particular needs: • Amplitude (Q) – the percentage amount of variation in the RPM • Interval time (R) – how long we stay at the peak or valley of RPM change • Speed variation cycle (P) – the pitch of the RPM variation The result is reduced or eliminated chatter during turning operations. Use of HSSC is advised when absolute accuracy is required when machining challenging parts. Variation control ON Variation control OFF Figure 1: HSSC prevents chatter by automatically adjusting variables according to pre-set or custom-programmed parameters 14-OKUM-0060 HSSC and VSST White Paper_2PGDOC_Option2.indd 2

OKUMA HSSC and VSST VARIABLE SPINDLE SPEED THREADING (VSST) In the past, changing RPM during threading was out of the question. That’s because most machines cannot maintain thread pitch when changing RPM, thus scrapping the part. But Okuma recognized that in some thread cutting applications, chatter can exist and can be very difficult to control without the ability to vary the RPM. Today, with the power and speed of the OSP CNC control, we can vary RPM while accurately maintaining the lead during threading, thus preventing the introduction of chatter. This unique Okuma function is used heavily...