CNC Controls - For Chipmakers, By Chipmakers

Last month I had the opportunity to discuss CNC controls with several customers from the great state of Minnesota. Hegman Machine Tool held a two-day Lunch and Learn event, and as I do in all of my presentations, I introduced Okuma’s OSP-P control and its functions to shop owners, CNC machine operators and chipmakers. That’s right, chipmakers. Not button pushers. Chipmakers are individuals who know how to cut metal, how to process parts and how to perfect cutting conditions. A great example of chipmakers is a small company, H&L Machine from Chisago City, Minnesota. H&L Machine, a three-generation shop, had a grandfather, son and grandson all in attendance. Did the three of them leave their shop and make the hour drive just for a free lunch? Not a chance. They came to learn about new technologies in chipmaking. They were there to ensure that their generational shop continues to thrive in today’s world of intense competition.

Harmonic Spindle Speed Control (HSSC)

The concept of Harmonic Spindle Speed Control (HSSC) is not new to chipmakers. Basically this function constantly changes the RPM of a lathe spindle in order to prevent harmonics or vibration (chatter) during a cutting operation. I always try to relate our OSP functions to a technique of “how they did it in the past.” With HSSC, the machinist of the past would manually use the spindle speed control knob, turning it up and down, varying the RPM. In this presentation, something unique happened. I saw the grandson turn to his grandfather and smile, because he knew that his grandfather performed this technique and that this was how he perfected a cut on a particular work piece in their shop.

Today, the grandson learned how technology has advanced this chipmaking technique. HSSC works in the same fashion, however with this function, the OSP CNC control, with the addition of a few lines of NC code, automatically adjusts the following variables:

• 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.

Variable Spindle Speed Threading (VSST)

Now let’s Go Beyond the basic function of HSSC. Let’s apply this CNC control functionality to threading! In the past, chipmakers knew one thing that is a NO-NO - changing RPM during threading. This is as bad as picking up the wrong number with the half-nut lever on a manual lathe. Changing RPM will vary the thread pitch, rendering the part useless. But Okuma recognized that in some thread cutting, chatter can exist and can be very difficult to correct without the ability to vary the RPM. Again relating this OSP function to a technique of “how they did it in the past”, on large diameter pipe, oftentimes chipmakers would wrap heavy duty rubber around the pipe to prevent the introduction of chatter in the thread cutting operation.

Today, with the power and speed of the OSP CNC control, we can vary RPM while maintaining lead during threading, thus preventing the introduction of chatter. This unique Okuma function is used heavily in the oil field industry on our LOC lathe product line.

In summary I’d say that in this Lunch and Learn, at least two people gained valuable knowledge. A grandson learned that his grandfather knew his stuff and a grandfather learned that the OSP CNC control was made for chipmakers by chipmakers. HSSC is a standard feature of the P200/P300L OSP CNC control. VSST is standard feature (part of our Thread Cutting Suite) on our LOC lathe product line and is available as an option on all other OSP-P200/P300 lathe controls.

What do you do to prevent chatter in your operations? Are you doing it the way it was done in the past? Comment below or contact us, and together we’ll determine how best to automate your techniques.

Tim Thornton is Controls Product Specialist, Okuma America Corporation