From Manual To CNC Mills: A Three-Phase Transition

V & G Dynamic Machine & Tool, Inc. of Marble Falls, Texas, uses high-end VMCs and CNC mills and employs skilled machinists and CNC operators to support the development of new instrumentation and technology for the semiconductor industry.

When Volker Steffen founded V & G Dynamics in 1988, the company was doing mainly repair work using two manual mills. Mr. Steffen knew that if he had CNC there was the promise of longer runs and production of complex parts—giving access to new markets and increasing sales and profitability. But these benefits come with a cost in terms of capital, training and learning. Mr. Steffen was looking for a way to implement CNC gradually—a transition that took the characteristics of his shop and people into consideration.

He discovered an opportunity at an open house held by his local dealer. "I was at an open house at a machine dealer one weekend, and I saw a manual mill with some sort of external motors mounted on the table," Mr. Steffen says. "The dealer showed me how the mill was doing CNC work by having the power feeds move the table, under the control of a PC. Best of all, I didn't have to start using a computer right away. I could just use the power feeds in the 'Teach Mode.' You move the table to a desired position, press 'set' on the pendant, move to the next position, press 'set' again, and so on. At the end of the sequence you press 'run,' and the machine plays back exactly the moves you told it to execute. It's that simple."

On seeing this, Mr. Steffen first began considering doing more than just manual mill work. V & G had grown to include a lot of small-volume (1 - 500 piece) production work, but Mr. Steffen was not at the point where he needed to spend tens of thousands of dollars on a single CNC. So in 1993, he decided to first retrofit one of his manual mills with the "intelligent power feeds"—a basic two-axis Servo II automated control system with the "Teach" pendant, made by Servo Products Company of Pasadena, California—which he mounted himself on a Summit manual mill with a Sargon digital readout. The cost of the retrofit was well within his reach, and the promise of increased production made the whole deal attractive. Within days, production was at levels he had never seen before, and both he and his machinists were using the "Teach Mode" feature without problems.

Such use of a basic retrofit package makes sense for shops where owners and operators don't have prior experience with CNCs. In the case of V & G, its manual mills had essentially become three different machines with one simple retrofit: one that still does manual work, one that uses the Teach Pendant and one that can perform CNC work (when connected to a dedicated PC). The DRO interface adds accuracy to the Acme lead screw by using the scale for positioning accuracy instead of the encoder on the motor. In addition, the DRO enhances the machinist's productivity.

With the Servo II control system used for the retrofit, one-of-a-kind or production run parts can be machined, and the table can be moved either using the pendant or handwheels. The "taught" programs are limited to straight line and angle cuts. The system cannot be taught to machine a circle. Subroutines can be called up, and program steps can be changed, added or inserted. It's easy to delete entire programs from pendant memory, or delete a subroutine call—which is useful when "programming" on the fly. An operator also can set, clear or drag axes travel limits (for example, reset limit beyond current position) and can playback a program held in the pendant's memory.

The Servo II control system can be made more productive by hooking up a PC, which simply can be used to transfer programs between the PC and the pendant; with Servo CNC software and a dedicated PC, the machine has full CNC capabilities. This comprises the second step in the gradual conversion to CNC machining. Programs "written" on the pendant can be transferred to the PC for storage and for re-use at a later time. The transferred pendant programs are converted to common CNC codes. Conversely, programs can be written and edited on the PC and transferred later to the pendant, though only a limited set of CNC codes are available. This means two things: Operators can generate CNC code without knowing programming, and they can execute previously written CNC code without using the control (it's done via the pendant). Production goes up, and accuracy and repeatability improve. The absence of a steep learning curve makes training the operators brief and inexpensive.

V&G began by doing most of its CNC work using the conversational mode programming on the control. By going through a step-by-step process, the operator answers simple questions about the current job, and the control automatically develops a program, which is then seamlessly translated into G-code that can be used on any Servo CNC machine. Even if the operator makes a mistake in the programming, he or she can easily edit the specific line that needs correction.

However, after a while Mr. Steffen realized that the next step for the company would have to be a full-fledged migration to CNC. The use of CAD systems had by then become common, and for that he needed a CNC mill. But he also still wanted to be able to perform manual work on his mills.

"After having converted several manual mills, the workload picked up significantly, and about that time CAD systems really began to matter. CAD systems made molds with complex curves and radii possible, so without a real contouring CNC we couldn't do that kind of work. We needed a machine that would do it all—do CNC work but still let us perform manual milling. We needed a machine that was easy to operate." Had Mr. Steffen purchased a CNC machining center with no manual functions, he would have had to learn and absorb into his plant all of the complexity of the CNC process before getting a return. His selection of a machine with manual capabilities that was upgradeable to full CNC allowed him to get an immediate return and make the transition more gradually.

When Mr. Steffen started shopping around in 1997, he realized that many entry-level CNC mills have comparable features and fall into a similar price bracket. Servo Products manufactured a CNC mill that included the manual milling and the Teach Pendant. The Servo 5000 three-axis bedmill with the Servo II control system facilitated the three-in-one operation he was already used to, and that feature sealed the deal. Also, since the Servo II control uses the same PC-based, bi-directional programming (pendant to PC and PC to pendant) he used before, he could continue to use the same programs and procedures he had developed for the Servo II retrofit mill.

For shops like V & G, the most immediate benefit of going to true CNC milling is the ability to download CAD-generated tool paths into the CNC control. The fact that the Servo CNC control is a PC-based system made the switchover easy for Mr. Steffen. "Having a PC-based control means that menus on screens look familiar, and replacement components are readily available. Servicing was easy, as I once found out by changing the board on the control myself," he says.

Concerns over how his CNC mills would fare over the years worried Mr. Steffen. "We really had to have the confidence in what we buy. Having used Servo power feeds for years before, I had the confidence in the company, and so going to them when we decided to go CNC made total sense."

The combined benefits of V & G's migration to CNC include sustaining a 99.9 percent on-time delivery rate and a 99.9 percent part acceptance rate. Today, V & G specializes in doing work for the semi-conductor industry. "Our company manufactures parts utilizing CNC milling as well as CNC lathes on all types of conventional and exotic materials. Today our shop is computerized with many CNC machining centers, but we still manufacture parts with our Servo Machines," says Mr. Steffen.

Many job shops still rely solely on manual mills, not by choice but because CNC is a big jump in terms of investment and training. A CNC machine capable of manual milling maximizes production flexibility while reducing the amount of space required by two separate mills. Most importantly, this shift from manual milling to CNC machining can be gradual, affordable and easy to implement and learn.