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 GNC 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."
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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 arc 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