Digital Power Feed Increases Mill Productivity And Lot-To-Lot Repeatability

How do you improve the performance of a manual milling machine without the expense of retrofitting a CNC? One answer is with a power feed. But as the demand for faster feed rates, smoother surface finishes and tighter tolerances has grown, the need for improved power feed technology also has grown.

When power feeds first appeared about 30 years ago, they were an inexpensive way to mount a motor on the ballscrew, which increased productivity and delivered consistent feed rates to machine a smoother surface finish. A lever determined speed, forward and reverse. Mechanical limit switches stopped tables from crashing

A recently introduced power feed, called the Turbo Drive, from Servo Products Co. (Pasadena, California) is representative of a new generation of power feeds now on the market. Servo Products is one of the earliest manufacturers of power feeds. This generation of power feeds features digital operation that improves performance on a manual mill with faster feed rates, rapids and a smoother surface finish, as well as improved lot-to-lot repeatability. The new power feed delivers feed rates up to 50 ipm and rapid traverse rates up to 80 ipm. According to the builder, these speeds increase productivity as much as 200 percent compared to earlier models.

Digital technology on a power feed such as the Turbo Drive allows starts, stops and reversals without a delay, because, like a CNC control, it automatically calculates the maximum deceleration and acceleration rates. This feature helps avoid an overload situation and enables full power to be utilized without damage to its brushless DC motor.

Also like a CNC control, but with the ease of a power feed, the new power feed's digital control features 0.1 inch resolution, which enables the use of material feed rate tables to set precise feed rates for a given cutter and material. This feature results in more consistent feed rates for smoother surface finishes. Another advantage of digital technology is the capability to record the feed rates on a setup sheet for future reference. By adhering to recorded feed rates, lot-to-lot repeatability is enhanced every time the job is run or that particular combination of cutter and material is utilized.

With a digital turns counter that has a resolution of 0.1 inch, the operator can keep track of position more precisely, while fine positioning is still achieved by the dials. With resolution of 0.001 inch, the power feed's digital control promotes tighter tolerances, although actual tolerances depend on the specifications and condition of the milling machine to which the power feed is attached. Repeatability, also dependent on the mill, can be within ±0.002 inch, the company says.

Finally, one of the little-thought-about benefits to power feeds is the reduction of operator fatigue caused by hand cranking a heavy knee into position. Putting a power feed on the knee may let the operator finish the shift with a little more energy.