CNC Technology

Consider a blank sheet of paper on the desk before you and imagine that you wish to define specific locations on the paper relative to the center of the sheet. You could start by drawing a vertical and a horizontal line on the paper and identifying these by the letters X and Y (Figure …

Computer control of machine tools has numerous advantages and capabilities. One distinct advantage is rapid and high-precision positioning of both workpiece and cutting tools. Modern CNC machines can position cutting tools and workpieces at rapid traverse feed rates of several hundred inches per minute to an accuracy of .0001 in. Once programming is complete, and tooling is set up, the machine tool …

Additional capabilities of this machine include sharpening of reamers, taps, drills, and single-point cutting tools. Having a power-driven workhead permits cylindrical grinding (Figure L-179). The workpiece may be held in a threejaw chuck (Figure L-180) or on a magnetic grinder chuck (Figure L-181). The internal grinding attachment permits internal cylindrical grinding (Figure L-182). The swiveling capability of the workhead permits regrinding of lathe …

A lathe mandrel is a common and useful machine shop tool. Precision mandrels are finished by cylindrical grinding after they have been machined and heat-treated. Finish grinding the mandrel will provide you with basic experience in cylindrical grinding. Refer to a working sketch (Figure L-130) to determine the required dimensions. Selecting the Wheel For a hardened …

Most common is simple traverse grinding (Figure L-119). This may be done on interrupted surfaces (Figure L-120) where the wheel face is wide enough to span two or more surfaces. Multiple-diameter-form grinding (see Figure L-13) is a type of plunge grinding in which the wheel may be form dressed to a desired shape. In …

The workpiece in on-centers cylindrical grinding is mounted between the head and footstock centers. This effectively provides a single point mounting on each end of the workpiece, permitting maximum accuracy to be achieved in the grinding operation. The angle and finish of center holes in the workpiece is extremely important. The results of a cylindrical grinding job depend on …

On the center-type cylindrical grinder (Figure L-110), the workpiece is mounted between centers much as it would be in the lathe. The plain cylindrical grinder (Figure L-111) has a fixed wheelhead that cannot be swiveled, only moved toward or away from the center axis of the workpiece. The table can be swiveled to permit the …

Effect—Chatter or vibration marks (Figure L-107) Cause—Interrupted cutting due to wheel balance; wheel not concentric to spindle; external vibrations; or a “skipping wheel” resulting from loading or glazing Solution—Rebalance wheel; true wheel; re-dress wheel; relocate grinding machine and isolate from external vibration Effect—Irregular scratches or fishtails (Figure L-108) Cause—Swarf in the grinding fluid; swarf dripping from wheel …

The vee block (Figure L-87) is a common and useful machine shop tool. Precision types are finish machined by grinding after they have been rough machined oversize (about .015 in.) and heat-treated. Finish grinding of vee blocks will provide you with a variety of surface grinding experiences. Refer to a working drawing (Figure L-88) …

The first step in surface grinding is to check, and if necessary grind-in, or true, the chuck. Truing the chuck is usually not necessary unless it has been removed and reinstalled or a new chuck is being used for the first time. Any grinder chuck should be checked occasionally and, if necessary, trued by grinding a …