Surface Grinding Operations

Introduction, Safety, and Mounting the Grinding Wheel Surface grinders machine flat surfaces, like milling Safety: see cautions in text Mounting: Remove spindle nuts to release old wheel Perform ring test Use blotter and clean, burr-free washer Jog spindle and run to test

FIGURE 7.3.1 Loosening the spindle nut on most grinders requires two wrenches. © Cengage Learning 2012 FIGURE 7.3.2 Wheels should always be ring tested before they are installed. Ring testing checks the wheel for soundness. © Cengage Learning 2012

A B FIGURE 7.3.3 (A) A permanent magnet and (B) an electromagnet. The control for the electromagnet offers the ability to vary the magnetic force exerted on a workpiece which can limit distortion of thin workpieces. All images © Cengage Learning 2012

Workholding Devices Magnetic devices Permanent magnet vs. electromagnet Magnetic parallels, V-blocks, angle plates, sine chucks Angle plates, V-blocks, and collet blocks for milling can be used for grinding Grinding vises different from milling vises

FIGURE 7.3.4 The gold lines on the chuck represent the lines of magnetism. The workpiece should span 3 or more of these lines to be safely secured. Notice the back rail on this chuck. It is used to help align a workpiece on the chuck. © Cengage Learning 2012

FIGURE 7.3.6 Magnetic parallels extend the magnetic field FIGURE 7.3.5 Blocking consists of placing pieces of ferromagnetic metal around the workpiece. This is done to help hold the workpiece secure during the grinding operation. When using this method it is important to make sure the blocking material is shorter than the actual workpiece. © Cengage Learning 2012 FIGURE 7.3.6 Magnetic parallels extend the magnetic field of the magnetic chuck. © Cengage Learning 2012

FIGURE 7.3.8 Magnetic sine chucks can be used to hold a Magnetic V-blocks. © Cengage Learning 2012 FIGURE 7.3.8 Magnetic sine chucks can be used to hold a workpiece at a preset angle. The angle is set by using a gage block build as with a sine bar. © Cengage Learning 2012

FIGURE 7.3.9 A workpiece is often passed over a demagnetizer after grinding. © Cengage Learning 2012 FIGURE 7.3.10 Grinding vises are very accurately ground and can be used to quickly and accurately secure workpieces. © Cengage Learning 2012

Wheel Dressing Dress and true wheel before use Dressing sharpens, truing stops runout Dress/true aluminum oxide/silicon carbide wheels: with diamond dressing tools Superabrasive wheels: true first with brake truing device, then dress with dressing stick FIGURE 7.3.11 Truing makes the wheel face run true to its axis and dressing sharpens the wheel. © Cengage Learning 2012

A B FIGURE 7.3.12 “A” shows a single point dresser. “B” shows a cluster point dresser. © Cengage Learning 2012

FIGURE 7.3.13 Preferred location of the diamond dresser on the left edge of the chuck. © Cengage Learning 2012 FIGURE 7.3.14 Proper dresser position is an important safety consideration. The diamond should be offset to the left of the wheel centerline. If the diamond is angled in its holder, the angle should be placed as shown. © Cengage Learning 2012

FIGURE 7.3.15 The dresser is being positioned near the edge of the wheel. © Cengage Learning 2012 FIGURE 7.3.16 The dresser is fed across the face of the wheel to perform the dressing operation. Feeding the dresser slowly will result in a wheel having a slightly more closed structure while feeding faster will produce a slightly more open structure. © Cengage Learning 2012

FIGURE 7.3.17 Illustration of brake truing. © Cengage Learning 2012

Grinding Parallel Surfaces Most basic/common operation Often best to start with largest surface Secure workpiece and clean before grinding Grind magnetic chuck periodically to keep surface flat FIGURE 7.3.18 The grinding wheel should travel all the way off the work piece at the end of each longitudinal pass. All images © Cengage Learning 2012

FIGURE 7.3.19 The table should be cross-fed far enough so that the wheel travels off the front and rear of the part. All images © Cengage Learning 2012

FIGURE 7.3.20 When touching off, the grinding wheel is positioned so that only about 1/8" of its width is over the work. Layout fluid can make it easier to see when the wheel touches since the dark blue provides a good visual contrast to the workpiece. © Cengage Learning 2012 FIGURE 7.3.21 The arrows show the direction of feed as a surface is ground. © Cengage Learning 2012

Grinding Perpendicular Surfaces and Angles Perpendicular surfaces: set parallel to magnetic chuck or use angle plate or grinding vise Angles: use magnetic V-block, sine bar and angle plate, or magnetic sine chuck FIGURE 7.3.22 Angle plates are often used to grind a workpiece square. If setup properly, two perpendicular surfaces of the workpiece can be ground without repositioning the work on the angle plate. Here the part is positioned so that the left side extends past the angle plate while the side facing up is ground. © Cengage Learning 2012

FIGURE 7.3.23 Without repositioning the work on the angle plate, it is turned on its side for grinding the adjacent side. Clamps must be repositioned for clearance with the grinding wheel. © Cengage Learning 2012 FIGURE 7.3.24 A precision grinding vise can be used in place of an angle plate when grinding perpendicular surfaces. © Cengage Learning 2012

FIGURE 7.3.25 Two surfaces of the workpiece can be ground without reclamping the work by turning the grinding vise on its side. © Cengage Learning 2012

FIGURE 7.3.26 Magnetic V-blocks are helpful when grinding 45-degree angles. © Cengage Learning 2012 FIGURE 7.3.27 Using a sine bar and gage blocks to position the workpiece on an angle plate. © Cengage Learning 2012

FIGURE 7.3.28 Magnetic sine plates can also be used with gage blocks to set up angles. This method is very accurate. © Cengage Learning 2012 FIGURE 7.3.29 The vertical walls of the step and the slot of this workpiece have been finished using side grinding techniques. © Cengage Learning 2012

Side Grinding Use periphery of wheel to grind surface parallel to magnetic chuck and side to grind vertical surface Dress side before grinding Mount work parallel to table travel FIGURE 7.3.30 The dresser should be positioned on end and aligned with the centerline of the wheel for side dressing. © Cengage Learning 2012

FIGURE 7.3.31 Dresser being used to dress the side of the wheel. © Cengage Learning 2012

FIGURE 7.3.32 Dressing a small undercut into the wheel can help reduce the amount of surface-to-surface contact between the workpiece and the wheel. © Cengage Learning 2012 FIGURE 7.3.33 Dressing a small undercut can also be performed by hand using a dressing stick. © Cengage Learning 2012

FIGURE 7.3.35 Positioning of the wheel near the surfaces to be ground. FIGURE 7.3.34 A dial indicator being used to align the workpiece with the longitudinal travel. © Cengage Learning 2012 FIGURE 7.3.35 Positioning of the wheel near the surfaces to be ground. © Cengage Learning 2012

FIGURE 7.3.36 Grinding horizontal and vertical surfaces. © Cengage Learning 2012 FIGURE 7.3.37 A collet type fixture can be used to produce cylindrical or angular surfaces. © Cengage Learning 2012

Grinding Cylindrical Work and Grinding Problems Grind cylindrical features, radii, and angles using indexing feature Grinding problems Burning work surface Scratches on work surface Waviness/chatter on work surface

Grinding Cylindrical Work and Grinding Problems (cont’d.) FIGURE 7.3.38 (A) The center of the workpiece should be in line with the center of the wheel when using a spin fixture. (B) Lower the wheel head while rotating the fixture handwheel to grind the cylindrical surface. All images © Cengage Learning 2012

FIGURE 7.3.39 Angular graduations or an indexing ring can be used to set up angles for grinding. © Cengage Learning 2012 FIGURE 7.3.40 A V-block fixture can align the workpiece by moving the V-block from the centerline of the fixture. A dial indicator can be used to ensure that the cylindrical surface is running true. © Cengage Learning 2012

A wavy surface may indicate a loose or out-of-round grinding wheel. FIGURE 7.3.41 Burn marks appear as dark streaks in the surface of the workpiece. © Cengage Learning 2012 FIGURE 7.3.42 A wavy surface may indicate a loose or out-of-round grinding wheel. © Cengage Learning 2012