Tc 9-524 fundamentals of machine tools

OFFHAND GRINDING
Offhand grinding is the process of positioning and feeding
the workpiece against a grinding wheel by hand. Offhand
grinding is used for reducing weld marks and imperfections
on workpieces, and general lathe tool, planer tool, shaper tool,
and drill grinding. Deciding depth of cut and feed is based on
the operator’s knowledge of grinding.
Offhand grinding is performed on utility grinding machines
which generally have fixed spindle speeds and fixed wheel
size requirements, so that the cutting speed of the wheel is
constant and cannot be changed for different materials.
Therefore, the operator must use care in feeding and not
overload the wheel by taking too heavy a cut, which would
cause excess wear to the grinding wheel. Similarly, he must be
careful not to glaze the wheel by applying excessive pressure
against the wheel.
The one variable factor in most offhand grinding is the
selection of grinding abrasive wheels, although limited to one
diameter. For example, a softer or harder wheel can be
substituted for the standard medium grade wheel when
conditions and materials warrant such a change. Lathe tool
grinding is described in Chapter 7. Drill sharpening and drill
grinding attachments and fixtures are described in Chapter 4.
TOOL AND CUTTER GRINDING
Grinding Milling Cutters
Milling cutters must be sharpened occasionally to keep them
in good operating condition. When grinding milling cutters,
care must be exercised to maintain the proper angles and
clearances of the cutter. Improper grinding can result in poor
cutting edges, lack of concentricity, and loss of form in the
case of formed tooth cutters. Milling cutters cannot be
sharpened by offhand grinding. A tool and cutter grinding
machine must be used.
Bench-Type Tool and Cutter Grinding Machine
The bench-type tool and cutter grinding machine described
here is typical of most tool and cutter grinding machines. It is
designed for precision sharpening of milling cutters, spot
facers and counterbores, reamers, and saw blades. The
grinding machine contains a l/4-HP electric motor mounted to
a swivel-type support bracket which can be adjusted vertically
and radically on the grinder column. The column is fixed to
the grinder base which contains T-slots for attaching grinder
fixtures used to support the tools that are to be ground.
The motor shaft or wheel spindle accepts grinding wheels on
each end. One end of the spindle contains a wheel guard and
tool rest for offhand grinding of lathe tools and so forth. Cup,
straight, and 15º bevel taper abrasive grinding wheels are
used with this machine. Fixtures used for grinding tools and
cutters include a center fixture for mounting reamers, taps,
and so forth between centers; an outside diameter fixture for
chucking arbor-type milling cutters and shanked peripheral
cutting edge tools; and an end mill fixture for supporting end
cutting tools to the grinder base.