The Daily Grind
A common tool found in machine shops and metal fabrication facilities alike is the metal grinding machine, usually just referred to as a grinder. While certain types of grinders can remove large amounts of material in an operation, many are used for smaller jobs, such as more intensive finish work where they smooth the rough spots left on a workpiece after all other operations are completed.
Grinders are powered tools that usually use a spinning abrasive wheel, disc, or cylinder to remove material. Like sandpaper, grinding wheels feature small abrasive grains that chip away minutely at the workpiece as they encounter it at high speed. Unlike sandpaper, where the grit is just glued to the surface, grinding wheels are composed of abrasive material. This allows a grinding wheel to keep working as it wears down or the abrasive grains are broken off.
Metal fabrication processes usually leave burrs along cut or drilled edges, making the grinding machine an essential part of daily operations in most shops.
History of the Grinder
Mechanisms for grinding different materials have been in existence for thousands of years. The concept of removing small pieces of an object by forcibly applying a rough or sharpened harder object to its surface in a fast motion was discovered by primitive humans. They developed hand tools out of stone, wood, and bone that could chop, saw, drill, and grind. Methods to grind grain by hand to prepare it for easier consumption were invented, and some of the earliest grinding machines were developed specifically for this purpose. The ancient Greeks developed a grain grinding mill that was powered by a water wheel and used a tooth gearing mechanism. These concepts were adapted over the centuries in the design of machines that could grind wood, stone, and eventually even metal.
In the 15th century, the great inventor Leonardo da Vinci conceptualized a lens or mirror grinding machine a century before the telescope was even invented. His proposed device had variable settings and utilized gears for its operation. He also sketched out the design for a needle grinding machine for the textile industry that he calculated could turn out 400 needles an hour, automatically loading and unloading them.
While Ambrose Webster had assembled a small grinder in Massachusetts in 1860, the real start of the metal grinding machine industry began in 1868 when the Brown & Sharp Manufacturing Company produced the first officially recognized universal grinding machine to accurately fabricate cylindrical work. Once it was publicly exhibited at the 1876 Centennial Exposition, other manufacturers began to follow suit and developed their own machines.
Types of Grinders
Metal grinding machines include the following types:
- An angle grinder is a handheld power tool that usually makes use of an abrasive disc or thin cut-off disc to remove excess material from a workpiece either by grinding or abrasive cutting. They are often used for finishing work.
- A belt grinder is like a belt sander in design and operation, but while sanders just remove minor imperfections from a workpiece, the more powerful belt grinders are designed remove a larger portion of material.
- A bench grinder is so named because it is designed to be mounted to the top of a workbench. Most are designed with two different grinding wheels, a courser one for material removal and a finer one for finishing a workpiece. The grinding wheels can usually be interchanged with buffing wheels or wire brushes. Bench grinders are often used for sharpening cutting tools.
- A centered grinder is a style of cylindrical grinder that fixtures the workpiece on an axis between two spindles while it is being ground.
- A centerless grinder is a style of cylindrical grinder which uses two rotary wheels, one of which is driven, to secure a workpiece in place between them on a work rest.
- A CNC grinding system is a highly advanced type of tool and cutter grinder used for crafting precision parts for high-tech industries, such as aerospace, automotive, and medical products.
- A creep feed grinder is a machine that can remove a large amount of material—up to a full depth of cut—usually in a single pass. Both cylindrical grinders and surface grinders can be designed as creep feed grinders.
- A cup grinder is another name for a vertical spindle surface grinder.
- A cylindrical grinder is usually used for shaping the outside of a workpiece that is capable of being rotated through a central axis. The workpiece and the grinding wheel both must be simultaneously rotated.
- A D-bit grinder is a tool bit grinder that gets its name as an abbreviation of the Deckel Company, a German machine tool producer that was the original manufacturer of that type of grinder. It was designed primarily to produce single-lip cutters for pantograph machines, a popular type of simple milling machine used for copying parts (later made obsolete by CNC mills).
- A die grinder is a handheld high-speed tool that has a small grinding bit. Originally developed for creating contours of dies, die grinders have many applications where metal or other materials must be machined by hand. While they can be electric, they are usually powered by a shop’s compressed air line.
- A disc grinder is another term for an angle grinder.
- A gear grinder can refer to any machine that is used to machine or finalize a gear, such as a mill, hobbing machine, or a specialized grinder. Gear grinders are also used for removing material from the center of shafts.
- A flick grinder is referenced in an obscure article on Wikipedia, but no other information is available about it on the Internet, implying that it may be a machine that had a limited manufacturing run, or that the article was a prank or possibly a stunt to promote a specific product. It supposedly resembles both a surface grinder and a tool and cutter grinder, while being less accurate than either of them, but more accurate than a bench grinder.
- A hand grinder is the predecessor of the bench grinder, having a similar design, but is hand powered instead of using an electric motor.
- A hobbing grinder is another term for a gear grinder.
- A horizontal spindle surface grinder is a type of rotary surface grinder that uses the face of its grinding wheel to process the workpiece, usually leaving a very flat, fine, precision ground finish.
- An internal diameter grinder is a type of cylindrical grinder. Also called an inside diameter or ID grinder, it was developed for grinding out holes inside of hollow cylinders, with the small grinding wheel and the larger workpiece rotating in opposite directions.
- A jig grinder is used almost exclusively by tool and die makers to create jigs (templates used for accuracy in fabrication), as well as dies and fixtures.
- An outside diameter grinder, also called an OD grinder, is a type of cylindrical grinder designed for grinding the external surface of a cylindrical workpiece.
- A pedestal grinder is essentially a bench grinder that is mounted on a pedestal to be freestanding in a shop. They are sometimes larger than bench grinders.
- A peripheral surface grinder is another name for a horizontal spindle surface grinder.
- A plunge grinder is a type of outside diameter cylindrical grinder where the grinding wheel stays in contact with a single point on the workpiece, rather than traversing the length of it.
- A portable grinder is another term for an angle grinder.
- A radius grinder, the predecessor to CNC tool and cutter grinders, is a specialized grinder used for processing complexly shaped tools and grinding spherical surfaces.
- A reciprocating surface grinder is a surface grinder where the workpiece is secured to a rectangular table that traverses under the grinding wheel.
- A right-angle grinder is another name for an angle grinder.
- A rotary surface grinder is a type of surface grinding machine that has a circular table that rotates a workpiece under a grinding wheel.
- A side grinder is another term for an angle grinder.
- A surface grinder, like its name implies, grinds the surface of a workpiece, usually for material removal rather than finishing work. One of the most common types of grinders, its adjustable head can be lowered to bring the grinding wheel into contact with a workpiece which is mounted to either a horizontally moving table or a rotary table.
- A swing-frame grinder is a powered rotating grinding wheel mounted into a framework that can be moved to different positions over a stationary workpiece.
- A thread grinder is a CNC machine that cuts the threads of a screw with an abrasive grinding wheel.
- A tool and cutter grinder, sometimes referred to as a T&C grinder, is used for producing drills, endmills, step tools, and tool bits. It can also be used to sharpen such tooling and other cutting tools. It is usually a CNC machine with up to 5-axis control over multiple grinding wheels.
- A universal grinder is a type of cylindrical grinder that allows both the wheel head and the work head to be swiveled. They can either be inside diameter (ID) or outside diameter (OD) grinding machines.
- A vertical spindle surface grinder is a type of rotary surface grinder that has its grinding wheel mounted on a vertical spindle and uses the side of the wheel to grind.
- A wheel face grinder is another name for a vertical spindle surface grinder.
The Grand Old Grinder
A staple in metalworking shops, the grinding machine in all its forms has helped to shape the technology of our day, from manufacturing to military, from automotive to aerospace. Grinders have been used by humankind for millennia, and no matter how precise the metalworking technologies developed in the future become, some form of the grinder is likely to be with us for a very long time.