Angle grinder

Angle grinder, also known as a side or disc grinder, is a handheld power tool used for cutting, grinding and polishing.

Angle grinders can be powered by an electric motor, petrol engine or compressed air. The motor drives a geared head at a right-angle on which is mounted an abrasive disc or a thinner cut-off disc, either of which can be replaced when worn. Angle grinders typically have an adjustable guard and a side-handle for two-handed operation. Certain angle grinders, depending on their speed range, can be used as a sander, employing a sanding disc with a backing pad or disc. The backing system is typically made of hard plastic, phenolic resin, or medium-hard rubber depending on the amount of flexibility desired.

Safety

How to use an Angle Grinder

Through a sound power level and vibrations study conducted by the National Institute for Occupational Safety and Health, grinders under an unloaded condition ranged from 91 to 103 dBA.

Uses

Angle grinders may be used both for removing excess material from a piece or simply cutting into a piece. There are many different kinds of discs that are used for various materials and tasks, such as cut-off discs (diamond blade), abrasive grinding discs, grinding stones, sanding discs, wire brush wheels and polishing pads. The angle grinder has large bearings to counter side forces generated during cutting, unlike a power drill, where the force is axial.

Angle grinders are widely used in metalworking and construction, as well as in emergency rescues. They are commonly found in workshops, service garages and auto body repair shops. There is a large variety of angle grinders to choose from when trying to find the right one for the job. The most important factors in choosing the right grinder are the disc size and how powerful the motor is. Other factors include power source (pneumatic or electric), rpm, and arbor size. Generally disc size and power increase together. Disc size is usually measured in inches or millimetres. Common disc sizes for angle grinders in the U.S.A. include 4, 4.5, 5, 6, 7, 9 and 12 inches. Discs for pneumatic grinders also come much smaller. Pneumatic grinders are generally used for lighter duty jobs where more precision is required. This is likely because pneumatic grinders can be small and light yet remain powerful, because they do not contain heavy copper motor windings, while it is harder for an electric grinder to maintain adequate power with smaller size. Electric grinders are more commonly used for larger, heavy duty jobs. However, there are also small electric grinders and large pneumatic grinders.
Tags: Jig grinder , Surface grinding , Bench grinder , Centerless grinding , Cylindrical grinder , Tool and cutter grinder

Centerless grinding

Centerless grinding is a method of material removal through grinding, similar to centered grinding except for the absence of the spindle. It has high throughput, i.e. a large number of parts can be manufactured in a short time.

The workpiece is set up between the regulating wheel (or back up wheel) and the grinding wheel, and is supported by the work blade (or work rest). The work rest is located between the wheels. The work is placed upon the work rest, and the latter together with the regulating wheel is fed forward forcing the work against the grinding wheel. Axial movement of the work past the grinding wheel is accomplished by tilting the regulating wheel at a slight angle from horizontal. An angular adjustment of 0 to 8 or 10 degrees is provided in the machine for this purpose.

Centerless grinding is classified into two types:

Throughfeed grinding - the workpiece is fed into the machine along the work blade

Plunge grinding - the workpiece is placed between the wheels on a work blade and the grinding wheel is plunged into the workpiece.

Some of the benefits of centerless grinding include the ability to grind parts with geometries that do not allow them to be OD ground, the ability to remove three, five and other odd numbered lobing on the shaft of a part, and to maintain size beyond what is typically capable of an OD grinder due to the low overall pressures spaced out along the workpiece.

An example of a centerless ground application is the outer diameter of the bearing races.
Tags: Jig grinder , Surface grinding , Bench grinder , Angle grinder ,  Cylindrical grinder , Tool and cutter grinder

Cylindrical grinder

Cylindrical grinder is a type of grinding machine used to shape the outside of an object. The cylindrical grinder can work on a variety of shapes, however the object must have a central axis of rotation. This includes but is not limited to such shapes as a cylinder, an ellipse, a cam, or a crankshaft.

Cylindrical grinding is defined as having four essential actions

The work (object) must be constantly rotating

The grinding wheel must be constantly rotating

The grinding wheel is fed towards and away from the work

Either the work or the grinding wheel is traversed with the respect to the other.

While the majority of cylindrical grinders employ all four movements, there are grinders that only employ three of the four actions.

Types

There are five different types of cylindrical grinding: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding.

Outside diameter grinding

OD grinding is grinding occurring on external surface of an object between the centers. The centers are end units with a point that allow the object to be rotated. The grinding wheel is also being rotated in the same direction when it comes in contact with the object. This effectively means the two surfaces will be moving opposite directions when contact is made which allows for a smoother operation and less chance of a jam up.

Inside diameter grinding

ID grinding is grinding occurring on the inside of an object. The grinding wheel is always smaller than the width of the object. The object is held in place by a collet, which also rotates the object in place. Just as with OD grinding, the grinding wheel and the object rotated in opposite directions giving reversed direction contact of the two surfaces where the grinding occurs.

Plunge grinding

A form of OD grinding, however the major difference is that the grinding wheel makes continuous contact with a single point of the object instead of traversing the object.

[edit]Creep feed grinding

Creep Feed is a form of grinding where a full depth of cut is removed in a single pass of the wheel. Successful operation of this technique can reduce manufacturing time by 50%, but often the grinding machine being used must be designed specifically for this purpose. This form occurs in both cylindrical and surface grinding.

Centerless grinding

Centerless grinding is a form of grinding where there is no collet or pair of centers holding the object in place. Instead, there is a regulating wheel positioned on the opposite side of the object to the grinding wheel. A work rest keeps the object at the appropriate height but has no bearing on its rotary speed. The workblade is angled slightly towards the regulating wheel, with the workpiece centerline above the centerlines of the regulating and grinding wheel; this means that high spots do not tend to generate corresponding opposite low spots, and hence the roundness of parts can be improved. Centerless grinding is much easier to combine with automatic loading procedures than centered grinding; throughfeed grinding, where the regulating wheel is held at a slight angle to the part so that there is a force feeding the part through the grinder, is particularly efficient.

Control methods

There are three basics ways in which an operator can interact with a cylindrical grinder. Either manual manipulation of the machine, Numerical Control with a punched card system or using Computer Numerical Control using a pre existing interface designed for that machine or by using a PC as an interface to communicate with the grinder. The first two options are rarely if ever used today. CNC operated cylindrical grinders are the most technologically advanced, efficient, reliable systems in the manufacturing industry.

Applications

The cylindrical grinder is responsible for a plethora of innovations and inventions in the progression of science and technology. Any situation in which extremely precise metalworking is required, the cylindrical grinder is able to provide a level of precision unlike any other machine tool. From the automotive industry to military applications, the benefits the cylindrical grinder have given us are immeasurable.

History

The origins of the cylindrical grinder, as with all other modern machine tools, stem from the experimentation and invention of John Wilkinson and later Henry Maudslay who built the first the horizontal boring machine and first engine lathe, respectively. The cylindrical grinder owes much of its development from the onset of the Industrial Revolution, particularly to the advent of reliable, inexpensive steel production and later the improvement of the grinding wheel. The basis for the modern day cylindrical grinder was first built in the 1830s by two men working independently, Jonathan Bridges and James Wheaton . It is unclear as to which man had first produced the machine but both are closely tied to the first historical appearance of the modern day tool. It took another 40 years before further improvement and refinement of the tool occurred.

The Brown & Sharpe company in Providence, RI was one of the first builders of the Wilcox & Gibbs Sewing Machine, one of the first piece of precision machinery to be used in a residential setting. Joseph Brown believed that the shaft and needle bars of the sewing machine must be crafted from hardened tool steel. It was this desire that lead to their experimentation with building a cylindrical grinder. The first attempt was simple a small lathe with a grinding wheel mounted to it. Subsequent attempts lead to the cylindrical grinder displayed at the 1876 Centennial Exposition and the subsequent patent.

It is important to note that Brown & Sharpe cannot be given sole credit of pioneering advances in cylindrical grinding. A man in Waltham, Massachusetts, Ambrose Webster had created a small grinding machine in 1860 that contained all of the improvements Brown & Sharpe claimed to be their own original invention. Even more so, the emphasis on precision, accuracy, and reliability was championed by Charles Norton.

Norton was an employee of Brown & Sharpe who quit the company with the desire to further pursue his belief that the cylindrical grinder is not merely a finishing tool but could be a staple of the machine shop. He founded the Norton Grinding Company, where he continue improving the cylindrical grinder to use faster rpm values and more precise grinding tolerances. He was acknowledged for his work on April 18, 1925 when he won The John Scott Medal and Premium for his invention of "accurate grinding devices of high power". These standards developed by Norton were the status quo until about the middle of the 20 century.
Tags: Jig grinder , Surface grinding , Bench grinder , Angle grinder , Centerless grinding ,  Tool and cutter grinder