Angle Grinder
An angle grinder is a handheld power tool used for 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 that can be renewed when worn. Angle grinders typically have an adjustable guard and a side-handle for two-handed operation. There are myriad different disks that are used for various materials and tasks, such as cut-off disks (Diamond Blade), abrasive grinding disks, sanding disks, 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. Some motorists carry battery-powered angle grinders to remove wheel clamps.
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's, and arbor size. Generally disc size and power increase together. Disc size is usually measured in inches. Common disc sizes for angle grinders include 4, 4.5, 5, 6, and 7 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 due to the fact that pneumatic grinders can be small yet remain powerful, while it is harder for an electric grinder to maintain adequate power with smaller size. Electric grinders, however, are more commonly used for larger, more heavy duty jobs. This is not to say that there are not small electric grinders and large pneumatic grinders.
Angle grinders, however, can be dangerous due to the high rpm involved and the sparks and bits of metal that fly off as they cut and grind. Another dangerous aspect of angle grinders is that a bad cutting disk can shred when in use. A third risk is that if the edge of the grinding wheel binds in a corner the torque from the spinning wheel will jerk the tool violently. These safety hazards can be mitigated. Proper safety equipment while using an angle grinder would include safety glasses, gloves, and in more heavy duty operations hearing protection and a face shield. While using an angle grinder can occasionally result in injury, use of proper protective gear will greatly reduce the risk.
The angle grinder can be contrasted with other varieties of grinders; see grinding machine, bench grinder and other diamond tools.
Grinders & Grinding Machine
A grinding machine is a machine tool used for producing very fine finishes or making very light cuts, using an abrasive wheel as the cutting device. This wheel can be made up of various sizes and types of stones, diamonds or of inorganic materials. For machines used to reduce particle size in materials processing see grinding.
Construction
The grinding machine consists of a power driven grinding wheel spinning at the required speed (which is determined by the wheel’s diameter and manufacturer’s rating, usually by a formula) and a bed with a fixture to guide and hold the work-piece. The grinding head can be controlled to travel across a fixed work piece or the workpiece can be moved whilst the grind head stays in a fixed position. Very fine control of the grinding head or tables position is possible using a vernier calibrated hand wheel, or using the features of NC or CNC controls.
Grinding machines remove material from the workpiece by abrasion, which can generate substantial amounts of heat; they therefore incorporate a coolant to cool the workpiece so that it does not overheat and go outside its tolerance. The coolant also benefits the machinist as the heat generated may cause burns in some cases. In very high-precision grinding machines (most cylindrical and surface grinders) the final grinding stages are usually set up so that they remove about 2/10000mm (less than 1/100000 in) per pass - this generates so little heat that even with no coolant, the temperature rise is negligible.
Types of grinders
These machines include the
- Belt grinder, which is usually used as a machining method to process metals and other materials, with the aid of coated abrasives. Sanding is the machining of wood; grinding is the common name for machining metals. Belt grinding is a versatile process suitable for all kind of applications like finishing, deburring, and stock removal
- Bench grinder, which usually has two wheels of different grain sizes for roughing and finishing operations and is secured to a workbench. It is used for shaping tool bits or various tools that need to be made or repaired. Bench grinders are manually operated.
- Cylindrical grinder which includes the centerless grinder. A cylindrical grinder may have multiple grinding wheels. The workpiece is rotated and fed past the wheel/s to form a cylinder. It is used to make precision rods.
- Surface grinder which includes the wash grinder. A surface grinder has a "head" which is lowered, and the workpiece is moved back and forth past the grinding wheel on a table that has a permanent magnet for use with magnetic stock. Surface grinders can be manually operated or have CNC controls.
- Tool and Cutter grinder and the D-bit grinder. These usually can perform the minor function of the drill bit grinder, or other specialist toolroom grinding operations.
- Jig grinder, which as the name implies, has a variety of uses when finishing jigs, dies, and fixtures. It's primary function is in the realm of grinding holes and pins. It can also be used for complex surface grinding to finish work started on a mill.
Bench Grinder
A bench grinder or pedestal grinder is a machine used to drive an abrasive wheel (or wheels). Depending on the grade of the grinding wheel it may be used for sharpening cutting tools such as lathe tools or drill bits. Alternatively it may be used to roughly shape metal prior to welding or fitting. Wire brush or buffing wheels are often mounted in place of the grinding wheels and are used to clean or polish work-pieces.
Safety issues
Goggles or safety glasses need to be worn to protect the operator's eyes from the sparks and metal filings that result. Depending on the workpiece and time of exposure, hearing protection may also be required, the dust produced is also potentially hazardous.
The toolrest (or workrest) should be mounted slightly below the center of the grinding wheel with less than 3 mm clearance from the wheel. This prevents the work from jamming between the toolrest and the wheel.
Grinding wheels designed for steel should not be used for grinding softer metals, like aluminium. The soft metal gets lodged in the pores of the wheel and expand with the heat of grinding. This can dislodge pieces of the grinding wheel.
Wire brushes require particular attention for the safety of the operator and bystanders as the metal wires may become dangerous projectiles as they detach from the wheel.
The machine needs to be securely mounted to a pillar or a bench to be used safely and effectively, often with an emergency stop switch or pedal fitted close by the machine, for use in emergencies.
Polishing & Polish Tools
finishing process refers to the process of embellishing and/or protecting the surface. The process starts with surface preparation, either by sanding by hand (typically using a sanding block) or power sander, scraping, or planing. Imperfections or nail holes on the surface may be filled using wood putty or pores may be filled using wood filler. Often, the wood's colour is changed by staining, bleaching, ammonia fuming and a number of other techniques. Some woods such as pine or cherry do not take stain evenly, resulting in "blotching". To avoid blotching, a barrier coat such as shellac or "wood conditioner" is applied before the stain. Gel stains are also used to avoid blotching.
Once the object surface is prepared and stained, a number of coats of finish may be applied, often sanding between coats. Commonly used wood finishes include wax, shellac, drying oils (such as linseed oil or tung oil), lacquer, varnish, or paint. Other finishes called "oil finish" or "Danish Oil" are actually thin varnishes with a relatively large amount of oil and solvent. Water-based finishes can cause what is called "raising the grain" where surface fuzz emerges and requires sanding down.
Finally the surface may be polished or buffed using steel wool, pumice, rottenstone and other polishing or rubbing compounds depending on the shine desired. Often, a final coat of wax can be applied over the finish to add a slight amount of protection.
French polishing is not polishing as such, but a method of applying many thin coats of shellac using a rubbing pad, yielding a very fine glossy finish.
Different tools used to apply wood finishes include rags, rubbing pads, brushes, and spray guns. The processes involved and the terminology for the materials used are quite different in Britain than the processes and terms used in the USA. For instance, the process of replicating the look and feel of traditional French polished wood is more commonly done in the UK by "pulling over" precatalysed lacquer, whereas in the US a "rubbed" finish is more common. Americans also seem to be more casual in their approach to wood finishing, using products available from local hardware stores. In Britain supplies are more often ordered via the manufacturer representative and are for "Professional Use Only" without instructions appearing on the tin.
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