A right-angle grinder, commonly known as an angle grinder is a very powerful and useful tool but can also be a very dangerous tool if not used correctly.
Selecting the correct size machine is essential to ensure a safe operation – for instance using a 230mm diameter machine to grind down welds on palisade fencing will prove to be very unmanageable and quite possibly very dangerous.
Conventional angle grinders come in various sizes ranging from 100mm up to 230mm diameter, with the 115mm and 230mm diameter as the most popular in South Africa.
When selecting the correct angle grinder, the size of the disc that will be used should be considered. A disc too large for the given machine (i.e. using a 125mm diameter disc on a 115mm diameter machine) will run at a higher speed than it is rated for, resulting in a very dangerous operation. Disc size diameters are clearly displayed on the labels for easy reference.
Further to selecting the correct sized disc, power and speed of the angle grinder also plays a significant role. POWER refers to the measurement of input or output wattage that the machine uses (depending on the manufacturer). Generally, the rule of thumb is that a higher power rating ensures a better performance of the abrasive product. When an abrasive disc is cutting or grinding, it is putting additional load on the machine. If the machine is under-powered, the extra strain may cause a reduction in motor speed, causing potential damage to the machine and underperformance of the disc. More often than not, an underperforming disc then results in more pressure being applied by the operator which then makes the disc perform even worse and also potentially causes disc breakages.
SPEED on the other hand, is clarified as the rate at which the disc will turn (measured in Metres per Second and stated as the RPM). The maximum operating speed of a standard cutting or grinding disc is 80 metres per second (peripheral speed). Depending on the size of the disc, this will then relate back to a higher or lower RPM rating; 80m/s on a 115mm disc equates to 13 300 RPM, while 80m/s on a 230mm disc equates to 6650 RPM. For this reason, it is imperative that an angle grinder must only be used with a disc size particularly made for that machine.
Another very important factor to consider would be the standard accessories. All angle grinders should have a safety guard that must be fitted to the machine at all times , a handle and a retainer nut for securing the disc. Retainer nuts are available in various types and they are for fitting the disc to the machine, including are some that don’t require a spanner to fasten and loosen. Regardless of which type, make sure that you are not over tightening it as these machines are designed to self-tighten on start-up, therefore requiring only tightening by hand.
Remember to inspect discs for potential damage prior to use. The periphery of the disc should be intact, not chipped or frayed and it should be flat, not warped. Never attempt to bend or twist the disc as the fibre reinforcing will be damaged and potentially form a dangerous crack.
Safe usage and operation pictograms are displayed on each disc label that should present the following markings:
- OSA – Organisation for Safety of Abrasives: These manufacturers commit to certified quality management with documented processes and internal testing facilities of the highest competence ensuring product safety for the end user
EN Standard – European safety requirement for bonded abrasive products (such as cutting and grinding discs – EN 12413)
Safety pictograms – these pictograms show the required PPE to ensure safety for the operator and includes gloves, ear protection, eye protection etc.
Material Applications – the disc will identify which type of materials it may be used on. Note that this will quite possibly only be a general identifier (such as “Metal”). Contact the manufacturer should you require more detail on specific applications.
Wheel type – this will tell you whether the disc is manufactured for free hand cutting, stationary machine cutting or grinding applications.
A cutting disc should never be used to grind with or cut anything but in a straight line. Bending the disc to cut a curve or radius will result in the fibre reinforcing becoming damaged and may cause wheel failure.
For grinding applications, a minimum grinding angle of 30 degrees is essential. This is what is termed the angle of attack. The optimal range is between 30 and 40 degrees to the surface. Should you increase the angle of attack, the disc will be dressed more and the effectiveness of the grind will be reduced. This could also lead to chatter marks and large, deep scratches in the workpiece. Should you reduce the angle of attack, you run the risk of overheating the face of the disc which will cause the disc to start fragmenting and may become a major safety hazard.
Taking the time to choose the correct tool and using this in conjunction with the highest quality, value for money abrasive products will ensure that you complete your task safely and with minimal effort.