Using an Angle Grinder Safely for Cutting and Grinding
How to Use an Angle Grinder Safely
An angle or hand grinder is a power tool regularly used by construction workers and contractors. However, it's also an invaluable tool in the home workshop or around the house, with a multitude of uses for DIY and crafts. As the name suggests, it can be used for grinding and cutting but also sanding and wire brushing. But like any power tool, grinders can be dangerous if used incorrectly. This guide shows you what safety precautions to take before and during cutting and how to cut properly.
Angle Grinder Uses
Angle grinders are used for cutting and grinding
- Iron, steel and other metals
- Metal roof cladding, corrugated iron and other steel sheeting
- Brick, stone and concrete
- Slates and building tiles
- PVC waste pipe
- Rusted bolts which can't be undone
- Rebar in concrete
- Grinding and sharpening garden tools
- Welds on steel and also cleaning of welds
Sanding and wire brush accessories are used for:
- Removing paint
- Cleaning rust from steel
- Sanding wood
If you need to cut up stuff for disposal in your trash, an angle grinder is invaluable. Sure, you can use a hacksaw for doing most of these tasks, but a grinder is super quick. Angle grinders make use of a disk of abrasive material spun at a high rotational speed by an electric motor in order to perform the cutting action.
Types of Hand Grinders
Angle grinders can be powered by compressed air or gas (petrol). However, mains powered or cordless versions are the most most likely types to be used by the average DIYer.
Precautions to take when using a grinder
- Make Your Work Environment Safe
- Use Personal Protective Equipment (PPE)
- Check Your Grinder is in Good Condition and Safe to Use
- Choose the Right Disk For the Job
- Use the Grinder Correctly
1: Make Your Work Environment Safe !
All work environments need to be safe, but when using a power tool, a trip or fall can result in a serious accident. Tools are often driven by powerful motors or engines and the business end of the machine can be an abrasive cutting disk, a blade with sharp teeth or a sharp drill bit. As the saying goes "flesh is no match for steel", so safety is paramount.
Here are some tips:
- De-clutter Your Workspace. Tool boxes, scattered tools, lengths of steel and timber and power cables can cause trips and falls. Keep everything to one side where it can be accessed if needed.
- Illuminate Your Workspace Adequately. Proper illumination using background lighting and an optional floodlight/spotlight ensures that you can see what you are doing and don't have to strain your eyes. This is especially important when using goggles which can somewhat obscure vision if they become fogged or dusty. Personally I find a head torch is great as it directs a beam of light exactly where needed. Alternatively you can work outdoors if weather conditions allow it. The advantage of this is that sparks are less likely to be a hazard, illumination is better and dust and fumes tend to dissipate
- Power Cables and Flexes. Keep these behind you so they can't end up getting cut or tripping you up.
- Provide Adequate Ventilation. Grinding and cutting will produce dust and metal particles, sparks and fumes. Open doors and windows and try to direct sparks away from you.
- Flammable Materials. Remove gasoline(petrol), diesel, gas cylinders, solvents, sawdust and other flammable materials from the work area. If this is not possible, direct sparks away from these items. Paper and oily cloths are also a fire hazard.
- Rain and Water. Don't work during rainy weather or use a tool which has become wet without drying it thoroughly. For added safety, power the angle grinder from a socket or extension lead fitted with a GFCI (RCD) adapter.
- Jewelry, Loose Clothing and Earphones. Remove jewelry and bracelets, loose clothing such as scarves and anything else which could possibly get caught up in the rotating grinder disk and shaft. If you have long hair, keep it up under a cap
- Fire Extinguisher. Make sure you have one of these handy in the event of fire. The extinguisher should be of the proper class. A powder extinguisher is suitable for class A, B and C fires
- Be Aware of Those Around You. Keep children and pets out of your work area
2: Use Personal Protective Equipment (PPE)
Personal Protective Equipment (PPE) should be worn to protect your hearing, lungs, eyes, hands and feet from injury. Clothing and gloves should be tight fitting so that they don't get caught and pulled into the tool.
- Eye protection. Safety goggles need to be worn to protect eyes from flying particles and sparks. These should be to EN166B , ANSI Z87.1 or equivalent standard. A full-face visor/shield gives additional protection should the disk shatter.
- Ear Protection. Muffs or earplugs will lessen the risk of hearing damage.
- Hand Protection. Gloves provide protection from sparks, and small fragments of disk and waste metal thrown out by the disk. They also protect your hands from general wear and tear, i.e. minor cuts, scuffs and abrasion. Gloves may give some protection from hot sharp edges of cut metal, but this depends on the rating of the glove and thickness/material used. Some people advise that gloves should never be worn when using an angle grinder because the tool could be classed as rotating machinery and gloves could get caught in the disk. However, this shouldn't happen during normal use as both hands are holding the grinder and the guard should be in place. In any case, gloves should be tight fitting and not "baggy", so that you can hold the tool securely.
- Breathing Protection. Use a suitable dust mask to protect against fumes and dust particles. This should seal properly around the face. Tiny particulate matter (dust particles) entering your lungs over a prolonged period can eventually cause lung disorders, maybe even cancer.
- Footwear. Wear steel toe cap shoes or boots with good grips. If you are working with heavy items which could drop when cut up, this will protect your toes. Footwear should also incorporate steel insoles to protect feet in the event of walking on nails or other sharp objects in the work area.
- Overalls and/or Leather Apron. These protect clothes from sparks. You can of course use old clothes, but avoid flammable materials. Watch out for sparks falling into pockets or turn-ups.
3: Check Your Grinder Is in Good Condition and Safe to Use
An angle grinder like any power tool should be maintained in good condition and given a quick inspection before use. Check out the following:
- Flex and Plug. The flex should be securely attached to the tool and plug. Exposed cores in the flex at these entry points (where damage often occurs), should be remedied by rewiring the plug or grinder. Cracked and damaged flexes with exposed inner cores should be replaced.
- Check the Guard. The guard on an angle grinder is an essential component which should be in place at all times. It protects the user from sparks thrown upwards and backwards and also takes some of the impact if the disk shatters, by deflecting chunks of material downwards. It also may give some protection for your face if the grinder falls back against you while grinding overhead (a practice which you should try to avoid. If there is no alternative, always wear a full face visor). The guard should be adjusted to the correct angle, giving maximum protection by deflecting sparks and disk fragments away from the operator. If the grinder needs to be used in a confined location or to make a vertical cut, the guard should be adjusted to suit. Usually it is only necessary to loosen screws or a bolt, twist the guard and re-tighten the fastener. Any build up of slag on the inside of the guard should be periodically removed.
A secondary but equally important function of the guard is to shield the back of the disk from making contact with your hand, potentially causing a serious injury.
- Side Handle. This should be tightly screwed into the tool.
- Ventilation Slots. These should be kept clear to prevent overheating of the motor
- Use a GFCI (RCD) adapter. You will likely have one of these fitted at the "fuseboard"/ electrical panel, but as added insurance against lethal electric shock in case this fails, it's wise to use an adapter on the plug of your grinder or extension lead. For more details see this article: What Causes Electric Shocks? How an RCD Can Potentially Save Your Life
4: Choose the Right Disk for the Job
- Use the Proper Disk for the Material Being Cut. (e.g. masonry or metal)
- Check the Disk for Defects. Cracks, missing chunks or other defects in a disk are a potential hazard. Never use a damaged disk which could potentially shatter and throw out fragments at high velocity with fatal consequences
- Never Use a Cutting Disk for Grinding. Cutting disks are thin and not designed to withstand side pressure, unlike disks used for grinding. They can over flex and shatter. If you grind with the side faces of a cutting disk, this will thin the disk, overstress it and potentially result in a disk explosion, showering you with disk fragments. Grinding disks shouldn't be used for cutting either
- Disks Should Never be Used at a Rotational Speed Greater Than They Were Designed For. Disks are marked with the maximum RPM (Revolutions Per Minute) specification. The larger the disk, the lower the maximum speed it can rotate at. This means that you shouldn't use a worn-down 9-inch disk on a 4 1/2 inch grinder
- Make Sure the Flange Nut is Suitable for the Disk and Tightened Fully
- Make Sure the Disk is Seated Properly Before Tightening. Usually the flange nut is turned upside down when used with thinner disks, otherwise the spigot or raised rim around the perimeter of the hole in the nut will prevent the nut from clamping down on the disk.
- Don't Use a Disk After the Use by Date. Grinder disks have a use by date. This is due to a concern about moisture and/or ageing resulting in softening of the binding resin and weakening the disk. Disks may be perfectly ok after the use by date, but it's better to play safe, not stock up on disks and use them before the date marked. Disks should be kept in a cool dry place
- The "hollow" on a depressed centre disk should be facing outwards.
A shattered disk can kill!
If you need to cut stainless steel, special disks made from a hard abrasive material can be used, which won't wear away as quickly. Thinner disks are available for cutting metal sheeting such as roof cladding. These cut quicker with less friction so there's less damage to protective coating/paint on sheets. However, they also wear away somewhat quicker. Diamond abrasive disks can be used for cutting brick, stone, concrete, slate and roof tiles.
Angle grinders are commonly available in 4 1/2", 5", 6" and 9" sizes. Air powered grinders are also available.
Never use cutting disks for grinding!
Accessories for Angle Grinders
You can also use sanding disks. These attach to a rubber/plastic pad fitted to the grinder. A sanding pad can get into spaces inaccessible to an orbital or belt sander.
Don't use attachments not designed for the grinder, e.g. circular saw blades. I don't recommend the use of "chainsaw" type circular attachments as these are extremely dangerous if they become blunt.
Always unplug the grinder before changing disks
5: Use the Grinder Correctly (Safe Cutting Techniques)
Read your manual before use and become familiar with your power tool.
Be alert at all times and watch out for the unexpected and others coming into your workplace. Children should never be in the vicinity while using dangerous power tools. Don't use an angle grinder in the rain because you may end up getting an electric shock. The shock could startle you and the likelihood is that you could drop the grinder and potentially cause injury to yourself.
If possible, don't use a grinder overhead you because if you lose control, it could drop down on top of you.
Don't use a grinder if you are tired.
Tiredness can result in poor concentration and the possibility of an accident and personal injury. Keep your feet spread apart. This braces your body better and makes it less likely for you to be thrown off balance.
Ensure that the power flex and any extension cords are behind you and can't fall into the path of the cutting disk. If the work-piece isn't heavy, hold it in a vice on a bench or clamp it to a surface.
Never hold a piece of metal in your hand to cut it!
I did this once and the grinder disk caught in the metal, flung it up into the air, and I didn't find it until a month later on top of a shelf! You can usually hold a length of metal down by standing on it with two feet, however, it's questionable whether this is safe. The danger is that the disk could snag in the metal and rip it from under your feet, causing you to lose your balance, especially if you're using a 9-inch grinder. If cutting outdoors, lengths of steel can be supported on short sections of 9 x 2 or similar so the disk doesn't make contact with the ground. Position the cutting point so that it overhangs the support. This ensures that the weight of the waste will open up the cut as the material falls away.
Don't cut in the span between two widely spaced supports.
The cut may close up as you cut through, potentially causing the disk to bind. Use adequate protection either side of the cutting point.
Never use a grinder without a side handle
The side handle gives you more control over the tool in the event of kickback and torque reaction (the body of the tool twisting about the centre of rotation of the disk if it snags).
Don't position your body behind and in line with the plane of the rotating disk
Hold the grinder to one side so that the tool and wheel won't hit you in the event of kick back.
Hold the tool with a firm grip using both hands.
Keep one on the body of the grinder and trigger and the other hand on the side handle. Don't use it single handed. If the disk gets stuck in the work-piece, it is almost certain that it will be pulled out of your grip and potentially cause an accident. Even while holding a grinder with two hands, you need to be prepared for this, especially when using a large 9-inch grinder. If the disk binds, release the trigger immediately to avoid burning out the motor and if the disk is still turning, allow it to come to a stop before removing it from the cut.
If you are cutting, you will probably have a guideline drawn on the workpiece. Start the grinder, allow the disk to reach max speed (Large grinders may have a slow start-up feature to prevent the "kick" on power up) and place the disk gently in contact with the back of the work-piece so that you cut towards yourself. You can cut from the front of the workpiece, however, it can be more difficult to control the grinder as the disk tries to climb out of the cut or moves down in front of the edge of the metal being cut. When cutting from the back, the disk is less likely to drop over the edge as the workpiece is under the back of the disk.
Brace your arms in case the grinder kickbacks in the cut.
If you are cutting on the ground, keep your legs out of the way in case the grinder slips. If a climbing cut (cutting from the front of the workpiece with sparks being thrown downwards) is essential because material must be cut in place and can't be held in a vise, make sure sure you keep your head out of the way. Otherwise, you can be hit in the face if the grinder kicks back upwards. This is why I reckon it's safer to cut stuff on the ground where it's at arm's length and further away from the face. Apply gentle and constant pressure and the metal will start to become red hot. At this stage, it becomes softer and cuts easier.
Don't force the disk into the cut. This can overload the machine or cause it to catch on the workpiece.
Angle the grinder so that sparks are thrown backwards either to one side of your legs or between your legs. Don't allow them to concentrate on one point on your clothes for any length of time or they will cause them to ignite (been there, done that!). A leather apron although cumbersome will protect clothes.
Keep the disk straight and avoid twisting it in the cutting slot to prevent it sticking and causing kickback.
If the disk binds, it can shatter or throw out fragments.
When the waste is almost cut away, take care that the disk doesn't get trapped.
Cut through the material and allow the waste to fall away or move to one side. Remove the disk from contact with the material, release the trigger on the grinder, allow the disk to spin down to a stop, watch out that you don't scuff the flex with the disk and only then allow it to rest on the ground. The workpiece and waste will be extremely hot at this stage, so allow them to cool down before handling.
Don't walk around your work area while holding a grinder which is powered up. This applies to all power tools.
Grind off sharp edges on the workpiece and waste (if it is being reused).
Keep your two hands on the grinder at all times and hold it firmly until you release the trigger and the disk comes to a stop.
If you use the grinder single-handed, you risk losing control of it.
I have had minor accidents while moving a grinder while holding it with one hand and not keeping track of where my other hand was. Luckily these were just minor scuffs. This is why it is important to wear gloves.
It's probably safest to cut on the ground if you're cutting long sections of metal because they can be supported underneath and only drop a few inches as waste is cut away. Also, the grinder will be low down and less likely to cause an injury if for some reason it dropped out of your hands. Unfortunately, if you have a lot of material to cut, and do this on a regular basis as part of your job, this practice would probably cause back strain long term. So cutting at waist level would be advisable.
Never hold the workpiece in your hand while cutting. Always secure in a vice, or use clamps.
How to Use an Angle Grinder for Cutting Metal Cladding
The best way to cut metal cladding is to first mark the cut line using a Tippex style marker. Then cut through the ridges first, followed by the valleys. I found the best way to avoid kickback is to cut the ridges from the back, pulling the grinder towards me, then cut the valleys, pushing the grinder away from me. Because cladding is so thin, the disk can tend to catch in the edge and the grinder will jerk. So you need to experiment to avoid this. If you can imagine a tangent to the edge of the disk, this should be at an acute angle to the sheet to avoid catching. In any case, use light pressure to reduce the chances of this happening. Thin disks as used for stainless steel are best for minimising friction and avoiding burning of the paint coating.
Hitachi Grinders from Amazon
This from Amazon is rated at 6.2 amp / 110 volts (680 watt). This is a good general purpose grinder, adequate for cutting and grinding most stuff around the home (this is the latest version of the grinder I use in the photos). You can also use it with a wire brush for de-rusting and removing paint. Higher powered versions are available up to 1000 watts from this advertiser for quicker cutting through heavier material. G12SR4 model
Grinding Metal and Stone
Grinding by its very nature may involve using the grinder at all sorts of angles. Try to direct sparks away from you and watch out where they land. Remember all flammable material should have been placed safely out of range. Again watch out for kickback so you need to hold the grinder firmly. Re-adjust the guard if necessary to shield yourself from sparks and angle the plane of the disk at about 30 degrees to the workpiece.
Other Uses for Grinders
An angle grinder can be used instead of a bench grinder for sharpening blades (e.g. a lawn mower blade), plus the consumable disks are much cheaper to replace than the grinding wheel (stone) on a bench grinder.
Safety When Grinding Near Edges
Take care when using a wire brush or grinding disk near edges. Tilt the grinder slightly so that only the edge of the brush or disk furthest away from you spins out over the edges on a workpiece. If the bristles move towards an edge, they can snag, cause the grinder to jerk and kickback if you apply too much pressure.
Where Should You Keep Your Head?!
Debris is thrown out in the plane of the disk and the guard should catch anything which comes in your direction.This is why a guard should be used at all times. If you offset your body and head to one side, you should be out of this plane, and I reckon this is the safest thing to do. However theoretically, a thrown fragment could hit the edge of the guard, be deflected and hit you. In any case, it is easier to keep your head to one side to see what you are doing. Some grinders are provided with a guard which encloses both sides of the disk for added security. However this can be more cumbersome and obstructive while working.
Making Accurate Square Cuts With a Grinder
If you want to accurately cut box section steel, mark all around the perimeter using a square and scribe tool or Tippex marker and then cut each of the four faces in turn. You can also buy a jig which holds a grinder onto a hinged arm which can be raised up and down so that square cuts can be made. An alternative is a metal cutoff saw. These usually have a 12 inch abrasive, or tungsten carbide tipped blade, enabling accurate square or mitred cuts to be made on hollow or solid section steel up to 4 inch in cross section.
Cleaning Your Hands
Ideally you should wear gloves to protect your hands from rust, oil and other grime on the material you're cutting. However you may need to dispense with gloves in order to do any marking out/fine work, and inevitably grime will end up on hands. A hand cleanser will do a better job than soap at removing grime, and many cleansers contain a fine abrasive (just like toothpaste does) which helps cleaning. When you use any hand cleaner, it's a good idea to use a moisturizer afterwards to replace the natural oils washed from skin. This prevents cracking or uncomfortable dryness if you suffer from eczema/dermatitis, psoriasis or other skin conditions.
Recommended Hand Cleansers
Gloves protect hands, but if you have to work barehanded, an abrasive hand cleanser will do a much better job than soap at removing grime and is pretty much essential. I use for removing oil and grease from my hands. It's also good for removing oil paint, tar, soot and general garden grime. (even used it once for taking black bicycle grease out of a white carpet!) Dreumex anti-bacterial Pumice Heavy Duty Hand Cleaner, available from Amazon
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2012 Eugene Brennan