Using an Angle Grinder Safely for Cutting and Grinding

What are Angle Grinders Used For ?

An angle or hand grinder is an invaluable power tool in the home workshop with a multitude of uses for DIY and crafts. As the name suggests, it can be used for grinding and cutting:

  • 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 and rebar in concrete
  • Grinding and sharpening garden tools
  • Cutting/grinding and cleaning up welds

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.

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.

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.

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Typical 4 1/2 inch, 600 watt grinder manufactured by Hitachi
Typical 4 1/2 inch, 600 watt grinder manufactured by Hitachi | Source

Angle Grinder Safety

  1. Make Your Work Environment Safe
  2. Wear Safety Clothing
  3. Check Your Grinder is in Good Condition and Safe to Use
  4. Choose the Right Disk For the Job

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 a floodlight 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


Kitted out for the job with eye and  ear protection and dust mask
Kitted out for the job with eye and ear protection and dust mask | Source

2 - Wear Safety Clothing

Safety clothing should be worn to protect your hearing, lungs, eyes, hands and feet from injury. Clothing and gloves should be tight fitting so that it doesn't get tangled 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 gives additional protection should the disk shatter.
  • Ear Protection Muffs or ear plugs 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. 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 towards the ground. 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 regularly cleaned to prevent overheating of the motor

Close up of disk and protective guard. This should be in place at all times and adjusted properly
Close up of disk and protective guard. This should be in place at all times and adjusted properly | Source
The guard prevents sparks or shattered disk fragments from being thrown up towards the operator. It also prevents your hand making contact with the disk.
The guard prevents sparks or shattered disk fragments from being thrown up towards the operator. It also prevents your hand making contact with the disk. | Source

4 - Choose the Right Disk For the Job

A shattered disk can kill!

  • 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, and potentially result in a disk explosion, showering you with disk shrapnel. 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
  • Don't use a disk after the use by date I only learned this recently but disks have a use by date. Presumably 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 probably 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

If you are fitting a depressed centre disk on a grinder, the "hollow" should be facing outwards.

If you need to cut stainless steel, disks made from hard abrasive can be used which won't wear away as quickly. Thinner disks are available for cutting metal sheeting such as roof cladding.Thinner disks cut quicker but also wear away 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.

Abrasive and diamond cutting disks
Abrasive and diamond cutting disks | Source

Accessories For Angle Grinders

Wire brushes are available for cleaning and removing rust and paint from metal and wood. These can fling out steel bristles so you need to wear eye and face protection.

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.

Sanding disk and backing pad
Sanding disk and backing pad | Source
Knotted wire brush
Knotted wire brush | Source

How to Cut With an Angle Grinder - 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 because the cut may close up as you cut through, potentially causing the disk to bind

Hold the tool with a firm grip using both hands, one on the body of the grinder and trigger, the other hand on the side handle. While I have sometimes used a grinder with just one hand, this is not recommended. 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, 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 work piece. 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 arms 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 overload the machine. 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 work piece 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.


Support long sections so they don't sag, trapping and binding the disk
Support long sections so they don't sag, trapping and binding the disk | Source
Clamp the workpiece firmly in a vice and start cutting from the back. Small pieces should always be held in a vise or clamped while cutting, otherwise they can go flying!
Clamp the workpiece firmly in a vice and start cutting from the back. Small pieces should always be held in a vise or clamped while cutting, otherwise they can go flying! | Source
Direct sparks backwards
Direct sparks backwards | Source
Keep your feet spread apart for stability. You can let the sparks fly backwards between your legs, alternatively you can stand to one side of the workpiece.
Keep your feet spread apart for stability. You can let the sparks fly backwards between your legs, alternatively you can stand to one side of the workpiece. | Source

Dewalt 4 1/2 inch Grinder with a Powerful 10 Amp Motor

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.

When grinding, Sparks can be directed to one side
When grinding, Sparks can be directed to one side | Source

Using a Wire Brush

Take care when using a wire brush. Tilt the grinder slightly so that the edge of the brush furthest away from you spins out over the edges on a workpiece. If the bristles move towards an edge, they can cause the grinder to jerk and kickback if you apply too much pressure.

Bristles of a wire brush should travel out over the edge of the workpiece
Bristles of a wire brush should travel out over the edge of the workpiece | Source

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 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.

Guard enclosing both sides of disk
Guard enclosing both sides of disk | Source

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.

Metal cut off saw
Metal cut off saw | Source

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.

Fast Orange - Tough Hand Cleaner from Amazon

Hand cleaner with pumice which acts as a mild abrasive. Ideal for cleaning all sorts of grime from handling steel. Recommended for removing resins, oil, grease, tar, grime, soil, printers' ink, epoxies, paint, rubber cement, gasket and tile cements.

© 2012 Eugene Brennan

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Comments 11 comments

Kevin Kolb 4 years ago

Hi

Maybe I'm wrong but I have always been taught to have the grinder shoot the sparks away from you and come into the cut from the far side. That way if it binds it doesn't come directly back at you. I'm confused about your approch on grinding. It seems from the pictures that this is very awkward to spread your legs to allow sparks to travel through. Please advise khardways@aol.com


eugbug profile image

eugbug 4 years ago from Ireland Author

Hi Kevin. The sparks will always travel towards you as the lower side of the disk is traveling towards you. You can let the sparks fly between or to one side of your leg. Also by cutting from the back of the metal, similar to the way timber is cut with a chainsaw, if the grinder binds it will be pulled away from you. This is safer than cutting from the front as the disk can be thrown up out of the cut.

When grinding, you can hold the grinder so that the disk is angled about 15 degrees from the horizontal and sparks can be thrown fully away from you.

See Bosch manual page 6 http://docs-asia.origin.electrocomponents.com/webd...

You can also cut perpendicular to the way you are facing as they show in the manual


Hal 3 years ago

When grinding metal that is below waist level is it ok to sit and grind. I find this position to be most comfortable than bending awkwardly.

Thanks


eugbug profile image

eugbug 3 years ago from Ireland Author

Hi Hal, I don't see any reason why you can't grind while sitting down as long as you deflect the sparks away from you. The only danger I can think of is that if the grinder slips out of your hands, it is likely to drop down onto your legs or knees, causing injury. If your legs are under a bench, obviously this is less likely. Also make sure the workpiece is well secured, otherwise if it is small and the disk catches it, it can be thrown towards you. In the photos I am grinding while bending down and personally I find it a better way of bracing my arms by keeping them outstretched. You can also work at a bench with the work piece held in a vice.


Ben 2 years ago

I was reading about the dangers of burning PVC pipe. Apparently burning PVC releases dioxin gases (nasty cancer causing gas). I figured that angle grinding PVC would release dioxin gas, seen as materials cut using an angle grinder heat up quite a bit.

Do you know if cutting PVC with an angle grinder does in fact cause the release of nasty gases?


eugbug profile image

eugbug 2 years ago from Ireland Author

I've never cut PVC pipe with a grinder until today, usually I just use a hacksaw (or a reciprocating saw can be used). If the wall of the pipe is thick, e.g. heavy gage plastic gas line, heat could build up with the disk buried in the wall of the pipe, and friction could probably produce enough heat to cause the plastic to smoke. In any case unless you are cutting pipe regularly on a day to day basis, I would doubt whether the fumes would have any detrimental health effect.

I tried cutting some 1 1/2 PVC waste pipe. There was no smoking or fumes, just a slight smell of hot PVC. It's important to use light pressure. Excessive pressure increases friction and this may cause burning. Cutting produces very fine PVC dust so it's best to use a dust mask.


Peter 20 months ago

Hi Many thank for your blog.

Do you know if the risk of lose control or brake the disc is the same with a 1200 Kw, 1100 Kw, 900 Kw... 5" angle grinder.

I want to buy a grinder.

But paddle switch, electromagnetic brake, and kickback stop, exist only with 1200 Kw. Do you know why? Do you think I can reduce the cost of my purchase choosing a small 700 W grinder

Thanks.


eugbug profile image

eugbug 20 months ago from Ireland Author

The powers you quote, 1200, 1100 and 900 would be watts not kilowatt (i.e "w" not "kw).

Anyway for a given size of grinder, 5 inch in your case, the rotational speed will be the same for all three powers, but a 1200 watt tool is capable of producing more torque, and as a result, force at the edge of the disk, without slowing down. So it allows you to grind away material quicker since speed isn't reduced. The reason for the electric brake and kickback stop is to try to cope with the extra force the motor can produce if the disk stalls completely or semi-stalls. The kick-back phenomenon is due to both the angular momentum of the disk, and also the reaction of the workpiece due to the torque of the motor.

So there is a potentially greater risk with the higher power machine (just as there is with a larger 9 inch grinder), but the safety feature is supposed to cope with this risk. The higher powered machine will let you work faster but is likely to be more expensive.


Peter 20 months ago

Many Thanks.

Your explanation of the phenomenon is very clear .


Bill Walt 14 months ago

Thanks for your info. Knew most of this but I always enjoy reviewing safety facts just to make sure I'm doing it right or that someone didn't come up with a better idea than what they were teaching in the 1970's. Thanks for your time and knowledge, Bill


eugbug profile image

eugbug 14 months ago from Ireland Author

Thanks Bill, glad you liked it!

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