DIY Basics: Essential Guide To Grinders, Files and Rasps
‘There’s a huge range of power and hand tools available to help you grind, file or roughly shape just about anything from timber, metal, and even stone,’ says Handyman expert Frank Gardner.
‘But the sheer diversity can sometimes make it difficult to decide on what best suits your needs.’
The good news is that many of these tools can be adapted to suit different tasks, so one tool can often fill in for another and save the day.
‘If you haven’t got an angle grinder fitted with a metal grinding disc to smooth a metal edge, then a mill file will do the job, but just take a little longer,’ says Frank.
The daily grind
These DIY essentials fall into three broad and overlapping categories.
GRINDERS are power tools that operate at high speed to cut everything from metal to tiles, while also being able to clean off rust and strip paint.
FILES are hand tools designed to abrade a range of tough surfaces such as metals and ceramics. They are available in various shapes and levels of coarseness.
RASPS are similar to files but have more jagged teeth and are designed primarily for working with timber. Along with Surform tools, they are great for rough-shaping curved or irregular workpieces.
The Wheel Deal
Angle grinders are popular with DIYers due to their versatility. With the correct wheel or disc fitted they can cut, sand, polish and even carve.
They are classified by the diameter of disc or wheel they are compatible with. The most popular sizes include 100, 115 and 230mm, and generally, the larger the disc size, the more powerful the grinder.
The wattage is also a good indication of how much the grinder can handle, as it specifies how much current is required to drive the motor.
Angle grinders are popular with DIYers due to their versatility
Grinder set up
AUXILIARY HANDLE can be moved for left or right-handed operation.
WHEEL GUARD can be rotated around the cutting wheel and locked using a quick-release lever.
VARIABLE SPEED CONTROL reduces the grinder’s RPM, as recommended for polishing applications.
SPINDLE LOCK BUTTON stops the spindle shaft from rotating, so that the flange holding the wheel can be loosened or tightened.
SPIN DIRECTION INDICATOR allows the grinder to be orientated so that sparks are directed safely away.
TRIGGER LOCK SWITCH is used to keep the trigger pressed for continuous operation.
WRENCH HOLDER keeps the pin wrench handy for changing the wheels and accessories.
LIVETOOL INDICATOR glows when the tool is plugged into mains power.
Using a grinder
FIT THE ACCESSORY Check that the wheel is in good condition and fitted correctly. Check the guard is firmly mounted in the best position and run the tool without load for a few seconds.
CLAMP THE WORKPIECE Make sure the workpiece is firmly clamped and orientated so sparks will be directed away from any fire hazards, then switch on the tool.
DON’T OVERLOAD THE GRINDER Avoid adding extra pressure, letting the weight of the grinder do the work. If it cuts out, switch it off and make sure it’s clear of the workpiece before restarting and letting it spool up to full speed.
BE MINDFUL OF SPIN DIRECTION Keep an eye on the spin direction indicator to ensure the accessory is spinning away from the workpiece, minimising the risk of kickback.
Angle grinders are a leading cause of DIY accidents. Before using one for the first time, read the manual and follow the safety instructions.
WEAR GOGGLES or a face shield, dust mask, gloves and hearing protection, plus long sleeves.
NEVER REMOVE THE GUARD unless the accessory specifically requires this and the manufacturer’s instructions allow it. Never try to mount a circular saw blade on an angle grinder.
DISCONNECT THE CORD before changing accessories, as even the most careful user can accidentally activate the power switch on the tool. Keep bystanders away and don’t use the grinder near flammable materials.
Choosing a wheel
When selecting an accessory, check the information on the back to ensure you will be using it for its intended purpose. Also check that its nominal operating speed matches that of your grinder.
Common accessories include fibre-reinforced cutting and grinding wheels, diamond wheels, wire wheels, cup brushes and abrasive discs. Others include rubber pads that can convert the grinder to a polisher.
When mounting the wheel, make sure that the double-sided flange holding it to the spindle is the right way up. The packaging or disc itself will clearly indicate which side of the flange should be tightened against it.
POLISHING BUFFS can shine up steel and other metals but should be used with a variable-speed grinder
CUT OFF DISCS are ideal for quick rough cuts on steel pipe, angle iron, reinforcing bars and threaded rod.
WIRE WHEEL BRUSHES are great for cleaning, and paint, corrosion and rust removal in hard-to-get-at spots.
ABRASIVE DISCS are excellent for removing surface coatings like paint or corrosion from timber and metal.
MULTI-CUTTING BLADES with tungsten carbide tipped teeth can cut aluminium, plastics, fibreglass and particleboard.
CONTINUOUS DIAMOND BLADES are used wet or dry to cut ceramic tiles, granite, marble and hard stone.
METAL GRINDING WHEEL clean up cutting burrs, smooth out welds and sharpen blades.
CUP BRUSHES remove rust and old paint from metal surfaces. They are best on broad surfaces like barbecues
CONCRETE GRINDING DISCS are for rough grinding of concrete, stone and fibreglass surfaces.
Files are simple hand tools made from hardened steel with rows of teeth or ridges that are used to cut away small amounts of materials, ranging from metal and plastic to rust and sometimes timber.
Several factors determine how aggressively a file cuts, as well as what objects it is best suited to.
CUT refers to the pattern on the working surfaces, with a single-cut file having parallel rows of ridges. A double-cut file has a second set of rows that cross the first, turning the ridges into fine teeth.
COARSENESS is broken into three categories. Single is the smoothest, second is medium and bastard is the coarsest grade of teeth.
LENGTH of a file dictates how much material it is capable of removing in a single full stroke.
SHAPE or profile is what makes a file useful for specific jobs, such as inside a circular recess.
Files are simple hand tools made from hardened steel with rows of teeth or ridges that are used to cut away small amounts of materials
A double-cut file has a second set of rows that cross the first, turning the ridges into fine teeth
Make sure the material to be filed
is softer than the file. In other words, don’t try to file hardened steel with a hardened steel file.
SELECT THE BEST FILE for the job as there are many types available in various sizes, shapes, degrees of coarseness and tooth geometries.
CLEAN THE FILE regularly to remove fine metal shavings, called pins, stuck in the teeth, using a purpose-designed file brush or stiff wire brush.
Choosing a file
There is a huge variety of files available, some of which are for general use and others for highly specialised applications.
To tidy the cut end of a threaded rod, use a half-round file, which has a narrow edge that can get right into the groove of the thread.
A round profile is best to clean up a welding job or remove the burr edge around a hole drilled in metal. Start with a second-cut file, then
use a single for a fine finish.
For sharpening a mower blade or filing away rust, a bastard file will get the job done quickly.
FLAT FILES are general-purpose tools with a slightly tapered shape and a rectangular profile.
ROUND FILES are used to smooth or shape circular openings, small curves and concave shapes, and enlarge holes.
HALF-ROUND FILES are used on rounded and flat surfaces with one flat side and one rounded side.
MILL FILES are used for fine-finishing lathe metalwork as well as sharpening various cutters and blades.
CERAMIC FILES feature carbide grit for smoothing and sanding out rough edges on ceramic tile and marble.
FILES BRUSHES are used to remove pins of metal and shavings of timber or plastic clogging the file’s teeth.
SQUARE FILES are shaped to file internal corners and angles, and to square up holes and mortises.
WARDING FILES have a narrow tip for toolmaking and hobby applications. Originally designed for filing keys.
CONTACT POINT FILES are small, thin and flat for electrical, magneto and distributor applications.
Using a file
The ridges or teeth of a file are cut into the surface at an angle, and the best way to achieve a smooth and consistent finish is to work with this feature, moving the file in even strokes on a diagonal along the length of the workpiece.
Step 1. Chalk the file
Chalk the file liberally before use, rubbing it into the ridges. This will increase the resistance of the file to being clogged by pins, without reducing its performance.
Step 2. Clamp the workpiece
Clamp the workpiece in a vice, positioning it so the file won’t abrade against the jaws. Start filing with the file handle in one hand and the palm of your other hand on the end.
Step 3. File on the push stroke
File on the push stroke, pressing down firmly and working along the length of the workpiece in a sideways motion instead of sawing the file back and forth on a single small area.
Rasps and surforms
Rasps and Surform tools are closely related to files, but instead of being typically used for metalwork, they are designed for shaping timber.
The teeth of a rasp are larger and more jagged than the even ridges of a file, perfect for removing large amounts of material.
As with files, the teeth are made of hardened steel. They are arranged in an alternating pattern, to make them cut more efficiently and to minimise the roughness and grooving of the timber surface.
With a perforated metal cutting surface that resembles a cheese grater, Surform tools are designed to remove large amounts of timber very quickly and easily.
Surforms don’t clog and leave shavings rather than sawdust, and the relatively rough finish is easy to smooth because the cutting action is done by tiny flat blades instead of teeth with a triangular profile.
This tool is often used for tasks that could be done with a hand plane, but which carry a risk of damaging the finely honed blade, such as roughly shaping reclaimed timber.
Surforms come in a range of configurations, with frames that can be held like hand planes, oversized rasps and small peeler-like shaping tools.
Once a Surform is dulled through use, it is impractical to sharpen, so replacement blades in flat and curved profiles are available.
Surform tools are designed to remove large amounts of timber very quickly and easily
The pointy teeth of rasps are less prone to clogging than the finer ridges of a file, and they are particularly useful for removing timber from rounded surfaces or areas that are awkward to reach.
As with files, working on the diagonal in single strokes reduces grooving and results in a finer finish, but removes less material than working the rasp back and forth using a sawing action.
Even now, some boutique rasps are made by hand, because tiny irregularities in teeth placement are introduced by the crafting process, called stitching. These variations mean that the timber worked with such a file has a smoother surface.
When rasps are manufactured with digital accuracy, every second row of teeth normally cuts exactly the same path, making parallel furrows or grooves in the timber surface.
To emulate the desirable features of handmade tools, some rasps are manufactured using a template that is modelled on hand-stitched teeth.
No matter how well-made a rasp is, though, it still leaves a rough finish that needs to be smoothed further.
The most popular way to do this is using abrasive paper, but in some cases, such as inside corners or round holes, files are more practical to use.
No matter how well-made a rasp is it still leaves a rough finish that needs to be smoothed further
The pointy teeth of rasps are less prone to clogging than the finer ridges of a file
High-speed rotary tools are among the most versatile power tools, and a major proportion of the attachments available allow them to be used like miniature angle grinders or bench grinders.
With a typical no-load speed of about 30,000rpm, these tools are perfectly suited to cutting and grinding metal, sanding, buffing and polishing, as well as making light work of intricate filing jobs.
The biggest advantage of using a rotary tool for these applications is accuracy and, if a cordless model is chosen, portability is another bonus.
A grinding attachment can be used to effortlessly sharpen a mower blade without removing it from the mower.
Miniature fibre-reinforced metal cutoff wheels can be used to trim aluminium angle as easily as an angle grinder, but with far greater precision and much less mess.
High-speed rotary tools are among the most versatile power tools
A power file is technically a type of belt sander, but its practical applications are much more closely related to the kinds of jobs that files and rasps are normally used for.
The narrow arm that extends from the tool can be manoeuvred into similarly confined or awkward spaces as a file or rasp.
The belts feature a coarse grit, and filing control is achieved using the variable speed dial. For precise filing of timber or metal, select a slower speed, increasing the rate for faster removal of material.
A power file has practical applications that are closely related to the kinds of jobs that files and rasps are normally used for
Bench grinders are about as simple as power tools can be. The usual setup consists of a central motor whose spindle extends out of
both sides of the tool, with a stone grinding wheel mounted on each end.
An adjustable rest on each side provides a platform for the tool or workpiece, which is pushed against the rapidly spinning wheel that sharpens or shapes it.
A transparent shield, often fitted with a magnifying lens, is mounted over the edge of each wheel to deflect metal shavings.
There are also attachments such as wire wheels and cloth buffing discs that can be mounted in place of the grinding wheels to further extend the range of tasks this tool can perform.
Bench grinders are about as simple as power tools can be