TOOLS

Economics

The overall economic calculation when purchasing tools and more especially power tools is very important; as it often happens that “cheap” tools turn out to be uneconomically expensive on account of their generally bad performance or short service life and where the tool, which appeared “more expensive” on the surface turns out after only a short period of use better value-for-money in terms of performance and overall service life and therefore the more economical decision.

Quality

Two essential criteria for tool quality need consideration – the working quality of the tool and the work progress the tool will offer the user. This is however subjective and really depends on the user and the working task being performed; for example, a user using a tool which is perfectly designed for him or her and the working task, will be more content than with a no frills “cheaper” product, that isn’t as perfectly designed.

Outline

Power tools are usually designed for a special job which means that there are many different types of power tools on the market with a great variety of versions and models. The construction must be sturdy, easy to maintain and capable of continuous performance. The weight plays only a minor role, for instance, in cases where freehand or overhead work has to be done frequently. Noise, dust emissions and vibrations must be taken into consideration by the manufacturer.

Terminology

AC/DC motor

Electric motor which can be operated with both alternating and direct voltage.

Ampere

Unit of measurement for the electric current, current intensity.

Attachments

Accessories built onto machines to extend their range of applications.

Back flange

Disc-shaped clamping device used to attach usually disc-shaped application tools on the tool spindle. Typically found
on angle grinders and rotational saws.

Battery for cordless tool

Rechargeable battery cell.

Battery voltage

Nominal voltage of a rechargeable battery, depending on the battery type and the number of battery cells.

Belt guide

Device to adjust the belt travel; the sanding belt is inserted and centered exactly with an adjusting knob while the tool is running in order to prevent the belt from running off during operation. Centering also stops the belt from slipping off and getting caught inside the machine housing.

Blade guard

Device to prevent unintentional contact with a tool cutting edge.

Brushes (electrical)

Carbon brushes are simply known as brushes and are used as power supply to the rotating armature of a universal or DC motor.

Clutch

Technical term for the separating point in the line of force (torque) of machines where the driving mechanism can be disconnected from the output shaft. Power tools usually have a pre-set maximum torque to suit the tool and application before the clutch would engage.

Constant-Electronic

Electronic regulating device which holds an adjustable rotational speed or a fixed predetermined rotational speed constant under changing loads. This method is used, for example, for angle grinders, impact drills, planers and circular saws.

Contact pressure

This is the manual pressure exerted by the tool user to achieve optimum penetration of the substrate being drilled at the correct cutting speed of the drill bit. In the case of impact drills the drilling performance depends largely on the applied contact pressure.

Cutting speed

The cutting speed is specified for work on different types of materials; it ensures the best possible work results.

Dead man’s switch

Switch that cannot be locked, i.e. if you let go, the switch returns immediately into the off position.

Depth stop

Accessory part of drills and rotary hammers designed for the limitation of the drilling depth.

Direction of rotation

The direction of rotation of a power tool is defined by looking at the direction of the line of force. Clockwise direction of rotation is known as right-handed rotation.

Disengaging clutch

Clutch which interrupts the line of force for a short time or permanently when a specified torque is reached.

DIY tools

Machine tools constructively adapted to suit the needs of DIYers.

Drill chuck

A drill chuck is a clamping device attached to the end of the drill spindle which holds the application tool (drill bit). The purpose of the drill chuck is to ensure a non-positive, friction-locked connection between the application tool and the drill. Chucks are available in two distinct types:

1. Keyed chuck – a chuck with a toothed wheel rim. It is opened and closed using a chuck key.
2. Keyless chuck – a chuck which can be tightened without using a chuck key; usually by hand.

Drilling

Drilling is a term describing the process by which through holes or blind holes are produced and their follow-up treatment like countersinking or tapping.

Chiselling

Depending on the material to be processed, chiselling is understood to be the cutting, chipping or demolishing of materials by percussive action. The percussive forces required for chiselling cannot be generated by the simple serrated striking mechanisms used in hammer drills. Consequently, hammer striking mechanisms have to be used in this case.

Power tools used for chiselling

Typical power tools for chiselling include:

• Rotary hammers
• Demolition hammers

Rotary hammers

Rotary hammers, have a rotation stop feature which allows you to switch off the rotation of the application tool. In this mode they can perform the same tasks as chipping or demolition hammers and are used for light chipping and breaking applications. Modern rotary hammers are equipped with electronically adjustable speed and hammer force. They come with a tool holder which can be locked in varying positions with the tool-free clamping systems SDS-plus, SDS-top or SDS-max.

Cordless

Within the last decade cordless power tools have reached a market share of over 25 percent of all power tools sold world-wide. The reasons for this are their easy handling, convenience and their performance capacity which has increased substantially in recent years with the continuous improvement in battery technology.

Screwdriving

Professional screwdrivers are always single-purpose machines used to reach the best possible work results in the shortest possible time. Drills are only suitable for occasional screwdriving in the do-it-yourself sector. Cordless drill-drivers are an exception to this. Screwdriving can be categorised as follows:

• General Screwdriving – wood working etc.
• Roofing – self drilling and tek screws
• Dry walling

Once the screwdriving category is recognized, the fundamental difference lies in the speed and where the screwdriving conditions must be determined. There are basically two screwdriving conditions:

• soft screwdriving conditions
• hard screwdriving conditions

This rough distinction enables a preliminary decision on the screwdriving technique to be applied. Soft screwdriving conditions exist if a joining part is located directly under the screw head (or nut) and yields when the screw is turned in further after the screw head contacts the surface, and thereby the screw is pulled into the part to be joined. A typical example of soft screwdriving conditions is given when a screw is driven into wood: if more torque is applied after the screw head has come to rest on the surface, the screw will be pulled further into the wood. This means that the penetration depth has to be limited in soft screwdriving conditions.

Hard screwdriving conditions exist if a joining part is located directly under the screw head (or nut) and does not yield even if more torque is applied after the screw head contacts the surface. A typical example of hard screwdriving conditions is given when a screw is driven into a metal thread: if more torque is applied after the screw head has come to rest on the surface, the screw will not be pulled further into the metal. If the torque is high enough, the screw will be destroyed. That means that the tightening torque has to be limited in case of hard screwdriving conditions.

Power tools used for screw-driving

One can now proceed to choose the suitable screw-driving tool, where two basic methods are available:

• screw-driving with depth limitation
• screw-driving with torque limitation

Screw-driving with depth limitation

So-called depth-stop screwdrivers are used for depth-limited screw-driving. A typical feature of this type of screwdriver is that the screwdriver shaft stops rotating in no-load operation and starts to turn only when contact pressure is applied. During depth-limited screw-driving the screw is screwed in at full torque until the head of the screw comes to rest on the material or alternatively, if countersunk head screws are used, it penetrates into the material until the screw head is flush to the surface. The screw-driving process is stopped when this point is reached.

Outline

Power tools require accessories for the fulfilment of their specific working tasks and the accessories discussed here are the usual application tools such as drill bits, abrasives and screwdriver bits which can be used for many purposes and different applications.

Terminology

Abrasive

Generic term for application tools and materials available in various forms such as sandpaper, grinding wheels, or discs used for sanding/grinding.

Backing pad

Flexible, round grinding pad used to support fibre sanding sheets on angle grinders.

Bit

Short term describing small application tools such as screwdriver bits.

Brad point

Drill bits equipped with an advance feed thread. The brad point pulls the bit into the material almost by itself and the operator has to supply little feeding power.

Core cutter

Pipe-shaped drilling tool with toothed cutting edge at the front side. Instead of the entire hole diameter only a ringshaped gap is drilled to save energy.

Countersinking bit

Drilling tool with short, tapered tool point. Countersinking bits are used to shape drilled holes to accept countersunk screws or to deburr drilled holes.

Cutting disc

Grinding disc of reduced width for separating or depth cutting.

Die

An internally threaded nut (tool) for cutting male threads on bars or pipes.

Diamond blade or saw

A circular saw or blade with abrasive industrial diamonds set round its rim (periphery).

Drill bit

Application tool designed for the production of drilled holes; usually a twist drill – drill bits comes in various forms and sizes.

Fine sanding

Sanding operation during the final stage of surface treatment. The grit of the abrasive is usually higher than 240.

Drilling

The following questions have to be answered in order to select the optimum drill bit, rotational speed and applied pressure:

• Which material is the hole being drilled into?
• What diameter is the hole going to have?
• Is it a through-hole, a blind hole or a deep hole?

If these facts are known one can make the right selection.

The following requirements are important for drilling:

• the borehole must be true to measure
• work progress should be as fast as possible
• the drill bit should last as long as possible (maximum service life)

These three demands are affected by the drill bit material, the geometry of the cutting edge and the way the bit has been manufactured. Large-diameter bores in thin materials are not drilled with solid bits but are cut out with so-called core bits (which are rather milling cutters) or hole saws.

Drilling in metal

Twist drills are almost exclusively used for drilling in metal. These popular application tools are also known as “spiral bits”. Drill bit material It is not recommended to use drill bits made of standard tool steel for drilling in metal. These bits lose their dimensional accuracy after a short time, become blunt and are not suitable for efficient and precise drilling in metal.

The tool geometry of the cutting edge is selected to suit the type of hole drilled and the material into which the hole is drilled. The cutting edge angle, the point angle and the spiral flute angle largely determine the properties of the drill bit.

Cutting speed

The selected rotational speed, and with it the cutting speed of the bit, depend on the hole diameter and the drilled material. A difference has to be made here; the cutting speed is material-specific and therefore constant for one and the same material. On the other hand, the cutting speed naturally depends on the drill bit diameter (cutting edge circumference). By selecting the right rotational (motor) speed one has to maintain the material-specific cutting speed. The selection is based on these rules:

• The possible cutting speed depends on the work material
• Small drill diameters require a higher speed than larger drill diameters to maintain the ideal cutting speed.
• Use the correct cutting speed to ensure ideal drill bit performance in the material being drilled.

Drilling in Brick – Concrete – Stone

Drill bits for brick, concrete or stone differ fundamentally from drill bits for metal, wood and plastic. Concrete or brick is a material which does not produce chips. Therefore one cannot use chip-forming methods for processing concrete or brick. The working principle applied here is to crush the structure by scraping or impacting. In both cases the (brittle) structural cohesion is destroyed and the drilling dust created thus is removed from the drilled hole up the spiral “twist” grooves of the drill bit.

Brick or stone materials with light, porous cohesion like weak concrete, or porous brick can be drilled by using rotary tools, whereas concrete materials with strong cohesion and/or hard aggregates like structural or precast concrete can only be drilled by a combination of impact and rotary motion. The most important distinguishing features of drills for brick, concrete or stone are:

• cutter material
• tool geometry
• flute shape
• fitting
• dust extraction

A great number of different drill bits for “drilling” brick, concrete or stone are available on the market. Best results are obtained by using drill bits which have been adapted especially for the processed material – see Table 9.7 It is also important to remember that large-diameter bores are no longer drilled with solid bits but as ring gaps with so-called core cutters. The cutting edges “teeth” of core cutters consist either of inserted tungsten-carbide cutters or diamond-tipped segments. The latter must be used with rotation-only and without impact.

Drilling in Wood

Drill bits for wood and wood materials are quite different from those used for drilling in metal. Although it is possible to use spiral bits for metal also in wood, the quality of the drilled hole will never be satisfactory. The main reason for this is that wood is a natural work material with variable texture and hardness which, in addition, is not homogenous and has a fibrous structure. This can divert the drill points of conventional spiral bits at the start or during the drilling of a hole. The point angle is responsible for the displacement of a portion of the (soft) work material which produces the well-known tearing at the point where the bit leaves the material. For the same reason bores near the edge can split the material.

Drilling other materials

As a rule, the same drill bits are used for drilling in plastic as for metal. In general, the same principles apply with respect to individual criteria as mentioned above on “drilling in metal”. However, there are some plastics which require special tool geometry and/or special cutter material. The following recommendations are general recommendations for drilling in different types of plastics.

1. Thermoplastics

   Thermoplastics are rather soft. Drill bits with sharp cutting edges are a must here. Bits which have already been used for drilling in metal should not be used to drill high-quality holes in thermoplastics.

2. Thermosetting plastics

   With respect to the sharpness of the cutting edge, thermosetting plastics are not as sensitive as thermoplastics. Nevertheless, it is recommended that separate drill bits be used.

3. Fiberglass-reinforced plastics (GFRP)

   Due to the embedded glass fibres, GFRP have a strongly abrasive effect on the cutting edges of drill bits. Blunt cutters tend to squeeze the material more than cut it. As a consequence, the glass fibres are quite exposed in “frayed” holes and increase the capillary action under the influence of moisture. Penetrating moisture can make the fibreglassplastic- compound brittle around the drilled hole and connecting elements might loose their hold in the material after a certain period. This problem can be solved by resharpening the drill bits frequently (which is slow and takes time) or by using special drill bits with razor-sharp tungstencarbide cutters.

4. Cast minerals/composites

   Cast minerals are plastics which contain mineral fillers to improve their compression resistance or to give them a decorative appearance like solid surface composite kitchen tops. The mineral components of these composites require the use of sharp carbide drill bits.

5. High-performance plastics

   High-performance or superplastics are synthetic materials with special properties. They can be rather soft plastics like PTFE (polytetrafluoroethylene) or very hard plastics like PC (polycarbonates). These materials often require the use of special tools; information on drilling these types of plastics can be obtained from the manufacturers of these materials.

Drill Chucks

Drill chucks are used to clamp application tools like drill bits to drills. Their advantage is that you can tighten tool shanks of varying diameters with them. A distinction is made between keyed chucks and keyless chucks.

Key-type chucks are tightened and released with the help of a cog-shaped chuck key and an external crown gear. The jaws, usually three, have to be tightened individually by applying the chuck key in all three chuck holes to make sure that the application tool is concentric and safely gripped.

Saws blades are application tools on which the chip-producing cutting edges (teeth) are arranged in consecutive linear fashion and come into action one after the other. The motion of the saw blade is based on one of three basic principles:

• stroke
• rotation
• circulation

1. Stroke-type sawing

   In the case of stroke-type saws, the saw blade is moved back and forth or up and down. Depending on the tooth geometry, the saw blade cuts only in one direction (usually) or in both directions. Saw blades usually cut during the pulling motion. With narrow stroke-type saw blades it is possible to cut tight curves with high accuracy as found with Jigsaws.

2. Rotational saws

   Rotation saws have their saw teeth arranged along the circumference of a circular blade. This type of saw blade construction is
   mechanically very stable and therefore highly durable. One can select very high rotational speeds and resulting high cutting speeds ensure rapid work progress. The cutting motion is mono-directional which has a positive effect on the service life of the saw teeth. The effective surface of the saw blade in the sawn gap ensures excellent saw blade guidance. For this reason they are perfectly suited for precise, straight cuts. However, on account of their working principle they cannot be used for curve cutting.

3. Circulating saws

   In the case of circulating saws the saw teeth are arranged either along the edge of a continuous belt (band saw) or a chain (chainsaw). Circulating saws operate with high cutting speeds and ensure rapid work progress.

Saw blade geometry

Most saw blades available on the market today are optimised for applications with wood. The large selection of blades makes it easy to choose the right type for the saw blade for the job at hand and where the following criteria can assist in making the correct choice.

Tooth material

Either CV steel, HSS or hard metals (car bides) are used for tooth material. CV-teeth are used for larger rake and relief angles which yields sharp, aggressive but less durable saw blades and typically used in wood and plastic applications. The use of HSS allows a similar geometry where the teeth are more resilient, but tend to break more easily due to their hardness and are typically used in metal applications.

Circular saw blades are round-shaped cutting blades designed for use with mitre saws, table saws, radial arm saws, cut-off saws and standard circular saws. Many circular saw blades can be used interchangeably between machines….but using the right blade for the application is paramount….it improves performance, quality and efficiency.

Circular saw blades vary widely in quality and price. More expensive blades usually have features that extend the longevity of the blade while enhancing performance. Cheaper and poor quality blades may dull quicker or produce rougher cuts, so make sure you weigh up the benefits of the blade in addition to only the initial cost.

Construction, Dimensions and Teeth

Construction – Circular saw blades are usually constructed of steel or carbide-tipped steel. Steel blades are inexpensive but the teeth can dull quickly and are often only used for DIY applications. Carbide-tipped blades, on the other hand, are extremely durable, and offer better value for money and can last up to ten times longer than steel.

Dimensions

There are three dimensions to keep in mind when you’re shopping for circular saw blades – diameter, arbor size and kerf. The first two dimensions, diameter and arbor size, are determined by the saw. Blade diameters start at 160mm but the most common diameters are 185mm for circular saws, 230mm for table saws and 230mm and 250mm for mitre saws. Arbor sizes range from 16mm to 30mm – check your saw or owner’s manual too see what size blades you need.

Kerf is the thickness of the blade. Thick-kerf blades last longer and can usually be re-sharpened, so they tend to be more expensive.

• Thin-kerf blades are sharper and faster when new but dull quickly
• Thin-kerf blades remove less material from the workpiece during cuts
• Thick-kerf blades hold up to nails better and resist wobble

Teeth

As described previously , blades with more teeth yield a cleaner cut and blades with fewer teeth deliver faster cuts with rougher edges.

Note: For masonry and metal applications, you need to use an abrasive wheel (cutting disc) or diamond blade.

Cutting and grinding discs are used for abrasive cutting and abrasive grinding and in this context one has to be aware that the diameter of discs is reduced through wear and that this will reduce one the maximum depth of cut and the overall abrasive efficiency.

Abrasive materials

The abrasives mainly used for these applications consist of the following materials:

• natural corundum
• silicon carbide
• aluminium oxide
• zirconic corundum

These abrasives are used for different purposes depending on their properties.

Natural corundum

Natural corundum is one of the oldest abrasive materials developed – with modern power tools it is not very durable and very
seldom used, although still used for low quality, hand-operated abrasives.

Silicon carbide (SiC)

SiC has a hard, sharp-edged structure which makes it especially suitable for processing hard and tough materials. And also
used for masonry, paintwork and synthetic material applications.

Aluminium oxide (Al2O3)

Aluminium oxide (also called special fused alumina) is very hard and tough. It is particularly suited for processing long-chipping
materials like wood or metal.

Zirconic corundum

The microcrystalline structure of zirconic corundum produces new and sharp edges when it becomes worn which has a self-sharpening
effect. For this reason it is especially recommended for tough-hard materials such as corrosion-proof steel.

The term cutting is used to describe in-depth grinding. The working principle is rotation. The grinding process is carried out by the edge, the circumference of the abrasive (cutting disc). The power tools used for this purpose are either angle grinders or abrasive cut-off machines. The working process resembles sawing with a circular or radial arm saw.

Cutting applications
Cutting metal

Cutting metal by using cut-off wheels (cutting discs) is quite common and typically carried out manually using stationary equipment like an angle grinder in a cut-off stand, which provides good and dimensionally accurate results. The service life of the cutting disc limits the cutting depth since the disc diameter diminishes with increasing wear. The peripheral velocity (cutting speed) is also inevitably reduced and with it the abrasive efficiency and the work progress. The power demand depends on the diameter of the cutting gap (and therefore the diameter of the disc). Modern cut-off wheels with disc widths of approx. 1mm allow fast cuts with little heat development.

Cutting plastics

Cutting synthetic materials with cut-off wheels (cutting discs) produces frictional heat in the actively involved section of the disc. This heat is not removed or dissipated by the synthetic material. Local overheating and melting of the plastic are the consequences. Certain plastics disintegrate under the influence of heat and change their colour and properties as a result. These melting and disintegration processes clog up the texture of the abrasive medium which becomes unusable. Therefore abrasive cutting is not recommended for plastics other than that of thin-walled profiles.

Cutting wood

Cutting wood with cut-off wheels (cutting discs) produces frictional heat in the actively involved section of the disc. This heat is not removed or dissipated by the wood. Local overheating and burn marks on the wood are the consequences. Therefore abrasive cutting is not recommended for wood or wood materials.

Sanding

Sanding is a surface treatment principally used to improve the surface quality. The actual application tools used during sanding are abrasives which use their edges to grind the material to dust and depending on the principle and the type of sanding tool used one can process even, concave or both surface types.

Typical applications
Sanding and grinding metal

Sanding with rotation (circulation) is the optimum processing method since the high peripheral speeds ensure good work progress. The centrifugal force propels worn out abrasive grains and the removed material out of the sanding area. Sanding with oscillation or circulation is less favourable in terms of finish quality since the sanding dust and broken off abrasive grains cannot be removed quickly enough and tend to produce scratch marks in the surface.

Sanding plastics

Most plastics become deformed under the influence of heat. If they are heated too much they can melt or disintegrate. Therefore, heat development when sanding should be reduced to a minimum when working with plastics. In practice, one should sand plastic with reduced operator pressure and low peripheral speed. Abrasives with an open structure develop less heat during sanding and should therefore be preferred. In the case of large-scale sanding operations, it is better to remove the material roughly with coarse-grained abrasives, and to switch to finer abrasives for the finish. Large-grained abrasives clog up less quickly and the cooler sanding process of the larger grains prevents the plastic from melting.

Sanding wood

Wood and wood materials are comparatively soft and are quite easy to sand; however, the fibre structure of the wood has to be observed during sanding. Sanding across the fibres (unavoidable for rotational sanders) removes the material (stock) quickly and creates a rough surface. It would be better to use a finer grain abrasive when sanding softer type woods which will be more time-consuming but will prevent one from oversanding the workpiece. Resin pockets are also a disadvantage when sanding wood, since they clog up the abrasive and smear the surface. As a tip remove the resin deposits by milling or dissolving them with suitable thinners prior to sanding.

Sanding painted surfaces

Coats of solvent based paints like varnish behave to some extent like plastics: if they become too hot they can melt or disintegrate which has a negative effect on their surface quality. Consequently, heat development should be reduced to a minimum. In practice, one should therefore sand these surfaces with reduced operator pressure at low peripheral speeds. Abrasives with open structure develop less heat during sanding and should therefore be preferred.

Sandpaper types

There are a number of sandpaper types found on the market today and available through hardware and the like.

Sand/Quartz/Glass

Hard enough for sanding timber, but doesn’t have very sharp edges.

Garnet

Garnet is a mineral with sharp points, ideal for sanding soft materials like wood. It breaks down quickly when used on hard materials; a good choice for final sanding.

Emery

Emery is a mix of corundum and magnetite and is good for rust removal, polishing, de-burring and corrosion and paint removal. The synthetic grits give a superior sanding performance.

Aluminium oxide

Aluminium oxide is tough and the wedge-shape grit makes it suitable for smoothing and polishing steel, bronze, fibreglass, plaster, hard timbers and even stone.

Silicon Carbide

Silicon carbide is the hardest and sharpest abrasive and can be used wet or dry. It is suitable for cutting harder materials like metal, paint, plastic, and fibreglass. It is used to sand primers, sealers, paints and non-ferrous metals, as well as for final finishing.