How a Power Drill Works
If you have a power drill, you can step up your capacity for fast, accurate work. By making use of attachments, you can make jobs such as sawing and sanding quicker and easier. You may eventually want to go a stage further and invest in more sophisticated power equipment for your workshop. Whatever the extent of your power ‘armoury’, you can learn from this section on Power Tools how to get the best from it.
How a drill works
Electrically powered tools suitable for home repairs and improvements range from the basic electric drill to more specialist and costly items such as radial arm saws and mechanical routers.
From the average householder’s point of view, the most satisfactory investment for general work and repairs is an electric drill power unit which can be used to drive a range of attachments. These can be bought as and when the need arises.
Drills are usually graded by their chuck capacity or, in other words, the maximum diameter of twist bit shank which can be secured in the chuck. This is usually 6.5 or 8 mm (¼ or 5/16 in) but can be greater on heavy-duty professional models.
The figures below, which give suitable drill speeds for various jobs, show that two-speed or variable-speed power units are more flexible than the less expensive single-speed units and are thus a wiser investment.
The cost of a single-speed unit together with a speed-reducing device is usually higher than for a variable-speed drill. Reducers for single-speed drills can be either electronic or mechanical.
Electronic reducers are fitted to the supply cable and allow the required speed to be selected by knob or dial control.
Mechanical reducers are fitted to the tools themselves, either instead of or into the chuck. Neither is as convenient to use as a variable-speed drill.
Most power tools are now fitted with double-pole switches which cut off both live and negative cores in the supply cable, thus completely isolating the motor electrically. When the switch is pressed to the `on’ position, current passes to one of the field coils and from there to the armature via the carbon brushes and commutator.
The armature main shaft speed of 20,000 revolutions per minute is geared down to approximately 3000 rpm. This reduction of speed increases the ‘torque’, or driving force. A fan is fitted internally to lower working temperatures.
Light-duty sleeve bearings are fitted to some power tools but better-quality models have needle or ball bearings, which are more suitable for continuous use.
Electrical connections in the motor are usually welded. The soldered connections on some models may fail if excessive heat or sparking occurs, for instance as a result of overloading or worn or clogged carbon brushes.
Care and maintenance of a power drill
A drop in speed while a power tool is in use, usually accompanied by a lowering of motor pitch, is a sign of overloading. To avoid the damage which this can cause, remove the tool from the work and run it at full revs for a few seconds before using it again This not only avoids abuse but also helps to reduce overheating.
Automatic cut-outs, which come into operation when overloading occurs, are fitted on some models. After a stoppage, these should be reset to ‘on’ only after removing the tool from the work.
Examine the carbon brushes periodically. These can be cleaned with turps substitute and, if necessary, with a very fine ‘0000’ abrasive paper. To ensure correct replacement, note the position of the brushes before removing them. Replace badly or unevenly worn brushes and have the entire tool overhauled by the manufacturer or his agent.
Undue commutator sparking indicates In electrical fault — leave this repair to a qualified expert.
Occasionally open up the gearbox, clean out the old grease and repack with the lubricant recommended by the maker.
Double-insulated tools are quite safe to use with the two-core cables provided, but tools with three-core cables must always be connected to a three-pin plug and socket.
Always use a drill with the cable hitched over your shoulder, out of the way.
Unless chuck keys are kept in the holders provided or tied to the supply cable, they are easily mislaid. A spare key is an invaluable accessory.
