The power mitre saw is a special type of circular saw designed for precision wood cutting. It replaces the mitre block used with a hand saw, and the various mitre saw mechanisms that attempt to support a manual saw in a framework. It excels at any cut where a precise angle is required. Typical applications include cutting studwork, cutting mitres for picture frames, dados, skirting, architraves and coves. plus all sorts of general-purpose carpentry and joinery.
As with all circular saws, the mitre saw cuts extremely quickly, so serious accidents can happen very fast. In addition, it is a "fixed" power tool that leaves the operator with both hands free. This automatically poses further risks since there is more opportunity for hands to get close to the sharp end. Great care must always be taken to ensure that your hands are out of the path of the blade.
Ear defenders and eye protection are strongly advised. When handling rough timber gloves should also be warn.
A good work environment also helps greatly enhance safety. Either a proper saw stand, or additional roller stands, or work benches should be used to fully support the work while it is being cut.
A dust extractor is well worth using if you're cutting much timber, since as with any circular saw, a mitre saw will produce copious amounts of sawdust.
The maximum size of material the saw can handle is dictated by two things: the diameter of the blade being used, and the type of mechanism used by the saw. Note that with most saws the cutting capacity is greater for straight cuts than it is for angled ones.
The quality of the blade will also have a large impact on the quality of the cut. Most mitre saw blades are optimised for cross-cutting since the limited maximum width of cut severely curtails the ability to rip cut! The best blades will also have a different tooth pitch and profile from conventional cross-cut blades - often having a negative rake. This allows for a cleaner cut with less tear-out.
This is the simpler type of mitre saw. The majority of the budget saws available are of this type. The saw is suspended above the work on a simple hinged mechanism. to make a cut, the operator simply pulls the saw down towards the work. The maximum size of cut is dictated purely by the size of the blade. The smallest a chop saws typically use eight-inch blades. These are big enough to make a straight cut through a 4"x2", and also to make a bevelled cut through 5" skirting - but often only using the less precise tilting mechanism. However it may have insufficient capacity to make a mitre cut through 4"x2". Bigger blades give a bigger depth of cut, the largest mitre saws typically have 10 to 12 inch blades.
Chop saws can only usefully be used for through cuts, since the leading edge of the cut will always have a round profile to match that of the blade. As a result most saws do not have any method for limiting the depth of cut.
The sliding mitre saw is more sophisticated than the simpler machines, since in addition to the hinged mechanism described above, it also has a facility where the saw will slide along a rail or guide. This allows the saw to perform a much wider cut for a given blade diameter. In addition it is now possible to make a flat bottomed cut which opens up the possibility of using the saw for producing lap joints and other joinery where non through cuts required. As result of this, many sliding saws also include a mechanism to limit the depth of cut. The maximum depth of cut available with a sliding mitre saw is usually no greater with the simple chop saw, however even a small saw with only an eight-inch blade will often be able to cut material up to 12 inches wide.
All of the saws will have some form of angular scale to show the angle of cut. Better quality saws may also have a variety of pre-set positions or stops on the scale to make selecting commonly used angles quicker and easier. the most acute angle that can usually be cut is 45 degrees although some high end saws may do up to 60 degrees - at least on one side.
With most saws the head can be tilted over. This allows angles in the vertical axis to be cut. On many of the budget saws this facility is less sophisticated than the horizontal angle selection, and often there is no calibrated scale to select precise angles.
The angled and tilt cuts can be combined to to produce a compound cut. This can be very useful for some complex joinery tasks such as cutting struts and hip beams in roof construction.
As mentioned above the quality of the blade will have a large influence on the quality of the cut. The other major factor that governs cut quality is the quality of the saw mechanism itself. The first and primary requirement is that of rigidity. If it looks like you can park a battleship on top of it without moving a millimetre, then it's probably a good one! A good mechanism will enable the blade to be plunged without any movement or "give" in any other direction. This will help to keep the cut straight and square right through.. The next quality indicator is the ability to accurately and easily select angles, and to have the angle actually cut match that shown on the scale. Good quality saws also need to run smoothly. Hence the quality of the saw bearings dictate the amount of blade eccentricity and hence the "finish" to the cut surfaces. No matter what the saw feels like initially, dust sealing and construction will often be lacking in low end saws. This can lead to a saw that won't rise and fall properly and be almost impossible to adjust. Disassembling and cleaning will usually help - but buying a better class of tool may be a better investment if you are using it often.
For sliding mitre saws, another vital component that will have a great impact on the quality of results achievable, is the sliding mechanism itself. This should slide smoothly and freely, and have no play or backlash in the horizontal or vertical directions. It should also allow no rotation around the slide axis (saws with twin slide rails tend to outperform those with a single rails in this respect). In addition, the saw should stay smooth and taught, and not get sloppy with use or age.
The amount of power produced by the motor is also significant. While straight cuts put relatively little load on the motor, tilted plunging cuts can put a very high strain on it.
The blade guard mechanism should work effectively, sliding out of the way easily and without causing any jolt in operation of the mechanism, and not limiting the depth or width of cut.
A budget saw will be more than capable of cutting timber for studwork, or building a garden shed. However it will often not have the capacity for cutting skirting boards, or the accuracy required for tasks like making picture frames, or cutting mitres on visible trims and coves when furniture-making.
A big high end sliding mitre saw is absolutely ideal for cutting timbers for pitched roof construction, or any other general site or construction work. It will also be very good at producing accurately dimensioned timber for furniture and cabinet making.
The best choice of motor is an induction motor, although this is available on relatively few saws. For saws with the more traditional universal motor, a "soft start" facility is highly desirable since eliminates the kick at start up. Budget saws will have motors that are not rated for continual use, however use of a mitre saw is by its nature not a continuous activity, so this may be less of a limitation than with some types of power saw.
Good angular scales are highly desirable, and some way of accurately and quickly selecting commonly used angles is also a very useful.
Don't be too swayed by features such as laser line generators since these are rarely accurate enough to give you any useful additional information.
Some saws incorporate dust collection, others will typically have a port to enable connection of an external vacuum extractor.
Probably the most useful accessory you can get for a mitre saw is a dedicated bench with in feed and out feed supports. these simplify the whole job of holding, measuring and cutting the timber.
Check all the safety features are present and operate correctly. Check all the movements of the saw operate smoothly without any jerks or graunching. High end saws don't come on to the second hand market that often, since most people who have got them to want to to keep them! The budget saws are more readily available however as the existing owners wish to upgrade to something better.