However good your table saw is, the cut will only be as good as the blade fitted. Let’s look at important points and how to choose the right one for the job.
In a previous blog I talked a little about the versatility of the table saw and how to operate it safely. To realize its full potential the right blade must be fitted. Condition of the blade is also important. Blunt, chipped or missing teeth, a warped plate and resin build up will drastically reduce the accuracy and effective cutting power of your saw.
TYPES OF BLADES.
I’ll only look at Tungsten Carbide Tipped (TCT) Blades. High Speed Steel blades are rare these days, although they still have a place in specialist applications where their much thinner kerf and greater initial sharpness outweigh their disadvantages.
FLAT TOP (FC)
Flat top or raker blades have their teeth ground square across the top, giving a chisel shape to each tooth. This pattern, with its chopping rather than slicing action, gives good waste clearance and fast cutting with the grain. It is most suitable for ripping, used for cross cutting it will produce a poor finish and severe tear out.
ALTERNATE TOP BEVEL (ATB)
ATB blades have their teeth ground at alternate bevel angles, one tooth angled one way, the next the other way. This gives a slicing action to both sides of the blade, making it the most suitable for cross cutting.
ATB blades with extreme bevel angles are used for clean cutting of veneers, laminates and melamine faced boards. They produce a superb finish and are especially good for mitering. Their downfall is that they wear very quickly.
Combination blades are also available which feature both ATB and FT tooth patterns. The idea is that they should give a good finish together with fast waste clearance. In practice they don’t perform noticeably better that an ATB blade with a modest bevel angle. They will leave a flat bottomed kerf when used for grooving though.
These blades have teeth which are ground in 2 alternate patterns: first is an FT grind with chamfered corners, second a lower profile standard FT grind. The chamfered tooth cuts the centre of the kerf whilst the following raker tooth cuts the sides. The whole purpose of this pattern is to minimize tear out, especially on melamine faced board. These specialized blades are generally produced with zero or even negative rake angle to resist wear from abrasive materials such as MDF.
CLARIFYING TOOTH ANGLES.
The Rake Angle
is the angle at which the face of each tooth is ground, measured against the radius of the blade. As a general rule, the greater the rake angle, the faster and rougher the cut. Thus a deep ripping blade might have a rake of 18º to 20º, a general purpose blade around 15º, a good cross cut blade about 10º and a specialized blade for melamine board anything from 5º to -7º.
The Side Clearance Angle
is the angle at which the side of each tooth is ground, measured against the radius of the blade. As a general rule, the shallower the angle, the finer the finish. It also means more friction and therefore heat, so a shallow side clearance angle is only worth using on end grain and where finish is critical.
A typical kerf width is between 3mm and 4mm. Blades with a narrow kerf width of as little as 2mm to 2.8mm are available. The advantages of a narrow kerf are:
Less power required to drive the blade, therefore improved performance from small machines.
Less waste produced, important when cutting valuable exotics, less of your money on the floor!
The drawbacks are faster wear and a greater risk of heat build up. Too much heat can distort the blade’s plate – which is also thinner than that of a standard blade.
NUMBER OF TEETH
Circular saw blades are graded in terms of their total number of teeth. The only way to compare will be between blades of the same diameter. I will assume a blade of 250mm (10”) for this example. It is the most common size for table saws.
General rules are:
Fewer teeth means faster cutting but the trade off is a rougher finish.
The thinner the material being cut, the more teeth are required. More teeth mean a better finish, but a slower rate of feed. You get the idea!
RIPPING – When fast ripping, clearance of the sawdust produced (in the form of bulky shavings, relatively speaking) becomes a major issue. Good clearance will be obtained with a large gap between teeth, allowing a deep gullet. So a dedicated 250mm ripping blade should have no more than 24 teeth. Some rip blades have a hump behind each tooth. This is not a fashion statement, it is a chip limiter. Its purpose is to restrict the amount of cut. The hump not only saves wear and heat build-up, it also reduces the risk of kickback from a blade jammed in the cut.
CROSS CUTTING - Fine cross cutting demands many teeth to sever the wood fibers cleanly. The waste is a fine dust which is easy to clear so it isn’t a problem. For relatively thin material, 96 teeth will give good results, medium thickness around 80 teeth and heavier sections, 60.
GENERAL PURPOSE – For general purpose cutting between above two extremes, the following rule of thumb is useful:
With the blade set to just clear the thickness of the material, it should have no less than two and no more than five teeth in the cut.
A FEW NOTES ON QUALITY:
Sawblade quality starts with the plate itself. However well the teeth are ground, if they are wobbling about on the edge of a buckled plate, what is the point! Good plates are roller tensioned, visible as a faint ring on the plate at about three-quarters of its diameter. Not easily found at your local hardware centre, I know! A good plate is also dead flat. This is easily checked with the blade of an engineers square or similar.
The second most important factor is the quality of tooth grinding. This is less easily checked, although a magnifying glass will reveal some truths. Whilst peering at that tooth, have a look at the brazing – this should be smooth and free of pinholes. Lumpy brazing is a bad sign!
Carbide quality is hard to check. If the manufacturer talks of “micrograin” and quotes a grade number, you should be reassured.
The arbor hole is a vital element as a misaligned, oversized, or eccentric hole will ruin a blade’s performance. It is something that is often overlooked but is a good sign of quality: Good holes are reamed to exact size, a process that leaves a smooth burnished finish. AVOID blades with sharp burred holes. Any indication that the hole has been punched out is cause for instant rejection.
As always, price and brand name is normally a good indicator of quality – you do get what you pay for, most of the time!
RECOMMENDATION – WHICH BLADE?
If you are a specialist, you will have special requirements but for the average guy at the bench, it is easier to suggest a basic requirement. Assuming a 250mm (10”) blade, your first buy should be a 40 to 48 tooth ATB blade with a 5 - 10º bevel. This blade will cope with most work and will be your general purpose workhorse.
Add the following as they are needed: If you use a reasonable amount of rough sawn hardwood, a 24 tooth FT ripping blade will prove useful.
For fine cross cutting, joint-cutting and board work, keep an 80 tooth ATB blade with a 10 - 15º bevel nice and sharp.
If you want to cut a lot of melamine board, then the clean cut and wear resistance of a 80 tooth, negative rake, triple chip blade is you weapon of choice.
Remember, it is better to have a limited number of quality blades than a stack of cheap ones!
Resin build up on the blade will drastically reduce its performance. Clean your blades often. I use oven cleaner in a spray can. Spray the circumference of the blade with the white foam and let it soak for a while before scrubbing with an old tooth brush. Then wash off under running water and dry with the towel you stole from the bathroom! A second treatment might be necessary for stubborn deposits.
You won’t believe the difference it makes; feels like you just fitted a new blade!
Next time you go to the hardware shop, ask the “expert” some informed questions….Then watch for faces that drop and listen to the ummms and ahems!!