Blades of Glory - How to ensure your saw blades are glorious

Sawing

We've all rocked up at the traffic lights next to some guy in a Ferrari, an Audi, or our personal favourite, a lowered Mitsubishi Lancer that looks like it could dump its chassis any minute. They're blasting techno, sunglasses on an overcast day, you know the type.

Of course, they’re revving the hell out of this poor machine but when the lights go green, they stutter away in a cloud of exhaust fumes, while the Toyota Corolla next to them glides smoothly into the distance.

Just as you can spend a fortune on a car but never learn to drive, you can spend a huge amount on a table saw, just to stutter into poor cuts because of the poor – or misdirected - quality of your saw blades.

This goes for just about any machine – look beyond the flashy lights and buttons at what’s performing the grunt work. That’s where you want to spend your money, at least at the start.

The terminology

Alright, let’s start with the basics: Kerf is the width of the tooth – a full kerf blade is 3.1 mm, or 1/8 inches, a thin kerf blade is 2.4 mm or 3/32 inches. There’s more carbide on a full kerf, which means it cuts wider, takes more material and emits a lot more sawdust.

The teeth are bigger, which means they stay sharper longer and you can get more resharpens. Half kerf are for smaller, lower-powered saws. Less sawdust, less power, for smaller projects – but unless you’re an industrial company or taking on huge projects, this is often the most desired blade.

The quality of the blade is very important with table saws, because the quality of the cut is very dependent on the quality of the blade and the number of teeth. There are three types of blade (although the number of teeth are only a rough guide) ripping blades (24 to 30 teeth), combination blades (30 – 60 teeth) and cross-cut blades (60 to 90 teeth).

Ripping, Cross-Cut and Combination blades

Bare essentials: ripping blades are better suited to long, straight cuts because they cut quicker. Cross-cuts are better for fine, smaller, slower cuts. Combination are a bit of both.

Ripping blades have large gullets (space between blade teeth) that help to remove the material and lessen kickback. These blades are removing strings of wood in addition to sawdust, which creates a more accurate cut with less friction and helps in reducing heat accumulation.

Cross-cut blades cut across the grain of the wood. This means they need a higher number of teeth to ensure smooth finishes and eliminate tear-out. These blades are mainly removing fine sawdust, so they don’t need large gullets.

Then you have combination blades. Like most general purpose blades, they do an okay job of ripping and crossing without attaining a professional level.

This can be cost-effective for hobbyist woodworking – don’t get fooled into over-speccing for your project, sometimes you just don’t need it.

Your blade performance basics

There are three main features that affects how the blade performs:

  1. The number of the teeth on the blade
  2. The angle of the face of that tooth to the blade
  3. The bevel: the angle of the top of those teeth

In general, the more teeth you have the cleaner the cut is going to be, but more teeth also slows the cut down. Rip blades generally have less teeth, 30 teeth rather than 48 means it will cut more quickly, making it better suited to longer cuts ripping through the timber.

The next thing that affects performance is the angle of the tooth. If you imagine a line drawn from the centre of a blade out to the edge, the angle is actually the angle of the face of the tooth to that line.

A steeper angle pulls the wood into the blade and that creates a fast cut, but it can also affect the quality of the cut, making it rougher if you're using really brittle materials like melamine, or some of the other man-made chip boards. Be careful with these steep angles, 20 degrees and above.

These really steep angles can have a negative effect on the quality of the cut and can tear out and shatter some of those fibres.

The last main feature you have to understand is the bevel of the teeth. If you're looking at the teeth from the front, each tooth has an angle. That angle is called the bevel. If each tooth’s angle alternates in direction, this is called an Alternating Top Bevel or an ATB blade.

One tooth is angled to the left, the other to the right the entire circumference. Why is this important? Because it ensures there's a really sharp point in contact with the timber at all times.

Cross-cutting and general-purpose blades will generally have ATBs. Ripping blades will normally be dead flat, which means they’re going to cut out much bigger pieces each time. This creates a faster cut, but if you're trying to cross cut it's going to bash the timber on every tooth.

The last difference between most saw blades is the size of the gullet. As we said, the ripping blades’ wide gullet allows it to cut out long strands. They're going to be bigger chips and so the larger gullet allows for the clearance of those chips.

If you're going to be cross cutting and you're cutting against the grain, each chip that you're pulling out is going to be much smaller. So never use a blade with a large gullet, it will ruin your timber!

 

 
 

 

How to tell a saw blade’s quality?

If you’re ever looking at the quality of a sawblade cut, look at the bottom of the timber. This is where you’ll see the actual quality of your blade – this is where the blade is raising through the material, driving it out of the cut. If you can barely see a line on the bottom, you know you’ve got a decent blade. If there’s significant tear-out on the top of the timber, you know you’re in trouble.

This is why you don’t buy a ripping blade and assume that it will be able to perform a bit of cross-cutting, you won’t get a smooth cut when a general-purpose blade may have ticked all your boxes. If you buy a cross-cutting blade for long, rough pieces of wood, be prepared for a much slower, almost-arduous cut. But if you’re working on projects that size, you probably already know that.

The problem with tear-out is you can’t match the two pieces of timber with glue or other joinery because the grain is too altered. You’ll clearly be able to see the cut line. With the right blade, you won’t be even be able to see the cutting line.

It all comes down to the more teeth the finer cut, but where people go wrong is over-speccing. You can go up to 90 teeth blades but there’s nothing wrong with 60-teeth for ultra-smooth cross-cutting. In terms of features, look for laser-cut blades with large, meaty carbide tips. This makes them quieter and extends the lifespan, allowing plenty of re-sharpens.

Last but certainly not least are engineered expansions slots (those little fish-hook holes in the blade face). They reduce blade noise, prevent warping under heat and are very important to maintain the blade shape and accuracy.