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Why You Need a Flat-Kerf Joinery Blade

 

Most woodworkers start out with a cheap, general purpose table saw blade. In time they realize that cheap blades often produce rough cuts, so they upgrade to a better general-purpose blade, or even a combination blade. That's a good move. A good blade will last a lifetime in many small shops. And general purpose or combination blades are excellent choices because the same blade may be used for both crosscuts and rip cuts. But as your skills progress, there's another type of saw blade you should consider, because it will greatly expand your capabilities as a woodworker. I'm talking about a flat-kerf joinery blade.

 

Flat-kerf blades are used for finger joints, tenons, rabbets- all sorts of table saw joinery. Basically, they can do everything a dado set can, and many things a dado set can't. We'll get to those details shortly, but first let's talk about what makes a flat-kerf joinery blade different from the blades most woodworkers use.

 

General purpose blades feature what's called an “alternating bevel design” (ATB). Each tooth is ground at the opposite angle as the one before it. This creates rows of knives that shear the wood fibers, and depending on the quality of the blade, those alternating bevels can produce a clean crosscut across the grain, and a serviceable rip-cut along the grain.

 

Combination blades, on the other hand, feature what's called an “alternating bevel raker design” (ATBR). These blades have a flat-ground raker tooth after every four beveled teeth. This raker tooth helps the blade produce slightly cleaner rip cuts than are possible with an ATB blade, while still producing the same, clean crosscuts.

Watch the video...

...or read about it.

Neither a general purpose (ATB), nor combination (ATBR) blades are well suited for cuts that don't go all the way through the workpiece, such as dados and other joinery, because they won't leave a clean, flat-bottomed kerf. ATB blades leave a V at the bottom of each kerf. ATBR blade will remove some of that V with their added raker teeth. But because the points of the beveled teeth are usually ground slightly higher than the flat tops of the raker teeth, the result is something referred to as bat ears. These blades work well for cutting parts to length and width, but not so well for most joinery applications, especially any joint that will be visible, such as rabbets, dados, finger joints, lap joints, or even tenons.

 

If you're going to create these joints at the table saw, you should own a flat-kerf joinery blade. These are essentially rip blades, in that all the teeth are ground flat- there are no alternating bevels. The clean, flat bottom of a kerf cut with joinery blade is far superior to the rough surface left behind by other blades. No bat-ears mean better looking joints.

It is worth noting that a dado set will also cut a flat-bottomed kerf, so you can use one of the blades in your set for some joinery. The downside of a dado set is that the teeth are usually wider than 1/8", so they can't be used for some fine joinery. And dado blades typically possess fewer teeth, which may lead to rougher cuts across the grain (depending on the quality of the set). In fact, if you haven't yet bought a dado set, or you have a dado set that you're not happy with, I would consider a flat-kerf joinery blade before I would a new dado set. It can do anything a dado set can with just a few more passes. Dado sets are more convenient if you have a lot of the same wide dado to cut, but If I could only have one of the two, I'd probably choose a flat-kerf joinery blade for its lower price and added versatility.

Also, the Freud and Amana blades are really not designed specifically for joinery. They are heavy duty rip blades for making through cuts with the grain in thick hardwoods. They just happen to also leave a flat-bottomed kerf. However, the Ridge Carbide blade is specifically designed for table saw joinery. The teeth are precisely ground to 1/8" wide. (Both Freud and Amana claim theirs are 1/8, but I found them both to be slightly over-sized.)

 

But the biggest difference is in the number of teeth. The Ridge Carbide blade has twice as many teeth as the 24-tooth Freud and Amana. This makes it better suited to cutting across the grain, in my opinion, especially when working with veneered plywoods. And while I can't prove it, I believe the more teeth you have sharing the workload, the longer the blade will stay sharp, and therefore the longer it will last.

 

The only other brand I know of that makes a 40-tooth flat-kerf joinery blade is Forrest, and theirs is about $50 more than the Ridge Carbide, for what I am convinced is the same quality. That's why I recommend the Ridge Carbide.

If there's a downside to the Ridge Carbide, it's that those extra teeth aren't well suited to heavy duty ripping. The more teeth on the blade, the less efficient it is at clearing the sawdust from the kerf during these aggressive cuts, which may lead to slower cutting, and some extra blade marks or scorching. So, I consider the Ridge Carbide “box joint” blade to be purely a joinery tool. You won't get double duty out of it as a heavy duty ripping blade, as you might with the Freud or the Amana. But frankly, few woodworkers need a heavy duty ripping blade anyway. A good general purpose or combination blade will serve that purpose.

 

To summarize: Any of these three blades will give you a clean, flat bottomed kerf for most joinery. The Freud is a good choice if you're on a tight budget. The Amana is a good choice if you also want to use the same blade for heavy-duty rips in thick hardwoods. But the Ridge carbide is my choice because its thicker teeth (and more of them) should lead to a longer life and to cleaner flat-bottomed kerfs across the grain, especially if you work with a lot of plywood. And the Ridge carbide blade is more precisely ground to leave an even 1/8" wide kerf, making your finer joinery cuts more precise.

 

Whichever blade one you choose, you are sure to agree that a flat-kerf joinery blade will help you step up your woodworking game. For more great tips, tricks and tutorials designed to make you a better woodworker, be sure to check out the latest issue of Stumpy Nubs Woodworking Journal. You can read and subscribe for free at stumpynubs.com. Happy joinery!

 

Ridge carbide Flat-Kerf Box Joint Blade

(Use this discount code on Ridge Carbide blades: SNWJ10)

Freud 24-Tooth Heavy Duty Rip Blade

Amana Industrial Quality Rip Blade

My favorite daily use, combination saw blade (not for flat-kerf joinery) (Discount code SNWJ10 applies to this one as well)

 

 

 

There are only a few good blades on the market that will produce a true, flat bottomed kerf with no bat ears. I own three different brands. One is a Freud Industrial 24-tooth heavy-duty rip blade. It costs about $65. Amana also makes one they call an industrial quality ripping blade for $90. I like the Amana slightly better than the Freud. They both do a decent job at the bottom of the kerf, but the Amana seems to leave a cleaner surface on non-joinery through-cuts, such as when I'm ripping thick hardwood or ripping the edges of boards I'm going to glue up to make a wider panel.

 

But that's going beyond joinery. And for pure joinery, I wish I had saved my money. Because I discovered the Ridge Carbide TS2000 flat-top box joint blade. It's a bit more expensive than the Amana. (With the discount code “SNWJ10”, you can get it for about $116. Otherwise it's $129.)

 

The reason I prefer the Ridge Carbide blade is because the teeth are thicker than those on the Amana. Thicker carbide means you can sharpen it more and get a lot more life out of your investment.

Only the special "box joint" version of Ridge Carbide's TS2000 Super Blade will leave a true flat-bottomed kerf.

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