Thursday, August 15, 2013

Plywood Blades

So many teeth, sharks are jealous
Saw blades, unsurprisingly, are cool. Also, there are hundreds of different kinds of them. One that's particularly useful is a plywood blade.

Long post on saw blade alert...

The Freud LU79R010 Thin Kerf Ultimate Plywood & Melamine Saw Blade is essentially what I discuss throughout the article. I actually bought the Freud 7" diameter version because I needed it for my circular saw, but the design is essentially the same.

Why are they so useful? Because plywood is a made up of a bunch of layers of unsightly, but really stable and strong, wood. You cover the unsightly wood with a veneer of good looking hardwood.

Yeah those five thick layers in the middle... you don't want to see those. It's the two minuscule layers of veneer that you want to see.
The problem with veneer is that it is so thin that unless you have a dead sharp blade and a good balanced saw, it will splinter along the cut line. This exposes the unsightly wood beneath. This... is bad. This is a big problem, especially if you are trying to build something with no trim to create a lightweight minimalist design.

This is a chipped veneer; I wasn't joking about it looking bad
There is, however, a (partial) solution: The plywood blade.

It's red too, the color of danger and communism
A standard blade typically has fewer teeth:

The standard blade on the table saw. Fewer teeth but still sufficiently badass, think of the literally thousands (tens perhaps) of lineal feet of wood this blade has killcrushmurdered
A plywood blade has more.

Our table saw takes a blade with a 10" diameter. The blade we typically use has 40 teeth. The line of plywood blade that I bought has 80 teeth on its 10" blades. The additional 40 teeth helps create a cleaner cut through the vulnerable veneer. Each tooth is taking a smaller bite. When the blade tooth hits the wood, it chops some space away. A blade with a smaller number of big teeth takes a bigger bite each time the tooth his the wood. A large number of smaller teeth put less stress on the wood because it's taking much smaller bites. A machete and a scalpel will both cut you, but the scalpel will do it a helluva lot more precisely and with a lot less mess.

Also, I didn't buy a 10" plywood blade for the table saw (I already have one of those). I bought a 7 1/4" diameter blade for a circular saw. The 7 1/4" blade has 60 teeth that are spread out along a shorter circumference.

The reason I picked up a plywood blade for a circular saw is simple. Plywood comes in big, bulky, 4' x 8' sheets, which are awkward to handle. A circular saw allows me to cut down a sheet into a more easily manageable size before taking it to the table saw.

Another interesting thing about blades is their balance. A saw spins a blade many thousands of times a second, if it's out of balance even a tiny bit, that causes wobble that wears out the tools and creates a poorer quality cut. High quality blades are very precisely balanced.

Look at the channel and little round punch out

Look at the funky squiggly line and hook-shaped punch out

The punched out shapes I told you look at in the captions on the last two pictures are part of the blades' designs to increase their balance. I'm not an engineer, so I'm not really sure why it works, but it does.

Lastly, a word about kerf. "Kerf" means how thick the blade is. If you have a 1" wide board and you rip it with a blade that has a 1/8" kerf (wide blade), then you turn 1/8" into sawdust. This blade is a "thin kerf" blade.

0.079 inches of sweet slicing joy
This blade has a thickness of only 0.079". That means less wood is turned into sawdust. That means less waste. That is a good thing no matter how you cut it (groan).

Kerf of the standard table saw blade is approximately 1/8"
If you look really closely at the teeth on the blades, they stick out wider than the width of the blade itself. This creates a wider kerf, but also provides spaces for the wood to slide easier. Standard kerf blades have about 1/8" kerfs.

Zoomed in tooth

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