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Saw blades - What is a hook angle and what is a kerf?

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So in another thread we were talking about the "kerf" on my sawblade for my new 19.2Volt cordless circular saw (or trim saw, as they call it).

That led me to a bunch of questions. What are all those numbers on the saw blade packages?

What is the "Hook Angle" and what is a "kerf"?
That's not a bunch of questions, it was only 2. A bunch is 3 or more.

Kerf is the width of the blade at its widest part where it would cut wood. Or it is the space in the wood that is removed by the blade. Typicaly a table saw blade has exactly 1/8" kerf. Unless it is a thin kerf blade offered by most manufactures. I like freud blades the best but there are lots of others out there.

Hook angle is more complicated. if you put a straight edge from the center of the hole and out to the tooth tip, the angle of the cutting tooth in relation to the straight edge is the hook angle.

If there is a space there it is positive hook angle and if the tooth is partially behind the straight edge it is negative hook angle.

You would use a positive hook angle say 5 to 10 deg. for a table saw where you push the wood through the blade.

You would use a negative 6 deg. hook angle for a sliding mitre box or radial arm saw where the wood is held stationary and the blade is pulled through. With a positive hook angle in this application, the blade would try to climb through the wood on its own and the operator would have to actually hold the sliding arm from going too fast. This is very dangerous, having to slow down the moving blade, so a negative hook angle is a must.

With hook and kerf out of the way.... There are a bunch of different tooth designes to discuss too!
Quick lesson on blade tooth designs. All descriptions are carbide tipped blades, looking at the teeth as if the saw was going to cut towards you (with the blade out of the machine of course!)

There is a Flat Top tooth (FT). This has flat ends so the bottom of the kerf will be flat.

There is a Alternate Top Bevel (ATB) This tip design has the top of the tip angled slightly first to the left then the right. This has a cleaner cut on the sides, but the bottom of the kerf will have a slight hump in the middle

There is Alternate Top Bevel + Rake (ATB+R) Same as ATB with one exception. Every third tooth has a flat square tooth with the corners slightly beveled. This cuts good on the sides and the R cleans out the bottom of the kerf.

There is triple Chip (TC). Every other tooth has both corners cut off at a 45 degree angle and the other tooth is square and flat. This is good for laminated wood and plywood.

There is Hollow Ground (HG). Every other tooth has both corners cut off at a 45 degree angle and the other tooth is not flat but hollow ground (concave) at the tip. This makes clean cuts in Melamine coated wood.

There are a few others but these are the most popular. On well made blades, the plate, which the teeth are silver brazed onto, is not just a stamped out piece of metal. It is milled down out of a thicker piece to exact flatness. Then there are small cuts in some blades from the teeth to about 1/3 to the center. This eliminates heat warping due to expansion, and if engineered correctly will quiet the blade hum somewhat. All the different manufactures have there own ideas what works best so there are slight variations from company to company.

Amana, Delta Machinery, Forrest and Freud, are some of the better blade companies. But you can expect good results from Dewalt and Craftsman too.

Now all you need is a table saw, radial arm saw, power miter saw, circular saw, or a small trim saw to go with all those blades!
What about the number of teeth on a blade?

So on a 10" blade for example, 24 teeth to 36 teeth is for rough cutting, and cutting framing lumber like 2x4's etc. It is also used for ripping lumber (cutting with the grain).

40 - 50 teeth would be a combination all purpose blade that you could use for either ripping or cross cutting, and get pretty good results.

60 - 80 teeth would be for fine finish cross cutting. This would give excellent chip free results.

90 or more teeth would be the ultra smooth fine finish cross cutting blade.

So you see, the more teeth the smoother the cut but there is a trade off. Cross cutting only over 60 teeth.
If you try to rip with a fine cross cutting blade, you will struggle pushing it through the saw and will be bringing it to be sharpened real soon. I have tried this, I know! You can't be lazy and not change the blade to make a few rip cuts! It gets expensive!
The cost of the 80 - 90 or more tooth blades is very high. Upwards of $125.00 per blade. So unless you need a dedicated blade just to crosscut, then the combination blade (around 50 teeth) is the most versatile.
TheGuru: That's not a bunch of questions, it was only 2. A bunch is 3 or more.

Actually, it was a "bunch" of questions:

1. What are all those numbers on the saw blade packages?
2. What is the "Hook Angle"
3. and what is a "kerf"?

When being snarky it's important to also be right.
When being snarky it pays to note that this thread is 5 YEARS OLD!
tee hee hee.



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