July 01, 2004

The Secret Life of Tools - 1.2

That's right, its back... For all those insomniacs that didn't get enough on the first go around, here's some more blather on blades...
Today in the extended entry, I'll be droning on about the types of blades, and what makes them different from one another... Now, I have warned you... This is going to be terribly dry stuff...

So last time I talked a bit about keeping blades sharp, and when to change them... This time let me talk about the finer points of the things physically...
The vast majority of blades have what is called a "set" the set is how much the teeth are wider than the body of the saw. By having a set, you end up with less binding as well as being able to cut curves when you need to. (curves should only be done with tools designed to do so, do not cut curves with tools using circular blades! Think jig saw, or saw-z-all, or band saw) Tied in to the set is the shape of the teeth on the blade... There are three basic tooth shapes, and they get mixed up to create blades that perform differently... The types are: Beveled, Raker, and Centered. (ok, I can't find a proper name for the centered tooth, I'll describe it below)
The Beveled tooth has a point ground to one side of the blade or the other... These teeth are used in opposite pairs on blades. They cut first one side of the kerf, and then the other side, leaving a small inverted V of material at the bottom of the cut. These teeth cut smooth sides, and rough bottoms.
Raker teeth are flat topped teeth, made the width of the kerf. They cut with a flat bottom but tend to leave a very messy edge.
The Centered tooth is sharpened from both sides so that it only cuts a flat bottomed V in to the stock. They are never used as the only type of tooth as they do not clear any material outside the blade body.
If you go out to buy a blade, you will be hit with quite a selection to choose from. You need to think about what kind of cutting you do naturally before selecting one. However, there is a pretty safe option available to put on almost any saw for almost any material... Look for a "combination" blade. The tooth pattern will be ATR or Alternate Tooth Raker. That translates to two opposite beveled teeth followed by a raker. These blade cut nicely through just about anything, and leave a reasonably nice edge. I run ATR's on both my table saw, and the radial arm saw as we deal with lots of plywood, so grain direction is an unknown... These blades are usually 24 teeth on a 10" blade. I run a Triple Chip Grind blade for plastics and laminates, which is a raker, followed by a centered tooth... Its up in the 80 tooth range so it cuts smoothly, and doesn't shatter the plastics... I have a couple other specialty blades, but they almost never see use.
The next trick I pull with my blades is that I use what are called "thin kerf" blades. A typical 10" blade will cut an 1/8" kerf. A Thin Kerf will cut 3/32". 1/32" doesn't seem like much does it?... Think of it this way, you are only cutting 3/4 of what the regular blades cut. I can tell you that adds up... These blades are not the secret of the universe however. They have a much higher tendency to heat warp under heavy use, and if you manage to hit something like an imbedded stone, or nail, they with shatter their teeth in short order. They seem to hold up pretty well for us here as the crew is sharp enough to look for screws/staples/nails... All our blades are generally coated with Teflon too, so the pitch and sap from the pine doesn't build up to heavily... Every now and again, check your blades for that buildup, you'll be amazed how much of it sticks to the blades...
When you get in to a band saw or other straight type blades, there are some other options. Most notable is the "wavey set" blade. Rather than grinding alternate teeth one way or another, these blades teeth meander back and forth through the work. It has always been most noticeable to me on hack saw blades... I could do a whole post just on band saw tooth styles, but I'm not going to... We don't use band saws nearly enough here that I would consider myself an expert in the minor differences you get from the different teeth...

Posted by Backstage at July 1, 2004 01:58 PM
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