What is the recommended height of the blade on a table saw while operating?

Question

I have been watching a lot of videos lately about table saws. In those videos I usually see cuts are being made with the blade just barely clearing the piece. For example:

^{Image from HammerZone}

Conversely I see some where the blade is very high above the piece.

^{Image cropped from Wikipedia}

In the second example I do not see a reason to have the blade up that high to cut the piece. There would be a obvious safety issue with more blade being exposed but is there a reason to keep the blade up that high?

Answer 1

If you call up Freud and ask, they'll tell you that you want one full tooth to clear the top of the wood, but no more.

There are a couple of reasons for that recommendation- first is safety. A tooth that clears the surface on the up swing then re-enters on the down swing may not follow the same planar path due to harmonics and vibration related physics. A tooth that is held firmly by the material it is cutting is less likely to catch.

The reason why you want a whole tooth to extend through the work surface has to do with the shape of a tooth and debris clearance. Circular saw blade teeth (even carbide ones) are often wider at the tip than they are at the base. This tapering allows for less binding and cleaner cuts than a straight tooth would.

Answer 2

The common argument for raising the blade is that the front of the blade is making a more downward cut, theoretically reducing the chance of kickback and increasing cut quality. While this may produce a better-quality cut in plywood, the kickback argument relies on flawed logic, since kickback is often produced by the kerf pinching the back of the blade or by a workpiece or offcut getting pinched between the back of the blade and the fence. It also means the back of the blade is following a more vertical path as it exits the table, increasing the possibility that your workpiece or offcut will be raised off the surface of the table and out of your control.

The argument for lowering the blade is that less exposed blade means you have a smaller chance of an amputation if you accidentally position your hand in the line of the cut and make contact with the blade.

There are various modern recommendations, all of which are very similar:

• the blade should be raised so its peak is 1/8" to 3/8" higher than your workpiece
• the blade should be raised so 1 full tooth is exposed above your workpiece
• the blade should be raised to expose half of the gullet (if there are multiple depths of gullets as in some combination blades, this recommendation applies to the shallowest gullets)

As TX Turner briefly noted, the purpose of having some clearance above the blade is to allow the gullets to empty. If the gullet does not have adequate clearance, it may not be able to dump its payload before its corresponding tooth takes another bite. When this happens, the gullet becomes packed with sawdust, producing friction on each subsequent pass, commonly causing the blade to wander and/or burn the wood.

Answer 3

I set the blade to the minimum height that is required to make the cut, typically about 1/8" above.

There isn't really a need to have it higher for purposes of clearing the sawdust. If you look at the geometry of a table saw blade, the cutting action is happening at the front of the blade, as the cutters push through the wood. The gullets will fill on the down stroke, and inertia will clear the gullets down into the body of the saw.

Kickback occurs when the piece being cut is picked up by the back side of the blade, usually due to the saw kerf being pinched. Having the blade lower reduces the length of the blade that is in the kerf, which can help reduce the chance of kickback (although a splitter or riving knife is far better).

Answer 4

Generally I'd put the blade only as high as necessary to clear the top of the board being cut. There is, however, one occasion when raising the blade significantly above the work piece is valuable. That would be when you're making a stopped cut. In this case, the higher the blade is, the more vertical the cutting surface is, thus making a cleaner stopping point.

Answer 5

Well I noticed two things about the pictures you posted. The first is a ripping blade and the second is a cross cut blade. That might have something to do with it.

The first is a crosscut blade and the second one is a 'cross' between a rip saw and a cross saw, doesn't have the kicker on each tooth. (though there still might be a reason for height between cross cutting a board and ripping).

However, what I was able to find was that the more blade you have showing the more blade is available to be grabbed and cause a kick-back (pinching the blade). Cross cutting a piece of wood is less likely (IMO) to cause a pinch and kickback. So that might be part of the reason for the differences.

The different comments also suggested a good riving knife will help reduce the chance of kick back in these situations too.

I personally just like it closer to board height to have less exposure to the spinning teeth of the blade.

Answer 6

For most saw blades there is a optimal height range of the blade due to tooth contact when cutting thin materials, and/or when you want rapid cuts. The higher the blade the less teeth would contact the material, and the higher the possible feed rate. This also depends on the spacing of the teeth on the saw.

Whenever possible, there should be a minimum of 2 teeth contacting the work piece at all times. If you try to feed it too fast in this scenario, the saw blade should gradually slow down until the motor stalls.

Lets say you are cutting something relatively thin with a low tooth count saw, it would be possible to increase the height of the blade until the thickness of the work piece can fit between two saw teeth. This creates a hazardous condition where you could feed the piece of wood fast enough to violently lock/seize the saw and damage the blade.

If too many teeth contacts the work piece and the angle is very shallow you have a increased risk of lifting the work piece off the table, usually due to feeding it too fast. This would be a kick-back risk because then the material could then twist and bind the saw blade.

The ideal saw blade height would usually be the height where 2-4 teeth are contacting the work piece at the same time during a cut.

This really only applies to the common saw blade tooth shapes, without a feed speed limiting tooth safety feature. Some saw manufactures have a built in feed limiting tooth profile, it looks like a tail or ear behind the carbide, it is to prevent the blade from taking too big a bite out of the wood. These feed limiting tooth designs are also commonly see in chainsaw blades.

Also, if you can cut with a safety guard on, use it. Less worry about how a large exposed blade is more dangerous.

Answer 7

I prefer a higher blade setting. I actually think it is safer in a number of ways, but having the blade plainly visible strikes me as much more likely to avoid inadvertent contact with the blade.

Perhaps more important is making sure that the saw is properly set up. If the blade and fence are exactly parallel, the chances of kickback (except with stock that tends to "close" behind the cut due to stresses in the wood) are minimal or non-existent. I have had a couple of kickbacks, one hit me and hurt a lot, the other shot out the back of the saw and left a notable indentation in the wall behind me. Both were because the space between the blade and the fence was ever so slightly smaller at the back of the blade than at the front. Proper setup of the saw is important not only for safety, but for quality of results.

Techniques also matter. Push sticks are a must for any cut less than 2" wide. Also, while it can be a bit awkward, keeping your whole body to the left of the blade will mean that if piece being cut kicks back, it kicks back into something besides you.

Answer 8

I don't have time to read through the litany of guesswork by armchair engineers, but many pages into this no one mentions that the saw blade gullets should protrude above the cut by 1/4" "or so" for proper blade cooling. Hot blades dull quickly. 90% of these are cautionary guesses by people scared of saw blades. Rightly so, that's why people in the business make guards, and use push-sticks.