Table Saw Blade Height Above Material

      Here's a long, thoughtful discussion of the practical and safety aspects of setting blade height when working with a table saw. November 13, 2009

Question
We recently had someone cut on a table saw when drawing his hand back after making a cut. He observed that the blade had been set very high for cutting something thick and he just left it at that height, which contributed to the accident. In addition to insisting that the guard be re-installed, I want to issue a memo addressing the blade height issue. The problem is that opinions are all over the map on the topic and I would like to write an instruction with some legitimacy. Any thoughts on where to find such information?

Forum Responses
(Cabinetmaking Forum)
From contributor T:
Sorry to hear about the accident. I always leave the teeth just higher than the piece being cut but just under the height of the carbide tooth, 1/8" to 3/16".



From contributor B:
OSHA.


From contributor E:
Sawstop! Other than that, I agree with contributor T. Hope your employee is okay.


From contributor A:
Rule of thumb is to see a bit of the gullet. Did this saw have a splitter on it?


From contributor V:
Riving knife and guard is a good practice. The worst I've been hurt is when cutting a 3" x 3" x 3/4" piece with the blade set up high, then as the piece got between the front and back of blade, the piece was able to turn and get caught by the back teeth - wham, ouch! Yes, just a 1/4" or so above works fine.


From contributor P:
Sorry for your worker's injury. The original tool manual is a great source of information, especially for tablesaws. Most manuals can now be found online if you don't have one anymore. The Delta table saw manual states. "Before starting the saw, raise the saw blade so that it projects about 1/8" above the work surface."


From contributor K:
My old shop text book also recommends 1/8" to 1/4" max above material. It would also tell your employee to use a well-made push stick.


From contributor A:
There is a great chance of kickback with only 1/8" of tooth. Many of the newer blade designs (Forrest Woodworker II) or a 40 degree laminate blade have almost that much in bevel. I guess the manual assumes that kickback is not an issue when properly using a riving knife with anti-kickback. Not a great assumption considering that until recent history (10 years?) most people left the factory guard on the upper shelf for permanent storage. It's a shame it took so many years for decent removable riving knives/splitters to make it onto the US market. Imagine how many fingers could have been saved by high quality safety equipment provided with a Unisaw or Powermatic 66. I was taught in the mid 90's that the guard was more dangerous than nothing at all. I bought the Beisemeyer overhead guard with the splitter when I bought my Unisaw.


From contributor J:
My experience is that the correct answer depends on what you're cutting. In terms of safety, you just want the tips of the teeth to be exposed, so roughly an eighth of an inch. But that doesn't always give the best results for blade life and/or cut quality.

I find melamine usually cuts better with the blade an inch or so above the surface. If I'm ripping rough stock to width, then I want at least 3/8" or so above the surface to allow the blade to stay cool and to deal with any variations in stock thickness. If I'm cutting sheet materials where I'm not as worried about chipout, then I keep the blade lower.

In reality, if the operator is doing something unsafe (like putting his hand too close to the blade), then that's where to begin. Blade height will just minimize the degree of the wound. It won't prevent one from careless operators... unless it's a Sawstop.



From the original questioner:
Thanks for your input. As a professional in this trade for 28 years, I believe that on average, at least 5/8" should project out of the material with a 10" or 12" blade. When the blade gets too low and the approach angle gets too oblique, the material wants to ride up the blade at the most inopportune times, resulting in awkward moves and great danger of problems. All of the documentation out there suggests, as the majority of you have, that the blade be +- 1/4" above the top of the material and this is what I will have to put in my documentation in case somebody gets hurt.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
It is the rake angle (or hook, as it is sometimes called) that determines if the blade will cause the piece to ride up. The hook angle for a radial arm saw is zero or slightly negative to prevent the saw from pulling into the wood being cut. If you use this same blade on a table saw, the wood will most certainly try to climb up and kick back. I am always surprised at how often the wrong blade is being used on a saw, creating a serious safety problem. The 1/8" projection is correct for sawing wood.


From contributor G:
1/8th inch, Gene? The rule I was given in shop class 40 years ago, and have used (and still use) is that you need to set the blade so that the bottom of the gullet is almost visible above the board, to both clear the swarf and get the tooth approach angle correct as it begins its cut down through the board. I admit that was in the day of steel blades, and only cross/rip or combination. Is your recommendation based on the development of newer blade geometries? I would like to catch up.


From contributor Q:
Your fingers have no business being behind the front of a spinning blade, ever. Follow that one simple rule, and keep your fingers.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
If the gullet is allowed to project above the piece (it always is below), then half the sawdust will exit on the top side and half on the bottom side. As the vacuum system is designed for the bottom side, the top dust will fill the air.

Regarding geometry, draw a straight line from the tip of a tooth to the center of the circular blade. Draw a second line perpendicular to this line starting at the tip of the tooth. There are three angles: the first is the clearance angle which is between the second line and the back of the tooth. This clearance is necessary so the back of the tooth (some might call it the top rear) will not rub; the second angle is between the radial line and the face of the tooth. This is the hook angle (or rake angle for a knife). As mentioned, a radial arm saw with any hook at all will grab and pull into the piece of wood. Further, with a zero rake, the saw will tend to throw a piece back (which is not a problem for a radial arm saw, but is a big problem for a table saw and most other saws). The final angle is sometimes called the sharpness angle. This angle is a measure of the amount of steel and how easily the heat will be carried away. The three angles must total 90 degrees. Okay?



From contributor G:
No, not okay. The proper geometry is the one that cuts best. Dust collection is not a relevant feature, merely a side issue. A while back it was discounted totally. Now for health reasons it is not, but the optimal cutting angles are not driven by dust collection. In the sense that the blade does not cut better or safer if the sawdust can only escape on the bottom side. (To the extent that maximal dust collection is an issue, it is best handled with an additional overhead collection through a combination blade guard and dust pick up.)

I have drawn the geometry out as you suggested, and I suggest others do so as well. You will see that the lower the blade is in the cut, the shallower the approach of the tooth is to the plane being cut through. The tooth does not, compared to a bandsaw, cut down through the material, but rather scrapes forward, towards the operator. Now there may be other features of current blade design that explain why this shallow (low angle) approach may be as good as a steeper one (which intuitively, to me at least, seems both safer and more efficient). All I get is a minimal downward thrust vector and a maximal forward thrust vector by using a shallow cut.



From contributor M:
To the original questioner: I think you've asked one of those questions where there is no one answer. With the variety of materials being cut in the shop, the blade height required to produce a quality cut is going to vary from product to product. Try cutting a sheet of laminate or 1/8" with the blade only 1/8" above the material. Not very safe, in my opinion.

Find all the factors that contributed to the accident. Every accident I have been around was a combination of multiple errors. Excessive blade height can certainly be the difference between a near miss and a major loss, but I would bet there were several other errors that occurred as well.

Last, lose the memo, grab some safety glasses, and invest in some one-on-one training. A well-trained saw operator can manage varying blade heights.



From contributor A:
As Gene mentioned, it has most to do with rake.

The worst combination would be a sliding miter chop saw blade (-6 degree) cutting a piece of lumber on a table saw at any blade height. The 1/4" (about the full tooth on a carbide blade) becomes obvious as a blade starts to dull. 1/8" will promote kickback.

At the end of the day, the reason for keeping a high blade when cutting melamine or laminate has nothing to do with safety... only quality of cut. The newer melamine blades like a Forrest/CMT has + 40 degrees of rake, making it not necessary to raise the blade an inch above the work to maintain quality of cut.



From contributor A:
Big oops on my last post (not enough coffee on a rainy day). The hook (not rake) is + 5 -7 degrees on the newer melamine versus negative on Amana. The bevel angle is 40 degrees.


From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
A small hook angle and a saw that is set with low protrusion above the surface is not correct. For this reason, many saws for table saws have a fairly large rake (or hook) to make the blade cut more downward and not have as much kickback force.

Remember that what I stated previously is for cutting wood, as stated in the posting. For different materials, for different cuts, and for different saw types, there are different blades with different rakes. (I do not know how band saws got into this discussion, but a band saw will have a negative rake angle much of the time.)

The "best" saw setup and saw blade is one that is safe. Safety is more important than quality. Safety includes risks to the operator from the blade, flying pieces of wood, and exposure to dust. Using a dust collector on the top of a table saw is indeed possible and is done, but how often do we see it? Seldom.

Anti-kickback devices should always be used.

There is not just one safe setup, so if one safe setup gives a poor quality cut (and that poor quality is not due to wood issues, such as over-drying), then we do want to try other safe options to improve quality. Such options may include higher protrusion with a blade guard and/or kickback features.

Wood dust is an issue today. Part of the reason is that we are exposed to many other chemicals which seem to make our bodies more susceptible to exposure to carcinogens. In the past, it seemed that cedar was the big risk, but now it seems that all wood dusts have a risk. Certainly, some of the non-US woods (especially tropical woods) have skin and breathing allergy risks that are very serious and have been for many years. Cutting glued woods also poses some risks. Cutting treated woods is an extreme. The bottom line is that dust issues must be of very large concern today for both short term and long term health issues.



From contributor C:
Height of the blade depends on what you are cutting. When I miter 4" wide stock, the blade is at full height. I do not use a guard, but a riving knife is good for ripping. I use a push block made out of a 2x6 and when it gets cut up, I make a new one. It gives very good control. Bottom line is no matter what you are doing, keep the location of that blade in mind! Another item is to keep in mind where your hands will be if something does go wrong!

While I am at it, there was an article about a surgeon cutting his fingers on a table saw and wearing gloves. A loose glove is dangerous; the latex stretch fit gloves are another story and are used a lot in my shop. They are much safer and give an excellent grip on the wood.

Again, keep in your vision where the blade is. I have been in woodworking many years and still can count to ten!



From contributor K:
I like a high blade, as it seems to cut smoother and easier. To protect against this high blade, I use the Mesa Vista Magnetic Feather Boards every time unless the cut makes it impossible to do so.

Even with those, I never forget that I am working with a tool with great potential to get me, so I stay away and keep my fingers away from the blade and use push sticks whenever possible.



From contributor C:
In regard to push sticks, I do not use them! Make a push block out of a piece of 2x6 by cutting or ripping the bottom away, leaving an inch or so at the back, round over the top. With that you have absolute control. A word of caution: never use a pushing device that captures your hand. Example is a hand saw handle.


From contributor K:
I use a variety of pushing/controlling devices depending on the job and the size of the work piece. Sometimes the flat block design won't work, but it is a good one for many things. Mine typically hold down as well as push forward and aren't so fancy that I am tempted to save them.


From contributor E:
In teaching woodworking, I use a hotdog as an example of a finger. First thing I do is adjust the blade to the height of the board's thickness - I overlap about 1mm. Then I intentionally cut the hotdog and let the students see that if we place the height of the blade correctly, the cut will be minimal and could probably just be stitched by the doctor. Then I let the students check the boards and find no chip off. Second simulation: I adjust the height up, then cut the same hotdog, and you see your finger cut off... I let my students see the boards, and they find chip off.

If you set the blades too high, the angle of the cut is changing, the teeth are cutting downward with high force that will force the ply to chip off. If you set the blade just the height of the board's thickness, then the angle of cut is not downwards - it's cutting about a 30-45 deg (estimate) angle. This will lessen the chip off. If you still have chip off of your ply, check the tip of your blades. You might be dull or some teeth are lost and you need to retooth.



From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Sounds to me like you are a very good teacher. Your posting is accurate. I might add that if the saw does not have the correct hook, cutting will not go well either.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor D:
I believe I am well qualified to discuss this topic after a serious kick-back several months ago (six stitches, some tendon damage left index finger). I was cutting a 3/8" piece of plywood, approximately 14'x18". I was using the "1/8" theory with a brand new Worker II 60. For a split second I relaxed pressure just before I pushed through the piece. The plywood was slightly warped (as is most) and wham! The work piece ever so slightly rose on the back of the blade, caught a tooth, and ouch! I still don't have full use of my finger, and believe me I have a significantly enhanced respect for power tools, whether it be a saw, jointer, router, etc.
Since then, and after reading what seems like thousands of commentaries on blade height, I am of the firm opinion that having the gullet close to the top of the work piece is the correct technique, at least for me. Of course, all other safety techniques are necessary and I believe that a higher height creates more downward pressure at the front of the blade and less of a chance that the piece will ride up and over the blade. Tip: Keep your machines well-tuned and don't ever think it can't happen to you!



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