Table Saw Blades & The Laws of Physics
If you wanted to make a device to throw pieces of wood at a high rate of speed, how would you design it? You could look at the machines used in sports for throwing things and start with a spinning disc, say 10″ in diameter. If you had the disc sticking up from a solid table, and had another solid piece at a right angle to the table and parallel to the blade, all you would need to do would be to put a hunk of wood between the spinny thing and the solid parts. Sounds a lot like a table saw, doesn’t it? When we think of the risks of using a table saw, we think of the teeth, but the spinning parts of the blade that don’t do the cutting are where many table saw accidents begin. Many table saw accident stories begin with “the wood I was cutting suddenly went flying . . .”. This forum post from SawMill Creek is an example of that. The likelihood of this sort of thing happening is directly related to the size of the wood. If the length of the material is shorter that the exposed part of the blade, and the material is trapped between the blade and the fence the odds of the material kicking back are quite high. This is why you should never use both the miter gauge and the fence together. That is obvious if you’re cutting completely through the material. What’s not so obvious is that the same laws of physics are at work, even if you’re only making a partial cut, such as the shoulder of a tenon. I know that many of our readers have done this for many years without getting hurt, and will likely want to argue about this. It isn’t as dangerous as making a through cut, but that doesn’t mean it is entirely safe.
The temptation to use the fence as a crosscut stop is understandable. It’s there, it’s accurate and it doesn’t take much time to set it. If you’re not going all the way through the wood, you may get away with it, but it is still a risky operation. But you can reduce the risks to nearly zero if you take a few seconds to clamp a block of wood to the fence ahead of the blade. You still have all the benefits of the fence’s adjustability, and repeatability. The only downside is you have to hold the work firmly to the miter gauge. That really isn’t a negative, it’s what you need to do to stay in control of things.
As you can see in the photo above, as I make the shoulder cut for a tenon, the space between the end of the board and the fence prevents the wood from being trapped and propelled. My hand is a safe distance away, and it isn’t moving toward the blade. That takes care of the shoulder cuts, but how can I quickly remove the excess material to make a tenon? There are a bunch of ways to do it. I could switch to a dado blade, I could use a tenoning jig, or I could make the cut on the band saw. Let’s say I don’t have or don’t want to use any of those methods. I only have a couple tenons to make and I don’t have much time. How can I waste the rest of the tenon? The last thing I would do would be to shove the end of the board into the side of the blade. Here is a way that is faster and safer:
After the shoulder is cut, I can make a series of crosscuts, moving the work away from the blade after each pass. I don’t need a stop because I’m moving away from the shoulder. I don’t need a precise distance between the cuts. My hands are always in a safe position and moving in a safe direction. If something goes wrong or I get distracted my hand isn’t moving toward the saw blade. OK, but what about all that stuff between the saw kerfs; how do I remove that to get a nice smooth tenon?
Here are two simple devices that a lot of woodworkers apparently don’t know about, a chisel and a bench hook. After making the cuts at the table saw, I put the wood on the bench hook to hold the piece firmly with my hand in a safe location, and slice off all the waste with a chisel. It doesn’t matter how you feel about hand tools, this is quick, easy and nearly foolproof. It takes far less time than it would to nibble all this stuff away at the table saw, and the results are just as good if not better.
Speed doesn’t mean much if you have to head to the emergency room. With an understanding of how the tools work and the material behaves, there isn’t any reason that you can’t work efficiently and safely at the same time. If you have to ask “Is this safe?” you should stop, look at the process and don’t go any farther until you can say, “This is safe.”
Popular Woodworking Magazine is committed to working safely, and we have made available articles on table saw safety that every woodworker should read.