Dental Hygiene Sawmaker Style: A Close Shave With Occam’s RazorJune 18, 2010
How many times have you heard it said that sharpening a saw is easy? Or worse, that it’s no harder than sharpening a chisel or plane iron? Now, show of hands, how many of you believe that? Yeah, I didn’t think so. I don’t believe it either.
I tend to think that saw sharpening is challenging enough that once you get it you feel as though you’ve accomplished something. It’s neither the hardest nor easiest thing you’ll ever do. Lots of people try it and have trouble. I remember when I first learned to do it I started out like everyone else following all of the steps you are supposed to follow—it didn’t take long for me to realize that some of what I was doing seemed downright unnecessary. So I started to think it all through for myself from scratch, and what I wound up with is a method for sharpening saws that I use to this day. I’m willing to bet that if I showed you how I do it, even if you’ve never been able to do it before you could get it.
Probably most of you already know what Occam’s razor is, but here it is quickly anyway—it’s the idea that given two explanation for something, the simpler of the two should be preferred. That’s basically all I did with saw sharpening. Gave it a close shave with Occam’s razor. I don’t expect everyone to agree with me—when was the last time you saw everyone in woodworking agree about something? I don’t either think the other way of sharpening saws is wrong—that would be foolish; it obviously works and serves many people well. I guess my larger point is simply that I don’t think there is just one right way to do it.
There are a number of smaller differences in what I do, but the biggest and most obvious one is that I file from just one side of the saw. I don’t file half of the teeth then flip the saw around to file the remaining teeth. That works, but I think it is needlessly convoluted for most filing. The only filing for which flipping the saw around is actually necessary is for sloped gullets, but I don’t think sloped gullets are worth doing most of the time anyway. In dry hardwoods, which is mostly what people are cutting, I think what people really need are simply very sharp and well tuned saws.
The thinking behind filing half the teeth then flipping the saw around is that by doing so you equalize any errors. However that isn’t really what happens—that would only be the case if you did the same thing to the saw from both sides. But in reality you don’t do the same thing to the saw once it’s flipped around. Things change. You rotate your file to assume the proper rake angle while now filing with the teeth facing the other direction. On paper you are using the same rake angle, but in practice you are in fact introducing more physical manipulations of the file and more chances for inconsistency and error. It seemed to me that you could skip this whole rigmarole and simply file every gullet while maintaining a single physical rake orientation for the file.
Working this way gives you a big advantage. When shaping teeth you can work directly on any tooth and in any gullet you wish that you see needs adjusted–you don’t have to save any until you flip the saw around. You are freed up to pay attention to the things that are really important when sharpening a saw—you aren’t observing any longer what needs to happen from which side of the saw.
I find working this way remarkably accurate. It just doesn’t involve the usual acrobatics of saw sharpening as it’s come to be practiced. I think the received wisdom on the topic is something that sounds so compelling when you hear it, people haven’t really questioned it. But I do think there is some precedent for sharpening saws the way I do—if you read the passages on saws in Moxon, it seems pretty clear that he’s describing a saw being sharpened by filing in every single gullet—he says it pretty clearly actually. He describes filing one tooth then says to file all the rest—no skipped gullets. When he writes about setting teeth, then, he does describe skipping gullets. So I think he writes just exactly what he means. I think the more interesting question would be why people ever started flipping saws around to begin with?
There are of course objections people could raise, so let me address them. What about the burr created by filing? If you file from just one side, it will be all on one side of the saw—won’t that affect how the saw cuts? Not in my experience, no. Not at all. It’s something that sounds good on paper but that doesn’t amount to a hill of beans in practice. Saw sharpening is full of stuff like that—a theoretician’s cornucopia. If you are creating burrs that big and intrusive when you file there’s either something wrong with your file, or how you’re filing, or with the steel you’re filing.
Another item like that deals with filing into teeth set toward you vs. filing teeth set away from you. Won’t the ones set away from you get sharper than the ones set toward you, as the steel will cut more smoothly on the ones set away from you? Again, no, not in practice. Maybe under an electron microscope, who knows. But in practice it doesn’t matter at all. What about big and little tooth? Won’t you be constantly struggling to keep the teeth set toward you the same size as the ones set away from you? Not really. You have direct control the whole time over the size of the teeth—you simply remove metal where it is needed and don’t remove it where it’s not needed. It’s very direct and intuitive.
What about crosscut teeth? Do you file them from one side too? Sure. If you were to flip a saw around you’d file fleam in from opposite directions anyway—there’s still less muss and fuss when you don’t flip the saw. You just keep the same rake angle and only change your fleam angle—the back of one tooth is the front of the other on the opposite side of the saw. It’s the same geometry, just filed in from one side of the saw, not from two.
What about tiny errors in tilting your file? Those would cancel each other out by flipping the saw around? Sure they would, if your errors were actually just a single consistent error repeated over and over again the whole time. Good luck being that consistent with your errors. There’s no such thing as filing that doesn’t involve errors. Tiny random errors don’t adversely affect anything. I think this is another case of theory and practice not matching—nobody is perfect, nobody. Our errors aren’t even perfect errors. I think we imagine our errors are more consistent somehow than they are. If we did have some consistently noticeable tick in how we filed that was bad enough that it adversely affected the saw and made it pull to one side or something like that, don’t you think you’d be better served fixing your filing technique? It would take an error of that visibility and magnitude to cause a problem—the normal random sorts of stuff that happens, it doesn’t matter which side of the saw it happens from.
So what do you think? Anybody want to learn to sharpen saws? It works. I promise.