For the manner in which men live is so different from the way in which they ought to live, that he who leaves the common course for that which he ought to follow will find that it leads him to ruin rather than safety.

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Thursday, October 27, 2011

On saw sharpening...

My 18" Disston D-100 loaded into the vise. A good saw vise can be had at an antique store. I see plenty of them can find one. I always start with the handle to my left. I file from the handle down to the toe. Being a cross cut saw, file every other tooth...and we'll visit more on that in just a moment.

At most, only two files are needed for a given saw. The big one is a 10" single cut mill bastard. The smaller one is a 5" double extra slim triangular file. The size of the teeth dictate the size of the triangle file, I try to go with the smallest file possible, in this case the saw is 11ppi. There's different schools of thought on that, and it's a matter of personal preference. The mill bastard is to joint the teeth. Jointing the teeth is just the act of filing straight down the tooth line to bring all the teeth to the same height. This saw just needs a light touch for the jointing before sharpening. Sometimes there will be more work involved. I have an Atkins 53 that will require significant work and I'll cover how I tackle that one in a later post.
As you can see, I have started up the tooth line. This picture illustrates the fleam angle. Fleam is the angle at which the file crosses the tooth line. This saw will have about 25 degrees, seeing that it is a crosscut. This angle is variable and depends on what you want from the saw. Incidentally, a rip saw would have zero or close to zero fleam.  At this point, you want to go down the tooth line while filing every other tooth. I find that the flat section at the tip of the file is handy for getting lined up. It helps me feel my way into the tooth. I don't have a good illustration for rake...I'll discuss that at the end, but it's a player in the equation at this point as well.
This is after sharpening every other tooth. You can see that the teeth appear to be different sizes. That is due to the fleam, for the most part. In this particular case, it is also due to the fact that I'm changing the geometry of the teeth slightly. The handle of the saw is to the left, which means that the leading edge of the teeth is to the right. The angle at which the leading edge slopes BACK from vertical is called rake. A vertical leading edge is said to have zero rake. I try to get close to zero when I sharpen, but I still get a little angle. Mostly due to the fact that I don't use a guide block to hold the file. For me, these little differences are perfectly acceptable. Once I have filed all the way down the tooth line, I will turn the saw so that the handle is one my right and work back down...starting on my right side.
I've tried like hell to get a good picture of a tooth line. It's not easy. Anyway, this is after I have gone both ways down the blade. The saw is sharp. I like to say that a freshly sharpened crosscut saw should look scary. As I type this, I have several rather deep scratches in my hands from being careless and reaching over the saw as its clamped in the vise. Even though the saw is sharp, the work is not done. It still requires tuning.
Tuning a saw requires taking a test cut and watching the results. In this case I marked out a line on the board and cut it. I was going to show that process here, but decided to work on that another day. Anyway, if you look at the above cut, you will notice there is a change in the cut about half way down the kerf. Why? The saw was coming off the line. What you want to do in the tuning process is check which way the saw deviates from the line. Here it started pulling to my left slightly. What you want to do is run a sharpening stone down the side of the blade along the offending side. Once...just once, and start cutting again. If the saw starts tracking straight, you're good. If not, then stone the offending side again.  after this cut was finished. It was still a little rough, which is an indicator of too much set. What I did then, was stone both sides of the blade with two swipes each. Til I got...
...two nice parallel cuts next to each other.
But wait! There's more! That's right, for the outrageous price of TOTALLY FREE, I'm going to keep on gabbing! Aren't you lucky!
Ok, if you're still reading...This is obviously not an all inclusive guide to sharpening a crosscut hand saw. I could go into similar length with rip saws as well, which I fully intend to do, just not right now.
What this is, is saw sharpening from the beginner's perspective. In hopes to help out a fellow saw sharpening beginner. I have in my shop a total of eight hand saws. Six of which have been rehabbed and sharpened, two are waiting on sharpening.
Tuning is a simple process, but it requires your patience and willingness to pay attention to what you're seeing and react appropriately. It also requires a soft touch. When you stone a blade, just gently run the stone down the blade. Don't put a lot of pressure on it. I have a dedicated stone for this. A friend gave me a bucket of assorted tools that included an old oil stone. That oil stone has become my saw stone. I don't believe that this is the time for expensive water stones (or expensive Arkansas stones, etc). A less expensive stone will be perfectly appropriate.
Pay attention to the back side of the cut. I tend to push too hard sometimes. This leads to an increase in tear out on the back of the board. Let the saw do the work. Tear out is also a result of too little fleam. I don't know the perfect fleam number. Too much fleam leads to a saw that cuts quickly and cleanly, but dulls fast. Not enough means that it will have a stronger edge at the tooth, but will tear out more.
Rake angle is another important detail. Zero rake cuts aggressively, but is hard to start. Too much rake makes the saw slower, but easier to start.
Tooth set. I didn't cover how to set the teeth. We'll do that later. Essentially, it's the amount that each tooth gets bent over to the side. This effectively widens the cut and allows the blade to move through the wood without binding. You can typically get away with less set in a crosscut saw than a rip saw. This is due to the tendency for a board to spring back as it is ripped.
There's plenty more that can be covered. We could fill a couple of books. File size? Sloped gullets? The finer mechanics of everything mentioned above? And a thousand other topics. For now, I just hope that this post might just push one other noob like myself down the slippery slope into the hand tool world. A well sharpened hand saw is a joy to use. A well sharpened hand saw that you sharpened YOURSELF is even more so. That's it on saw sharpening for now. I have a few other saws that I will cover soon, and I hope that I (and maybe you) can learn a little more from it.

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