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Learning to resharpen western hand saws has several advantages in your woodworking. Sending your saw back to the manufacturer for sharpening means that the manufacturer chooses the geometry of the teeth and the user has little say in the customization of the saw to his or her specifications. By learning about tooth geometry, and how different angles of sharpening affect your work, you will be equipped to customize your sharpening process to suit the work that you do and to manipulate the teeth for the optimal speed and aggression of cuts. Sharpening saws is often intimidating, and it can be a good idea to buy an inexpensive saw to practice on and build confidence. This article will discuss sharpening as it pertains to western rip saws. Japanese saws are sharpened differently and cut on the pull stroke making the tooth geometry different.
Saws need to be sharpened relatively consistently, anywhere from every 3 to 6 months depending on how often you use the saw, how hard the saw steel is, and the type of work done with the saw (if you rarely use your saw, it may remain sharp for multiple years). The saw should always cut without much effort from the user; the user only steers the saw in the kerf. The saw teeth, when sharp, will cut with sufficient speed and accuracy on their own. Thus, if you feel that the saw is cutting slower than usual, that you need to muscle the saw through the wood to achieve good results, or if the points of the teeth seem rounded and not pointed, you will know it is time to sharpen your saw to return the teeth to working condition and make your sawing more efficient.
Saw sharpening is done with files. I like either Bahco or Grobet files. They are well made and will last with extended use. While cheaper files are available, they cut slowly and wear quickly, making them more expensive in the long run. Below is an image of a tapered saw file:
These files are informally referred to as triangular files, though in actuality they have six surfaces. Each "point" on the file actually has a small flat on it that serves to round the bottom of the gullet of the tooth. If the gullets bottom is sharp and not rounded, the metal is more prone to tearing and can break easily. By having a slight round on the file, the gullet has no sharp corners and won't be prone to tearing:
Note the small flat on the edge of the file where the two planes meet.
Highland Woodworking sells Grobet files which are available here. File size selection is important, but don't over-stress. You won't ruin your saw if you choose the "wrong" size. As long as it's pretty close it will work. Just less than half the file should sit in the gullet of the tooth (if you use a file that is too small, you will be wearing the entirety of the two file edges that sit in the tooth. This means that you won't be able to rotate the file and use a new corner, because you will have worn the next edge at the same time). Using a file larger than half the width of the file means that when you rotate the file, you are now working with an entirely fresh file surface, improving file cutting speed and the file's life. If well cared for, you should be able to get 3-4 saw sharpenings from each corner of the file (sometimes more depending on the length of the saw), which is about 12 saw sharpenings from each file. The files will continue to work beyond this point, but will cut slower. Pictured below is a drawing of a properly sized saw file sitting in the saw tooth gullet. More than half the file is left out of the gullet, ensuring that when the two surfaces sitting in the gullet wear out after a few sharpenings, you can rotate to expose a fresh edge.
You also don't want an oversized file because the flats on the corners mentioned above are larger than on smaller files. You don't need to worry much about the length of the file as much as the taper (slim, extra slim, extra extra slim). Other than these parameters, you shouldn't fuss over file sizes. Below is a table from Highland's website with general guidelines for file sizes depending on the number of points or teeth your saw has. This table will give you an exact answer if you need to buy only one or two file sizes. If you have a large saw collection, with saws that have different sized teeth, getting an array of files may be a good option.
Below, I have created an illustration explaining the difference between tpi and ppi (teeth per inch versus points per inch) referenced in Highland's table.
It is important to secure your saw very close to the teeth when sharpening in order to prevent the teeth from reverberating while you file them (a standard vise won't be adequate especially when dealing with backsaws, whose brass spine will get in the way of the vise's ability to clamp the saw close to the teeth; the vise will clamp on the thicker spine rather than the saw plate). A simple and inexpensive method used by Paul Sellers is to merely take a small 1 by 1 piece of pine and rip it down its length. Then stick your saw in between the two pieces and clamp the three components in the vise as one. Thomas Lie Nielsen offers a more permanent design in his book Taunton's Complete Illustrated Guide to Sharpening, that joins two pieces of plywood with hinges at the bottom and has two calls screwed on at the top. This is the saw vise used at Lie-Nielsen Toolworks to hand sharpen saws before being shipped. I have drawn a similar design, the one that I use, based on the Lie-Nielsen design below:
Saw Tooth Geometry
Tooth Geometry is described by way of a few primary terms. An understanding of how these factors work together to form the saw tooth's shape will let you customize your sharpening process based on your work.
Rake is the angle that the tooth is "relaxed" backwards from 90 degrees to the saw plate. The more rake (the further from 90 degrees), the slower and smoother the cut. The less rake, the more aggressive the saw will cut.
Saw teeth with little to no rake are difficult to start in the cut, but are desirable for cutting quickly once the saw has started on its track. Typically, when a machine files a saw, it files a consistent rake angle across the saw's length. This means that the manufacturer must choose a compromised angle. When filing by hand, however, you can alter the rake angle at different points along the saw's length. Thus, when I sharpen my rip saws, I start with about 15-20 degrees of rake at the toe (a very relaxed rake angle, making for an easy and non-aggressive start). I maintain this angle for the first inch of the saw plate. Quick Tip: Note the number of teeth to the inch your saw has. Then count the teeth as you file. For a fifteen tpi saw, I file at 15-20 degrees for the first 15 teeth. Then I know I have filed the first inch of the saw blade.
Next, as I continue down the length of the saw, I transition to a tooth geometry of 0 degree rake - a very aggressive cutting angle. When cutting with the saw, by the time I expose the aggressive teeth at the heel of the saw to the workpiece, the fine teeth at the toe will have already started the cut with ease. This makes for efficient, accurate cutting.
Below I have drawn a blowup of a sawtooth filed with a 0 degree rake pattern:
Note that the teeth stand plum and straight, making for an aggressive cutting pattern in comparison to the previous image with more rake, which has the cutting angle relaxed for a smoother, slower cut.
Fleam is the angle that the file is presented to the saw looking down on the plate from above. The orientation of the fleam angle is drawn below:
Ripsaws typically have 0 degrees of fleam, though some woodworkers will introduce a very slight amount of fleam on fine toothed ripsaws. Introducing fleam forms the tips of the teeth into knife points making them ideal for cross cutting. Crosscut saws typically have 15-20 degrees of fleam. In order to sharpen the crosscut saw, every other tooth is sharpened 15 degrees in one direction, the saw plate is flipped, and then every other tooth is sharpened 15 degrees in the opposite direction. On a ripsaw, since all teeth are filed 90 degrees across, you do not need to file every other tooth and then flip the saw around; this makes the sharpening of a rip saw much easier than a crosscut saw. The knife points formed by fleam angles help sever the grain as it cuts, which helps in cross cutting applications. For ripping applications, however, no grain must be severed. The rip tooth, filed straight across (0 degrees of fleam), forms chisel points that chip out wood in the kerf. Some craftsmen, such as Paul Sellers, advocate sharpening all backsaws and fine toothed saws (anything more than 10 ppi) for a rip cut while larger panel and handsaws should be filed one for rip and one for crosscut.
These are factors that can be experimented with when filing your own saw. My explanation has been based on my own experimentation and general recordings, but you may find a different tooth pattern that works better for you.
Converting the angle on an older saw, or changing the geometry on a new saw is a simple matter of positioning your file in the correct (new) orientation and pushing the file through the cut. Note: To prolong file life, only file on the push cut.
Resharpened Saws vs. Impulse Hardened Disposable Saws
Another factor to keep in mind is that not all saws are able to be resharpened. Most big box store hand saws have hardened teeth. If you try to sharpen these teeth, you will destroy your files before you will change any of the teeth. This Turbo-Cut Saw Blade sold by Highland Woodworking is also impulse hardened. Look for a black discoloration at the tips of the teeth as shown below. This is a sign that the saw blade is disposable and is not meant to be resharpened.
For certain types of work, you may want an impulse hardened saw that you don't need to worry about maintaining. Most saws that have impulse hardened teeth are also relatively inexpensive, so if you are not terribly concerned with the customization of your saw, this may be a good option that can be replaced when the teeth wear out without breaking the bank.
With this understanding of hand saws, and how different filing patterns can impact your work, you will be able to make the judgement for yourself as to how to customize the tooth pattern on your saw to suit the work you wish to do with a given saw. Whether it be an aggressive 3 tpi ripsaw or a fine tooth dovetail saw, the procedure is the same. I hope this information is helpful and if you have any questions, feel free to email me.
Click here to visit the Highland Woodworking Hand Saw Department
Samuel Colchamiro is a hobbyist woodworker who lives in NJ and works solely with hand tools. He enjoys writing, and is hoping to share his woodworking expertise with others to make their woodworking experience more enjoyable. He can be reached at email@example.com.
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