To get the most efficient use of a saw, it needs to be kept in good shape. Sharpening a hand saw yourself can save you some money, but it is a skill that takes some time and practice. Sharpening can be a three or four step process depending on the condition of the saw blade. In the case of a damaged or misused saw, or if the saw teeth are out of size or missing a tooth, you should start with leveling the teeth.
About Saw Teeth
A few words about how saw teeth are designed to function will help here. If you ever wondered why saw teeth are bent slightly to the side, there is a reason for this. Setting the teeth sideways alternatively to the right and left enables to saw to cut a groove in the wood (or kerf) slightly wider than the saw blade so that the blade has enough clearance to move in the forwards and backwards in the kerf without getting stuck or causing too much friction.
Rip saws are deigned to cut along the wood grain, they have teeth filed at 90 degrees to the blade to function a s a series of miniature chisels. Cross cut saws, conversely, cut across the wood grain. Their teeth are filed at from 65 to 70 degrees to the blade, acting as miniature knife blades on the sides of the cut.
The space between the teeth is called a “gullet". Saw teeth are specified in points per inch. Smaller teeth are better for hardwoods, larger for softwoods, which have less resistance to the saw and therefore produce more sawdust, which is carried from the kerf by the larger gullets more easily.
For leveling, take a flat hand file and mount it in a block of wood with a slot cut in it. Position your saw in a vise, clamped between strips of softwood either side of the blade, with the teeth pointing up. Press the file-holding block against the side of the saw blade; this will act as a locating jig to ensure an even result as you run the file back and forth over the teeth. The next step is the shape the teeth.
Saw files are used for shaping the teeth on saws. Want you are trying to do here is to maintain a consistent pitch to each tooth. By pitch I mean the angle that the leading edge of the tooth is leaning at towards the front end of the saw. Position the saw lower in between the softwood pieces in the vise so the blade is protruding the minimum possible while still exposing the teeth.
Saw files are triangle shaped, 60 degree to a side, and the perfect size to use is twice the depth of the teeth. Place your saw file, with one of the 3 corners fitting into a gullet, keeping it horizontally held and at 90 degrees to the blade. File with an even, forward stroke, holding the file end in one hand and the tip with your other hand’s thumb and forefinger.
This is one of the parts of hand saw sharpening that takes some skill, so take your time. Each individual gullet needs to be filed until all flat spots between teeth are gone, and the teeth shape is consistent, keeping the original pitch of the saw. Deburr the blade after the filing with an oilstone, once over lightly.
The next step is to set the teeth in order to make the right kerf width. For this I always use a tool called a saw set. This is a handy little cast iron tool like looks a little like a set of pliers, designed to bend the saw teeth to precisely the right angle. You squeeze the handles together and a pre-set plunger forces the tooth against a wheel-shaped anvil.
Adjusting the saw set to the right pitch for your saw is easy. At least if you know what pitch your saw blade is, which you should anyway. Just squeeze the handles together and undo the set lock screw. Letting the handles loose, adjust the anvil so that the pitch number you want (embossed on the top edge) lines up with the plunger. Then tighten the handles together again and tighten the set lock screw.
You only need to bend the top half of the tooth to set them here. Start at one end of the saw, put the saw set over a tooth, line the tooth up with the anvil and give it a squeeze. Alternating teeth, move down the saw and repeat until the end of the blade. Now reverse the saw in the vise and repeat with the remaining teeth, such that they are set to the opposite side from the others.
Before we go on tot the final sharpening, make sure that the set is even by holding your saw horizontally in your hands at eye level against a light source. You’ll be able to clearly see any unevenness. Carefully adjust the out of set teeth with the saw set.
To complete the process of sharpening your saw you will now file the front edge of each tooth to the proper angle. The saw should be back in the vise between the strips of softwood, with the saw handle to your right hand side.
For rip saw blades, put the saw file on the front edge of the first tooth set towards you. Holding the file horizontal and at 90 degree angle to the blade, stroke two or three times, steady yet firmly. File each alternate tooth the same way, making your way down the blade. When you reach the end, reverse the saw in the vise and file the alternating teeth now set towards you.
For cross cut blades, proceed the same way, except hold the file at a 70 degree angle to the saw blade, with the handle of the file angles way from the handle of the saw. Make sure you respect the same rule when you reverse the saw blade for the alternating teeth. A final dressing with the oilstone will remove any filings.
A good hand saw should remain rust free for many years, but you can extend the life of the steel by wiping the blade down with an oily rag before using it, and before any long-term storage. Some saws come with protective tooth covers, and these can help during storage and moving about as well.
Photo by jacke747; Creative Commons Attribution