Popular Woodworking 2006-10 № 157, страница 18
Arts & Mysteries The Mystery of Saw Teeth Pitch, rake, fleam and set all contribute to the performance of your tool. A recent review of dovetail saws in a competing magazine discussed the attributes of different saws as if their characteristics were mystically endowed by their manufacturers. I'm certain the top-rated sawmakers would approve of such a review. In reality, the performance of any saw is based primarily on the shape of its teeth. The following four attributes, pitch, rake, fleam and set, can tell you a great deal about how a saw will perform. By learning how a saw's teeth make the cut, you'll be able to choose a saw that will perform well for your work. If you sharpen your saws, you'll need to know this information so you can make changes (or avoid making changes) to the performance of your saws. Pitch: Count Your Teeth Pitch is used to describe the size of individual teeth. It is expressed in one of two ways: teeth per inch (tpi) or points per inch (ppi). The pitch of a saw's teeth is chosen in accordance with the thickness and hardness of the stock it's being used to cut. If too fine a pitch is cho- As a community, we simply cannot abdicate the selection of saw teeth to manufacturers who do not and cannot work wood enough to be experts themselves. These 10 ppi teeth stopped cutting long before exiting the tenon's 5"-long kerf. This is the reason finer-pitched saws are not universally better. sen, the teeth will clog and stop cutting before they leave the kerf. This slows the cut. If too coarse a pitch is chosen, you run the risk of splitting the stock. Over the years, workmen have come up with rules of thumb governing how many teeth your saw should have for a given thickness of stock. I think six teeth in the kerf is a good place to start for long handsaws. So if you are sawing 3/4" stock, with your saw held at a 45° angle, then the length of your kerf through the work is actually 1V4" long. So to keep six teeth in your 1V4"-long kerf at all times, you need a saw that has 5 ppi. Now if you are sawing dovetails or other joints where the first nick the saw makes must by Adam Cherubini Having no power tools, Adam relies on hand saws for the construction of his furniture. You can contact Adam atadam.cherubini@verizon.net. be right on and where you must finish accurately to a line, I think you need to keep 10 teeth or so in your kerf. If you saw dovetails with your saw held perpendicular to the board's face you will need a 14 ppi saw in 3/4" stock to keep 10 teeth in the work at all times. What's the pitch of this saw again? It depends on how you measure it. Either way this is one coarse saw. I wish every one of you owned this 1890 Disston No. 7 handsaw. 28 Popular Woodworking October 2006 |
