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Understanding Carbide Planer Knives
Question
Forum Responses
From contributor R: I would agree with contributor T - carbide would be my choice. I would tend to lean toward the solid carbide as well. From Dave Rankin, forum technical advisor: I agree also. The one thing to ask is what grade of carbide. The harder carbides can be more brittle and this causes edge breakage. The softer carbides may not last as long. When making that decision, be sure to advise the seller about the species that you run now and plan to run. From contributor A: Anybody care to elaborate on why the solid carbide knives tend to be of higher wear? We use plenty of C4 on sawblades. Why not on carbide tipped knives? I personally wouldn't want that hard as they would chip easily on that occasional stone or staple I plane through. The cost difference is substantial. I currently run a set of M3 and a set of Amana carbide tipped. From contributor T: Carbide is graded by hardness and toughness. Hardness translates to wear resistance and toughness translates to impact resistance. The C scale that most people know is a very generic measure of the carbide grades available today. Besides the hardness and toughness of these materials, you need to consider grain structure. Carbide is made up of small particles that are held together by a binder. The smaller the particles are and the tighter they are held together, the sharper the cutting edge can be. As a general rule, the higher the grade, the better the edge quality. As an example, C1 carbide is one of the toughest grades, but it is not very hard. This makes it stay sharp for less time, but is less likely to chip or break under rough use. Now C4 carbide is one of the hardest carbides used in the woodworking industry. It is very hard, making it last much longer, however it is very brittle, making it a poor choice for rough applications. Harder grade carbides do not work well in applications requiring large sections to be brazed into steel. This is due to the expansion and contraction that the steel goes through as it is heated up and cools. Harder carbides usually crack or chip while the product is cooling down. As a result most carbide tipped knives only use carbide grades of C1 or less. Solid carbide knives can be made in any grade of carbide available as they are not heated during manufacturing. The biggest thing to consider when choosing what type of knives to use is the application:
From contributor A: Thank for the explanation. I was aware of most of your info except for the inability to braze the harder carbides. Makes perfect sense. Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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