With all that said, there are still differences in hardness for various woods, and there is a standard scale, called the “Janka” scale that is used to rate the relative hardness of various woods. HSS just doesn’t stand up to that kind of grit very well. This is why so much cnc router work prefers Carbide tooling even though wood is relatively soft. In the case of materials like MDF and Plywood, their manufacture can result in abrasive grit being embedded in the layers and that grit matters more than the wood in feeds and speeds. Hardwood seeds have a covering–shell or fruit, while Softwood does not.Īnother factor influencing all this has to do with the manufacturing process for the material. Balsa seems soft but is technically a Hardwood. “Hard” Wood versus “Soft” Wood has more to do with the seeds of the Wood than the actual hardness. Soft Plastics allow a nice clean chip to be sliced off, almost like you slice cheese with a knife. It refers to the chipping characteristics of the plastic. Plastics, similarly, can behave differently–hard plastics as a name is a bit of a misnomer (though it is the industry standard in tooling catalogs). They have to do for example with the behavior of the sap relative to the sawdust and how the chips are made. It turns out that the characteristics that affect the feeds and speeds for cnc wood cutting are different than hardness. Mild steel is 120, hardened steel is 900, and tungsten carbide is 4000! Red Oak, for example, has a Brinell Hardness of about 3.7. Even Carbide is not all that much harder than hardened steel whereas it is phenomenally harder than even the hardest woods. What determines the “Size” of a Sweet Spot?Ī lot of this is all up to that relative difference in hardness between material and cutter. “Size” of Sweet Spot refers to how wide a range of numbers are safe. Imagine there are actual numbers on our Sweet Spot diagram. For harder steels and difficult materials like Titanium, the sweet spot gets very small indeed. In general, the sweet spots for woods are much larger than for metals. You can learn all this and much more from our free Feeds and Speeds Tutorial, but for now, let’s stay with this idea of a Sweet Spot. But, over heating and chip loading are the two main tool life enemies that are directly feeds and speeds related. – Excessive Tool Deflection or Runout can lead to wear that will eventually break the tool.Ī lot else can shorten a tools life–chipped edges in some materials, materials like stainless steel can “work harden” and suddenly become much harder during the cutting process, and some materials like aluminum try to weld themselves to the cutting edge if lubricant or appropriate tool coatings are not used. This destroys a tool suddenly and is more commonly what beginners see. – Tools can break because the flutes get too full, the chips have no place to go, and the tool jams and snaps off. This destroys a tool gradually, though gradual can mean a matter of minutes if the tool is hot enough. Running too slowly relative to feeds also generates a lot of heat due to Rubbing. Tools have a certain maximum speed, called the “ Surface Speed” that governs how fast they can run against a given material. – They get too hot, which softens the tool and results in a dull edge. Tools usually fail for a couple of main reasons: It’s important to note you can get into just as much trouble running too slowly (due to rubbing) as running too quickly. You can optimize MRR (Material Removal Rate), Surface Finish, and to an extent a blend of all three. The green areas reflect ideal Sweet Spot matches for a material and cutting conditions. A typical Sweet Spot looks like this schematically: The Sweet Spot determines how the relationship between speed (spindle speed rpm) and feedrate need to come together for good cutting results. This is due to the size of the “sweet spot” that relates feeds and speeds to good results in a material, together with the relative hardness of the woods (or other materials) versus the cutters (HSS or Carbide). Use them if you need to fine tune for maximum performance.īut, for basic roughing work, also be aware that you can do a lot with just the main sub-categories. The short answer answer is that there are hundreds of sub-categories corresponding to individual wood species accessible via the “More” button. People wonder why we don’t have a lot more categories. To access the full variety of woods under each family, use the “More…” button on G-Wizard. You can see them in our G-Wizard Feeds and Speeds Calculator Wood’s Material menu: When calculating feeds and speeds for wood, we generally look at 4 different families. The most common CNC machine for cutting wood is a CNC Router. Here’s your comprehensive guide to CNC Wood Cutting and Feeds and Speeds Calculator Wood, together with Tips and Techniques that are specific to cutting wood on a CNC Machine.
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