Edge Splintering
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When metal is machined with an end-mill, a burr often forms along the top edges of the cut. A similar phenomena occurs in woodworking. In wood, this "burring" manifests itself as splintering of the top edge following the grain away from the cut. The degree of splintering depends on the type of wood, the speed of the cutting edge, the chip-load (feed rate), and the sharpness and shape of the cutting tool. If the tool and/or cutting parameters are poorly matched to the wood being cut, splintering can be so severe that small features can be totally obscured and the piece ruined. The speed of the cutting edge and the chip load can be tuned with great precision in CNC based woodcutters. The sharpness and geometry of the cutting edge are another matter altogether. While you can always start with an new, sharp tool, the shape and attack angle of the cutter will determine how long the tools stays sharp and how well it cuts as it inevitably wears down. Historically, one way to tell when a tool was getting dull was to observe the degree of splintering and change the bit when the splintering became too severe. It is probably not possible to fabricate an end-mill that never splinters any kind of wood. However, proper design and testing coupled with fine tuning rotational speeds and feed rates can make it possible to fabricate tools that will reduce splintering to such a degree that the splinters can be removed with a soft tooth brush as with this test cut in black walnut ( 0.0625" dia., 0.125" depth, 50 in./min. feed @ 40,000 RPM). |
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