Wood cutting is a process in which a tool acts on wood, creating a relative movement to obtain wood products of a certain shape, size and surface condition. It is the main process with the largest share in the processing of wood, and its quality has a great influence on the process of gluing and decorating the surface.
The wood cutting mechanism includes the mechanical properties of wood, the material of the tool, the method and geometry of its processing, the relative movement between the tool and the wood being processed, the mechanism for achieving a certain movement and cutting. force, has found application in industrial practice and science, an independent discipline is formed on the basis of research.
Several basic wood cutting shapesThere are many forms of cutting wood, the most common ways are:
SawingMost widely used in woodworking. Saws include circular saws, band saws, frame saws, wire saws and chain saws (for cross section only), etc., which are multi-blade cutting tools.
Each tooth is a cutting edge that has a front (the front of the tooth), a back (the back of the tooth), and two sides. The line of intersection of the front and back is the main edge, and the line of intersection of the front and two sides is the two side edges. The space between two teeth is alveolar.
The cutting of the circular saw is done in a rotary motion, the working part of the band saw is in a linear motion, the cutting of the frame saw is in a linear reciprocating motion, and most of the feed motion is in a linear motion. There are two cutting directions: longitudinal section and cross section, and it can also be used for slotting and stud making.
planning
The milling machine and the workpiece make a relative linear motion to complete the cutting process at the same time. Planers or manual planers used in manufacturing are mainly used for planing or planing notches, line angles, etc., mechanical planers have planers driven by cranks, tracks or chains, and planers woodworking machines - for the manufacture of wood wool. etc.
The characteristic of planing is that one of the workpieces and the cutting tool must be fixed and combined with each other to complete the cutting motion and the feed motion. Most planers hold the workpiece in place while the cutting tool performs the cutting and feeding motions simultaneously. The planing method has low labor productivity, but the kinematic unevenness that occurs when using a rotating tool for plane processing can be avoided on the surface to be machined, so it is difficult to replace it with other cutting methods.
Milling
The cutting tool is a cutter that can be used for flattening, surfacing, surface die cutting, rotator shaping, etc., and for milling tenons, grooves, etc. chips, cut logs into square materials and use a raw board for processing. Milling heads are divided into three main types: cylindrical, conical and end, depending on the position of the blade relative to the axis of the milling head.
When milling is used to machine planes, it is circular milling. Since the surface obtained by machining is similar to planing, the cutter and milling machine used for circular milling to machine planes are commonly called planers and planers. During the cutting process, the cutter makes a high-speed rotary motion. With the exception of parts such as processing and shaping rotators, the feed is basically a linear motion. The path of the cutting process combined by these two is a cycloid.
At the same time, a corrugated kinematic unevenness is formed on the treated surface. Circumferential milling can be divided into climb milling and climb milling. If the milling tool rotates against the feed direction of the workpiece, it is upward milling, otherwise it is climb milling. Typically, pressure planers and four-sided planers use up-cutting, and wood shredders usually use up-cutting.
Common defects in wood chipping
Raised wood texture (chord cut surface)
Defect type: three types of defects
Features: on the cut surface, parts of early and late wood cannot form the same smooth surface and have concave-convex wood fibers. As a rule, part of late wood is convex.
Reasons: processing softwood with a significant difference in hardness between the early part of the wood and the late part of the wood, cutting wood with high humidity, cutting with worn blades.
Wooden burr (string cut surface)
Defect type: three types of defects
Properties: The grains on the surface of wood are sticking woody hairs or fluffy woody hairs.
Cause: One end of the fiber or fiber bundle on the cutting surface has been cut off and remains on the work surface.
Wavy knife marks (radial section)
Defect Type: Class 1 Defect
Features: The cutting surface is not a perfect plane, but a wavy surface.
Cause: Occurs when using a rotary cutter equipped with multiple cutting teeth to machine a plane and a swim path.
Raised wood grain (end face)
Defect type: three types of defects
Features: small depressions formed by exfoliated fibers on the cutting surface.
Causes: This defect often occurs when cutting softwoods with a significant difference in hardness between early and late wood.
Knife marks (radius section)
Defect Type: Class II Defect
Features: When cutting, the trajectory of the first and second cuts is different on the cut surface at the junction.
Cause: Occurs when cutting with a portable planer.
Prevention methods: reducing the depth of cut, blocking the moving path of the planer, etc. can reduce the occurrence of cutting defects in the form of tool marks.
Exfoliating wood fibers (string cut surface)
Defect type: three types of defects
Characteristics: On the cut part of the late wood is separated from the border between the early and late wood.
Causes: This defect often occurs when cutting softwood materials with worn tools or when applying excessive cutting force to the cutting surface.
Rolled corrugation and gnawing head (section diameter)
Defect Type: Class II Defect
Features: When the roller feed method is used for the planer, the indentations of the roller mold left by the roller along the length of the sheet are called gouges when they reach the end.
Causes: Roller dents are caused by improper roller adjustment, and the main cause of sticking is due to incorrect adjustment of the pressure mechanism or unreasonable design.
Chip offset (section radius)
Defect Type: Class II Defect
Features: The indentation left on the cutting surface is usually a white spot about 1 cm long.
Cause: An indentation left by chips adhering to the cutting edge on the cutting surface.
Reverse grain dent (chord section)
Defect type: three types of defects
Characteristics: There are dents caused by shedding of blocks or peeling of small fibers on the back side of the fibers of the cutting surface.
Causes: When the grain direction of the material being cut is inclined at a slight angle to the cutting direction or when sawing wood with inclined grain, especially when cutting wood with knots, this defect easily occurs.
How to avoid: When cutting knots, it is better to have a certain blade angle and choose appropriate cutting conditions.
ResumeWhen milling, defects of the second and third types can be avoided, but the occurrence of defects of the first type is inevitable. To obtain a good finished surface, it can be processed by grinding or planing.
However, during flat chip planing for processing, defects of the second and third types also occur due to poor adjustment of machines and tools and improper selection of cutting parameters. Therefore nit is necessary to properly set up the cutting machine and tool, and select and set the appropriate cutting parameters.