How to draw and dimension rectangular splines
As a commonly used coupling component in mechanical transmission, rectangular splines must be drawn and dimensioned in strict accordance with national standards to ensure component interchangeability and assembly accuracy. In mechanical drawing, the drawing of rectangular splines must clearly convey the structural characteristics, distribution of the teeth, and their assembly relationship with other parts. Dimensioning must accurately reflect the spline’s key parameters to provide a basis for processing and inspection. Mastering the correct drawing and dimensioning methods for rectangular splines is a crucial step in the mechanical design and manufacturing process.
The drawing of rectangular splines requires standardized drawing methods based on the view selection and representation method. In the main view, a full or half-section view is typically used to illustrate the spline’s internal structure. The teeth are drawn according to their actual outlines, and the addendum, root, and index lines are clearly distinguished: the addendum is represented by a thick solid line, the root by a thin solid line, and the index line by a thin dotted line. For spline shafts, when the axis is horizontal, the visible portion of the teeth should be drawn in full, while the invisible portion should be represented by a dashed line. For spline holes, the cross-section of the teeth should be filled with hatching in the cross-section view to distinguish the base from the teeth. In the end view, the distribution of the teeth should be depicted. A simplified drawing method is typically used, where only the outline of some teeth is drawn, and the remaining teeth are connected with thin dotted lines. The number of teeth should also be noted. For longer splines, a broken drawing method can be used, where the middle portion is omitted with a broken line to shorten the drawing, but the actual length dimensions should be noted. In addition, the detailed structure of the spline, such as chamfers and fillets, needs to be drawn in proportion. The chamfers are generally 0.5×45° or 1×45° to avoid interference during assembly.
The dimensioning of rectangular splines must include the basic parameters and positioning dimensions of the teeth to ensure that the geometric accuracy of the splines can be accurately controlled during processing. The basic parameters of the teeth include the major diameter (D), minor diameter (d), key width (b), and number of teeth (z). These parameters are the characteristic dimensions of the spline and must be marked directly on the drawing. The major diameter is the outer diameter of the teeth, the minor diameter is the inner diameter of the teeth, the key width is the distance between the two side faces of the teeth, and the number of teeth is the number of teeth evenly distributed. These parameters must be selected according to design requirements and national standards. For example, the parameters of a rectangular spline are 8×36×32×6, where 8 is the number of teeth, 36 is the major diameter, 32 is the minor diameter, and 6 is the key width. When marking, they must be noted in this order on the guide line. The positioning dimensions include the length of the spline (L), the fitting dimensions with other parts, etc. The length dimension must be marked on the main view, and the fitting dimensions must be marked with tolerance grades according to assembly requirements, such as H7/f6 for major diameter, H7/h6 for minor diameter, H9/f9 for key width, etc., to ensure the correct fit between the spline shaft and the spline hole.
Tolerancing for rectangular splines is a crucial component of dimensioning, directly impacting the spline’s fit accuracy and performance. National standards categorize rectangular spline centering methods into three types: minor diameter centering, major diameter centering, and key side centering. Minor diameter centering is the most widely used, so the minor diameter has the highest tolerance requirements, typically IT6-IT7. The major diameter and key width tolerances are determined based on the centering method and application requirements, generally ranging from IT7-IT9. When marking tolerances, the tolerance zone code should be indicated after the basic dimension, such as minor diameter d = 32H7, major diameter D = 36f7, and key width b = 6f9. Capital letters indicate the hole tolerance zone, while lowercase letters indicate the shaft tolerance zone. Positional tolerances for key teeth, such as symmetry and equal indexing, should be specified according to accuracy requirements. Symmetry tolerances are generally 0.01-0.03mm, and equal indexing tolerances are generally 0.02-0.05mm to ensure uniform force distribution on the teeth. In addition, the surface roughness of the spline also needs to be marked. The surface roughness Ra value of the minor diameter, major diameter and key side is generally 1.6-3.2μm, and the Ra value of the non-matching surface is 6.3-12.5μm.
Simplified drawing and annotation methods for rectangular splines improve drawing efficiency and are suitable for high-volume production and simplified drawing requirements. In simplified drawing, the main view can only show the index line and a portion of the tooth top line, with the remainder represented by fine dotted lines. In end views, only the complete outline of one tooth can be drawn, with the remainder represented by fine dotted lines, and the number of teeth indicated alongside. When simplifying annotation, a code notation method can be used, with the basic spline parameters and tolerance zone codes collectively marked on the guide line, such as “Spline 8×36f7×32H7×6f9 GB/T 1144-2001.” GB/T 1144-2001 is the national standard code for rectangular splines, indicating that the spline’s design and manufacturing comply with national standards. For recurring splines, detailed annotation can be used for the first occurrence, with subsequent occurrences requiring only the code to simplify the drawing. However, it is important to note that simplified drawing and annotation methods must not affect the spline’s processing and inspection requirements; critical dimensions and tolerances must be clear and unambiguous.
The drawing and dimensioning of rectangular splines must be based on actual production practices, taking into account the feasibility of the processing technology and inspection methods. When drawing the spline shaft, the CNC machining sequence of the key teeth must be carefully considered, such as turning the major and minor diameters first, followed by milling the key teeth. Therefore, the dimensioning on the drawing must align with this CNC machining sequence to facilitate understanding and operation. When dimensioning the key width, the measurement method must be considered. Vernier calipers or spline gauges are typically used, and the dimensional tolerances must match the accuracy of the measuring tool. For high-precision splines, geometric tolerances, such as cylindricity and parallelism, must also be noted to ensure transmission accuracy after assembly. Furthermore, technical requirements, such as heat treatment methods and surface treatment requirements (e.g., “quenched and tempered 220-250 HBW” and “surface galvanized”), must be clearly stated on the drawing to meet the required performance of the spline. Standardized drawing techniques and accurate dimensioning ensure that the design intent of the rectangular spline is effectively implemented, guaranteeing product quality and reliability.
