Helical Thread (conical teeth)(trapezoidal teeth)

thingiverse

Parametric thread designing module: Simple parameters: 1. Major Dia 2. Pitch (linear distance/turn) 3. Tooth Angle 4. Bolt height 5. Nut Height 6. Nut Radial thickness 7. Tolerance between screw and nut Chamfer, Hex head for bolt are optional for the user ((Please also download "hexnut.scad" for chamfered hexnut in "helical_thread.scad")) Core calculations: t = radius of circle (primary primitive shape) t/n = eccentricity of twist (radius of twist) (primary is translated by this number from the origin on any one axes perpendicular to the axis of linear_extrude) v1-v5: (simplified) n = (2 x major_dia x pitch x tan( tooth_angle/2 )) - 1 t = major_dia/2 x n/(n+1) v6: (generalised) n = (major_dia x (1 - cos( 180*pitch )) x tan( tooth_angle/2 )) - 1 t = major_dia/2 x n/( n+1 ) Generalised formula allows for a smoother tooth profile and accurate tooth angle v7: For pitch < 1mm/turn n = (2 * major_dia * pitch * tan(tooth_angle/2)) - 1 [simplified] For pitch >= 1mm/turn n = (major_dia * (1 - cos(180*pitch)) * tan(tooth_angle/2)) - 1 [generalised] t = major_dia/2 x n/(n+1) (for both pitch<1mm/turn and pitch>1mm/turn) Generalised formula is more accurate than simplified, but not valid for pitch values < 1mm/turn, whereas simplified formula is less accurate but valid for pitch values < 1mm/turn. Hence both used conditionally. Working values: (print layer height = 0.1mm) (nozzle = 0.4mm) (print speed = 50%) Pitch = 1 Tooth Angle = 90deg Tolerance = 0.4mm Pitch = 1 Tooth Angle = 70deg Tolerance = 0.5mm Pitch = 1.5 Tooth Angle = 70deg Tolerance = 0.6mm Note: 1. "hexnut.scad" only produces the nut, not the thread. (helical_thread.scad uses it to cut thread using boolean subtraction) 2. Keeping Tooth Angle fixed, with increasing Pitch values the required Tolerance reduces 3. Keeping Pitch fixed, with decreasing Tooth Angle the required Tolerance increases 4. Booleans have been used in chamfering of thread and hexnut, so $fn = 100 may slow preview and rendering 5. Latest version of code is v11 Update: added trapezoidal teeth threads for better prints (no drooping on the edges)