kapy academy

Herringbone gear with a D-bore

A gear drawn with two clicks, extruded with a twist, bored with a D for a shaft, chamfered on every tooth by one revolved triangle, and mirrored into a herringbone. Seven steps: the External gear tool, a twist, a through-all cut, a subtracting revolve and a 3D mirror.

7 steps

What it builds

  • Sketch
  • Extrude
  • Cut
  • Revolve
  • Mirror (3D)

  1. Step 1

    Sketch the gear

    Click Create sketch and pick the XY plane — the blue square lying flat on the grid. Then pick External gear (the gear dropdown of the sketch toolbar). Click the origin: that is the centre. Then click a second point about 20 mm out: that second click sets the gear's size (its pitch radius, where it will touch another gear). You do not type a tooth count: the tool works it out from that radius and the short module line it draws along it — the tooth size.

  2. Step 2

    Extrude it 5 mm with a 10° twist

    Click Finish Sketch, select the gear and Extrude it with Distance 5 and Twist 10, then confirm with OK. The profile rotates ten degrees as it rises, so every tooth becomes a helix — a helical gear runs quieter than a straight one because each tooth engages gradually.

  3. Step 3

    Sketch a D-shaped bore on the top face

    Click the top face and pick New sketch on face. Draw a Circle centred on the origin, radius 3 mm, then a horizontal Line across it 2 mm from the centre (above or below, it does not matter), from rim to rim — its two ends snap onto the circle. The line splits the circle into a big D and a small segment: the flat is what stops a shaft from spinning in the bore.

  4. Step 4

    Cut the D through everything

    Click Finish Sketch, select the big part of the circle (above the flat) and pick Cut. Set Up to to Through all so the bore comes out of the bottom however thick the gear becomes later. Confirm with OK.

  5. Step 5

    Sketch the chamfer profile on the XZ plane

    Click Create sketch and this time pick the XZ plane — the green square standing on edge through the centre; it sees the gear side-on. Draw a right triangle just outside the tooth tips, about 5 mm a side, its top edge about 2 mm above the gear's top face and its outer corner about 23 mm from the centre. Use Line in one chain of three: a horizontal top edge, a vertical edge down the outside, and the 45° hypotenuse back to the start. Only the hypotenuse decides what gets cut, so letting the triangle stand proud of the gear costs nothing — and it gives you a band to click on in the next step.

  6. Step 6

    Revolve it into a chamfer on every tooth

    Click Finish Sketch, then click the part of the triangle that sticks up above the gear's top face. Pick Revolve. For Axis, click the vertical blue line through the centre of the gear (the world Z axis); the Angle stays at 360°, and Combine must be Subtract. Confirm with OK. The triangle sweeps a cone that shaves the tip of every tooth at once — a chamfer on forty teeth with a single operation.

  7. Step 7

    Mirror it into a herringbone

    Double-click the gear to select the whole body and pick Mirror (3D). For the Plane choose the world XY plane — the small blue square at the origin. It sits under the gear, so orbit to look from below if you cannot reach it, or simply click the gear's bottom face, which is the same plane. Turn on One body and confirm with OK. The copy hangs under the original with its twist reversed, and the two meet in a V at the seam: a herringbone. The opposed helices cancel each other's sideways thrust, so this gear needs no thrust bearing.

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