Tutorial Intermediate ⏱ 15 minutes

Gear Blank

Create a gear blank with outer diameter, central bore, keyway, and bolt holes — the starting geometry for gear manufacturing.

What You Will Build

A 100mm OD gear blank with 30mm bore, 8mm keyway, and 4 bolt holes on 70mm PCD. Ready for gear tooth cutting operations.

Operators Used

Circle/Centre,R Points/On,C,N Line/Parlel,YAxis,D

Define the Gear Blank Geometry

Plan all dimensions before starting.

Gear blank dimensions:
  Outer diameter (OD): 100mm  → radius 50mm
  Central bore:        30mm   → radius 15mm
  Keyway width:        8mm    → half-width 4mm
  Keyway depth:        4mm    → extends to radius 19mm
  Bolt hole PCD:       70mm   → radius 35mm
  Bolt holes:          4 × M6 clearance (6.6mm dia)

Create the Outer Diameter and Bore

Create the two main concentric circles.

P_centre = (0, 0)

Circle/Centre, P_centre, R=50, 0  → C0: OD (100mm)
Circle/Centre, P_centre, R=15, 0  → C1: bore (30mm)

Both circles concentric at origin.

Create the Keyway in the Bore

Create the keyway geometry in the central bore.

Keyway: 8mm wide, 4mm deep
  Left wall:  X = -4
  Right wall: X = +4
  Top:        Y = 15 + 4 = 19mm from centre

Line/Parlel, YAxis, D=-4  → L0: left keyway wall
Line/Parlel, YAxis, D=+4  → L1: right keyway wall
Line/Parlel, XAxis, D=19  → L2: keyway top

Trim L0 and L1 to bore circle C1 (upper portion only)
Trim L2 between L0 and L1
Trim C1 to create keyway opening at top

Create the Bolt Hole Pattern

Place 4 equally spaced bolt holes on the 70mm PCD.

Circle/Centre, P_centre, R=35, 0  → C2: pitch circle (PCD=70mm)

Points/On, C2, N=4, Angle=45, 0
→ P0 = (24.749, 24.749)   [at 45°]
→ P1 = (-24.749, 24.749)  [at 135°]
→ P2 = (-24.749, -24.749) [at 225°]
→ P3 = (24.749, -24.749)  [at 315°]

Starting at 45° places holes between the keyway and the cardinal positions.

Starting at 45° avoids placing a bolt hole directly above the keyway, which would weaken the blank.

Create the Four Bolt Holes

Create M6 clearance holes at each bolt hole centre.

Circle/Centre, P0, R=3.3, 0  → C3
Circle/Centre, P1, R=3.3, 0  → C4
Circle/Centre, P2, R=3.3, 0  → C5
Circle/Centre, P3, R=3.3, 0  → C6

All holes: 6.6mm diameter (M6 clearance)

Clean Up and Verify

Delete construction geometry and verify all dimensions.

Edit → Clear All Points
→ P0-P3 deleted, all circles unchanged

Verification:
  OD = 100mm ✓  (C0 radius = 50mm)
  Bore = 30mm ✓  (C1 radius = 15mm)
  Keyway = 8mm wide, 4mm deep ✓
  PCD = 70mm ✓  (C2 radius = 35mm)
  Bolt holes: 4 × 6.6mm ✓
  Hole spacing = 2×35×sin(45°) = 49.497mm ✓

Tips & Best Practices

Place bolt holes at 45° offset from the keyway to avoid weakening the blank.
Keyway dimensions must match the shaft key standard for the bore diameter.
The gear blank OD is the pitch diameter plus addendum — verify with gear design calculations.
For a hub gear blank, add a larger diameter hub circle between the bore and OD.
Verify all dimensions with Measure tools before sending to the machine.