Tutorial Intermediate ⏱ 12 minutes

Bearing Pocket

Create a circular bearing pocket with a keyway — the standard geometry for shaft bearing housings in CNC milling.

What You Will Build

A 52mm diameter bearing pocket (for a 6205 bearing) with a 6mm wide keyway. Complete geometry for CNC boring and milling operations.

Operators Used

Circle/Centre,R Line/Parlel,XAxis,D Line/Parlel,YAxis,D Trim/L,to,C

Define the Bearing Pocket Geometry

Plan the bearing pocket dimensions. This example uses a 6205 deep groove ball bearing.

6205 Bearing dimensions:
  Outer diameter (OD): 52mm  → pocket radius 26mm
  Inner diameter (ID): 25mm  → shaft radius 12.5mm
  Width: 15mm

Keyway dimensions (for 8mm shaft key):
  Width: 8mm
  Depth: 4mm (into the bore)
  Position: top of bore

Create the Bearing Pocket Circle

Create the main bearing pocket circle.

P_centre = (0, 0)  [bearing centre]

Circle/Centre, P_centre, R=26, 0
→ C0: bearing pocket, diameter=52mm

This is the bore that the bearing outer race will press into.

Create the Keyway Lines

Create the two parallel lines that define the keyway width.

Keyway width = 8mm → half-width = 4mm
Keyway depth = 4mm → extends from R=26 to R=30

Line/Parlel, YAxis, D=-4  → L0: left keyway wall at X=-4
Line/Parlel, YAxis, D=+4  → L1: right keyway wall at X=+4
Line/Parlel, XAxis, D=30  → L2: keyway top at Y=30
   [26mm bore radius + 4mm keyway depth]

Trim the Keyway Lines to the Bore

Trim the keyway side walls to meet the bore circle.

Trim/L0, to, C0, End, YLarge
→ L0 trimmed: from (-4,-26) to (-4,26)
   [left wall meets bore at top and bottom]

Trim/L1, to, C0, End, YLarge
→ L1 trimmed: from (4,-26) to (4,26)
   [right wall meets bore at top and bottom]

Actually we only need the upper portion:
Trim/L0, to, C0, Start, YSmall  → L0 from (-4,26) upward
Trim/L1, to, C0, Start, YSmall  → L1 from (4,26) upward

Trim the Keyway Top and Bore

Trim the keyway top line and trim the bore circle to create the keyway opening.

Trim/L2, to, L0, Start  → L2 from (-4,30) to (4,30)
Trim/L2, to, L1, End    → L2 trimmed to keyway width

Trim/Circle, C0, Between, P_left_key, P_right_key, CCW
→ C0 trimmed: bore circle with keyway opening at top
   [the arc from right keyway point to left keyway point, going CCW through bottom]

Final profile:
  C0 (trimmed bore arc) + L0 (left wall) + L2 (keyway top) + L1 (right wall)

The keyway profile is now complete. The bearing pocket is the trimmed bore circle with the keyway opening.

Verify the Pocket Geometry

Verify all dimensions using Measure tools.

Measure → Radius/Diameter
Click C0 (bore arc)
→ Radius: 26.000mm  Diameter: 52.000mm ✓

Measure → Distance
Click L0, Click L1
→ Distance: 8.000mm (keyway width) ✓

Measure → Distance
Click C0 centre, Click L2
→ Distance: 30.000mm (bore radius + keyway depth) ✓

Tips & Best Practices

Bearing pocket tolerance is critical — verify the bore diameter matches the bearing OD tolerance.
Keyway dimensions must match the shaft key standard (DIN 6885 or equivalent).
The keyway depth is measured from the bore surface, not from the centre.
Use the Toolpath Simulator to verify the boring and keyway milling sequences.
For a blind pocket, set the Z-depth in CAM to the bearing width (15mm for 6205).