Tutorial Advanced ⏱ 20 minutes

Piston Crown Profile

Create a 2D piston crown profile for CNC 3-axis milling — demonstrating tangent arc construction between circular and linear geometry.

What You Will Build

A 2D piston crown profile for CNC 3-axis milling: 80mm diameter piston top face with a domed crown, two ring groove profiles, and a wrist pin bore. All geometry is 2D — suitable for milling operations on the piston crown face.

Operators Used

Circle/Centre,R Arc/Fillet,L,L Line/Parlel,XAxis,D Point/Intof,L,C Trim/L,to,C

Define the Piston Crown Geometry

Plan the 2D milling geometry for the piston crown face. This is a top-down view of the piston — all operations are 2D 3-axis milling.

Piston crown dimensions (top-down 2D view):
  Piston diameter: 80mm  → radius 40mm
  Crown dome: shallow dome across the top face
  Ring groove 1: 4mm wide, 3mm deep at radius 37mm
  Ring groove 2: 4mm wide, 3mm deep at radius 37mm
  Wrist pin bore: 20mm diameter at centre

All geometry is 2D — XyzPilot creates the
milling profiles for each operation.

XyzPilot is a 2D CAD/CAM system for CNC 3-axis milling. This tutorial creates 2D profiles for milling operations on the piston crown face.

Create the Outer Piston Diameter

Create the outer circle defining the piston diameter — this is the boundary for the crown face milling operation.

P_centre = (0, 0)  [piston centre]

Circle/Centre, P_centre, R=40, 0
→ C0: piston outer diameter, radius=40mm
   Diameter = 80mm

This circle defines the outer boundary of
all crown face milling operations.

Create the Wrist Pin Bore

Create the wrist pin bore — a through-hole milled through the piston crown face.

Circle/Centre, P_centre, R=10, 0
→ C1: wrist pin bore, radius=10mm
   Diameter = 20mm

This is a circular pocket/bore operation
centred on the piston axis.

Create the Ring Groove Profiles

Create the two ring groove circles. Ring grooves are circular channels milled into the piston skirt — in top-down view they appear as concentric circles.

Ring groove 1 (top compression ring):
  Groove centre radius: 37mm
  Groove width: 4mm → inner r=35mm, outer r=39mm

Circle/Centre, P_centre, R=35, 0  → C2: inner wall of groove 1
Circle/Centre, P_centre, R=39, 0  → C3: outer wall of groove 1

Ring groove 2 (second compression ring):
Circle/Centre, P_centre, R=35, 0  → C4: inner wall of groove 2
Circle/Centre, P_centre, R=39, 0  → C5: outer wall of groove 2

Note: In 2D top-down view, ring grooves appear
as concentric circular channels.

Ring grooves are machined as circular channels. The CAM toolpath follows the groove centreline circle at the correct depth for each groove.

Create the Crown Dome Profile

Create the dome profile across the crown face. In 2D top-down view, the dome is represented by a large-radius arc that defines the crown surface contour.

Crown dome: shallow dome, radius 200mm
  The dome arc passes through the piston edge
  and rises slightly at the centre.

For a 2D milling profile, the dome is represented
as a series of concentric depth contours:

Line/Parlel, XAxis, D=0   → L0: centreline
Line/Parlel, XAxis, D=10  → L1: 10mm from centre
Line/Parlel, XAxis, D=20  → L2: 20mm from centre
Line/Parlel, XAxis, D=30  → L3: 30mm from centre

Each line intersects C0 to define the
depth contour boundary at that radius.

The dome is machined using a ball-nose end mill following depth contours. Each contour is a circle at a specific depth — XyzPilot defines the 2D boundary circles.

Find Contour Intersection Points

Find where the depth contour lines intersect the outer diameter to define the milling boundaries.

Point/XLarge, Intof, L1, C0  → P0 = (38.730, 10)
Point/XSmall, Intof, L1, C0  → P1 = (-38.730, 10)

Point/XLarge, Intof, L2, C0  → P2 = (34.641, 20)
Point/XSmall, Intof, L2, C0  → P3 = (-34.641, 20)

Point/XLarge, Intof, L3, C0  → P4 = (26.458, 30)
Point/XSmall, Intof, L3, C0  → P5 = (-26.458, 30)

These points define where each depth contour
reaches the piston edge.

Verify and Set Up CAM Operations

Verify all geometry and set up the CAM operations for each milling feature.

Final geometry summary:
  C0: outer diameter boundary (R=40mm)
  C1: wrist pin bore (R=10mm)
  C2/C3: ring groove 1 inner/outer walls
  C4/C5: ring groove 2 inner/outer walls
  L0-L3: dome depth contour lines
  P0-P5: contour boundary points

CAM operations (all 2D 3-axis milling):
  Op 1: Crown face milling (C0 boundary)
  Op 2: Wrist pin bore (C1, circular pocket)
  Op 3: Ring groove 1 (C2/C3, circular channel)
  Op 4: Ring groove 2 (C4/C5, circular channel)
  Op 5: Dome contouring (depth contours L0-L3)

All operations: 2D profiles, 3-axis milling.

XyzPilot creates the 2D profiles for each milling operation. The CAM module assigns depths and generates the G-code toolpaths.

Tips & Best Practices

XyzPilot is a 2D CAD/CAM system — all geometry is 2D for 3-axis milling operations.
Ring grooves are circular channels — define inner and outer diameter circles for each groove.
The dome contour is machined using depth contours — each contour is a 2D circle at a specific Z depth.
Verify all circle diameters with Measure → Radius/Diameter before CAM setup.
Use the Toolpath Simulator to verify all milling operations before machining.

Operators Used in This Tutorial

Circle/Centre,R

Piston Crown Profile

Define the Piston Crown Geometry

Create the Outer Piston Diameter

Create the Wrist Pin Bore

Create the Ring Groove Profiles

Create the Crown Dome Profile

Find Contour Intersection Points

Verify and Set Up CAM Operations

Tips & Best Practices

Operators Used in This Tutorial

Circle by Centre and Radius

Horizontal Line

Line Circle Intersection

Trim Line to Circle

Related Tutorials

Flange Profile

Bearing Pocket

Pocket Machining Geometry