Tutorial Beginner ⏱ 8 minutes

Rounded Slot

Create a 60×20mm rounded slot — two parallel lines connected by semicircular arcs at each end. Common in fixtures, brackets, and adjustment slots.

What You Will Build

A 60mm long, 20mm wide rounded slot with 10mm radius semicircular ends. The slot is centred at the origin.

Operators Used

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

Define the Slot Geometry

Plan the slot dimensions. For a 60×20mm slot centred at origin: the straight sections run from X=-20 to X=+20, and the semicircular ends are centred at X=±20.

Slot dimensions:
  Total length: 60mm
  Width: 20mm
  Corner radius: 10mm (= width/2)
  Straight section length: 60 - 2×10 = 40mm

Key points:
  Left arc centre:  (-20, 0)
  Right arc centre: (+20, 0)
  Top line at Y=+10
  Bottom line at Y=-10

Create the Two Parallel Lines

Create the top and bottom straight sections of the slot.

Line/Parlel, XAxis, D=+10  → L0: top line at Y=+10
Line/Parlel, XAxis, D=-10  → L1: bottom line at Y=-10

Both lines extend infinitely — they will be trimmed in step 4.

Create the Two Semicircular Ends

Create full circles at each end. They will be trimmed to semicircles in the next step.

P_left  = (-20, 0)  [left arc centre]
P_right = (+20, 0)  [right arc centre]

Circle/Centre, P_left,  R=10, 0  → C0: left end circle
Circle/Centre, P_right, R=10, 0  → C1: right end circle

Trim the Lines to the Circles

Trim the top and bottom lines to meet the circles at the tangent points.

Trim/L0, to, C0, Start, XSmall  → L0 start at (-20,10)
Trim/L0, to, C1, End,   XLarge  → L0 end at (20,10)

Trim/L1, to, C0, Start, XSmall  → L1 start at (-20,-10)
Trim/L1, to, C1, End,   XLarge  → L1 end at (20,-10)

L0 now runs from (-20,10) to (20,10)
L1 now runs from (-20,-10) to (20,-10)

Trim the Circles to Semicircles

Trim each circle to keep only the semicircular end portion.

Trim/Circle, C0, To, C0_top_pt, CW
→ A0: left semicircle from (-20,-10) to (-20,10)
   Sweeps left (CCW from 270° to 90°)

Trim/Circle, C1, To, C1_top_pt, CCW
→ A1: right semicircle from (20,10) to (20,-10)
   Sweeps right (CCW from 90° to 270°)

Alternatively use:
Arc/Centre, P_left,  R=10, Start=270, End=90,  CCW → A0
Arc/Centre, P_right, R=10, Start=90,  End=270, CCW → A1

The slot is now a closed profile: L0 (top) → A1 (right) → L1 (bottom) → A0 (left) → back to L0.

Verify the Closed Profile

Confirm the slot profile is closed and dimensions are correct.

Final geometry:
  L0: (-20,10)→(20,10)   [top, 40mm]
  A1: right semicircle, r=10, centre=(20,0)
  L1: (20,-10)→(-20,-10) [bottom, 40mm]
  A0: left semicircle, r=10, centre=(-20,0)

Total length: 40 + π×10 + 40 + π×10 ≈ 62.83mm perimeter
Slot width: 20mm ✓  Slot length: 60mm ✓

Tips & Best Practices

The corner radius of a rounded slot must equal exactly half the slot width for a true semicircle.
Centre the slot at the origin for easiest construction, then use UCS to position it.
For an off-centre slot, create the arc centres at the actual positions.
Verify tangency: the lines must be exactly tangent to the circles at the trim points.
This profile is ideal for adjustment slots — the semicircular ends allow bolt movement.