Cut side: why parts come out the wrong size#

A bit has width. When it follows your line, it has to run beside the line, or on it. Which one decides the size of what you get.

      Outside                Inside               Centerline

    ○ ○ ○ ○ ○ ○
    ○┌────────┐○         ┌────────┐            ┌○──○──○──○┐
    ○│  part  │○         │○ ○ ○ ○ │            ○  part    ○
    ○│        │○         │○ hole ○│            │          │
    ○└────────┘○         │○ ○ ○ ○ │            └○──○──○──○┘
    ○ ○ ○ ○ ○ ○          └────────┘
  tool outside the line  tool inside the line  tool on the line
  → part = drawn size    → hole = drawn size   → half a bit each side

Cut side	Line becomes	Use for
Outside	The part's edge	Cutting out parts
Inside	The hole's edge	Holes and windows
Centerline	The middle of a groove	Grooves, scoring, open lines

The classic mistake#

Cut a part on centerline instead of outside and it comes out one tool radius smaller all round. A 6 mm bit takes 3 mm off each side, and the canvas shows nothing wrong.

Tuning a fit#

Stock allowance moves the cut away from the line:

Positive leaves material (for a finishing pass).
Negative cuts past the line (for a looser fit).

Sloped bits#

A V-bit or taper is narrower at the bottom. The app measures the offset at the top of the cut, so the wall touches your line at the surface and slopes in below it.

How-to: Cut out a part