Edge conditions
An edge symbol marked −0.3 on an external edge means burr-free: any undercut stays within 0.3 mm of the ideal corner, and a sharp corner conforms too. Enter the value from the symbol, sign first, for what it allows on an external or internal edge: the burr or passing, the undercut, a range and a direction, drawn as the zones the edge has to stay inside.
Burr-free: an undercut up to 0.3 mm, or a sharp corner.
- Burr
- None
- Undercut
- Up to 0.3mm
- Sharp corner
- Allowed
- Direction
- Either way: the value inside the angle
- As one range
- −0.3 to 0mm
How it’s calculated
Read the values as one range, excess material positive and undercut negative: +a is 0 to +a, −a is −a to 0, ±a is −a to +a, and two values are the upper limit over the lower. The size is measured from the ideal corner, vertically and horizontally, unless the value sits above the symbol (vertical) or right of it (horizontal).
Recommended sizes mm
| Value | External edge | Internal edge |
|---|---|---|
| +2.5 | Burr to 2.5, no undercut | Passing to 2.5, no undercut |
| +1 | Burr to 1, no undercut | Passing to 1, no undercut |
| +0.5 | Burr to 0.5, no undercut | Passing to 0.5, no undercut |
| +0.3 | Burr to 0.3, no undercut | Passing to 0.3, no undercut |
| +0.1 | Burr to 0.1, no undercut | Passing to 0.1, no undercut |
| ±0.05 | Sharp: burr or undercut to 0.05 | Sharp: passing or undercut to 0.05 |
| ±0.02 | Sharp: burr or undercut to 0.02 | Sharp: passing or undercut to 0.02 |
| −0.1 | Undercut to 0.1, no burr | Undercut to 0.1, no passing |
| −0.3 | Undercut to 0.3, no burr | Undercut to 0.3, no passing |
| −0.5 | Undercut to 0.5, no burr | Undercut to 0.5, no passing |
| −1 | Undercut to 1, no burr | Undercut to 1, no passing |
| −2.5 | Undercut to 2.5, no burr | Undercut to 2.5, no passing |
What do +, − and ± mean on an edge symbol?
The sign says what kind of edge is wanted. + allows excess material beyond the ideal corner, a burr on an external edge or a passing on an internal one, and no undercut. − allows only material removed inside the ideal corner, a break, chamfer or relief, and no excess; with one size the undercut runs from 0 to it, so it limits the break rather than asking for one that size. ± allows either, and is only used with a size; a small one, 0.05 mm or less, is what a drawing calls a sharp edge. The symbol limits the size of the deviation, not its shape.