GlossaryKind of term: Standard and conventionEdge requirement (ISO 13715)
What is an edge requirement?
An edge requirement under ISO 13715 sets how far an edge of undefined shape may deviate, as a burr or as material removed, each up to a stated value.
An edge requirement covers edges whose shape the drawing does not define, such as the edge where two machined faces meet. ISO 13715 gives an edge symbol with a value in millimetres for it. On an external edge a plus allows a burr up to that value and a minus asks for material to be removed, as a chamfer or a round, up to that value. On an internal edge a plus allows material to remain in the corner and a minus asks for an undercut. Two values give a lower and an upper limit.
What does the standard say about an edge requirement?
ISO 13715 covers edges of undefined shape; the current edition is from 2019. A small value with ± means that both a small burr and a small removal are allowed, which in practice counts as a sharp edge. The requirement sits at an edge itself, or as a general requirement near the title block with edges that differ indicated separately. A note such as ‘break all sharp edges’ falls outside the standard and leaves the size open.
How does an edge requirement work in practice?
The edge requirement decides how and how much you deburr. If a burr up to a generous limit may stay, the job can be finished when the machine stops. If every external edge has to be broken to a minus value, that can be done in the program with a chamfer mill or deburring tool, or afterwards by vibratory finishing, brushing or handwork. Edges in cross holes or on the back are often out of reach of the program and need handwork or another process. That time easily drops out of an estimate that counts only machine time; the number of edges and their access say more about that time than the part count.
What is an edge requirement often confused with?
An edge requirement is not a chamfer: a chamfer is a drawn dimension, such as 0.5 × 45°, while an edge requirement leaves the shape open within limits. Nor is it a roughness requirement: that concerns the surface, the edge requirement the edge between two surfaces. Deburring is something else again: it is the operation, the edge requirement the limit the result has to meet.
Frequently asked questions
What does a minus value on an edge symbol mean?
On an external edge, material has to come off up to that value: the edge is broken with a small chamfer or round. A plus value allows a burr up to that value instead. Two values give the lower and upper limit.
Is ‘break all sharp edges’ the same as an edge requirement?
It asks for the same thing, but without a size. Ask how much is meant, or record your assumption in the quote so the customer can see which edge they will get.
Does an edge requirement apply to internal corners too?
Yes, ISO 13715 also covers internal edges. A plus value limits the material that may remain in the corner, such as a cutter's radius; a minus value asks for an undercut. Whether a general requirement also covers internal edges follows from how it is indicated.