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	DIN 509
Area	Design of rotationally symmetrical components
title	Technical drawings - undercuts - shapes, dimensions
Brief description:	Standardization of the inside and outside undercuts for turned parts and bores
Latest edition	2006-12
ISO	-

Undercut on a rotationally symmetrical inner edge (light edges shown incorrectly)

According to DIN 509, an undercut is a removal on a rotationally symmetrical inner edge with a specific shape and specified dimensions, which gives the tool used the necessary space during production. Depending on the shape, an undercut can also be used to give the adjacent part the necessary space during assembly. This is only necessary if a sufficiently large radius or a sufficiently large chamfer cannot be made on the counterpart (Form E is not suitable for this, as the counterpart still requires a radius or a chamfer).

A distinction is made between undercuts for shafts (external undercut) and hubs (internal undercut).

Thread undercuts and runouts are specified in the DIN 76 standard.

function

1. The undercut is used to create free spaces, which are used as run-out zones in the production of tools such as turning tools and, above all, grinding wheels .
2. The radius used also reduces stress peaks, which are caused by steps in the turning contour and their notch effect .
3. As a functional element, certain forms of undercuts are required for assemblies / sub-assemblies in order to ensure that counterparts can be fitted flush when these counterparts cannot be made of sufficiently large chamfers or curves.

Standard designation

Undercuts are standardized in DIN 509. Undercuts are not shown in the front view of shafts. Unless otherwise stated, undercuts have a roughness of 3.2  µm .

Example:

• DIN 509 - F 0.6 × 0.3
  • DIN 509 - standard for undercuts
  • F - Code letter for the form of the undercut
  • 0.6 - radius of the groove
  • 0.3 - depth of the puncture

Undercut forms and their application

The two most common forms of undercut are E and F, but G and H are also used alternatively. The forms A, B, C and D are no longer used.

• E - radial recess if only the outer surface is required for further processing, e.g. B. for external or internal cylindrical grinding
• F - combined axial and radial recess for cases in which shell and flat surfaces are to be ground, e.g. B. in bearing shoulders for rolling bearings
• G - combined axial and radial recess, which is smaller than shape F and thus causes a higher notch effect , but is more space-saving
• H - combined axial and radial recess with a large radius to reduce the notch effect