Relief grooves
A 25 mm shaft ground on its diameter and its shoulder takes a form F 0.8 × 0.3 undercut: radius 0.8 mm, 0.3 mm +0.1/0 deep, running out 2.5 mm along the shaft and 0.2 mm into the face, and the part that beds on the shoulder needs at least a 0.05 mm countersink. Pick the form, the part’s diameter and its load (DIN 509, ISO 18388) for the undercut’s size, every dimension with its tolerance, and the mating part’s countersink.
The groove is drawn at the shoulder, true to scale, with the grinding wheel’s worn corner running out into it, or with the mating part against the shoulder.
DIN 509 · form F · Ø 25 mm, normal loads
- Undercut, r × t₁
- Radius r
- Depth t₁
- Length f
- Length g
- Into the face t₂
- Mating part's countersink a (min)
- Countersink Ø at the face (min)
How it’s calculated
The table gives each form’s sizes by the part’s Ø, over the first value up to and including the second, for parts under normal loads or under higher alternating loads; series 1 radii are preferred. The mating part needs a 90° countersink at least a deep each side, Ø d₁ + 2a at the face. G’s and H’s f and g are approximate. A bore takes the same sizes. This size: Ø 18–80 mm, normal loads.
Form F sizes
| r × t₁ | f | g ≈ | t₂ | Ø normal loads | Ø fatigue loads | a min |
|---|---|---|---|---|---|---|
| 0.2 × 0.1(series 2) | 1 | 0.9 | 0.1 | 1.6–3 | — | 0 |
| 0.4 × 0.2 | 2 | 1.1 | 0.1 | 3–18 | — | 0 |
| 0.6 × 0.2(series 2) | 2 | 1.4 | 0.1 | 10–18 | — | 0.15 |
| 0.6 × 0.3(series 2) | 2.5 | 2.1 | 0.2 | 18–80 | — | 0 |
| 0.8 × 0.3 | 2.5 | 2.3 | 0.2 | 18–80 | — | 0.05 |
| 1 × 0.2(series 2) | 2.5 | 1.8 | 0.1 | — | 18–50 | 0.45 |
| 1 × 0.4(series 2) | 4 | 3.2 | 0.3 | over 80 | — | 0 |
| 1.2 × 0.2 | 2.5 | 2 | 0.1 | — | 18–50 | 0.6 |
| 1.2 × 0.4 | 4 | 3.4 | 0.3 | over 80 | — | 0.1 |
| 1.6 × 0.3 | 4 | 3.1 | 0.2 | — | 50–80 | 0.6 |
| 2.5 × 0.4 | 5 | 4.8 | 0.3 | — | 80–125 | 1 |
| 4 × 0.5 | 7 | 6.4 | 0.3 | — | over 125 | 2.1 |
Which form do I use?
Form E relieves only the cylinder: use it when the diameter is ground and the shoulder’s face is not. Form F also reaches into the face, so both can be ground up to the corner. G and H are the small forms a 55° or 60° insert cuts, for parts without high alternating loads (G) or for both surfaces (H). Under higher alternating loads the table gives larger radii and shallower depths, which raise less stress at the shoulder. Whichever form, the grinding allowance has to be less than the depth, or the wheel grinds the groove away.