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ASME B94.29.1-1977 — Die Buttons — Basic Ball-Lock (Metric)
⭕ ANSI B94.29.1-1977 (“Die Buttons — Basic Ball-Lock (Metric)”) is the metric edition of the ball-lock die button standard, published by the American Society of Mechanical Engineers (ASME). Structurally and terminologically parallel to the inch edition B94.29-1970 but dimensioned entirely in millimetres, it covers metric ball-lock die buttons with round (M25.00), oblong (M25.01), square (M25.02), and rectangular (M25.03) holes up to 25 mm maximum pierced hole size. Metric buttons fit light-duty ball-lock retainers and are gaged for locking interchangeability with light-duty functional gages (M LGP). It is the direct selection, machining, and stocking reference for metric-based stamping toolrooms.
💡 The metric edition is positioned for light duty: metric buttons are designed for light-duty ball-lock retainers and light-duty M LGP gages, ideal for small-to-medium holes with frequent edge changes. Always match the retainer duty class to the button.
1. Scope and General Framework 📌
This Standard covers the American National Standard practice for basic metric ball-lock die buttons:
- Hole shapes: Round (M25.00), Oblong (M25.01), Square (M25.02), and Rectangular (M25.03).
- Size limit: maximum pierced hole size 25 mm.
- Retention: the ball in the retainer seats in the button’s ball seat, providing retention and radial location; releasing the ball frees the button.
- Mating standards: light-duty ball-lock retainers; locking interchangeability verified with light-duty M LGP functional gages.
- Relief form: straight or tapered relief, manufacturer’s option.
The ball seat is defined as the locking detent in the body that provides both the locking and alignment functions: the retainer ball fits into it to retain the button, and for shaped holes it also radially locates the button with respect to the retainer and other details. When the ball is forced back out of the detent, the button can be removed from the retainer and die.
⚠️ The metric edition requires two-point ball contact: the ball must contact two surfaces of the ball seat simultaneously. A one-point contact fails functional gaging — the lock is insecure, allowing button shift and edge misalignment during piercing.
2. Terminology and Structural Elements 🔧
The metric edition uses terminology consistent with the inch edition:
| Term | Symbol | Metric Definition / Engineering Role |
|---|---|---|
| Hole Diameter | P | Working (land) hole diameter in mm; P larger and W smaller for non-round shapes |
| Land Length | B | Length of the precisely sized working hole, including grind allowance; e.g., 4.0, 5.0, 6.0, 8.0 mm |
| Body Diameter | D | Cylindrical portion fitting the retainer bore; standard values 13.0–40.0 mm |
| Relief Hole Diameter | R | Maximum relief bore; straight or tapered per manufacturer |
| Overall Length | L | Total length, selected for retainer and block thickness |
| Chamfer | — | Angular surface at both ends of the body (1 × 45°) for entry and edge protection |
| Ball Seat | — | Locking detent in the body; two-point ball contact; locks and radially locates the button |
💡 Unlike the inch edition’s taper-relief emphasis, the metric edition permits straight or tapered relief at the manufacturer’s option. If slug discharge matters (thin stock, irregular slugs), specify the relief form on order.
3. Metric Size System 📏
The Standard groups buttons by hole-size range (Round, Table 1, Type M25.00):
| Hole Range (mm) | Relief R (mm) | Land B (mm) | Body Dia. D (mm) |
|---|---|---|---|
| 1.50–2.40 | 3.2 | 4.0 | 13.0 |
| 2.41–3.20 | 6.0 | 4.0 | 13.0 |
| 3.21–5.00 | 6.0 | 5.0 | 16.0 |
| 5.01–7.20 | 8.0 | 5.0 | 16.0 |
| 7.21–8.80 | 8.0 | 6.0 | 20.0 |
| 8.81–11.00 | 9.5 | 6.0 | 20.0 |
| 11.01–13.80 | 12.0 | 6.0 | 25.0 |
| 13.81–16.50 | 12.0 | 8.0 | 25.0 |
| 16.51–19.80 | 15.0 | 8.0 | 32.0 |
| 19.81–23.00 | 15.0 | 8.0 | 32.0 |
| 23.01–26.00 | 17.5/24.0/27.0 | 8.0 | 40.0 |
Body tolerances step with diameter (e.g., 13.0 mm: −0.007/−0.016; 20.0 mm: −0.009/−0.020); hole tolerance +0.01/−0.00; rectangular holes limited by the circumscribed diameter GMAX. All dimensions in mm.
⚠️ Metric body diameters use negative tolerances (e.g., 13.0 mm at −0.007/−0.016 mm) so the button enters a nominal “Go” ring gage. Centering and lock security are still verified as a whole by the M LGP gage, not by single dimensions alone.
4. Two-Point Ball Seat and Gaging 🔩
The metric edition states ball-seat geometry requirements explicitly:
- Two-point contact: the ball must contact two surfaces of the ball seat; one-point contact is unacceptable.
- Functional axis deviation: the ball-seat axis may deviate from true parallelism with the body axis by up to 0.006 mm/mm.
- Entry check: the body must enter a nominal “Go” ring gage for a 25.0 mm minimum length.
- M LGP gages: the ball seat conforms to U.S. standard M LGP functional gages (metric counterpart of the B94.17 series).
- Concentricity: hole to body (inside to outside), 0.01 mm max total indicator reading.
🚨 Lock security depends entirely on ball-seat geometry: too shallow or mislocated a seat prevents two-point contact, drops locking force, and the button can be pulled out during piercing. Verify every button with the M LGP gage after assembly — never rely on feel alone.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: choose hole shape and metric nominal size → locate the hole-range row and type (M25.00–M25.03) → take standard body D → match a light-duty ball-lock retainer → accept with M LGP gages.
- 🔧 Clearance: button bore = punch diameter + total clearance (typically 3%–8% of stock thickness), chosen within the standard range and finalized by grinding.
- 📏 Installation check: confirm two-point ball contact and full seating; inspect the seat and retainer ball for wear and contamination.
- 🔨 Maintenance: light-duty retainers are not for heavy stock or extreme loads; replace worn buttons as whole standard metric units.
6. Frequently Asked Questions ❓
❓ Q: How do B94.29.1-1977 and B94.29-1970 relate?
A: They are metric and inch editions of the same basic ball-lock die button standard. B94.29.1-1977 is fully metric (mm), up to 25 mm pierced holes, with light-duty retainers and M LGP gages; B94.29-1970 is inch. Choose per unit system; do not mix.
A: They are metric and inch editions of the same basic ball-lock die button standard. B94.29.1-1977 is fully metric (mm), up to 25 mm pierced holes, with light-duty retainers and M LGP gages; B94.29-1970 is inch. Choose per unit system; do not mix.
❓ Q: What is “two-point contact” and why is one-point contact unacceptable?
A: Two-point contact means the ball simultaneously touches two surfaces of the ball seat, giving stable locking force and reliable location. With one-point contact the ball merely rests on one surface — the lock is weak and vibration during piercing loosens the button.
A: Two-point contact means the ball simultaneously touches two surfaces of the ball seat, giving stable locking force and reliable location. With one-point contact the ball merely rests on one surface — the lock is weak and vibration during piercing loosens the button.
❓ Q: Straight vs. tapered relief in the metric edition?
A: The Standard permits either at the manufacturer’s option. Straight relief is simple and lets stable slugs pass directly; tapered relief self-guides slugs and resists jamming, better for thin stock and irregular slugs. Specify the form on order when discharge matters.
A: The Standard permits either at the manufacturer’s option. Straight relief is simple and lets stable slugs pass directly; tapered relief self-guides slugs and resists jamming, better for thin stock and irregular slugs. Specify the form on order when discharge matters.
🔍 Q: What do “light-duty retainers” and “light-duty gages” mean?
A: The metric edition is designed for light duty — paired with light-duty ball-lock retainers and light-duty M LGP gages. It suits small-to-medium holes and frequent changeover; heavy or large piercing should use heavy-duty designs or the inch series with heavy-duty retainers.
A: The metric edition is designed for light duty — paired with light-duty ball-lock retainers and light-duty M LGP gages. It suits small-to-medium holes and frequent changeover; heavy or large piercing should use heavy-duty designs or the inch series with heavy-duty retainers.
