Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ASME B94.29-1970 — Die Buttons — Basic Ball-Lock
⭕ ANSI B94.29-1970 (“Die Buttons — Basic Ball-Lock”) is the American National Standard governing ball-lock die buttons for stamping dies, published by the American Society of Mechanical Engineers (ASME) and developed by Technical Committee No. 16 (Punches and Dies) of Committee B94 in collaboration with the National Association of Punch Manufacturers (NAPM). It specifies types, dimensions, tolerances, material, and heat treatment for die buttons retained by a spring-loaded ball detent mechanism, with round (Type 25.00), oblong (25.01), square (25.02), and rectangular (25.03) holes and a taper relief bore. Ball-lock buttons are locked into precision retainers by a hardened spring-loaded ball engaging a ball seat on the button, allowing fast replacement without dismounting the retainer — the most widely used quick-change retention for high-speed, multi-station stamping dies.
💡 The core advantage of ball-lock is rapid changeover: a spring-loaded hardened ball in the retainer locks into the button’s ball detent, and the button can be pushed out and replaced without removing the retainer — minimizing die-setup and edge-maintenance time.
1. Scope and General Framework 📌
This Standard covers the standardization of basic ball-lock die buttons:
- Hole shapes: Round (Type 25.00), Oblong (25.01), Square (25.02), and Rectangular (25.03), formerly NAPM Nos. 25.00–25.03.
- Retention: a standard ball seat machined on the button body engages a spring-loaded ball in the retainer for locking and release.
- Relief form: taper relief — the slug bore expands conically, approximately 1/4 in. per foot (0.005–0.0208 in. per inch), self-guiding the slug.
- Related standards: retainers per USAS B94.16-1968 (standard retainers for single die buttons); functional gaging per USAS B94.17-1968.
The Standard allows the functional axis of the ball seat to deviate from true parallelism with the body axis by up to 0.006 in./in., and systematically defines lead-in chamfers (1/16 × 45°, 1/32 × 45°), taper relief, and other geometry so that products from different manufacturers remain interchangeable in standard retainers.
⚠️ Ball-seat position and conformance to the LGP (ball-lock gaging) gages of USAS B94.17-1968 are mandatory. If the seat location is out of tolerance the ball cannot latch reliably, and the button may shift or be ejected during piercing, damaging the cutting edge.
2. Technical Specifications and Tolerances 🔧
The Standard provides systematic size tables for each type. Key parameters:
| Parameter | Typical Values (in.) | Tolerance |
|---|---|---|
| Hole size range (P) | 0.064–1.035 (11 steps) | P +0.001/−0.000 |
| Relief hole diameter (R) | 0.125–1.062 | +0.010 |
| Land length (B) | 3/16–5/16 | +0.062/−0.000 |
| Standard body diameter (D) | 0.500–1.750 | +0.0005/−0.0000 |
| Taper relief | 1/4 in./ft | 0.005–0.0208 in./in. incl. |
- Material: tool steel.
- Hardness: hole and body, Rockwell C58–62.
- Concentricity: hole P to body D (inside to outside), 0.0005 in. max total indicator reading for round; 0.001 in. max for square and rectangular.
- Taper: hole P straight to 0.0008 in./in. max incl. taper relief (cutting end small); body D straight to 0.0003 in./in. max within diameter tolerance.
💡 The elegance of taper relief: the bore is smallest at the cutting edge and expands conically downward, preserving precise land dimensions while the taper self-centers and discharges slugs — more jam-resistant than straight relief.
3. Ball-Lock Mechanism and Retainer Interface 🔩
Ball-lock buttons must be used with standard retainers:
- Retainer: USAS B94.16-1968 covers standard retainers for single die buttons, with a hardened spring-loaded ball retained in an angular hole.
- Locking principle: as the button is pushed into the retainer bore, the spring-loaded ball engages the button’s ball seat, locking it axially and radially; pushing the button out releases it.
- Functional gaging: USAS B94.17-1968 (Gages — Functional, Ball-Lock Punches, Die Buttons and Retainers) defines LGP gages verifying locking interchangeability.
- Ball seat location: standard seat location is per the figure; non-standard locations must be specified on order.
🚨 The 0.006 in./in. deviation allowance for the ball-seat axis does not mean the seat can be machined casually. Depth, position, and matching with the ball diameter govern locking security; the ball must seat fully, or the lock is insufficient and the button can eject under high-speed piercing.
4. Size Tables and Series 📏
Size tables group buttons by hole-size range; each range maps to a standard body diameter and relief bore:
| Hole Range P (in.) | Body Dia. D (in.) | Relief R (in.) | Land B (in.) |
|---|---|---|---|
| 0.064–0.095 | 0.500 | 0.125 | 3/16 |
| 0.096–0.125 | 0.500 | 0.156 | 3/16 |
| 0.126–0.195 | 0.500 | 0.228 | 3/16 |
| 0.196–0.285 | 0.625 | 0.312 | 3/16 |
| 0.286–0.345 | 0.625 | 0.375 | 1/4 |
| 0.346–0.435 | 0.750 | 0.468 | 1/4 |
| 0.436–0.545 | 0.750 | 0.578 | 1/4 |
| 0.546–0.655 | 0.875 | 0.687 | 5/16 |
| 0.656–0.780 | 0.875 | 0.812 | 5/16 |
| 0.781–0.905 | 1.000 | 0.937 | 5/16 |
| 0.906–1.035 | 1.000 | 1.062 | 5/16 |
Square and rectangular buttons (25.02/25.03) use the same dimensions and tolerances except for hole P and W; rectangular holes are also subject to a limiting circumscribed diameter. All dimensions are in inches.
💡 Selection: find the required hole size in a range and read the standard body D, relief R, and land B directly. Because retainer bores are made to standard body diameter D, changing hole size never requires modifying the retainer.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: determine hole shape and nominal size → find the hole-range row and type number (25.00–25.03) → take standard body D → match a B94.16 retainer and check with B94.17 gages.
- 🔧 Clearance: button bore = punch diameter + total clearance (typically 3%–8% of stock thickness), chosen within the standard range and finalized by internal grinding.
- 📏 Installation check: after insertion, verify the ball is fully seated and the button is at full depth; validate locking interchangeability with functional gages.
- 🔨 Maintenance: inspect retainer ball and spring wear regularly; replace worn buttons as whole standard units.
6. Frequently Asked Questions ❓
❓ Q: Ball-lock vs. press-fit buttons (B94.28)?
A: Ball-lock buttons lock via a spring-loaded ball into a ball seat, needing no interference fit, and swap quickly without removing the retainer — ideal for multi-station dies with frequent edge changes. Press-fit buttons rely on interference for high load capacity but are harder to replace and depend on assembly quality.
A: Ball-lock buttons lock via a spring-loaded ball into a ball seat, needing no interference fit, and swap quickly without removing the retainer — ideal for multi-station dies with frequent edge changes. Press-fit buttons rely on interference for high load capacity but are harder to replace and depend on assembly quality.
❓ Q: Why taper relief instead of straight relief?
A: The taper (1/4 in./ft) lets the slug self-center and discharge smoothly while the cutting end stays small for accuracy — better jam resistance for thin stock and irregular slugs.
A: The taper (1/4 in./ft) lets the slug self-center and discharge smoothly while the cutting end stays small for accuracy — better jam resistance for thin stock and irregular slugs.
❓ Q: Why is a 0.006 in./in. ball-seat deviation allowed?
A: It bounds parallelism of the seat axis to the body axis while USAS B94.17-1968 gages still guarantee locking interchangeability among manufacturers. In assembly the ball must still seat fully; the deviation must not compromise function.
A: It bounds parallelism of the seat axis to the body axis while USAS B94.17-1968 gages still guarantee locking interchangeability among manufacturers. In assembly the ball must still seat fully; the deviation must not compromise function.
🔍 Q: How does this Standard relate to B94.29.1-1977?
A: B94.29-1970 is the inch edition; B94.29.1-1977 is the metric version of the same basic ball-lock die button standard, with identical structure and terms and dimensions in millimetres.
A: B94.29-1970 is the inch edition; B94.29.1-1977 is the metric version of the same basic ball-lock die button standard, with identical structure and terms and dimensions in millimetres.
