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ASME B94.6-1984 (2014) — Knurling
🔩 ASME B94.6-1984 (2014) is the authoritative American National Standard for knurling, developed by the ASME B94 Committee on Cutting Tools and reaffirmed in 2014. The Standard covers knurling tools built to standardized diametral pitches and their dimensional relations with the work blank, for producing straight, diagonal, and diamond knurling on cylindrical surfaces whose teeth have uniform pitch parallel to the cylinder axis or at a helix angle not exceeding 45°. Knurling is produced by displacement of the work material as it rotates under pressure against a knurling tool. The Standard’s central contribution is designing tools on the basis of diametral pitch rather than the traditional teeth per inch (tpi); with recommended blank diameters that are multiples of 1/64 or 1/32 in, good tracking (the ability of the tool teeth to mesh as they penetrate in successive revolutions) is obtained, improving knurl uniformity and appearance, eliminating costly trial and error, reducing tool failure and defective work, and shrinking the number of tools required. Its lineage runs through ASA B5.30-1953, later maintained by the B94 Committee.
💡 Tracking is the make-or-break of knurling: the tool teeth must mesh stably with the work or the pattern becomes overlapped, smeared, or flattened. B94.6’s diametral pitch system guarantees tracking at the source through the relation “blank diameter × pitch = whole number of teeth.”
1. Scope and Terminology 📌
This Standard applies to knurling tools (knurls and dies) and the knurled work they produce, covering:
- Cylindrical knurls: solid and insert types for engine lathes, automatic lathes, and the like.
- Flat knurling dies: both reciprocating and stationary types.
- Knurling: both the process and the knurled portion of the finished work.
- Diametral pitch: the total number of teeth in the circumference of the work divided by the basic blank diameter; for the tool, the total teeth in the circumference divided by the nominal diameter. Pitch and tooth counts are always measured in a transverse plane perpendicular to the axis of rotation, for diagonal as well as straight knurls and knurling.
⚠️ Terminology matters: “knurl” is the toothed tool; “knurling” is both the process and the knurled portion of the work. Drawings and process documents should use accurate terms and never confuse the tool with the pattern.
2. Tool Types and the Diametral Pitch System 🔧
The Standard divides knurling tools into three basic classes, specifying type, dimensions, and tolerances for each:
| Tool Type | Construction | Typical Application | Standard Table |
|---|---|---|---|
| Cylindrical knurl, straight tooth | Cylindrical wheel, teeth parallel to axis | Straight knurling on conventional lathes | Tables 1/4 |
| Cylindrical knurl, diagonal tooth | Wheel with teeth at helix up to 45° | Diagonal/diamond knurling on lathes | Table 4 |
| Flat reciprocating knurling dies | Flat die, straight or diagonal teeth, reciprocating | High-volume, special-machine knurling | Table 2 |
| Flat stationary knurling dies | Fixed die, work rolled to form | Automatics, special fixtures | Table 2 |
The heart of the Standard is the diametral pitch (DP) system: the ratio of teeth to nominal diameter is standardized, and recommended blank diameters are multiples of 1/64 or 1/32 in so that the number of teeth around the blank circumference is a whole number. The knurl teeth can then mesh precisely with the work tooth spaces, giving stable tracking. Table 1 gives preferred sizes for cylindrical knurls, Table 1A adds bench and engine lathe toolholder sizes, and Table 3 gives knurling data for fractional blank diameters.
🚨 Choosing the wrong blank diameter is the most common knurling defect: when the blank is not a recommended multiple, the knurl teeth cannot mesh with the work tooth spaces, producing overlaps, smearing, and even chipped knurl teeth. Always check the blank against Table 3 (allowing for the upset after rolling).
3. Knurl Patterns and Drawing Indications 📏
The Standard defines the three basic patterns and their drawing indications:
- Straight knurling: teeth parallel to the work axis; parallel-line pattern.
- Diagonal knurling: teeth at a helix angle (≤45°) to the axis; parallel diagonal pattern.
- Diamond knurling: two diagonal sets crossing into a diamond grid, formed by straight-tooth knurls as the tool feeds.
Clause 7 introduces the tracking correction factor Q, used to correct the mesh relationship in diagonal and diamond knurling; Clause 8 gives the method and data (Table 5) for producing diagonal and diamond knurling with straight-tooth cylindrical knurls. The Standard also shows the drawing indications for specifying knurling on engineering drawings.
💡 Diamond knurling is usually done with one straight-tooth knurl in two passes: first at 45° in one direction, then again at 45° the other way; the two sets of lines cross into diamonds. Table 5 supplies parameters and correction factors to avoid blind trial runs.
4. Dimensions, Tolerances, and Marking 📐
The Standard specifies dimensions, tolerances, and marking for knurling tools:
| Item | Provision | Typical Example |
|---|---|---|
| Cylindrical knurl dimensions | OD, bore, width, tooth count (Table 1) | 96 DP, 128 DP, etc. |
| Flat die specifications | Length, width, tooth count (Table 2) | Per machine travel and work size |
| Knurled OD tolerance | Recommended tolerances (Clause 6) | ±0.005 in, etc. |
| Marking | Marking on knurls and dies (Clause 5) | Pitch, type, maker’s mark |
⚠️ A knurl callout on the drawing must be complete: pattern type (straight/diagonal/diamond), pitch or DP, and knurled length. Missing any element forces the machinist to guess and invites batch rework.
5. Engineering Practice Essentials 🛠️
- 🔍 Blank diameter calculation: choose pitch so that blank diameter × pitch is a whole number (prefer multiples of 1/32 or 1/64 in), and allow for the material upswept by the teeth.
- 🔧 Feed and pressure: keep adequate tool-to-work contact; maintain steady radial pressure and longitudinal feed and avoid mid-cut stops that smear the pattern.
- 📊 Speed control: keep knurling speed moderate to prevent overheating and tooth pickup; use lower speed or multi-rib knurls on hard materials.
- 📋 Quality checks: verify a complete, uniform pattern free of overlap and pressure marks; accept OD per the recommended tolerances; replace worn knurls and recheck tooth form.
6. Frequently Asked Questions ❓
❓ Q: Why does B94.6 emphasize “diametral pitch” instead of teeth per inch (tpi)?
A: tpi describes only density and cannot guarantee mesh (tracking) between knurl teeth and the work tooth spaces. Diametral pitch ties the number of teeth around the work circumference to the blank diameter, so with recommended blank diameters the tooth count is a whole number and tracking is geometrically assured — yielding uniform patterns.
A: tpi describes only density and cannot guarantee mesh (tracking) between knurl teeth and the work tooth spaces. Diametral pitch ties the number of teeth around the work circumference to the blank diameter, so with recommended blank diameters the tooth count is a whole number and tracking is geometrically assured — yielding uniform patterns.
❓ Q: What is the difference between diagonal and diamond knurling?
A: Diagonal knurling is a single set of parallel diagonal lines; diamond knurling is two crossing sets forming a grid. Diamond patterns give better grip and are standard for handles, knobs, and anti-slip parts.
A: Diagonal knurling is a single set of parallel diagonal lines; diamond knurling is two crossing sets forming a grid. Diamond patterns give better grip and are standard for handles, knobs, and anti-slip parts.
🔍 Q: Why does the knurled OD grow larger?
A: Knurling forms by displacement: the tooth crests “push up” the material, so the finished OD exceeds the blank diameter by the amount of upset. The blank must therefore be sized as “finished OD minus rise,” and Clause 6 provides recommended tolerances and setting guidance.
A: Knurling forms by displacement: the tooth crests “push up” the material, so the finished OD exceeds the blank diameter by the amount of upset. The blank must therefore be sized as “finished OD minus rise,” and Clause 6 provides recommended tolerances and setting guidance.
❓ Q: How does B94.6 relate to the other B94 cutting tool standards?
A: They are all ASME B94 series but on different subjects: B94.6 is knurling, B94.51M/52M are saw blades, B94.9 is taps. Procurement and process documents should cite the appropriate standard in each case.
A: They are all ASME B94 series but on different subjects: B94.6 is knurling, B94.51M/52M are saw blades, B94.9 is taps. Procurement and process documents should cite the appropriate standard in each case.
