Technical Specifications

Tooth Form

A knurled tooth is V-shaped and the depth of the tooth is less than the depth of a theoretical V-form. The tooth has a rounded root and crest. The relationship between the actual depth of tooth to the theoretical V varies with the pitch of the teeth. On finer pitches, the tooth is a smaller proportion of the theoretical V-depth than coarser pitches. Also, female diamond patterns have shallower tooth depth than male diamond patterns.

RAPID offers 90° teeth angle as standard included pressure angle. As per customer requirement, RAPID manufactures custom teeth angles such as 80° and 60°.

Pitch Formulae

Axial pitch can be calculated from TPI or from Diametral Pitch (DP):

$$P_{mm} = \frac{25.4}{TPI} \qquad P_{inch} = \frac{1}{TPI}$$ $$P_{mm} = \frac{25.4 \times \pi}{DP} \qquad P_{inch} = \frac{1 \times \pi}{DP}$$

Where $P$ is axial pitch, $TPI$ is teeth per inch, and $DP$ is diametral pitch.

Conversion Chart for Straight Knurling

TPI	Axial Pitch (mm)	Nearest Standard Pitch (RAPID)		DP	Axial Pitch (mm)	Nearest Standard Pitch (RAPID)
10	2.540	2.5		64	1.2468	1.2
12	2.116	2.2		96	0.8312	0.8
16	1.587	1.6		128	0.6234	0.6
20	1.270	1.2		160	0.4987	0.5
25	1.016	1.0
30	0.846	0.8
35	0.726	0.7
40	0.635	0.6
50	0.508	0.5
80	0.318	0.3

Knurling Methods

In-Feed Knurling (Plunge) on CNC "X"

Straight or diamond knurling can be produced by using either one or two knurls mounted in a holder in the front or rear of the cross slide, which applies direct pressure to the work. Diamond knurls require greater pressure than straight or diagonal knurls, sometimes placing prohibitive loads on both machine and work, which can damage the machine.

End-Feed Knurling (To Chuck) on CNC "Z"

Straight, helical, or diamond knurling may be produced with knurling holders mounted on the compound or turret. Only straight and diagonal knurls can be used with the end-feed process; to produce helical and diamond knurling, the knurls are held in the holder to trace the helical or diamond path as they are fed over the blank.

Note: Knurls used for feed knurling should have chamfers.

Knurling Standard (IS: 3403-1981 & DIN82)

RAPID™ knurl patterns follow the profile and diameter standard defined in IS:3403-1981 and DIN82, at a standard 90° profile angle.

Pattern Types

Code	Description
RAA	Knurl with grooves parallel to axis
RBL	Left-hand knurl
RBR	Right-hand knurl
RGE	Left-hand / right-hand knurl, points raised
RGV	Left-hand / right-hand knurl, points indented
RKE	Cross-knurl, points raised
RKV	Cross-knurl, points indented

Key Definitions

• Profile Angle: 90° (standard)
• Pitch (P): the circular axial pitch of the knurl
• Nominal Diameter (d1): the outside diameter of the finished knurl, as stated in the workshop drawing; a function of the design
• Initial Diameter (d2): the workpiece diameter before knurling. It is smaller than d1, since the knurling operation enlarges the diameter through displacement of material

Initial Diameter (d2) Formulae

The initial diameter d2 for knurls with a 90° profile angle can be calculated from the table below, depending on the type of knurl and the size of pitch. These formulae don't account for rounding of the grooves from the knurling operation, or the specific properties of the material being knurled.

Type of Knurl	Initial Diameter d2
RAA: grooves parallel to axis	(no radial displacement)
RBL: Left-hand knurl	d1 − 0.5P
RBR: Right-hand knurl	d1 − 0.5P
RGE: Left/right-hand, points raised	d1 − 0.67P
RGV: Left/right-hand, points indented	d1 − 0.33P
RKE: Cross-knurl, points raised	d1 − 0.67P
RKV: Cross-knurl, points indented	d1 − 0.33P

Designation example: A cross-knurl, points indented (Type RKV) with pitch P = 0.8mm, conforming to this standard, is designated: Knurl RKV 08 IS:3468