Design and types of knurling tools

Design and types of knurling tools

By the knurling technique the outer surface of the parts is formed by means of a single-wheel or double-wheel knurling holder.

Figure 4 Straight knurling holder

1 knurling holder
2 knurling wheel

Figure 5 Spiral knurling holder

1 knurling holder
2 knurling wheels

The tools are toothed steel wheels (or rolls or knurls) pressing the pattern into the surface.

Straight knurling holders are solid and have one wheel (see Fig. 4). The wheel should run with a little clearance in the borehole as well as in the holder.

Straight knurlings are produced by means of straight or hollow knurling wheels (mostly cylindrical) with one wheel only in the knurling holder.

Figure 6 Straight knurling wheel

Figure 7 Hollow (concave) knurling wheel

The spiral knurling holder, the head of which is tiltable, holds two wheels (see Fig. 5).

Spiral knurling holders have a special matching edge bearing which must fit well at the upper edge of the tool slide when clamping so as to prevent the holder from being forced away during the operation.

Figure 8 Spiral knurling tool - clamping with matching edge bearing

1 matching edge
2 knurling tool
3 workpiece

With cross knurlings the tooth pitches (grooves) are crossing at right angles. Cross knurlings are produced by knurling with two wheels having straight teeth in opposite directions.

Figure 9 Cross knurling

Spiral knurlings are also produced by two wheels having tooth-type grooves in the form of a 30° right-hand or left-hand spiral (2 wheels with oppositely inclined teeth).

Figure 10 Spiral knurling

1 pair of knurling wheels
2 knurled portion
3 degrees (30°)

The groove distance is the pitch (t) which differs depending on the material, width and diameter of the workpiece.

Figure 11 Form and pitch of teeth

1 pitch (groove distance t)
2 spiral knurling wheel
3 straight knurling wheel

Table 1 Recommended pitches for straight, cross and spiral knurlings

Dimensions of the workpiece		for any material	for hard rubber	for brass aluminium, fibre	for steel
		straight knurling	cross knurling	spiral knurling
Diameter d (mm)	Width b (mm)	Pitch t (mm)
up to 8	any width	0.5	0.6	0.6	0.6
8...16	up to 2	0.5	-	-	-
	2...6	0.6	0.6	0.6	0.8
16...31	up to 2	0.5	-	-	-
	2...6	0.6	0.6	0.6	0.8
	more than 6	0.8	0.8	0.8	1.0
32...64	up to 6	0.6	0.6	0.6	0.8
	6...14	0.8	0.8	0.8	1.0
	more than 14	1.0	1.0	1.0	1.2
64...100	up to 6	0.8	0.8	0.8	0.8
	6...14	0.8	0.8	0.8	1.0
	14...30	1.0	1.0	1.0	1.2
	more than 30	1.2	1.2	1.2	1.6
more than 100	up to 2	0.8	-	-	-
	2...6	0.8	0.8	0.8	1.0
	6...14	1.0	1.0	1.0	1.2
	14...30	1.0	1.2	1.2	1.6
	more than 30	1.2	1.6	1.6	2.0

The knurling wheels are made of hardened tool steel and normally have a diameter of 15 - 20 mm. The teeth are similar to small cutting edges of tools.

Recommended pitches of straight, cross and spiral knurlings are given in the following table.