Threading Solutions - Vargus

Calculating the Helix Angle and Choosing
The Right Anvil
Flank Clearance Angle a
Threading
Technical Data
5°2' 5°2' 2°32' 2°32' 7°6' 1°14' 10° Vardex toolholders are
designed
to tilt the insert when seated in
60°, UN,
ISO
ACME BUTTRESS INSERT
the toolholder (10° for external,
15° for internal tooling).
This results in the differing flank
clearance angles, based on
the geometry of insert. To ensure that the side of the insert cutting edge will not
rub on the workpiece, it is most important that the insert helix angle be correct -
especially in profiles with small enclosed flank angles. This correction is provided
by Vardex anvils.
A - A
a
f
d
A
A
a = arctan (tan Ø /2 x tand)
Where: a - Flank clearance angle
d - Tilt angle
Ø - Enclosed flank angle
Calculating the Helix Angle
b
p
b
The helix angle is calculated by the following formula:
D
b = arctan P x
N x D
b - Helix angle [ ° ]
P - Pitch [inch]
N - No. of starts
D - Pitch diameter [inch]
Lead = P x N
The helix angle can also be found from the diagram below.
Helix Angle Diagram
Standard
helix angle
b
Feed towards
the chuck
1.5°
Standard toolholder
pocket angle
Feed towards
the tailstock
Reversed
helix angle
-b
1.5°
Standard toolholder
pocket angle
122
Anvil
angle
Anvil
angle
H1
H1
The dimension H1 (cutting edge height)
remains constant with every insert/ anvil
combination.
Feed direction towards the chuck
Feed direction towards the tailstock
RH Thread/ LH Tooling LH Thread/ RH Tooling LH Thread/ LH Tooling RH Thread/ RH Tooling
Pitch P*
[mm]
12
11
10
9
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
11
Special
Toolholders
Special Toolholders
Pitch P*
5° 4° 3° b=2°
[tpi]
b=1°
2” 4”
12
b = -2°
*For Multi-start threads,use the lead value instead of the pitch
Pitch diameter [inch]
6” 8”
2.25
2.5
3
3.5
4
4.5
5
6
7
9
11
14
18
24
b=0°
24
18
14
11
9
7
6
5
4.5
4
3.5
3
2.5
2.25
b=-1°