Technical Information
Laydown Threading
Laydown Threading Shim Selection Guidelines
It is essential to select the correct shim to ensure thread quality and
maximum tool life. These parameters are needed:
• Pitch
• Pitch diameter
• Number of starts
• Feed direction
NOTE: When considering method of thread cutting, the part’s shape and stability
and the fl ow of chips are determining factors in your decision.
Laydown Selection Chart
pitch (mm)
RH thread/RH tooling LH thread/LH tooling
LH thread/RH tooling RH thread/LH tooling
10 —
9 —
8 —
7 —
6 —
5 —
4 —
3 —
2 —
1 —
0 —
1 —
2 —
3 —
4 —
5 —
6 —
7 —
8 —
9 —
10 —
pitch (mm)
NOTE: For multi-start threads, use the lead value instead of the pitch.
To calculate the lead angle of a given thread, use this formula:
ß = thread lead angle
ß = Arctan
P•S
/ De
De = effective pitch diameter of thread wear
P = 1/TPI
TPI = threads per inch
S = number of starts
All toolholders are designed with an inclination
angle = 1.5°. When turning standard threads with
a lead angle of 1–2°, this guarantees adequate
clearance at the fl anks of the insert’s thread
tooth. The thread lead angle and the required
inclination angle of the insert are given by ß.
Cutting edge height is constant at every shim
and insert combination. All toolholders are
supplied with 1-1/2° lead angle.
single-start, lead = pitch
multiple-start, lead = pitch (x) number of starts
F100
widia.com
Diagram of Thread Lead Angles