TAHA Engineering Toolsby TAHA Knowledge Lab

Machining & Workshop

Single-Point Thread Depth Calculator

Thread depth, compound-slide infeed and an equal-area pass schedule for 60° threads.

Inputs

A V-shaped thread groove of depth h, with the compound slide feed direction at angle theta from the cross-slide direction.hcompound feedθ60°work surface
A single-point tool cuts a 60° groove to depth h. With the compound slide set at θ (often 29.5°), the tool moves h ÷ cos θ along the compound and cuts mainly on one flank. Diagram not to scale.

Measured from the cross-slide direction. 29.5° is common for 60° threads: the tool cuts mainly on its leading edge and lightly skims the trailing flank.

Enter it to get the minor diameter of the finished thread.

Leave empty for no schedule. Typical values are 4–12 depending on pitch, material and tool; follow the insert maker’s recommendation if available.

Result

Thread depth (radial, per side)
0.920152
Compound slide travel
1.05721
Change in diameter (2 × depth)
1.8403
Fundamental triangle height H
1.29904
Working
H = 0.86603 × P = 0.86603 × 1.5 = 1.299 mm Depth = 17/24 × H = 0.6134 × 1.5 = 0.9202 mm Compound travel = 0.9202 ÷ cos 29.5° = 1.057 mm

Cut to a depth of 0.920152 mm, which is 1.05721 mm on the compound slide. Check the fit with a gauge or mating part before the last passes.

Educational estimate — check the assumptions below.

About this calculator

When cutting a thread on a lathe with a single-point tool, you need to know how far to feed the tool in. This calculator gives the basic thread depth of 60° ISO metric and Unified (UNC/UNF) threads from the pitch, and — if you feed with the compound slide set over — how far to move the compound slide. It can also suggest a pass schedule in which each pass removes about the same area of metal, so the cuts get lighter as the tool goes deeper.

Formula

H = 0.866 03 × P

External: h = 17/24 × H = 0.613 43 × P    Internal: h = 5/8 × H = 0.541 27 × P

Compound travel = h ÷ cos θ    Pass i of N: depth = h × √(i ÷ N)

P = pitch (for TPI: 25.4 mm ÷ TPI), H = height of the fundamental 60° triangle, h = radial thread depth per side, θ = compound slide angle from the cross-slide direction.

Worked example

External M10 × 1.5 thread, compound set at 29.5°, 6 passes:

  • Depth = 0.61343 × 1.5 = 0.920 mm per side (diameter reduces by 1.840 mm; minor diameter 8.160 mm)
  • Compound travel = 0.920 ÷ cos 29.5° = 0.920 ÷ 0.8704 = 1.057 mm
  • First pass depth = 0.920 × √(1/6) = 0.376 mm; last pass = 0.920 − 0.920 × √(5/6) = 0.080 mm.

Imperial check: 1/2-13 external: P = 25.4 ÷ 13 = 1.9538 mm; depth = 0.61343 × 1.9538 = 1.199 mm (0.0472 in).

Assumptions and limitations

  • Depths are those of the <strong>basic</strong> 60° profile (ISO 68-1, ASME B1.1). Real thread depth also depends on the tool nose radius and the tolerance class; threading-insert makers publish the infeed depth for each insert, and that value takes priority.
  • Only 60° threads are covered. Acme, trapezoidal, square, BSW (55°) and pipe threads have different profiles.
  • The equal-area pass schedule is a common starting point, not a rule. Tough materials, small machines and long overhangs need more passes. Always finish by checking the thread with a gauge, thread wires or the mating part.
  • The internal thread depth assumes the bore has first been machined to the minor diameter D1.

Safety note

When threading towards a shoulder or chuck, plan how you will stop the feed. Keep hands clear of the leadscrew, change gears and rotating work.

References

  • ISO 68-1 / ASME B1.1 basic 60° thread profile: H = 0.866 P; external depth 17/24 H; internal depth 5/8 H.
  • Compound-slide infeed geometry: travel = depth ÷ cos θ.