Worm Gear Design Calculation Pdf

A worm gear box must contain a worm and a mating gear (helical gear) and normally the axis of the worm is perpendicular to the axis of the gear. Look at the picture below:

Formulas for gear calculation. To design a gear tooth profile which rolls through the mesh without friction. Formulas for gear calculation - external gears. Download Free Lecture Notes-Pdf Link-IX. A box must contain a worm and a mating gear (helical gear) and normally the axis of the worm is perpendicular to the axis of the gear. Worm and WormGear Design Equations and Calculator. Gears Engineering and Design. Equations for American Standard Fine Pitch Worms and Wormgears Per. P = Circular pitch of wormgear P = axial pitch of the worm P x, = in the central plane P x = Axial pitch of worm P n = Normal circular pitch of worm and wormgear = Px cos λ = P cos ψ.

Where,

Calculations for worm gears are the same as for. Worm Gearing 50 Lead Angle Worm threads are. Perature and the details of the gear mesh design. Worm gear.pdf - Free download as PDF File (.pdf), Text File (.txt) or read. Of a worm gear is related to its circular pitch and number of teeth Z by the formula.

D1 – Pitch Diameter of Worm

D2 – Pitch Diameter of Gear

Worm Gear Ratio Formula

C – Centre to Centre Distance between the Worm and the Gear

This worm gear design tutorial will discuss up to the selection of the module and pitch and the calculation of the number of teeth, pitch circle diameter and centre to centre distance between the worm and gear. We will use the AGMA formulae for doing the calculations. Design calculations of the other aspects of the worm gear will be discussed in a subsequent part of the tutorial.

Steps of the Design Calculation

• The axial pitch of the worm and the circular pitch of the gear must be same for a mating worm and gear. We will use the term Pitch (P) for both the pitch in this tutorial.
• Also, the module of the worm as well as the gear must be equal for a mating worm and gear.
• Now, let’s say we have the following design input:

Speed of the Worm (N1) = 20 RPM

Speed of the Gear (N2) = 4 RPM

• And, we have to find out the Module (m), Pitch (P), Number of helix of Worm (T1), Number of teeth of Gear (T2), Pitch circle diameter of Worm (D1), Pitch circle diameter of Gear (D2), Centre to centre distance(C).

• Select the suitable module and its corresponding pitch from the following AGMA specified table:

Module m (in MM) – Pitch P (in MM)

2 ————————-6.238

Worm Gear Calculation

2.5 ———————- 7.854

3.15 ——————— 9.896

4 ————————- 12.566

5 ————————- 15.708

6.3 ———————– 19.792

8 ————————– 25.133

10 ————————- 31.416

12.5 ———————– 39.27

16 ————————– 50.625

20 ————————– 62.832

• Say, we are going ahead with the Module as 2 and the Pitch as 6.238.

• Use the following gear design equation:

N1/N2 = T2/T1

And, we will get:

T2 = 5 * T1……………….Eqn.1

• Now use the following AGMA empirical formula:

T1 + T2 > 40………………Eqn.2

• By using the two equations (Eqn.1 & Eqn.2), we will get the approximate values of

T1 = 7 andT2 = 35

• Calculate the pitch circle diameter of the worm (D1) by using the below AGMA empirical formula:

D1 = 2.4 P + 1.1

= 16.0712 mm

• The following AGMA empirical formula to be used for calculating the pitch circle diameter of the gear (D2):

D2 = T2*P/3.14

= 69.53185 mm

• Now, we can calculate the centre to centre distance (C) by the following equation:

C = (D1 + D2)/2

= 42.80152 mm

• The below empirical formula is the cross check for the correctness of the whole design calculation:

(C^0.875)/2 <= D1 <= (C^0.875)/1.07

Observe that our D1 value is falling in the range.

Conclusion

The worm gear box design calculation explained here uses the AGMA empirical formulas. A few worm gear design calculator are available on web, and some of them are free as well.

In the next worm gear box design calculation tutorial we will discuss the force analysis of a worm gear box.

Related Reading

Helical Gear vs. Spur Gear: If you have observed a spur gear application, you may have noticed that spur gear can be replaced by helical gear. Where should a helical gear should be used? What are the benefits and disadvantages of doing so?

Input Parameters

Teeth type - common or spiral

Gear ratio and tooth numbers

Pressure angle (the angle of tool profile) α

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Module m (With ANSI - English units, enter tooth pitch p = π m)

Unit addendum ha^*

Unit clearance c^*

Unit dedendum fillet r_f^*

Face widths b₁, b₂

Unit worm gear correction x

Worm size can be specified using the:

• worm diameter factor q
• helix direction γ
• pitch diameter d₁

Auxiliary Geometric Calculations

Calculated parameters

Common gearing ZN

Axial module

Spiral gearing ZA

Axial module

Normal tooth pitch

Axial tooth pitch

p_x = π_x

Basic tooth pitch

Lead

p_z = z₁ p_x

Virtual/alternate number of teeth

Helix angle at basic cylinder

sin γ_b = sin γ cos α_n

Worm pitch cylinder diameter

Worm gear pitch circle diameter

d₂ = z₂ m_x

Worm outside cylinder diameter

Worm gear outside circle diameter

d_a2 = d₂ + 2m (h_a^* + x)

Worm root cylinder diameter

Worm gear root circle diameter

Worm Gear Design Pdf

d_f2 = d₂ - 2m (h_a^* + c^* - x)

Worm rolling(work) circle diameter

Worm gear rolling(work) circle diameter

d_w2 = d₂

Free Worm Gear Calculator

Worm gear root circle diameter

Center distance

Chamfer angle of worm gear rim

Worm tooth thickness in normal plane

Worm gear tooth thickness in normal plane

Worm tooth thickness in axis plane

s_x1 = s₁ / cos γ

Worm gear tooth thickness in axis plane

Work face width

b_w = min (b₁, b₂)

Worm Gear Ratio Calculator

Contact ratio

ε_γ = ε_α + ε_β

where:

Worm Gear Design Calculation Pdf Download

Minimum worm gear tooth correction

where:

Worm Gear Calculation Formula

h_a^*₀ = h_a^* + c^* - r_f^* (1 - sin α)