This study presents the design, fabrication, and performance evaluation of a low-cost rod twisting machine using

locally available materials. The machine was developed to improve productivity, consistency, and efficiency

compared to manual twisting methods. Mild steel rods of diameters 6 mm to 16 mm (500 mm length) were tested

under identical operating conditions. The required torque was determined using torsion theory, and a 3 kW

electric motor was selected based on power requirements. Experimental results showed that twisting time

increased from 7.7 s to 26.0 s with increasing rod diameter, the number of twists decreased from 9.67 to 4.67.

Rod twisting is a widely used metal forming process in industries for producing decorative and structural

elements such as gates, railings, and frames. Manual twisting methods are labor-intensive, inefficient and often

produce non-uniform result (Hossain et al., 2022). Mechanized systems improve consistency, reduced labor, and

enhance productivity (Dametew, 2017).

Machine design involves careful consideration of stress, power transmission, and material selection to ensure

durability and safety (Farouki & Linke, 2016; Khurmi & Gupta, 2025)

Ngala et al. (2016) developed a combined bending, twisting, and cutting machine aimed at reducing manual

labor and increasing production efficiency. Their study showed that integrating multiple operations into a single

system improves productivity and reduces fabrication time. However, the design lacked optimization for

Hanoofa (2014) focused on the design and fabrication of a pipe and rod bending machine, analyzing performance

in terms of production rate and material deformation. While their working primarily addressed bending, the

result indicated that mechanized systems significantly reduce material wastage and improve repeatability

compared to manual processes. Similarly Wang et al (2026) developed an analytical model for twisting

deformation in rod extrusion processes. Their study incorporated the effects of friction, material properties, and

deformation mechanics to predict twisting behavior. The results showed that accurate modeling of torsional

deformation enhances the predictability of machine performance and improves design reliability. This project

aims to design and fabricate a low-cost rod twisting machine using locally available materials while maintaining

structural integrity and operational efficiency.

The following are the design parameters:

i. Rod diameters: 6 mm, 8 mm, 10 mm, 12 mm, 16 mm

ii. Length of rod: 500 mm

iii. Material: Mild steel

v. Modulus of rigidity (G) = 80 GPa

vi. Speed N = 60, rpm

The requirement torque to twist a solid rod is

T = Torque (Nm)

d = diameter (m)

For 6mm diameter rod

T =

= 23.3 Nm

The calculated Torque for each Rod is tabulated in the table 1 below

Shaft Design

The shaft design was based on torsion equation from equation 1:

(2)

Using the maximum torque

Shaft diameter of 35 mm selected

= 2.8 kW

3 kW electric motor was used.

The motor speed = 1440 rpm

The desired speed = 60 rpm

Gear Ratio =

= 24

This ratio is too large for a single belt stage, two stage belt drive was used.

Stage 1: 4:1

Stage 2: 6:1

Table 5: Average Number of Twists with Error Bar

Table 6: Efficiency of Rod Twisting Machine

There is decrease in number of twist as the rod diameter increased. This is because thicker rods exhibit higher

stiffness and reduced angular deformation under the same applied torque.

Figure 4: Torque Variation with Diameter

Figure 5 illustrate the error bar graph for twisting time it shows a clear increasing trend with rod diameter,

indicating that larger rods require more time to achieve uniform twisting. Small error bars across all the diameters

Figure 5: Diameter Variation with Average twisting Time (Error Bar)

The error bar graph for the number of twists indicate a decreasing trend with increasing rod diameter, which is

consistent with the expected behavior of stiffer materials under torsional loading. The small and nearly uniform

error bars shows minimal variation between repeated trials, demonstrating high repeatability of the machine.

This suggests that the machine provides consistent twisting performance, particularly for smaller diameters

where deformation is more uniform. Slight increases at higher diameters may be attributed to increased vibration,

material heterogeneity, and higher torque fluctuations.

Figure 6: Diameter Variation with Average Number twists (Error Bar)

The experimental observations revealed that at larger diameters, mainly at 16 mm, slight cracks and non-uniform

deformation occurred. This shows that the applied torque approached the torsional strength limit of the mild steel

twisting. This suggests that while the machine performs effectively within lower and moderate diameter ranges,

its performance at higher diameter is limited, this may require design improvements such as increased torque

capacity, enhanced rigidity, or improved gripping mechanisms.

Efficiency increases with rod diameter because the motor operates closer to its rated capacity at higher loads. At

low loads energy utilization is poor. The maximum efficiency was calculated theoretically to be 92.52%, at 16

mm. Although real efficiency is expected to be lower (60-70%) due to mechanical losses in the belt drive system,

worm gear transmission, and frictional effects. At lower diameter, the efficiency is significantly reduced because

the machine operates under partial load conditions, leading to inefficient energy use.

stiffness. The machine shows high repeatability with minimal variation across trials. Maximum theoretical

efficiency of 92.52% was obtained, practical efficiency is expected to range between 60-70% due to mechanical

and transmission losses. For higher diameter exhibited increased resistance and minor defects, suggesting the

need for higher torque capacity or design improvements.