A wheel-manufacturing technology for rural workshops
Practical Action
Table 1: Capacity of wheel-rim bending device
Type of section
Maximum size that can readily
be formed
Minimum diameter that can
be formed
1. Roller in outer position (290mm centres)
flat angle round tube
100 x 12mm
40 x 40 x 6mm
25mm diameter
¾-inch water-pipe
450-500mm
400-450mm
Approx. 400mm
Approx. 400mm
2. Rollers in inner position (150mm centres)
flat angle round tube
100 x 6mm
25 x 25 x 5mm
16mm diameter
½ -inch water-pipe
Approx. 300mm
Approx. 300mm
Approx. 300mm
Approx. 300mm
The wheel manufacturing equipment also includes assembly jigs which ensure that the wheels
are set up accurately for welding and that a consistent quality of manufacture is maintained.
Wheel-rim bending device
The device is illustrated in Figure 1. It comprises a main frame in which are mounted two lower
fixed rollers (1), and a lever arm (2) which supports a central upper roller or forming tool (3).
The section to be formed rests on the two fixed rollers and is bent by the forming tool which is
forced downwards by the lever arm. Prior to bending, the section is marked out into equal
increments of 25-50mm, and during bending the section is fed over the lower rollers in these
increments. At each increment the lever arm is depressed to a preset stop (4) to produce a short
length of the desired curvature in the rim.
This method of incremental bending produces a formed circle in which the variation in radius is
of the order of 2mm. The amount of bending, and hence the diameter of rim produced, is set by
the adjusting screw (5). The section only needs to be passed through the device once to obtain
the fully formed rim so that it is possible to produce a rim in minutes.
Three forming tools are needed to cater for the range of sections listed in Table 1. Additional
tools can easily be made if other sections such as channel are to be formed. Two positions are
provided for the lower rollers. For the Outer position, less force is needed to bend the rim and
this position is used for forming heavier sections and larger diameter rims.
The Inner position is used to bend smaller diameter rims.
The bending device has two major advantages over conventional rolling machines. Firstly, the
simplicity of its construction: no rotating shafts, bearings or drive mechanisms are needed.
Secondly, the small degree of sliding movement at the rollers during bending means that un
hardened rollers can be used without risk of significant wear.
Assembly jigs
The most important function of the assembly jig is to ensure that the rim is aligned
concentrically with the wheel hub and axle. If this is not achieved the wheel will run
eccentrically and/or wobble from side to side, reducing the efficiency of the vehicle and
increasing the wear of both tyre and bearings.
The design of assembly jigs may be quite complicated in order to cope with changes in wheel
diameter and the various materials which may be used in different workshops. For instance an
assembly jig for split-rim wheels needs to be adjustable to cater for rim diameters to suit tyre
sizes from 13-inch to 16-inch. Also a great deal of care needs to be taken to ensure that the jig
is constructed as accurately as possible, otherwise the quality of wheels made on the jig will
suffer. However, the use of a well-made assembly jig greatly simplifies the construction of wheels
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