The term dividing can be applied to many characteristics, length, angle, volume,
weight, even potential (voltage) dividers, etc.. However, in the engineering workshop
the term applies almost entirely to dividing a circle. In the home workshop its uses
are likely to be many and varied though three applications probably account for most
of all dividing undertaken. These are, the production of gears, dials, and holes
on a pitch circle diameter (PCD).
The methods for achieving the correct angular divisions mainly split into three processes.
The use of a dividing head, a rotary table, or working out the X and Y co-ordinates
for use with a compound table. I use the term dividing head loosely as this applies
to any situation where the angle of rotation is controlled by holes placed round
a circle, or the teeth around the periphery of a gear. Photograph 1 shows the method
used on a semi universal dividing head, or to use the teeth on a gear wheel, Photograph
A rotary table consists of a round table that is rotated by means of a worm driving
a wormwheel below its table, Photograph 3. The worm driving handle incorporating
a dial to enable the table to be rotated by fairly precise amounts, rather like the
dials on a lathe or milling machine.
However, a full function dividing head will have a worm and wormwheel between the
dividing plate and the workpiece, and similarly, the input handwheel on a rotary
table can be fitted with a dividing plate. The demarcation between the two is therefore
blurred. In the home workshop though, I think it is true to say that most rotary
tables are not fitted with dividing plates so for this item I will be refer just
to a genuine dividing head. Where a rotary table is fitted with a dividing plate
then any reference to a dividing head will largely be applicable to the rotary table
Before we get down to using a dividing head it will be necessary to establish the
set up required to achieve the required division.
How many holes
With the most common ratio between dividing plate and the output spindle being 40:1
I will base my calculations on this value. Therefore, we will consider a 40:1 ratio
worm with a 60 hole plate. To rotate the output of the dividing head one full revolution
the worm will need to rotate 40 times, and as the plate has 60 holes the setting
arm will pass 40 x 60 holes, that is 2400. Any whole number that divides exactly
into this is then an achievable division.