Harold Hall
Dividing, Using a Dividing Head and other methods. Harold Hall
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-
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 also.
THE MATHEMATICS
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.
Metalworking
Workshop Processes
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Drawings