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Harold Hall

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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-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 2.

 

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

Dividing Head
Dividing Head, Shop made,
Rotary Tables, one shop made,
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 1

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 2

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 3

All pictures can be clicked on to provide a larger view

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Drawings