The pastime of metal working is one that has a rich tradition in western culture and continues to remain strong. Even in modern times with electrical gadgets galore there are still many hobby machinists that enjoy spending time in the workshop shaping all manner of metal components. You may also be surprised to learn that it isn't necessarily only an old man's game either and that there are many of the younger generation taking up the hobby of metal working. For those that are new to the activity and that are looking for some guidance we shall touch on rotary tables and discuss why they are such an important device for those looking to carry out precise metal machining.

Importance of precision

One of the most important things in metal working is to be able to shape the object into very precise dimensions. In order to do this it is important to have the object securely clamped in position before you proceed with using tools on it. Obviously you could use a vice to carry out this task. However, what if you need to shape the object at regular intervals that must be exact?

Rotating your work

Rotary tables are not only clamping devices that hold the object in place; they also have the capacity to rotate the piece a set number of degrees. The number of degrees by which the piece is rotated is controlled by worm gears that are key components of rotary tables. The worm gear is turned manually through operation of the worm crank, which in turn rotates the piece. Usually the worm gear ratio is 40:1, which means 40 turns of the crank will give you one full rotation of the work piece. One turn of the crack will rotate the object by 9 degrees.

Use of an indexing plate

In many instances the number of degrees that you wish to turn the object will not divide accurately by the number of degrees provided by the worm gear ratio. So for example when using the 40:1 ratio it could be that you only wish to rotate the work piece by 3 degrees - which would be done by rotating the crank by 1/3 of a turn. Obviously guessing at this could lead to mistakes and thus an inaccurate finished article.

This can be overcome through the use of indexing plates in conjunction with rotary tables. An indexing plate is a circular piece of metal with holes drilled at regular intervals. On the outside circumference the holes will be drilled at a ratio that matches the worm gears ratio. Then further towards the centre there will be another set of holes and so on. By turning the crank only a fraction of a full turn until the pointer attached to the crank drops into the relevant hole; the operator is able to rotate the object an exact number of degrees.

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