Suppose, for example, that the work is sprung laterally towards the tool point, then the work will be turned smaller in the middle, or if the work were sprung laterally in the opposite direction, it would be turned larger in the middle than at the ends. If the work is sprung vertically so as to approach or recede from the lathe bed, the amount of the error will be less than if it were sprung laterally, and the nature of the error will depend upon the height of the cutting tool with relation to the work. If, for example, the point is above the centre of the work, and the latter is sprung towards the lathe bed, the work will turn of largest diameter in the middle of its length; or with the tool point placed at the centre of the work, the same result will follow, whether the work be sprung up or down; but if the work be sprung up or away from the lathe bed, and the tool point be placed above the centre, the diameter of the work will be turned smaller than that at the ends.
Fig. 810.
When the work is to be turned from end to end or for a considerable distance, a follower rest such as shown in [Fig. 810] should be employed, being similar to the steady rest shown in [Fig. 802], except that it is open in front, and being fastened to the slide rest carriage, of course travels with the tool; hence the plates p may be either directly in front of the tool or following it, but if the work w has been turned true and parallel, the plates p may be in front of the tool, or rather may lead it.
The follower rest should always be set to the work when as near as practicable to the dead centre, in which case it will be easier to set it without springing the work.
Fig. 811.