This section is from the book "Lathe Design, Construction And Operation, With Practical Examples Of The Lathe Work", by Oscar E. Perrigo. Also available from Amazon: Lathe Design: Construction And Operation.
In a small shop where the possible investment in machinery is limited, many expedients are followed to fit machines to work for which they were not primarily intended. One of the conditions often confronting the small shop owner is to swing larger work than his lathes are made for, and yet these conditions do not occur often enough to justify the purchase of a larger lathe. The illustrations at Fig. 334 show two ways of increasing the swing of a lathe. At A, the method of using raising blocks to enable a 15-inch lathe to swing 20 inches over the bed is shown. The raising block equipmerit includes blocks for head stock, tail stock, tool rest and center rest as well as necessary bolts for attaching blocks to lathe. These can be procured from the lathe manufacturer in many cases.
The gap bed lathe is a popular machine tool for jobbing and repair shops, and the combination of the gap bed and lifting blocks as shown at B enables the machinist to do many jobs of repair work he would ordinarily be obliged to turn away. With a gap bed lathe, if a job of large diameter comes in, it is a simple matter to remove the bridge from the bed and swing the work. If opening the gap does not provide sufficient space, the raising blocks may be used as well.
Fig. 334. - Methods of Increasing Swing of Lathe Outlined.
In this manner, a lathe capable of swinging but 15 inches with bridge in place may be able to swing nearly twice that much with the raising blocks inserted and gap bridge removed.