Re: on bed design.

Anthony Rhodes

I'm coming to this quite late due to being busy with other matters. I've read your message and the 6 responses, and I'm interested in machine tool design, so I thought I might contribute.
The issue at hand is, firstly, to control the location of the cutter relative to the work piece with as much precision as possible. Where there may be a loss of such precision, it is preferable to take the loss where it will have the least detrimental effect on required accuracy of the work piece.
There is a mathematical benefit in a narrow guide way, On most lathes with inverted V-ways there is one such for the carriage and one different one for the tailstock. The narrow guide way, by its geometry, reduces the amount of skewing of the controlled element, ie the carriage or tailstock, as it is traversed along the bed. Even with vertical wear of the V-way the carriage or tailstock tend to stay at the same distance from the axial center of the bed. It has been calculated that vertical displacement below or above the axial center of the work piece has much less effect on the accuracy of machining, more effect on small diameter work pieces and much less on large diameter ones.
The above being said, there are many forms of bedways, dove tail and flat (or box ways in the modern terminology) being a couple of them, There are also single Vs, triple Vs, and four Vs, in addition to the common two V pattern. Common examples are small Asian lathes, as well as the AA 6" for single Vs, Monarch 10EE and Rivett 1020 for 2 Vs, South Bend and it's clones for 3 Vs, and American Standard for 4 Vs. Atlas and Myford use flat ways and Hardinge uses dove tails. There are, of course, many more for each form. There are also various displacements of the bedways. Slant beds are pretty well known, which provide benefits in clearing the bed and carriage of chips and lubricants or collants, and while I'm not aware of over head bedways for the carriage, I do know of such for the tailstock.
Each form of bed had some benefit in the eyes of the designer and manufacturer. In the end, there is probably more benefit in the choices of and processes used on the materials, and the care taken in precision of manufacture, than all the theoretical benefits from geometry. And care in use, maintenance, and adjustment will do more, than anything done before installation in the shop, to provide superior performance over a long, useful life. Ham fisted and ignorant people can destroy the best machine in a couple of days, whereas a considerate, knowledgeable user can make the lowliest machine turn out quality work over a long time, far beyond the reasonable expectations placed upon it from the day it left the manufacturer.
Berkeley, Calif.

In a message dated Thu Dec 31, 2015 2:03 pm (PST), jkling222 writes:
Most lathe have v ways (or combinations of v and flat ways). A few inexpensive lathes (such as Atlas) used flat beds. I imagine that this is a cheaper design to manufacture. A big mill and a big surface grinder would seen to provide efficiency in manufacture. But some precision lathes also have flat beds. So the design evidently is not all about cost savings.

Is there a reason that the majority of manufactures of lathes chose v ways?

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