Talk:Shonda Research

Horizontal round bedways are considered a bad solution in quality machine tool design. Besides many other drawbacks they are subject to considerable bending by gravity, so they work only for short bedways. Just some calculations about this effect now:

In european DIN/ISO standards, there is a demand of straightness for bedways of lathes (other machines similar) with standard precision of 0.02mm for 1000mm bedway length, for improved precision this accounts to 0.01mm on 1000mm.

For a round steel bedway, 2.5ft long with diameter 2" bending by gravity is 0.010mm, or 0.0004" This is without bending by weight from the carriage, with has to be added; all in all these bedways may fulfill the standard precision criteria for bedways (but not improved precision)

Longer bedways with round steel are nearly impossible, for 5ft length bending by gravity will be: diameter 2": 0.152mm or 0.006" diameter 3": 0.067mm or 0.0026" diameter 4": 0.038mm or 0.0015" diameter 6": 0.017mm or 0.0007" diameter 8": 0.009mm or 0.0004", which is acceptable for standard precision machine tools Bastelmike 2011/10/04

@Bastelmike: My understanding is that the roundways are bedded in concrete therefore their bending stiffness is not very important. Achieving good straightness is mostly dependent on precision alignment (optical, spirit level, etc) during embedment. ChuckH