On 7/21/2012 8:42 AM, andy pugh wrote: > On 21 July 2012 05:09, Jeshua Lacock <jes...@3dtopo.com> wrote: > >> 550 RPMs does not exactly strike me as spinning at high speed. Besides, >> wouldn't the gyroscopic force help stabilized oscillations? > No, centrifugal force acts as a positive feedback on any off-centre movement. > > As Steve has said, there are specs for this in the ballscrew > catalogues, and he seems to be suggesting that 25mm is fine for 10' > according to them. > > As a warning, whipping can be a deadly problem with long bars out the > back of a lathe headstock. They need to be restrained quite strongly. >
For example, see the "Types of end fixity" and "Critical speed" entries in http://www.roton.com/application_engineering.aspx From Figure 28, I infer that the critical speed for a 25mm (1in) drive screw 10ft long and supported at both ends is about 1000rpm. From Table 40 I infer that this speed drops to about 320rpm if one end is free and rises to about 1550rpm if one end is fixed and the other supported. See Table 40 for a definition of free, supported, and fixed. I once saw a student start up a lathe with about 3 feet of slender rod extending out the back of the headstock. In less time than it took the hapless student to hit the kill switch, that free end was tracing out a cone shaped path at speed. Hate to think what would have happened to anybody unfortunate enough to be within its range. The shop supervisor went white as a sheet. Given enough students (and I was one too!) everything that can happen, will happen. Regards, Kent ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
