On 15 December 2012 05:14, Przemek Klosowski <[email protected]> wrote:
> I think a tensile strength of a typical carbon steel M3 bolt should be > around 4kN---why does Inventor think this has to be torqued up to 78 tons? > Also, M6 should be 4x stronger---but Inventor thinks you need 1/15 the > number, not 1/4. I don't get what assumptions go into those numbers. It isn't exactly 4 x (as the effective diameters are not 2:1 because of the thread depth), but you have spotted an error. Inventor was (for some random reason) working on the basis of an M3 x 1.25 bolt. Such a bolt has a tiny CSA under the thread. Using the real pitch (0.5mm) gives a rather more convincing answer. This is the sort of error you make when you are too lazy to calculate properly and trust computers instead. My servo has a max torque of 9Nm, and a 4:1 ratio drive to a 5mm pitch ballscrew. That gives me (I think) a peak axial force of 45kN. So, around 15 M3 bolts should be OK. Using the bolted joint calculator says 150 bolts. I think it is limiting on thread pressure. However: The whole assembly is mounted into the casting by two 3/8 UNC bolts. Treating those as a mechanical fuse seems like suggest that I probably don't need much more than 8. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
