Google is your friend! ft-lb =Nm * 0.73756 So 75Nm = 55.3 ft lbs > -----Original Message----- > From: Gene Heskett [mailto:ghesk...@shentel.net] > Sent: Thursday, April 18, 2019 11:45 AM > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] Something to think about re the hack-a-day tool > changer > > On Thursday 18 April 2019 07:47:51 andy pugh wrote: > > > On Thu, 18 Apr 2019 at 10:22, Roland Jollivet > <roland.jolli...@gmail.com> wrote: > > > To recap; small steppers 'drive' the carousel around to tighten the > > > motor. > > > > No, the motor drives round the carousel to tighten the collet. > > > > It is really rather clever. Assuming that it can't work based purely > > on guess-work seems silly. > > No, not silly, experience Andy, experience reaching into the bank account > to replace tooling that broke by walking out of the holder when I > thought it was tight enough. > > > I suggested a very simple test using the same torque wrench as Gene > > presumably uses now to tighten his collets to the correct torque to > > test the hypothesis. > > All 4 of my 5 torque wrenches are in foot/pounds. The smallest is in inch > pounds. How much is 75Nm, in inch pounds. > > > > > > But, assuming a 5mm pitch screw and 5:1 motor reduction: > > (0.5 Nm stepper * (2 * pi) / 5mm ) * 5:1 = 3kN. On the end of a 75mm > > arm that is 235Nm. > > Correct torque for an ER20 is 75Nm. > > That is no where near tight enough to keep it from walking out of the > collet and breaking the tool because its digging 3/8" on a cut that > should be 20 thou if it hadn't walked out. Here I use an end wrench > about 15" long, ground thin enough to fit the flats on the TTS holder, > and a 10 or 12" crescent wrench and a pull on the wrenches that is > likely in excess of 100 lb-ft. I don't have a newtom-meters to > pound-foot conversion handy but that certainly is tighter than 75Nm. > > Ditto if using an R8 directly, the R8 gets tightened with a 20 volt > electric impact wrench driving an 8 point 10mm socket a lot tighter than > I can draw it by hand with the supplied toy 10mm endwrench. If not, the > TTS in the R8 may slip and walk out. The life of that socket before it > splits might be 50 times, its hell on good quality sockets. > > > > (Though I am not convinced that an ER17 can really lift a 300kg mass, > > so suspect I messed something up. ) > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users
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