Disabling the X- Y drives sounds fine to me. Let the gantry get taken for the ride. (assuming it's easily moved by hand with drives disabled) Once the nut is tight, reverse the carousel motor for a moment to undo the load. Then enable drives and do a Z up, then home the machine.
With a setup like this, homing after a toolchange would be prudent in any case. And it would only add a few seconds per tool. "Driving the carousel is an even worse idea. Then the diameter of the carousel becomes mechanical disadvantage" I don't agree. Driving the carousel is more akin to tightening with a hand wrench. Driving the gantry to do the same is probably beyond the ability of most small systems. On Thu, 18 Apr 2019 at 15:22, Todd Zuercher <to...@pgrahamdunn.com> wrote: > Driving the carousel is an even worse idea. Then the diameter of the > carousel becomes mechanical disadvantage and the subsequent moving of the > undriven x and y axis is guaranteed loss of position. > > Using the XY axis is probably the best option, for this kind of idea. But > I can think of several reasons the concept on a whole is a bad one. > > 1st My experience with collets is they, the tapers they fit in, and the > nut all need to be properly cleaned and inspected before reassembly and a > simple blast of air usually isn't good enough, especially if you are > milling wood products. > > 2nd Spindle bearing loading. This kind of tightening load is going to > directly load the spindle's bearings and will greatly reduce their service > life (at least on high speed router spindles like we are talking about > here). > > 3rd I think the potential of cross-threading or otherwise not starting the > nut right are too high to rely on this for auto tool changes. > > Todd Zuercher > P. Graham Dunn Inc. > 630 Henry Street > Dalton, Ohio 44618 > Phone: (330)828-2105ext. 2031 > > -----Original Message----- > From: Roland Jollivet <roland.jolli...@gmail.com> > Sent: Thursday, April 18, 2019 8:04 AM > To: Enhanced Machine Controller (EMC) <firstname.lastname@example.org> > Subject: [Emc-users] Something to think about re the hack-a-day tool > changer > > Sorry, guys, I really do understand how it works. I thought I was quite > clear.. > > That's why I said the l steppers 'drive' the carousel around. Notice the ' > '. Yes, to spell it out.... the motion of the X-Y steppers in a circular > motion results in the carousel rotating. The carousel rotates as a result > of the XY stepper motion....... > > The net result is that the carousel rotates while the nut is being > loosened. > The motive force for this to occur is the stepper motors. The carousel > itself is passive. > > This is a bad idea because; > - stiction can result in a much higher force to loosen the nut than > tighten it > - any lost steps in the stepper motors will result in a poor subsequent > trajectory, it will be fighting all the way > - there is no simple way to monitor the torque necessary, or applied. > > So... instead of using the steppers to effect the required action of > loosening the nut, rather move... the motive force to the carousel. > Visually the result is the same, but since the carousel is now DRIVEN > instead of just coasting around, the benifits are; > - geared DC motors of the required torque are readily available, or use a > windscreen wiper motor with a further reduction > - the motor current is easy to monitor > - disable the stepper drives so the gantry becomes passive and is pulled > around instead > - indexing of the carousel only needs a single switch to home it. > > Regards > Roland > > > > On Thu, 18 Apr 2019 at 13:50, andy pugh <bodge...@gmail.com> 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. > > > > 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. > > > > > > 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. > > > > (Though I am not convinced that an ER17 can really lift a 300kg mass, > > so suspect I messed something up. ) > > > > -- > > atp > > "A motorcycle is a bicycle with a pandemonium attachment and is > > designed for the especial use of mechanical geniuses, daredevils and > > lunatics." > > — George Fitch, Atlanta Constitution Newspaper, 1916 > > > > > > _______________________________________________ > > Emc-users mailing list > > Emcemail@example.com > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emcfirstname.lastname@example.org > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emcemail@example.com > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emcfirstname.lastname@example.org https://lists.sourceforge.net/lists/listinfo/emc-users