On Wednesday 28 August 2019 23:18:28 John Dammeyer wrote: > Yeah the backlash is pretty bad but even back in May 2007 when I > bought it the cost for all that mass was quite low. Now Grizzly > doesn't even sell that model anymore and the closest unit is almost > double. Add an exchange rate of over 30% and installing ball screws > will be cheap and has always been in the plans. > > I bought mine in Canada from House of Tools which is no longer around. > But this link will get you to it at Grizzly > https://www.grizzly.com/search?q=(g3616) > And the spec sheet doesn't list backlash. And backlash above 10 thou can get quickly messy. And those screws aren't Nooks. I'd be looking for a ball screw kit on fleabay. That will reduce the backlash to around a thou and things will be much happier. They will also need 5% of the motor torque to turn them compared to the acme or square thread screws in it now.
> > -----Original Message----- > > From: Sam Sokolik [mailto:samco...@gmail.com] > > Sent: August-28-19 7:52 PM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] MESA 7i92H Saga > > > > You must have a substantial amount of backlash? The backlash is > > taken out at max axis acceleration. that is why you need to have 2X > > acc for the stepgen_maxaccel. There is a chance that the axis > > could be accelerating and the backlash taken out at the same time > > causing 2x the acceleration being sent to the stepgens. > > > > On Wed, Aug 28, 2019 at 9:24 PM John Dammeyer > > <jo...@autoartisans.com> > > > > wrote: > > > Gene, > > > > > > You've got it backwards. The parallel port version is correct > > > which is why that line is there. > > > > > > > > setp parport.0.pin-07-out-invert 1 > > > > > > > > remove the above line, or set it false > > > > > > > > > net zdir => parport.0.pin-07-out > > > > > > Peter Wallace suggested I do this: > > > "If you are using LinuxCNC 2.8 you can set the stepgens dir > > > polarity parameter." > > > > > > Can't find a "dir polarity" parameter here: > > > http://linuxcnc.org/docs/html/drivers/hostmot2.html#_parameters_3 > > > > > > However there is an "invert_output" parameter . Still nothing I > > > can find online really guides me in the direction of doing it with > > > port inversion or how to use that invert_output since the dmesg > > > instructions in the above > > > > web > > > > > link don't help. > > > > > > However the other suggestion from Peter which was to set the > > > stepgen > > > > scale > > > > > to minus. Did that to both Z and Y axis and now homing works. > > > > > > I suspect because the parallel port implementation always reported > > > "unexpected real time delay" on start-up that it wasn't able to > > > actually keep up with the acceleration parameters in the .ini > > > file. Now with the 7i92H, the acceleration on the Z axis is way > > > too high for the Gecko run stepper motor. It's not losing steps > > > but doesn't sound happy. A bit of tweaking with values and it's > > > much smoother. > > > > > > I've also played around with the Y axis acceleration since it too > > > has a lot of mass to move; not only the X axis but also the X axis > > > table rotation mass. That's why the DC Servo has 4:1 instead of > > > 3:1 reduction like the X. Max ipm is therefore 120ipm for Y and > > > 150ipm for X. For the knee with the Gecko and 3:1 to the bevel > > > gear I get 24ipm. Any higher > > > > than > > > > > that and the stepper will skip. > > > > > > The backlash compensation is also far harsher. A series of jogs > > > in the same direction create almost no vibration on the head of > > > the mill (hand placed against it) but change direction and my hand > > > feels the bump as the backlash is first taken up. This was > > > especially noticeable on the knee with the slight bevel gear > > > connection to the knee screw until I dropped acceleration to a > > > much lower value than I had on the parallel port version. > > > > > > The 7i92H requires the STEPGEN_MAXACCEL to be double the > > > MAX_ACCELERATION. Setting it lower than that caused strange > > > motion problems so I suspect the only way to get rid of the hard > > > bump as backlash is taken out is to also reduce axis acceleration. > > > > > > Or buy ball screws which is on the list... > > > > > > John > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis 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
