> -----Original Message----- > From: Phill C [mailto:[email protected]] > Sent: March-19-20 9:36 PM > To: linuxcnc-users > Subject: Re: [Emc-users] A hal question? > > > > > On 20 Mar 2020, at 3:24 pm, John Dammeyer <[email protected]> > wrote: > > > >>> > >>> But it's here where I become a bit confused. A 60 tooth gear at 1200 > >>> RPM produces 7200 edges per second or 1 about every 139 > microseconds. > >>> Say we're rigid tapping 8 threads which means a total of 57600 > >>> pulses. If the hardware counter is 16 bit signed that's larger than > >>> the 32767 before the counter rolls over. If it's a 32 bit counter > >>> it's not an issue. > >>> > >> I doubt if that would be a problem at 1200 because it would following > >> error out from Z not being able to move that fast. Probably before the > >> tap ever touched metal going in. Another problem would also rear its > >> ugly heard is that the overshoot at the bottom of the hole would likely > >> exceed the length of the tap at 1200. I got concerned about blind holes, > >> and despite the belts yelping like michelin tires on hot blacktop, the > >> overshoot at the bottom of the hole was over 3 turns at 300 rpms when > >> swinging an 8" 40 lb chuck with a workpiece in it. Trade my 1hp motor > >> for a 10 and a bigger vfd might speed up the turnaround but my place > >> isn't wired for that kind of power. > >> > >> So I have modified most of my rigid tap routines to tell me how many > >> turns and how far the overshoot is at that taps pitch and show me in the > >> gui. So I can cut clear to the bottom of the blind hole w/o breaking the > >> tap. > > > > > > Hi Gene > > I can understand that one has to factor accel and decel into the picture. > The spindle won't stop suddenly and won't start instantly either. So the Z > axis > tracks the decelerating spindle and that needs to be factored into the depth > of the hole of course. > > > > The same is true for threading up to a shoulder. > > > > I have a spring loaded tap holder so even if there's a little bit of error > > my > system will ultimately not break the tap. Plus in the near future my spindle > will be step/dir run with an AC servo so theoretically the tracking of Z > verses > rotation will be as good as the system can provide. > > > > But it doesn't answer my question on how it works with a spindle using 0- > 10V plus DIR for the spindle while using STEP/DIR for the Z axis. How is the > Z > coupled to the spindle when the control over deceleration, as you explained > about yours, is somewhat loose. > > I would assume that Z is �coupled" to the output of the spindle encoder and > that the count is reset at each index > <http://linuxcnc.org/docs/html/man/man9/encoder.9.html > <http://linuxcnc.org/docs/html/man/man9/encoder.9.html>> > This link is broken and Jon just mentioned that the index is only used once at the start of tracked motion. John
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