Interesting. Don't need switches for that but do need an index on the leadscrew.
> -----Original Message----- > From: Stuart Stevenson [mailto:stus...@gmail.com] > Sent: December-04-22 5:26 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Home switches for LinuxCNC on a Lathe > > You might try the FADAL mill method. > > They use two arrows (markers). One on the moving member and one on the > unmoving member. You physically align the arrows and run the home routine. > The next found index mark on the encoder is the home position. > > regards > Stuart > > > On Sun, Dec 4, 2022 at 1:25 AM gene heskett <ghesk...@shentel.net> wrote: > > > On 12/3/22 22:56, John Dammeyer wrote: > > >> > > >> From what I understand you're talking about a normal parallel lathe so > > here > > >> are my thoughts: > > > Yes. And thank you. > > >> > > >>> The Z axis is more interesting. Before homing I imagine the tail stock > > >>> has to be loosened and moved all the way to the right as far away from > > the > > >>> headstock to ensure finding a home switch. Or a home switch could be > > >>> somewhere in the middle but then which direction to search? > > >>> > > >> > > >> I think the safest setup in this case (given your Z axis can crash with > > >> the tailstock if you forget to move it all the way to the right) will be > > >> having the home switch towards the chuck side (with a proper > > >> independent limit switch right at the left of the home switch to avoid > > >> crashes when homing). This way you can set up your homing sequence to > > first > > >> home the X axis to move it to a safe place and then home the Z axis > > towards > > >> the chuck. > > > > > > I'm guessing you are suggesting something like what Gene was that the > > home switch isn't at the end of travel but somewhere else and once > > activated never goes inactive in that same direction. So if you start a > > home sequence and the switch is ON you know you have to go to the right > > until it goes OFF. It can't over travel past the OFF position and go ON > > again. That approach lets the Home Switch be pretty well anywhere. > > > > > > Unless the limit switch is movable it's useless. My carriage can go > > much further to the left to turn near the part held in the 5C collet than > > it can with the part held in the 3-Jaw. So a crash into the spinning 3-Jaw > > can happen without ever touching the limit. And if the limit does prevent > > that one can't turn a part close to the collet. > > > > > >> > > >> How does one determine, with that tool tip, where the lathe centerline > > is > > >>> and set that so G54 X is 0.000? > > >>> > > >> > > >> I think you're asking about tool setting. If you have tool fixtures that > > >> ensure that whenever you change your tool you get the exact same tool > > >> position then it's just like a CNC turret. You just take a skim cut on > > the > > >> diameter (or maybe use some fine paper to gauge the tool against the > > >> workpiece) and then measure and input the diameter (or radius depending > > if > > >> you're in G7 or G8) in the touch off popup. > > >> > > > Thanks. I'm going to have to study that a bit further. > > > I understand that the machine coordinate for x at the home switch is > > 0.000. > > > > > > And measuring the tool tip relative to how it mounts into the AXA holder > > can be done creating an offset from the home switch.v Now each time the > > tool holder +tool is put into the AXA the distance from the tool table is > > offset from that home position and LCNC knows where the tip and can turn a > > diameter. Theoretically. > > > > > > However as soon as the holder is pivoted even slightly the distance of > > the tool tip relative to the home switch changes. And it changes > > differently depending on how far the tool protrudes out of the AXA holder > > right? > > > > > > So the tool measurements are only useful with the AXA in one position > > and that can change really easily in the home shop. We're not talking a > > commercial production operation where the setup is the same over a long > > period of time. > > > > > > I suppose if you can touch of or measure the new position of the tool > > tip you can then use simple trig to determine the angle that the AXA holder > > has pivoted. Unless it also slid in the T-Slot which now moves it in more > > than one dimension. > > > > > > Doe my explanation make sense? A small shop lathe where the operator > > can shift the tool bit around relative to the X home switch and even on the > > carriage relative to the Z home switch suggest a tool table for a LCNC > > lathe is virtually impossible. > > > > > > So I can manually turn that shaft. Leave the X axis where it is and > > measure the diameter; say exactly 1.000". Then click on the "Touch Off" > > on the display and enter half the diameter (0.5") for the offset. > > > Now a request to move the X to 0.480" to do a 0.020" deep pass should > > work right? > > > > > > But the tool table and for that matter the home switch and machine > > coordinate system is pretty well useless. Or have I missed something? > > > > > > John > > > > > > > > Don't adjust your antenna, you got it, John, the reception is perfect. > > The main reason for a home sw is the let the machine know where its at > > in the absolute sense, I've surveyed my bed for wear, and corrected it > > with a lincurve/offset module combo. Rather satisfying to see the X > > motor turn a bit as the Z is scanned. But, its effect is determined by > > the absolute z position established by the home switch. It does not > > respond to z touch off, only to the real position. > > > > Threading to any std, or to one you've invented is nothing but arguments > > to the G76 routine. I've even abused G76 to make compression fittings > > > > The main advantage to cnc'ing a lathe is that its far faster at > > executing the move codes than you can squint at a dial and do it by hand > > in between cuts, it turns the crank in milliseconds and gets on with the > > job. > > > > With no compound, mine was broken beyond redemption by a fall over no > > one mentioned before I bought it, so LinuxCNC IS my compound, and far > > more accurate than you can turn a compound and set it, fraction of a > > degree several digits right of the decimal point with submicron errors > > can be done by LinuxCNC. W/o a compound. > > > > It is all done with 2 stepper/servo motors and a raspberry pi4b, and w/o > > a PID module anyplace. The driver does it all, including stopping > > LinuxCNC in a millisecond if a motor can't get to where it was told to > > go. I can set a stopped chuck jaw in the way, and program a .2" a second > > move into the chuck jaw, it touches the jaw and springs back about 10 > > thou as the drivers shut down, without marking the jaw, or damaging the > > carbide chip in the tool. Tested many times doing that, but it has yet > > to actually shut down a job. > > > > And if you want to step out of the way of burning swarf, the programs > > linear speed can be turned way up, w/o worrying about getting holes > > burnt in your clothes by white hot swarf. Carbide tooling is right at > > home with those temps, human skin isn't. Coolant would be nice, but this > > 80 year old Sheldon has no way to collect the coolant to reclaim it. > > > > 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, 1940) > > If we desire respect for the law, we must first make the law respectable. > > - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/> > > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > -- > Addressee is the intended audience. > If you are not the addressee then my consent is not given for you to read > this email furthermore it is my wish you would close this without saving or > reading, and cease and desist from saving or opening my private > correspondence. > Thank you for honoring my wish. > > _______________________________________________ > 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
