The basic idea behind it is simple. Especially with 4 quadrants. So every 90 degrees a new arc movement is issued. The starting place is where we are. The arc has a larger radius since we're creating a spiral. The size of the new arc radius and it's position is set up so the tool remains at the specified WOC (Width Of Cut).
So where the IJ method shines is that if you set I and J up as offsets from the current position based on the new radius of the larger curve you can position the end point to be 90 degrees further around and engaged at say 40% of the tool diameter. And so on. The last pass in Jon's code then does a standard, non-changing center point with a slower feed and engagement WOC. I've not yet done the math to figure out why the radius is out by as much as 25% for starting and ending position. It doesn't actually make sense. The system doesn't know it's dong a spiral. It only knows where it is and that it needs to be at a new XY position and it does that following a curve defined by a radius. If it uses the start XY location to determine the radius point then it's possible that the end location won't match or the other way around. So perhaps MACH3 uses the end XY while Linux CNC expects the start and end XY to match given the center point of the arc via the I,J parameters. Totally different philosophy. Going to have to do some sketching on the CAD system to get my head around this. John > -----Original Message----- > From: Phillip Carter [mailto:phillcarte...@gmail.com] > Sent: September-23-19 4:05 PM > To: linuxcnc-users-list > Subject: Re: [Emc-users] G-Code issue with IJ > > I did the same as Chris and the end points are quite a ways off. > > I put a G21 at the top of the code and it loaded but if you zoom in it is an > ugly > spiral. > > > On 24 Sep 2019, at 1:29 am, Chris Kelley <tensait...@gmail.com> wrote: > > > > I plotted out that snippet of code in AutoCAD and the coded arcs don't line > > up with the end points. > > > > I'm not great with C but looking through Jon's code I wonder if it has > > something to do with how it will never output an arc with both I and J > > coordinates. > > > > I have no idea why Mach3 will run it, perhaps Mach has a much wider > > tolerance for arc-center-end-point mismatch or it is just converting the > > tiny arc moves to lines. > > > > On Mon, Sep 23, 2019 at 4:01 AM andy pugh <bodge...@gmail.com> > wrote: > > > >> On Mon, 23 Sep 2019 at 05:29, John Dammeyer > <jo...@autoartisans.com> > >> wrote: > >> > >>> > >>> The attached screen shot shows that LinuxCNC chokes on this. > Suggestions > >>> as to why? > >> > >> > >> Are you definitely in the right plane? > >> > >> Possibly tool diameter compensation is active? > >> > >> -- > >> 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 > >> 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
