Re: G53-57 was Re: Need Zero Help!!

Hi Ray,

Thanks for the comments.

By "alias", I'm referring to an association between T1 and say G54, T2
and G55, etc. But I could have that all wrong! I don't remember where
it was (could have been another controller program's documentation).

G92 sounds more like it is a "relative" offset.

I'll have to give this some more study.

Alan KM6VV


Ray Henry wrote:

>
> Hi Alan
>
> Comments mixed in
>
> > From: Alan Marconett KM6VV <KM6VV@...>
> > Subject: Re: G53-57 was Re: Need Zero Help!!
> >
> > Thanks Ray,
> >
> > I'd like to understand the use of G53-57 (fixture offsets) a little
> > better. The handbook has a little data. I got that G53 is machine
> > coordinates, and G54-57 are work coordinates (and that they alias to
> > T0-4?).
>
> I'm lost by the alias stuff but g53 is supposed to always be close to the
> zero position where EMC sets itself when you home your machine.
>
> This zero need not be where the switches are located but where you tell
> the program you want zero to be using the variables
>
> HOME = 0 0 0
> HOME_OFFSET = 0.0
>
> in each axis of the ini file.
>
> > so are they just saving AXYZ offsets (and tool comps?), which are then
> > added to the machine coordinates? Or is there more to it then that?
>
> That's exactly it. And these offsets are saved to the var file when you
> shut down so they are there when you start up again.
>
> For a bit of extra insurance, I wrote the Set_Coordinates.tcl script so
> that it writes them as you press <write> to set them. And after watching
> David Munro work with his bridgeport, I decided that we needed separate
> teach buttons for each axis. This way you can use one of those little
> ball nosed edge finders on each side of a corner of stock or the corner
> of your vice and capture each axis when you're ready. (I do need to add
> an automatic size offset for this.)
>
> > If I do G92 in "G53", this sets the machine coordinates; then if I
> > reposition to a new fixture, do I issue G54 and then G92 again?
>
> Quick answer is no because the g92 is still active. To deactivate it you
> would have to set zero position back to g92 0 or issue a g92.1 or g92.2.
>
> Let me take a minute and sort out two things. Setting the value of g92
> by itself and using it with other offsets. And then setting g92 with
> other offsets already active. For all of these examples I will use
>
> g55 offsets are x1 y1 z-2
> g56 offsets are x3 y1 z-3
>
> Actual distance to first side is -3.106
>
> I flip this part when complete into the second holder.
>
> Actual distance to second side is -4.106
>
> You need to work here with a great deal of caution because G92 will add
> or subtract an amount from all of the existing coordinate systems. I'll
> use BDI-TNG because I can sit here and surf, write this and run EMC all
> at the same time. (shameless plug for a product I sell)
>
> G92 is not real intuitive. For example if I drop z to where I'm about
> ready for the first surface cut (-3.1060) and right click the z display
> it will popup a widget that contains the value 0.0. If I press enter or
> ok it sets that axis position to zero by creating a work offset of z
> -3.106.
>
> As an aside, I could have put a value (2.0) in that popup rather than
> accepting the 0.0 and it would have computed the real g92 offset from the
> difference between the value I typed in and the current position of z.
> In this case using the previous distance of -3.106 the value 2 gave me a
> z -5.106 offset. In effect I told it that I wanted this place, -3.106,
> to be +2 and it did exactly that. This can be a killer!
>
> Whenever you set a g92 it adds itself to whatever offsets are already in
> g54-g59.3 when you activate them. If I'm using the g55 and g56 values
> above, and without thinking, ran the tool down and set g92. If my
> program called for a g55 at the start, where am I going to find the tool
> working? Well its down there among the ballscrews and gears again. The
> g55 will put it at -5.106 while the g56 will put it at -6.106.
>
> Now if I happen to have g55 g0 x0 y0 z0 already active when I position my
> endmill and right click to set a g92, I will get a different offset.
> >From here (z-2 but zero on the display) I again drop the tool in z until
> it is about ready to cut, (-1.106) click the display and set zero. The
> work offsets say that I've got -3.106 set for z. Now 2" was already
> apportioned to the existing g55 and g92 is set to -1.106. Now g56's work
> offset is -4.106. They are right where I wanted them.
>
> > After that, I should be able to switch "fixtures" by a G54-57 ?
>
> Yep! Only you can use all ten of them.
>
> Ray