Re: DIFFERENCE BETWEEN G90 & G91?

--- In CAD_CAM_EDM_DRO@y..., Fitch R. Williams <frwillia@m...> wrote:

> On Tue, 22 Jan 2002 00:48:09 -0000, "yethdear0" <yethdear0@y...>
> wrote:
>
> >Most machines "wake" up in G90 mode.
>

Safety blocks...

>. It seems to reduce
> the number of surprises I get.
>

While most machines wake up in G90, if you stop them in mid stream,
they may think that they are still in incremental, and the next time
you start the program. ###$$$*** Kerbango. That's why those safety
blocks are a good practice. Even though you may only have this
happen once a year, it's better to never go Kerbango and have a few
extra lines of code in every program.

If you program multiple tools, it is a good idea to put nearly the
same set of safety blocks before and after each tool change. It does
not improve the sequential safety of the program, but it enables you
to safely start in mid program at any tool within the process.

G91 incremental is useful for a situation in which you want to make a
number of copies of the same set of cutting moves, say 6 pockets in a
2 x 3 array. You can program an absolute move to each of the 6
absolute locations and then re-use the same chunk of G-code for each
pocket, in incremental mode. Each pocket will be relative to the
absolute position. You can also use a G92 to reset your Zero point
at each location, but a mid program start may lose your location (
not good). Using one set of absolute locations and then relatively
cutting around each one can be reset and not lose location. Just
remember the G90 at the beginning of the program, and at the end of
each relative G91 subroutine call.

Best Regards, Fred Smith- IMService

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