Re: [CAD_CAM_EDM_DRO] ENC coordinate systems

John Murphy wrote:

>
> I'm working on setting up a benchtop mill with EMC. Can anybody
> suggest resources for dxf to NC tool generation? Also, I'm interested
>
> in determining coordinate systems for standard NC (EMC). (i.e. I'm
> trying to figure out how I need to set up +x, +y, and +z to work with
> standard NC output? Is z=0 essentially the endmill at it's lowest
> setting, and z=3 three inches off of the surface? I'm still
> figuring this out, but was hoping for some insight.

These coordinates are relative to the part, not the machine. So, on a
conventional
milling machine, the table moves LEFT for +X, and right for -X. This,
of course,
makes the tool move RIGHT, from the part's perspective, for a +X move.
Toward the machine's base (away from operator) on the part, is +Y.
UP is +Z. You can set the zero reference anywhere you want. Often you
would set Z=0 with the tool touching whatever the part is on, but
sometimes
it is easier to touch off the tool on the top of the part, and then have
all work
done in -Z coordinates. To some extent, this depends on whether the top

or bottom of the part is the reference surface that matters. For
instance, if
the bottom of the part will be machined away later, then the top might
be the
reference surface to use.

>
> When I draw/generate my NC files (probably camexpert under linux with
> some hand editing to better support Z axis movements), How do I set my
>
> origin? I'm guessing I should match up 0,0 (x,y) in my drawing with
> a matching 0,0 position for the mill. Any suggestions here
> for linux based solutions would be great, I don't have windows).

You usually make some easily defined point on the part (like the lower
left
corner, as viewed from the top) as the XY reference. If the part
already has
a hole in it, the center of that hole can be the reference. An edge
finder
can be used to align the machine to the edge of a part. Do it twice and
you
are aligned to a corner.

> Each time I do a run, would I "locate" 0,0,0 for the mill, or can I
> use
> home switches (are magnetic switches accurage enough, do I need to use
>
> IR?).

If you have home switches, EMC can remember a fixture's offset from the
machine
home position. Then, every time you start EMC, you home the axes, and
the
offset you last used is automatically reestablished. I really have to
hook up my
home switches soon!

Jon