Re: [CAD_CAM_EDM_DRO] Re: Stupid Home SW location vs Limit SW locationquestion..

Actually, I used to 'indicate' some 'known' part of the jig or fixture, and
G92 that point for the new zero-zero-zero. Since production machines are
(well, should be) flexible enough to be able to run different parts
(fixtures), it'd be dificult to keep adjusting the homing switch to locate
some salient feature, each time you change a fixture. If you have a
toolchanger carousel on the right side of the machine, you might want
"HOME" to be in the N.W. corner of the table, to avoid the workpiece at
toolchange time.

RayHex

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> From: Jon Elson <elson@...>
>
>
>
> doug98105 wrote:
>
> >IMO, it makes no sense to put them anyplace except at the exteme
> >ends of travel. One of my commercial machines "homes" at the NE
> >corner, the other at the SW corner.
> >
> >
> One of the reasons for having home switches is to repeatably position
> the machine
> in the same place, relative to a fixture located for some time, or
> permanently, on
> the machine. On larger machines, thermal expansion can be a significant
> problem. If you locate your home switches far from the center of the
> machine's
> travel, then whatever errors develop due to thermal expansion between the
> home position and the part will cause the part to be cut with all

positions

> shifted by some amount. In a worst case, a very small part would be

totally

> unaffected by thermal errors itself, but its alignment with the fixture
> would
> be off. If your machine is in a well-regulated environment, that won't
> be a problem.
> But, in a basement or garage, there can be large temperature swings.
>
> If you put the home switch in the middle of travel, you halve the thermal
> errors, overall, but reduce the shifting of the fixture relative to the

home

> position by how close the fixture is to the home position.
>
> On some routers, etc. that have a fence built into 2 adjacent edges of
> the table,
> then the home position should probably be more toward the locating corner
> these provide. But, on a milling machine, where work is often located in
> a vise near the center of the table, then a central home would be best.