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

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.

Jon