Re: Newbie - Help & Clarifications - Home and Limit Swtiches

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Blue" <jo001k1132@b...> wrote:

> Hi,
>
> What you are asking questions about is only one way of establishing

a datum

> from which a part is machined, however there is another which does

not use

> homing switches.
>
> If the edges of the blank are used as datum and then the G-Code is

written

> from this point then this datum would be the home position.
>
> I do all my programming from this point and have no use for limit or

homing

> switches.

<snip>


But the idea brings up an interesting point.

End switches are there to protect the machine. I am REALLY glad I
have mine as it has SAVED me tons of grief. Having jogged to 0.07 to
change a tool is way different than jogging to 7.0. hitting an end
switch just haults the motion and allows one to resume from there.

Also, loading a file for one project that has the datum point near one
axis offers a wide range of motion in one direction. with a datum
point in the middle, that range in that same direction is greatly reduced.

I too set my tool to some datum point and run from there. I am
curious if there is any value in the software knowing where it is as
compared to the limits ? kindal like a machine reference as compared
to a part references or something.

Say you have a 12" working envelope and set your zero in the center.
you can move 6 inches in any direction till it hits a stop.

but what if you load the next program and it wants to move 7 inches ?
if the software knew it was going out of bounds, it could do
something. alert the operator, pause, something.

Another idea is a 'soft' end switch. say your plasma table is set to
run to within an inch of the end of the table. the soft switch would
tell it either be more careful or slow down or some such.


Dave

ps: as for the 'no use for limit switches' I find that many home brew
machines can EASILY self destruct. A plasma/router with 800 ipm
rapids running a 250 pound gantry to an end-switch is bad enough, but
no switches could be more disasterous. I sure wouild not like to be
between it and a wall.

Small PCB etching/drilling machines often have more mechanical force
available from the screws than the table can withstand. Damage can
result.

Switches are there because people didn't want to break their hard work
or expensive machines.

One can ASS-U-ME that the servo's or steppers will stall before
damaging something, but we all know what that means.