Re: E-Stop Revisited (PS on sherline auto changer)

Peter,

On small "desktop" machines, here's what I do:

As soon as the estop is pressed; I cut spindle power(with a "hockey
puck" SSR), drop power to the optos so the steps stop getting to the
drives, begin a timing circuit set to the worst case spindle run down
time, and raise the voltage to a "1" on the estop signal line going
to the computer.

Now the spindle is winding down, held in place by the still active
drives, and the computer has been "notified" that we have a problem
out here...

When the timer times out, I can assume the spindle is no longer
turning, so the enable for the drives is turned off, allowing free
movement of the motors. For machines going to others, I add
some "cool down" time before allowing the reset... (cool down for the
operator, not the machine<G>)

There are three steps to reset the hardware:

First, release the big red button. Then (after the cool down period)
press an "enable drives" reset (enables the axis drives, allowing
jogs once the control s/w has been reset). Next a separate button
resets the A/C (spindle is enabled, but if the control program has
done its job, the line from the computer controlling the spindle is
held down, preventing it from turning on. On a large machine, this
would be unacceptable,IMO. One would add a drop-out relay to prevent
the spindle from turning on, even if the control failed to shut down
properly.)

This takes care of all emergencies, EXCEPT electrical
(electrocution). On a small desktop machine, I feel this is adequate
protection as IMO, an electrical emergency is less likely than a
mechanical or positioning one.

(But my machines don't have wires running willy-nilly all over the
place like some I've seen! On some of those, one would be wise to
consider the possibility of the spindle cutting its own cord!)

In any event, The power switch is next to the estop on my control
box, and the box is convenient to the operator, so IF the electricity
needs turned off, it can be done rather rapidly.

Hope this helps,

Ballendo

P.S. I'm still dealing with the devil in the details on the Sherline
auto changer, so I'm not ready to commit to even a ballpark number,
except to say less than a kilobuck<G> And I can say for sure that air
is definitely helpful to the path I've chosen, tho' a fully
electrical version should still be possible. But like I said before,
it will be slower, cost more, and be harder to make. But we're
talking a "Sherline sized" compressor; something like a Gast or
Thomas type as used in hospitals... (of course if ya have a big ol'
honkin' compressor, that'd work too!)

Good news is, I think I CAN accomodate the flycutter, boring head,
and drill chuck. But its still early in the process...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Peter Cruickshank
<crankshaft_sg@y...>" <crankshaft_sg@y...> wrote:

> Hi;
>
> Ok, what's the conclusion on the E-Stop issue, should the big red
> button cut power to everything, or is s soft-stop good enough !
>
> I know that there are different opinons on this, but for the

general

> hme hobyist CNCer with a Sherline 5410, What's the recommendation ?
>
> Cheers
>
> PeterC