Hi,
you should not use Estop.....ever except in an emergency.
If you want to stop a program during a cut use <FeedHold>.
When you Estop the machine does an emergency shutdown, any moves in the motion buffer are deleted. Thus you lose reference, it maybe just a few steps but could be many steps.
Either way if you restart Mach those lost steps will interfere with the accuracy of your part, possibly even wreck it.
If you use <FeedHold> then the machine stops but only after it drains the motion buffer and decelerates to a stop......all without losing steps. From the time you hit <FeedHold>
until the machine stops depends on the motion buffer. The ESS has a default motion buffer of 180ms, so you can say that the machine will be stopped within 0.2 seconds,
which is pretty close to instantaneous. The advantage is that once your ready to start again you hit <CycleStart> an the machine starts from where it left-off but without any missing
steps.
Its been some years (8-9) since I used Mach3, and in fact don't even have a copy of it anymore, I use Mach4 instead, so I can't remember whether Mach3 has the ability to change or
program its behavior on <FeedHold>, it certainly does in Mach4. See the attached pic. You can choose whether a <FeedHold> stops the spindle and you can also choose whether a <CycleStart>
starts the spindle again after a <FeedHold>.
Craig