I've got a problem I cant seem to sort on my little DIY CNC router, my limit
switches don't work!


1) I've installed limit / end of travel switches on the x,y & z axes.
2) The switches are wired in series and wired to input 10 and enabled.
3) The switches are all normally closed, the input goes hi when switches
operate.
4) In diagnostics I can operate any of the switches manually & the program
senses it ok.

But.... when I jog any axis or run some code to move an axis, operating any
of the switches does nothing. I expected the motors to be disabled when I
operated a switch.

I've tried inverting the active level of the switches (ie hi/low active) and
have tried changing just about every other setting.

I've watched a couple of the mach3 videos (which have taught me a lot) but
cannot find out what the problem is.

Any clues guys?

thanks

In article ,
"Dennis" wrote:

I've got a problem I cant seem to sort on my little DIY CNC router, my limit
switches don't work!


1) I've installed limit / end of travel switches on the x,y & z axes.
2) The switches are wired in series and wired to input 10 and enabled.
3) The switches are all normally closed, the input goes hi when switches
operate.
4) In diagnostics I can operate any of the switches manually & the program
senses it ok.

But.... when I jog any axis or run some code to move an axis, operating any
of the switches does nothing. I expected the motors to be disabled when I
operated a switch.

I've tried inverting the active level of the switches (ie hi/low active) and
have tried changing just about every other setting.

I've watched a couple of the mach3 videos (which have taught me a lot) but
cannot find out what the problem is.

Any clues guys?

Yeah. Limit switches should cut the electrical power to the motors by
means of relays, not computers, precisely so confused CNC cannot break
the machine.

Joe Gwinn

On Sat, 24 Mar 2012 21:42:00 +0800, Dennis wrote:

I've got a problem I cant seem to sort on my little DIY CNC router, my
limit switches don't work!


1) I've installed limit / end of travel switches on the x,y & z axes. 2)
The switches are wired in series and wired to input 10 and enabled. 3)
The switches are all normally closed, the input goes hi when switches
operate.
4) In diagnostics I can operate any of the switches manually & the
program senses it ok.

But.... when I jog any axis or run some code to move an axis, operating
any of the switches does nothing. I expected the motors to be disabled
when I operated a switch.

I've tried inverting the active level of the switches (ie hi/low active)
and have tried changing just about every other setting.

I've watched a couple of the mach3 videos (which have taught me a lot)
but cannot find out what the problem is.

There are two reasons to put switches at known locations in the travel of
an axis:

1: to keep from crashing the axis into something hard.
2: to let the controller know where home is.

1 and 2 are two different things, and on anything high performance,
implementing 1 so you don't waste a whole bunch of travel is difficult or
impossible.

If your software is really using the switch as a _home_ switch and not a
_limit_ switch, then it will only pay attention to the switch when it is
homing -- and the homing algorithm will be something like "move the axis
toward the home switch at a known safe speed until the switch opens,
reverse direction and move _really slowly_ until the switch closes, then
call that spot 'zero'".

And, if your software is really _just_ using the switch as a home switch,
then it'll happily go "past zero" in normal operation.

Trying to implement a "don't crash" limit switch when you've got a motor
that takes a while to stop even at maximum opposite current is a pain in
the behind, because the mechanism _will_ keep moving for a while after
you slam on the brakes when its going fast, but if you approach the
switch slowly you'll need to power it in the desired direction to get it
to finish up. About the only way out of that quandary is to have a
normally-unused "shut-down lane" -- and who wants to pay for unused
travel in their machine?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On 2012-03-24, Dennis wrote:
I've got a problem I cant seem to sort on my little DIY CNC router, my limit
switches don't work!


1) I've installed limit / end of travel switches on the x,y & z axes.
2) The switches are wired in series and wired to input 10 and enabled.
3) The switches are all normally closed, the input goes hi when switches
operate.
4) In diagnostics I can operate any of the switches manually & the program
senses it ok.

But.... when I jog any axis or run some code to move an axis, operating any
of the switches does nothing. I expected the motors to be disabled when I
operated a switch.

I've tried inverting the active level of the switches (ie hi/low active) and
have tried changing just about every other setting.

I've watched a couple of the mach3 videos (which have taught me a lot) but
cannot find out what the problem is.

I don't know Mach3, and it is probably a configuration in there
somewhere. Something along the lines of "When you sense this -- STOP!",
instead of "When you sense this, make a note in a logfile or on the
screen and keep on truckin'. :-)

Or is there a "E-stop override" in Mach3 somewhere? Could this
be engaged?

But first -- are you using steppers or servos? Steppers stop as
soon as the computer stops talking to them. Servos keep moving at the
last commanded speed until the computer says to change to zero inches
per second (0 V command input to the servo amp).

And in either case, the stepper driver or the servo amp should
have a separate input to inhibit motion. This really should be
connected. (Some servo amps have separate inputs to inhibit motion in
the two directions, so you can have two limit switches, and still be
able to feed it commands to back it off the limit switch. It would
proably be easy enough to add those to stepper drivers too, if they
don't already exist.) The "stop in any direction" input connects to
the E-stop red mushroom button.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2012-03-24, Dennis wrote:
I've got a problem I cant seem to sort on my little DIY CNC router,
my limit switches don't work!

Did you start here?

http://www.machsupport.com/docs/Mach...all_Config.pdf

Lloyd

There is a difference between home switches (used for homing, which
means precisely determining the coordinate system), and limit
switches, which are used to activate the E-stop relay. The best
practice is not to combine these functionalities in one.

i

On Mon, 26 Mar 2012 14:07:32 +0800, "Dennis"
wrote:


"Dennis" wrote in message
.au...
I've got a problem I cant seem to sort on my little DIY CNC router, my
limit switches don't work!



Many thanks for all the suggestions guys - for now I've given up!

The switches work and the software senses them in diagnostics mode but
I cannot get them to work as limit / end of travel switches.

My machine is generally working & other issues like getting a better spindle
than the existing Dremel are higher priority at the moment.

Cheers


When you ask something again, I'd consider a forum with a large Mach3
user base. CNCzone.com is one example.

Karl

"Karl Townsend" wrote in message
...
On Mon, 26 Mar 2012 14:07:32 +0800, "Dennis"
wrote:


"Dennis" wrote in message
m.au...
I've got a problem I cant seem to sort on my little DIY CNC router, my
limit switches don't work!



Many thanks for all the suggestions guys - for now I've given up!

The switches work and the software senses them in diagnostics mode but
I cannot get them to work as limit / end of travel switches.

My machine is generally working & other issues like getting a better
spindle
than the existing Dremel are higher priority at the moment.

Cheers


When you ask something again, I'd consider a forum with a large Mach3
user base. CNCzone.com is one example.

Karl


Thanks Karl, I will.

not@home wrote in message
...
On Mon, 26 Mar 2012 03:18:36 -0500, Karl Townsend
wrote:

On Mon, 26 Mar 2012 14:07:32 +0800, "Dennis"
wrote:


"Dennis" wrote in message
om.au...
I've got a problem I cant seem to sort on my little DIY CNC router, my
limit switches don't work!



Many thanks for all the suggestions guys - for now I've given up!

The switches work and the software senses them in diagnostics mode but
I cannot get them to work as limit / end of travel switches.

My machine is generally working & other issues like getting a better
spindle
than the existing Dremel are higher priority at the moment.

Cheers


When you ask something again, I'd consider a forum with a large Mach3
user base. CNCzone.com is one example.


or the machsupport group

Thanks