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Author Topic: Confusion with 'Homing and Limit switches"  (Read 1917 times)

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Confusion with 'Homing and Limit switches"
« on: January 30, 2015, 09:09:05 PM »
Hi all, Just to set the scene....

I am fairly new to all this cnc stuff so please bear with me if can while I try and explain my dilemma.

After home building a very small MDF machine, I eventually purchased a Marchant Dice A4 sized machine as the MDF job wasn't really accurate enough. This came equipped with proximity sensors on only one end of each of the three axes (X,Y and Z).  However, I didn't buy the controls for the machine from Marchant Dice (they make their own PS/BOB/Driverboard all packed into a nice box which costs a lot of money...) as I had built my own driver board from a kit from HobbyCNC.

I have this now all wired up and everything appears to work superbly - I have cut several successful jobs now (after a steep learning curve) mainly using LinuxCNC. I am now dipping my toes in the water trying out Mach3 - which I am very impressed with so far - many more options when compared with the somewhat clunky (by comparison) linux setup. Never liked linux much to be truthful, it's just too different from Windows for me really.

Anyway, I have found that I am having a problem with the proximity switches insofar as - my reading of the Mach Manual suggests that these switches can/may/will - also act as limit switches.  My understanding of that means that, in the event of one of these switches being triggered whilst running a program, the machine should stop - in much the same way as if I had hit the E-Stop switch.

For me, this is not happening.  As I am using a trial version of Mach, I can't run large programs but even on very short instructions via the MDI screen I can easily over-ride the proximity switch (which does trigger) and crash the Z Carriage into the Y support.

On the other hand, I can do a 'Ref All Home' from the program screen in Mach and everything works perfectly - consistantly and with surprising accuracy. I am at a bit of a loss now as to why they don't stop the machine when it is clearly about to come off the rails!

If it has any bearing on the matter, I have the proximity switches wired to pin10 on the HobbyCNC board and the E-Stop wired to pin13.

I'm sure someone has come across this before - and it's more than likely I am being stupid - but I have to say that it is beginning to drive me around the twist trying to figure out why it works when 'Homing' but doesn't do so when it's an emergency while running code?

Can anybody help me out here.... :-\?

Offline ger21

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Re: Confusion with 'Homing and Limit switches"
« Reply #1 on: January 30, 2015, 09:21:09 PM »
In ports and pins > Input pins, you have to set up the switches for both home and limits. Basically, you need to define the switches twice.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Confusion with 'Homing and Limit switches"
« Reply #2 on: January 31, 2015, 08:04:02 AM »
Many thanks for that ger21 - much appreciated.  Have done as you suggested and all appears to work as expected now.

It has (as seems to be normal for me at least) raised another question. Once a trigger is activated, on whichever axis has been activated, I cannot re-set the the E-stop warning message sayng that the E-stop has been activated in order to 'move off' the activated switch - the motors are still being powered and I have to turn off the supply to be able to move them.  Is this normal with Mach3?

I suppose I could do that - and then do a 'GoTo Zero' followed by the 'Ref All Home' button to bring the machine back to its original zero - but it seems a long way round so that the coordinates are returned to a known point.  Its almost like an 'Override' button would be useful just to allow movement of the actvated swutch to be reversed thus allowing the DRO's to mantain their correct relationship - or am I just missing some other little undocumentd trick in Mach3?

willower

Offline ger21

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Re: Confusion with 'Homing and Limit switches"
« Reply #3 on: January 31, 2015, 10:13:47 AM »
On the settings or diagnostic page, there are two limit overrides. manual and automatic. Activate one and you'll be able to reset and jog off the switch.

When you hit a switch, mach3 loses position, so you'll have to Home again.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Confusion with 'Homing and Limit switches"
« Reply #4 on: January 31, 2015, 12:19:51 PM »
What can I say ger21, you are the man - without doubt!!!

I have been struggling with this for  a couple of days now, one post here and all is solved. The whole setup of the machine is sorted now, everything works the way it should. I bow to your vast knowledge of this program, you clearly have a lot of hours on your log-book that's for sure.

I really appreciate the all help that you have given me on this - i've read many of the other posts that you have made on this Forum - a lot of which have already helped me previously when I first started looking at Mach3 to possibly replace the ugly looking Linux setup that I have run prior to this.

It's now onwards and upwards as they say - I'll now try  a few small cutting excercises to get a feel of the program properly and will make the final choice when I see how things turn out in reality.

Once again, a thousand thanks for your support....

willower