limit switch override

[swarfmacdaddy]

I was hoping someone might be able to answer a question. I am putting 6 limit switches on my mill, One for z -,one for z+,x-,x+,y-,y+. I am also using turbo cnc4.I want to put a override switch in line with all said switches. This way, when i have an over travel condition i can override it without killing power to motors. I also want to use same switches for homing in the future when turbo cnc supports this. I know i need to take one leg from each switch to the override switch but how do i keep the signal that is going back to the port seperate? If i put all 6 legs to the switch then the port will see any switching activity as coming from all the switches and i want to know what switch was tripped. Just one more problem, The turbo documentation states that pins 10,11,12,13, and 15 are input pins. Thats 5 pins and i have 6 switches. Help!!! Am i making this to complicated? Do i need to find a switch that has 6 isolated poles in and out? thanks for any help any one can shed on this.

[Bubba]

Randy,
I use V4.x and have 7 switches actually. Assuming you are going to use the switches in NC (Normally Closed) configuration, put the switches for each axis in series. Then when 4.01 comes out, you will be set for the home switch option. If you are planning on NO (Normally Open), put the switches in parallel.
As for the override, what I do is press the F8 key and in continious mode, back off the axis that is causing the problem. Be sure to toggle the limit switches OFF to be able to do this!
I agree with you, as I also miss the message that tells me WHICH axis is at fault, but it is not to much of a pain to simply look at the various axis and it is easy to tell which one has tripped. No need for a seperate override! Of course this is with my setup and breakout board, so YMMV
Bubba

[swarfmacdaddy]

Bubba, Thanks for the reply. One thing though,I am using the switches in normally open mode. Would i wire as such? All positive dir to one pin and all negative dir to another pin? So i would end up using just 2pins for the 6 switches?

[Torsten]

This used to be one of the oldest schemes I know of
used by Pinguin CNC - EMC.

All positiv sides on one Pin
All negative sides on a second Pin
All home and Probe signals on a 3rd Pin

All normaly open switches.
This will support a unlimited number of axses and uses only 3 Pins.

Unfortunatly a lot of Pc Controller programs do not support this.
I guess the Programmers did not fully understand the benefits
of this kind of arrangement.

Many went with switches assigned to each axes wich requires more Pins
when they realised this they also made them act as home swiches to
conserve Pins needed, also this required special handling in software that
will require another Pin if Probeing is allso needed.

Once a Software is released it is unlikely this could be changed.

I really like your Idea about a override swich this would take it out of
the hand of the software entirely.

In the end however you will have to conform to the standards used by
the software you want to run.
One way they can assure having loyal customers. :-)

[Bubba]

Randy,
If I were to use a scheme such as that, why not just series or parallel ALL the switches? Then you use only one pin for the limits as the machine will fault out if any one of them activates? Not to be a smart butt, but the machine can only fault out in one direction at a time!
As Torsten points out though, a lot depends on the software that you plan on using.

Again, I use TurboCNC and it can be configured either way NO or NC. Personally, I yet have seen a need to home all axes simutaneously (sp?) [strike that, it don't look right:})] so lets say all axes at the same time. This is where I worked with the team at TCNC to get the program changed. I had previously written the necessary changes for V3.2x to allow single axis homing under G-code and it works great. I'm not sure, but believe the Machx series of controllers also allow you to set up the limits to suit yourself. Other programs, I have not used so cannot comment on them.

Bubba

[swarfmacdaddy]

Bubb, and torsten, Thanks for all the help!! I got it set up right. I was just hoping i could use home and limits also but i guess turbo wont support both for now.