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Limit switch issues
« on: December 25, 2015, 05:14:08 AM »
From the 1000's of threads here there may be an answer already, but after searching I have read all kinds of issues, but not one like mine....

7 years ago I purchased a POS machine from Thom Carr Company. At the time I knew how to operate a CNC, but not how to build one, or very much on how they actually operate. I've since learned a tremendous amount.

From the very first day I turned on the machine after connecting it to the computer, when homing, jogging, or during a program run, the limit switches didn't stop the various steppers from trying to drive the gantry into the netherworld.....I contacted the manufacturer and he poo pooed me and said they only work when homing...I thought at the time: well that doesn't make sense, that's like saying the brakes on your car will only work when it's in drive.....I should have listened to my gut.

I also asked about setting the home switches to the opposite end of the Y axis, he said "you don't want to do that"...why I asked? he never answered..."you just don't"....

Anyhow, I met a guy who also has a CNC and he came over to check out mine, I showed him the issue with the limit switches and he says "limit switches are supposed to stop the travel of the axis period..."

SO, here's my question:

how to correct this? lol......and is this true? that limit/homing switches are only designed to work when you hit the ref all home button? That when you jog, or run a program, they don't?

Offline olf20

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Re: Limit switch issues
« Reply #1 on: December 25, 2015, 07:44:45 AM »
I'll start out with the basics that I learned in the manual.
Limit switches are a must!!! Good ones that are sealed
in some way.
Wiring must be shielded with the shield wire grounded only
at one end. Usually in the cabinet.
Limit switches can and are used as limit and homing.
When a machine is homed the switches will act as homing
limits in sequence. I believe z is 1st, y is 2nd, and x is last.
After homing then the switches are limit of travel.
I know its a little confusing when setting them up but
remember the above and you will be able to sort out
the problems.
The Mach3 manual covers this very well.
Others will chime in and offer some more info.
olf20 / Bob
Mach3, Atlas Knee Mill, 4th Axis, VcarvePro, ESS, Super PID.
Been Heating with corn since 1998

Offline ger21

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Re: Limit switch issues
« Reply #2 on: December 25, 2015, 07:52:44 AM »
Go to Config > Ports and Pins > Input Pins, and see if the limits (X++, X--, etc.) are enabled.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Limit switch issues
« Reply #3 on: December 25, 2015, 10:41:53 AM »
I'll check out the shielding.....and the manual.....and to see if they are enabled x++ x--

They do "kind of sort of" work because when I hit reference all home, the z raises, then the x moves to the left and then the Y...instead of having my gantry move 48" away, I'll hit stop and then z will try to raise the carriage to 20 feet above the table.....and they never work when jogging or during a program run that had a value higher than the limit.

Just typing this out: I wonder if the maker wired them ONLY had homing switches NOT limit switches...that would account for them ONLY working during a homing operation.....
Re: Limit switch issues
« Reply #4 on: December 25, 2015, 11:26:09 AM »
Ok, this explains one issue to me: (which reinforces my concept that the people who wrote Mach3 were monkeys):

"Note that although Mach3 uses limited jogging speed, choice of direction is entirely up to you. Nothing
will prevent you, in either case, from jogging farther onto the switch and possibly crashing the axis
into a mechanical stop. Take great care."

This means that a limit switch or homing switch has no effect on the movements when jogging....so in other words, comparing it to the steering wheel on a car, if you don't start the motor of the car, you can turn the steering wheel past the limits and destroy the front end of your car....NICE! This is normally the point where I'd like to ask the people who wrote Mach3: what the hell were you thinking?
Re: Limit switch issues
« Reply #5 on: December 25, 2015, 11:56:40 AM »
You are clearly not comprehending what you are reading.
Slow down, take your time and pay closer attention to the details and it should become much clearer for you.
Otherwise, there are folks here more than happy to help you through it.

 Kind regards,
Russ

Offline ger21

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Re: Limit switch issues
« Reply #6 on: December 25, 2015, 11:59:38 AM »
Ok, this explains one issue to me: (which reinforces my concept that the people who wrote Mach3 were monkeys):


No.

When you jog into a limit switch, the machine will stop. What the quoted text refers to is AFTER the machine stops. At that point, it's up to you to jog it in the correct direction to get it off of the switch.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline BR549

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Re: Limit switch issues
« Reply #7 on: December 25, 2015, 12:06:25 PM »
That is NOT what that means. It simply mean that IF you hit a limit and mach3 stops YOU must be carefull about what direction you tell Mach3 to go in to back off the switch.  After you override the limit switch function to back off you can move in any direction. It is up to YOU to move in the correct direction to properly back off the switch.

The first thing you need to learn is to program the machine to stay inside of the table boundaries  . You cannot cut a 12 inch part with a 10 inch table boundary. And you must center your work inside of the boundary.

After you get that pounded into your head you will never touch a limit switch (;-).

As to switch functions there are Homing functions AND there are limit functions. They can USE the exact same switch. How they react depends on what mode the switch sees when it trips.  IF the switches are only setup as home switches THEN they will NEVER work as limit switches. and vise versa.

One thing you must understand about CNC is that the machine is basically as dumb as a box of rocks. It is ONLY as smart as teh person programing or driving it.  THAT is what makes the learning curve so steep. You have to learn about 3 disiplines at the same time in order to use it.

Best to take your time and learn one step at a time. Patience is the key word here. Reading and studying is the next important step. AFTER that it becomes a piece of cake and YOU become a geewiz and will have a ball working with it.  BUT without the learning period you are simply DOOMED to a world of frustration.



Re: Limit switch issues
« Reply #8 on: December 25, 2015, 12:30:57 PM »
"One thing you must understand about CNC is that the machine is basically as dumb as a box of rocks." truer words have never been spoken my friend! lol I learned that a LONG time ago....

My biggest issue with CNC and Mach3 in particular, is this is one area that never caught on to the KISS idea of life....(keep it simple stupid)....just about every other industry learned long ago that to progress, they had to drop the "trade talk" terminology that was like greek to everyone else....Take the auto industry: they don't call the things that stop your car: hydraulic lever actuated rotational halting devices, they call them brakes.

The thing that kills me the most about Mach3? The fact that you can hit "start" to start your program run...AND THE CNC ISN'T ACTUALLY TURNED ON! LOL....I haven't tried it, but I bet Mach3 will run, even if a CNC isn't connected to the computer!

(rant over lol)

The thing that kills me too about the "limit" switches? you shouldn't be able to jog PAST the limit switch once the limit is set. No ifs ands or buts about it. That is why the limit switch is there. Or does that make too much sense? Kind of like the rotational movement halting devices on your car.....if you press the brake pedal to stop the car the car stops. If you press harder you can blow all the hydraulic lines in the system OR force the pads through the disc and sheer the wheel assembly right off your vehicle....

Offline BR549

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Re: Limit switch issues
« Reply #9 on: December 25, 2015, 12:53:39 PM »
mIke the main problem you have is YOU are expecting the machine to do everything to protect itself from YOU (;-) That is not going to happen unless you program it to do so.

Yes Mach3 will run without the Machine turned on and so will just about every other CNC controller in the world UNLESS it was setup NOT to. You CAN set up Mach3 to do so as well. By the way that is called a feature not a defect ( offline/online)

The CNC world is NOT going to change to suite your mentality. It has been using the same terminoligy for about 50 years now.  The thinking has been IF you are not smart enough or willing enough to be able to LEARN the trade then it is best you take up Golf or knitting BUT bewarned THEY have their own unique terminoligy as well , Knit 1 pearl 2(;-). Besides the functions are NOT as exagerated as you make them.  A car brake and a CNC machine brake are the same thing (;-) .

When you learn to conform to the CNC world and NOT expect it to conform to you THEN you will start having Fun with it.

(;-) TP