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Moving off Limit switch
« on: May 06, 2008, 12:53:17 PM »
I put 4 limit switch (X++, X--, Y++ and Y--) on my CNC router, but for example: If X++ is triggered the RESET button starts to blink and I can't move to X- for moving off the limit switch?
I read the past posts and someone told to turn on the Limit override, but this is not good because when LIMIT OVERRIDE is on the X axis move + and - destroying the limit switch. ( If X++ limit switch is trigger the X axis cannot move to X++)

Is there a way to move off the limit switch without turn on the LIMIT OVERRIDE? ???

Offline Chip

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Re: Moving off Limit switch
« Reply #1 on: May 06, 2008, 01:23:53 PM »
Hi, Daniel

Selecting Limit Override is just to move off the Limit Switch then you turn it back Off.

Thanks , Chip

Offline jimpinder

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Re: Moving off Limit switch
« Reply #2 on: May 06, 2008, 01:23:56 PM »
If you select the Settings Page and tick Auto Limit Override - this will allow you to back off the switch.

Without being pedantic, you shouldn't make a habit of hitting them - you can set your soft limits to avoid it. The limits are there as a last resort.

Yes - you are right - if you turn off the limits - your switches get wiped out, which happened to me a time or two. My limit switches are now laser beams shining on detectors - which avoids the crunch.
Not me driving the engine - I'm better looking.
Re: Moving off Limit switch
« Reply #3 on: May 06, 2008, 01:59:52 PM »
I don't think software limits are trustable, because its easy to zero the axis in the middle of the movement then the machine will hit limit switch because the software limit will never reach.

There's a error in MACH 3, as I told before if X++ switch is reached the machine should not move more to X+ (This happen when tick Auto limit Override)

For me MACH3 deals with limit switch like an emergency stop (This is wrong), and I'm a idiot to use 4 pins for limit switch (it's better to tied the 4 limit switchs on only one parallel pin, thats because the MACH3 will stop the machine, and he doesn't have the capacibility to know what movement (+ or -) triggered the Limit switch.
Re: Moving off Limit switch
« Reply #4 on: May 06, 2008, 02:04:37 PM »
Is there a way to move off the limit switch without turn on the LIMIT OVERRIDE?

Offline Hood

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Re: Moving off Limit switch
« Reply #5 on: May 06, 2008, 02:05:03 PM »
Daniel,
 Softlimits are tied to machine coordinates so they will stop an axis from hitting  a physical limit no matter where you have your offset zero position.
 Basically, yes you have wasted your pins by using seperate inputs for each axis, a limit switch is an emergency stop, it is to prevent damage to your machine and the softlimits are there to be used as you are thinking the hardlimits should be set up.
Hood

Offline Chip

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Re: Moving off Limit switch
« Reply #6 on: May 06, 2008, 06:05:35 PM »
Hi, Daniel

Limit switches are Limit's, Last Line of Defense, An "E-Stop Situation".

It Requires "Further Action" By Selecting "Limit Override" and Joging off the switch in the proper Direction By the "Operator".

Many Machines work this way, Requiring "Further Action".

As Hood Stater,

Set up your Soft Limits, It is what your describing/looking for.

After you home Mach, It moves Just off the SW and it revert's/changes to a limit SW.
DRO's zero ("Current Position" & "Machine Coord" to 0,0,0).

Soft-Limits work, At/Just inside your Limits, In "Machine Coord" and will slow down your feed-rate and stop just before your Limit switches would Trip.

You can Jog and Zero your to a "New" Current Position and the Soft limits remain just inside your Machine Limit Switch's,

See Pictures Below:

Dashed Lines are Soft-Limit's 0,0 X100" by Y50" Table, Part is at 0,0 Current Position.

If you hit a soft-limit you can Jog off it but not Jog further into the switch.

If you don't trust Soft-Limit's the "Limit" sw's are there to Save you.

Mach provides a way to setup Limits & home swithces using the Same Switch's with 1 Input Pin. You wire all the switches "NC" Normally Closed and in series with one another.

Mach now's which axis is moving during Homeing and only looks for a switch to open,
As the Operator you should be able to See what's going ON.

Why trust any cnc Machine , Hand Crank it!!

Think About It, Chip
Re: Moving off Limit switch
« Reply #7 on: May 13, 2008, 03:41:12 PM »
In Mach 2, I could simple hold the Reset button down with the mouse while hitting a jog key (arrow key) to jog off of the limit switch. Is this no longer the case in Mach 3?

Offline Hood

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Re: Moving off Limit switch
« Reply #8 on: May 13, 2008, 04:00:41 PM »
If you go to the settings page you can choose to have Auto Limit Override, what this does is if you hit a limit you can then reset Mach and then jog away from it. The Jog will be at a lower rate than normal, this is so you have time to react if you accidentally jog the wrong way. Once you release the jog key the next time you press it you will have full jog speed again.
Hood
Re: Moving off Limit switch
« Reply #9 on: May 13, 2008, 07:30:19 PM »
One other option. Many of the homebuilt machines have easy access to the axis screw, pulley, belt or motor coupling. And of course many don't. But for those that do, when a limit is hit all goes dead and it's sometimes easiest to just turn the screw and move the axis off of the switch. On my lathe, it's quicker than the "clicking" and requires less than 1/2 turn. Then reset, re-reference and roll on.
That was in the early days....I've now learned not to hit them. Softlimits are there to protect them.
RC