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Continuing a job after an event stops it
« on: October 11, 2008, 08:43:05 PM »
I was in the process of making my first item on my mill with Mach3, and for whatever reason, it thought I hit the stop button in the middle of the job. Like an idiot, I just cleared the condition, and told it to run. The spindle never turned back on, and it quickly broke the bit. So, is it possible to re-start a job? Is it best to start over, or can one continue where they are? If I have to re-set where on the material to start, I'll never get it in the same position. Thanks for any comments or advice!
Re: Continuing a job after an event stops it
« Reply #1 on: October 11, 2008, 09:00:14 PM »
Spend the time to get good at re-zeroing the machine - You'll be doing this a lot for a while.  It's a good idea to always have some repeatable reference position on each part or fixture.  it can be as simple as a single hole, or a couple of edges you can reference to.  If you have home switches, just zero to your reference when you setup the part, and save the offsets as a fixture offset, and you can then quickly go back to it after an oopsie.

Once you've buggered the program, it's a good idea to back up the program to some good starting point.  I usually just back up to the start of the failed operation.  It's also a good idea to do an "air cut" just to make sure you've really got things back under control.  It's up to you to remember to turn the spindle and coolant back on if you either turned them off manually, or they were shutoff by a stop or E-stop.

Regards,
Ray L.
Regards,
Ray L.

Offline jimpinder

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Re: Continuing a job after an event stops it
« Reply #2 on: October 12, 2008, 04:54:37 AM »
I think Ray has just about covered it all.

It all depends whether you have stopped the machine on the emergency reset button, or on the feed stop button. On the emergency reset, there is a good chance you will have lost position so the main thing is - are your DRO's accurate - in other words is the reading still refering to the present position of the cutter. It doesn't matter if you have moved it by jogging etc, while you clear the fault, but it does matter if it slipped when the fault occured.

If it slipped then you must , as Ray said, set them up again, including the Z height.
On most of my mill work. I have it drill a hole at the 0,0 position, so I can move back to this if I want to.I have home switches as well, but find this an easy way to re-locate in relation to the program I am running. Set all the DRO's to zero and that is it done. Set the Z at the work height and away you go.

Whilst many of the instructions to Mach 3 will remain, as you have found it will not switch the spindle on again, or the coolant, these are on/off applications and not remebered.

You can "step through" your program on the screen, by using the down arrow on the GCode window,  without setting the machine going, and if you watch the tool path display, especially on the big display on Page 3, it will show the current cut as a white line. If you compare this with your workpiece, you should be able to work out where the program had got to.

You must be sure that Mach has all the information it needs to continue, and this is where you need to be reasonably familiar with GCode, because you have to look at the code, and think - if I were the machine, would I know what to do. This is not difficult - look at the code and if you see for example a G0 movement, you can reasonable expect that the cutter was moving from a to b, and that it would be up out of the way to do so. If the next move is G0 Z -0.5 say, then that is the cutter going down, and if the next move is G1 X*y*, then that is the next cutting move, so - rewind your program back to the G0 move (up arrow on the GCode window). Click on "set next line" and "run from here". Start your spindle (and coolant) and click on cycle start.

Where ever your cutter was (and you needn't have tried to get it back to where you think it was) it will move to the next position on the G0 move, then pick up the Z down move, and carry on with the G1 cut.

The important bit, as Ray said - are the DRO's accurate.






 
Not me driving the engine - I'm better looking.

Offline Hood

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Re: Continuing a job after an event stops it
« Reply #3 on: October 12, 2008, 05:36:25 AM »
I think the thing that has not been covered so far and which may be the most important is why your machine went into E-Stop in the first palce. There could be a variety of reasons for this which will depend on your setup, for example if you have limit switches fitted then it could be a noise problem. Could even be something as simple as a dodgy keyboard.

 Does this happen often? If it does then that is certainly the first thing to get sorted.

Another thing which although not directly related to this case is you must understand the difference between a Stop and  Hold, doing a Stop when in motion will lose position, how much depends on your individual machine.
 When the stop is pressed Mach immediatly stops all output to the drives but the axis may travel on slightlyy due to inertia and Mach has no way of knowing this and thus you have lost position. The Stop should only be thought of as an emergency stop, if you wish to stop in a controlled manner in a run of code you should press the Hold button and then if you wish to do something that requires the buffers to be emptied you can then safely press the Stop button without fear of loss of position.

Hood
Re: Continuing a job after an event stops it
« Reply #4 on: October 12, 2008, 11:20:29 AM »
One other thing to be aware of - I can't explain what's happening here, but it's bitten me several times....  I've had a problem come up that forced me to stop the program.  I then re-zeroed, backed up to the beginning of the last cut, and re-started the program.  On a few random occasions, Mach seemed to still be confused about where it was, and where it was going, as the first move after the re-start went to the wrong place.  Oddly, this has never been a result of Mach and the machine being out-of-sync, as I did a GoToZero, and it returned *exactly* to zero, and I was able to re-re-start the program from there, and it was fine.  It seems at times Mach gets whacked to where it is internally confused, and it makes a bogus move following a fault.  Sometimes, this move is off just a little, sometime, a LOT.  Once that one bogus move is out of its system, all is OK again.  That's why I suggested making the first cut after a fault an "air cut", both to verify you've re-started at an appropriate place in the program, and that Mach is not suffering from some minor transient brain damage.

Regards,
Ray L.
Regards,
Ray L.
Re: Continuing a job after an event stops it
« Reply #5 on: October 12, 2008, 07:05:48 PM »
I want to thank everyone for their responses. I've got limit switches, and they are prone to vibration (Used to be able to trigger a stop by lightly banging on one with a screwdriver handle), but I upped the MS it takes to register, and has just about eliminated all bounce. If I recall right, this was an ESTOP, which hasn't happened on it's own before. My material is just a few square inches of plexiglas, so I think I'll just start over if it happens again. I'm very new to CNC, and I was just curious if there was a reliable, established way to restart things, but for me I don't think I'll try. If it happens more regularly, I'll address it from the prevention point of view.

vmax549

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Re: Continuing a job after an event stops it
« Reply #6 on: October 13, 2008, 10:18:51 PM »
YOu MIght want to read up on RUN FROM HERE. WOrks good to restart from a  point in the code.

(;-) TP