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Author Topic: How to resume after G code is stopped safely - problem  (Read 10776 times)

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Re: How to resume after G code is stopped safely - problem
« Reply #20 on: January 20, 2018, 04:48:05 PM »
problem solved, check video if you are interested

https://www.youtube.com/watch?v=mG0e0Jv_jik
Re: How to resume after G code is stopped safely - problem
« Reply #21 on: January 20, 2018, 07:42:38 PM »
The why is very simple. All CNCs apply look ahead. They don’t process one command at a time. A G1 is a cutting move and what follows is important too. If it is the last cut the tool must come to a complete stop. If it is an arc and you have continuous motion enabled it needs to consider the radius to decide how to slow down but not stop. It also must calculate the deceleration moves involved. These calcs get done as quickly as possible and stuffed into a buffer that is feeding the commands to the motor. so to actually maintain position you need to empty the buffer in a feedhold. Hitting Stop basicly says forget about where the tool is and stop as fast as possible.  See your 300mm rapid? On my machine the rapid move is 7600mm/min!
Re: How to resume after G code is stopped safely - problem
« Reply #22 on: January 21, 2018, 03:08:59 AM »
The why is very simple. All CNCs apply look ahead. They don’t process one command at a time. A G1 is a cutting move and what follows is important too. If it is the last cut the tool must come to a complete stop. If it is an arc and you have continuous motion enabled it needs to consider the radius to decide how to slow down but not stop. It also must calculate the deceleration moves involved. These calcs get done as quickly as possible and stuffed into a buffer that is feeding the commands to the motor. so to actually maintain position you need to empty the buffer in a feedhold. Hitting Stop basicly says forget about where the tool is and stop as fast as possible.  See your 300mm rapid? On my machine the rapid move is 7600mm/min!
Hi, this is what I was asking whole time, thank you answering, now it have little more sense .

But I still do not understand, I am machining with feed 40 mm/min and I press Feed Hold and when I press Cycle start Mach3 takes feed 300 mm/min. So, it should continue with feed 40 mm/min not 300/min , that is problem in my opinion, I tested Feed Hold, Stop file, same result for me.

My machine have rapid 4000 mm/min but I set it to 2100 mm/min.
Re: How to resume after G code is stopped safely - problem
« Reply #23 on: January 21, 2018, 11:23:56 AM »
Mach 3 can’t rewind the buffer. So it starts up again at the next line after the buffer. Mach 3 can be restarted anywhere in the program. However you really need to think about this because if the 300mm feed rate got applied in the buffer then you need to start at a point before the 40mm feed was called and you should make sure the first move after that is a safe one. Preferrably it is a move to the clearance plane.
Re: How to resume after G code is stopped safely - problem
« Reply #24 on: January 21, 2018, 01:44:53 PM »
Mach 3 can’t rewind the buffer. So it starts up again at the next line after the buffer. Mach 3 can be restarted anywhere in the program. However you really need to think about this because if the 300mm feed rate got applied in the buffer then you need to start at a point before the 40mm feed was called and you should make sure the first move after that is a safe one. Preferrably it is a move to the clearance plane.

I read couple of time what you wrote and only question is that I am asking my self does Feed Hold button have any purpose then, if I press Feed Hold button, machine will not stop in same second, it will stop slow but safe and it should be able to continue from that line in G code where process was stopped when I press Cycle start button, if that is not the case I do not see any reason why Feed Hold exist (except to stop G code and to start after all from zero).

You say : "Mach 3 can’t rewind the buffer"

I ask my self why it should rewind buffer at all, I just want machining process to continue from point from where I pressed Feed Hold (Even I like more Stop file, but will pretend that I will use Feed hold, I tested both and I see no difference except feed hold is slower and it does not turn off spindle, and coolant and so on..)

So in buffer should be information that I set Feed to 40 mm/min and couple of commands down I use G01 movement , and all the way down I set Feed to 300 mm/min, why would in buffer be 300 mm/min , I do not understand that part? Is there any link wher I can find how buffer works (intuitive for me is that I should not even care how it works, logical would be if I press feed hold, it stops with one feed and when I want to continue it should carry on with same feed).

Offline Davek0974

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Re: How to resume after G code is stopped safely - problem
« Reply #25 on: January 21, 2018, 02:57:01 PM »
"Feed Hold" is exactly what it says - it will hold the process at the next opportunity i.e. it stops filling the buffer and allows it to empty then pauses or holds. I have used it a few times when i have not been happy with my hold-downs, paused, added another clamp then continued etc. It does not "Stop" the machine - for this you use the stop button or the big red button if its going to hit the fan ;)

Two different actions and two different methods of achieving them.
Re: How to resume after G code is stopped safely - problem
« Reply #26 on: January 21, 2018, 03:32:51 PM »
"Feed Hold" is exactly what it says - it will hold the process at the next opportunity i.e. it stops filling the buffer and allows it to empty then pauses or holds. I have used it a few times when i have not been happy with my hold-downs, paused, added another clamp then continued etc. It does not "Stop" the machine - for this you use the stop button or the big red button if its going to hit the fan ;)

Two different actions and two different methods of achieving them.

You are right , but then what is procedure to continue with same feed after Feed Hold is pressed and about what all I should take care before I dare to press Cycle start ? So to be more vivid, my tool changer does not moves, but my spindle rotates with 1000RPM and somewhere down in my Gcode there is command
S300 F300, few seconds ago before I pressed Feed hold was active command G01 -23.5  F40 mm/min, what you think what will happen if I press Cycle start (I know I must be boring probably :) ) ?


So in other words what should I do to be by text book in order to know outcome of result when I press cycle start if I pressed Feed hold before Cycle start?
Re: How to resume after G code is stopped safely - problem
« Reply #27 on: January 21, 2018, 06:05:00 PM »
I think Dave just told you, it works fine for him. What is different on your machine or controller than his?  If other people are having the same issue as you,  they would say so.  For me, with just a simple router, Feed Hold works as described per Dave. It runs the buffer out and stops and will restart at the next line.
« Last Edit: January 21, 2018, 06:07:45 PM by wmgeorge »
Retired Master Electrician, Commercial HVAC/R Service and lots of Hobbys.
Re: How to resume after G code is stopped safely - problem
« Reply #28 on: January 21, 2018, 06:10:21 PM »
zmajmr,
When you pressed feed hold it was already too late!  The speed change was already in the buffer. Seriously, thousands of machines operate this way without problem and you want to argue that it is wrong because you lack the necessary programming skills to do it correctly.  Work on that, you'll get there faster.

Offline RICH

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Re: How to resume after G code is stopped safely - problem
« Reply #29 on: January 21, 2018, 08:01:12 PM »
zmajmr,
Mach 3  is the way it is, there will be no updates or changes, and as already been posted things work the way they work and not how you want or envision how something  should work.
 
Get over it and use what you now  know  and move forward.

RICH