MACH 3 Questions

[edclayton1]

I have been working with my homebuilt plasma table and Mach 3 on and off for the past year now an I am beginning to realize there is still tons of stuff I still don't understand when it comes to successful plasma cutting and using Mach 3 and SheetCam.
First can someone explain to me or point me to a video or something for some help on understanding how to do a restart from a crash on a project if you cant afford to simply start the whole job over again? Say the program is going to make multiple cuts in the metal and it gets messed up after some of the cuts and the torch pops loose from the breakaway mount. I don't clearly understand how to back up in the G code and get the torch to go back to the exact place and height where it malfunctioned, etc.. so that I can try it again. Nor do I understand how to make it restart correctly from that point. I don't want to lose my reference point from the beginning and I don't want to rewind all the way back to the beginning and have the machine attempt to recut the areas that have already been cut successfully.
Also what does the DHTC auto/manual button do in Mach 3?
If I turn off DHTC altogether how does the software know how to set the cut height to .060"? From the settings in Sheetcam or??? I swear my pierce height usually looks like its too high and half the time the cut height looks too hi or two low even though the actual voltage vs. the preset volt seem to be matching up and the DHTC UP/DN seem to be working correctly. These problems seem to be worse as I use thicker and thicker metal to try to cut.
Do I need to zero my z axis at the beginning of every job or does Mach 3 or Sheetcam (g code take care of that automatically using the DCC or something like that?

[acourtjester]

I will try to help with the DTHC auto/manual this is like on/off, there are places in the G-code where it will be turned on/off too.
The torch height at the start of the cutting operation is controlled by the G-code, The DTHC then comes into play to control the torch height as the cutting continues to the end of that operation. You can run the G-code with out the plasma and then check the torch height as its moving around (pierce height then cut height). If you are using a floating head switch to establish there the metal surface is then your offset may be off. The will cause the pierce height to be off by the error in the switch offset.
To restart after a problem you look at the Mach screen (view of cutting action) and there is a up and down arrow at the right side. To back up you use the up arrow and move the G-code back to the last M5 and click on "set next line". You can also use this to move to the next cutting operation if you want to skip over a problem. If you look at the screen Mach will show a white area (line or dots) as you move around with the arrows so you have a display of where you are moving. In some areas if the restart is a distance from the problem you may want to to have the DTHC off for the start of the cutting and watch until the torch has moved very close to the problem area and then manually fire the torch and turn on the DTHC as the arc voltage will be wrong cutting over a kerf.
I zero my Z at the start of new part cutting operation but Mach will know where is is unless you change something.
I'm sure other have different ways to do these thing, good thing here you get many options.

[exapprentice]

Hi edclayton1

Hope this helps, this is the explination I got from Tom @ CandCNC on how to use set next line

Note the line number you stopped on in the G-code E-stopping can lose the absolute position so you need to re-reference your XY and Z to TABLE zero. You job reference point is only as accurate as the absolute postion reported by the DRO's. Re-home the axis to table zeros to reset the DRO position
Jog the torch out close to where it stopped
Turn the DTHC Auto Manual to MANUAL and DTHC to OFF
In the g-code window move to the line you stopped on and then backup to the M03 that starts that line THEN keep going to the M05 line of end of the previous cut
Hit the SET NEXT LINE and then RUN as soon as the Torch fires at the start of the bad cut turn it off with the screen button
Let the torch move along the cut path until you get about 1/4" or more from the bad spot and hit TORCH button to fire the torch. After the torch starts cutting new material flip the DTHC to AUTO and ON

It was a bit daunting at first but after a few **** ups you soon memorize the procedure and it works a treat

[edclayton1]

Thanks to the both of you for all the advise. Do you think most people zero out all the axis then start their cutting with the the buttons on and in auto or off and in auto. I've been starting with auto selected but dhtc off until the code turns it on which seems to happen right away anyway.

[tnbndr]

Try this topic: http://plasmaspider.com/viewtopic.php?f=55&t=14473
There is a whole forum section on Mach 3 you may want to peruse: http://plasmaspider.com/viewforum.php?f=48

[Bigdogbro1]

I use the "exapprentice" explanation from Tom at C & CNC. Always seems to work well to restart after a problem.

Hi edclayton1

Hope this helps, this is the explination I got from Tom @ CandCNC on how to use set next line

Note the line number you stopped on in the G-code E-stopping can lose the absolute position so you need to re-reference your XY and Z to TABLE zero. You job reference point is only as accurate as the absolute postion reported by the DRO's. Re-home the axis to table zeros to reset the DRO position
Jog the torch out close to where it stopped
Turn the DTHC Auto Manual to MANUAL and DTHC to OFF
In the g-code window move to the line you stopped on and then backup to the M03 that starts that line THEN keep going to the M05 line of end of the previous cut
Hit the SET NEXT LINE and then RUN as soon as the Torch fires at the start of the bad cut turn it off with the screen button
Let the torch move along the cut path until you get about 1/4" or more from the bad spot and hit TORCH button to fire the torch. After the torch starts cutting new material flip the DTHC to AUTO and ON

It was a bit daunting at first but after a few **** ups you soon memorize the procedure and it works a treat