Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: k-rigg on September 09, 2011, 12:43:07 AM

Title: Problem with THC and Mach 3
Post by: k-rigg on September 09, 2011, 12:43:07 AM
I have a plc for my torch height control, where it tells mach 3 through 3 inputs to raise, fall, and that the torch is on.  Because the THC goes down and senses the material before stating to cut, this process is started when a "torch on" signal is received from mach 3, then when the thc is done sensing the material and raised to pierce height, the thc itself controls the plasma and turns the plasma on and off.  I have to have the setting "allow thc to raise and lower torch anytime" option on under "mill options" in the ports and pins settings to let the THC achieve this.

Now my problem comes from if the stop button or emergency stop is activated when the thc is telling the torch up after the torch has touched the material and is heading toward the pierce height.  The torch continues to rise if you press the stop button to the pierce height, but does not when you press the emergency stop, this really isn't a problem because not matter which stop is used, the torch height is reflected accurately in the z dro.  The problem is when you rewind the g code and press cycle start, the z axis motor makes at high buzzing sound, but doesn't move, and the z axis dro reflects a move to the rapid height in that is designated in the first of the gcode.  This is a problem because sometimes ill press stop during the raising of the torch after the sensing when i realize something is wrong (plasma cutter not on, etc) and ill rewind it and it basically crashes the torch in the metal.  If you stop it in any other process during the gcode it does no do this, not even when the THC is going down to sense the material.

Title: Re: Problem with THC and Mach 3
Post by: BR549 on September 09, 2011, 09:30:04 AM
What name brand THC are you using?  What does the Gcode look like for the top of material routine?

Title: Re: Problem with THC and Mach 3
Post by: rrc1962 on September 09, 2011, 03:24:58 PM
If you're using the THC UP/DOWN inputs in Mach to control torch height, then the PLC should only be sending these signals after an ARC OK is sensed.  Everything up until the M03 (torch on), like the touch-off routine, should be done in Gcode, not the PLC.  The PLC just needs to monitor the ARC OK signal and when it has a good one, start sending THC UP/DOWN signals.  If you do it this way, you won't need the "allow thc to raise and lower torch anytime" option and the THC function in Mach will work properly.  Mach should not allow automatic THC moves unless a good arc is sensed.  I think that option was added for router folks who wanted to manually move the Z while running a program.