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General Mach Discussion / Mch3 plasma THC min and max question
« on: June 27, 2010, 04:44:32 AM »
Hi,
We've built a plasmacutter recently and have some problems with the THC.
The problem is that however we set the THC min and max between values, e.g. 0 .. 3mm,
but Mach allows it to go under the minimum value.
Especially when the tourch goes on, the arc Voltage gets high for some subseconds till the material is cut through,
at that point Mach contols the Z down, because the THC down input gets active. This would be OK, if it
checks the THC min value and would not allow the Z to go lower than 0 (THC min), but it controls the Z into negative and
pushes the tourch into the material which is not so good.
We've somehow overcame the problem with generating the G-code with some delay after the tourch activation and only after the delay
switching on the THC. This solves the problem, because the arc Voltage normalise before the THC goes on, but I'm still confused why Mach
allows the Z to go lower than the set THC min value?
Video of the machine first testings: http://www.cncdrive.com/MOV00355.3GP
I have another question which is not really required for the machine, but interests me: How to set a negative value into the THC min/max. fields?
I mean Mach does not accept a "-" (minus) character to be written into these fields, however the basic screen includes a negative value on first startup.
So, I'm wondering why I cannot write a negative value into the THC min and max. fields?
All ideas are appritiated!
Cheers,
Balazs
We've built a plasmacutter recently and have some problems with the THC.
The problem is that however we set the THC min and max between values, e.g. 0 .. 3mm,
but Mach allows it to go under the minimum value.
Especially when the tourch goes on, the arc Voltage gets high for some subseconds till the material is cut through,
at that point Mach contols the Z down, because the THC down input gets active. This would be OK, if it
checks the THC min value and would not allow the Z to go lower than 0 (THC min), but it controls the Z into negative and
pushes the tourch into the material which is not so good.
We've somehow overcame the problem with generating the G-code with some delay after the tourch activation and only after the delay
switching on the THC. This solves the problem, because the arc Voltage normalise before the THC goes on, but I'm still confused why Mach
allows the Z to go lower than the set THC min value?
Video of the machine first testings: http://www.cncdrive.com/MOV00355.3GP
I have another question which is not really required for the machine, but interests me: How to set a negative value into the THC min/max. fields?
I mean Mach does not accept a "-" (minus) character to be written into these fields, however the basic screen includes a negative value on first startup.
So, I'm wondering why I cannot write a negative value into the THC min and max. fields?
All ideas are appritiated!
Cheers,
Balazs