Really strange cuts in FC last night

Wow…so I had designed a simple logo for someone…I will post it when I get back to the shop…
very basic round logo.
what happened was I did a dry run to check use of sheet…worked great
ran the program the first cut went perfectly…so I did lined up another piece to cut…no changes in program…just changed the steel on the table…
started FC…and 4 inches into the cut the Z started to slowly rise right to the top…THC did not engange until it was 5+ inches from when it started to rise…but wghen it enaged the torch was still running and I had to do an emergency torch shutdown.

started the cut again with the help of FC…it cut the whole piece fine…
did another piece…it cut fine…
each time I did a pice to cut all I did was return to zero…place a new piece of metal on the table to use up some scrap…
another piece on the table…this time on the second cut on the outside of the circle FC somehow started the circle way off center and almost cut the first circle in half…did a pause…reset and gave up for the night…

has anyone else ever had something like this?

I am going to go though all my cables…

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I had the z axis issue like you did and the fix was the jumper mod that Langmuir posted. Once I did that I had no more issues with z axis rising or FC randomly rebooting. It seemed to be a electrical noise issue

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well it is not the board issue…my first gen board died and they replaced it with a new second gen board…and i checked for the shunt…it is installed.
gonna see if one of my wires got moved recently

What was the Live Voltage you were seeing during the rising?

Is THC lighting the ‘UP’ indicator? You say it wasn’t active so possibly not.

Was the IHS indicator lit up at the bottom of FC? If the IHS circuit opens when the THC is ‘Active’ it will move Z up .060" and hopefully close the circuit. If not, it will continue up until it closes. This is so that if your torch hits the plate for whatever reason during cutting it will retract up as fast as possible to avoid it. Possible something is loose there?

I do appreciate the

all good things I will print up and post to try and remember to look next time it happens…

but being a noob at this I still panic when something goes wrong…