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Author Topic: Mach4 plasma acting weird, z commanded over soft limits  (Read 449 times)

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Offline ROTM

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Mach4 plasma acting weird, z commanded over soft limits
« on: October 25, 2022, 04:33:24 PM »
Good day.
I got my plasma working and for the most part it is working well.
usually at the beginning of my day I start my cnc, home it and leave it on.
So it is ready to go when I need to do something.

2 main issues:
1. For some reason when I went to run a program for plasma the head just kept diving into the plate.
so I thought my ohmic sensor was not working...so I lowered it and make sure Ohmic lit up in the screen so it was working...hit cycle again it dives into the plate.
I shut everything down restart everything load the same program and it worked good....anyone had this experience?

2. For some reason out of the blue I get z commanded over soft limit even though it just cut about 50 piece out of the same plate and same job ...i get this ....any solution to this.

Thank you!







Re: Mach4 plasma acting weird, z commanded over soft limits
« Reply #1 on: October 25, 2022, 04:58:13 PM »
Hi,
just a guess, but do you have THC?

THC usually works an an 'overload axis'. This means that the Z axis works normally, but the THC height variations are applied to a mythical extra Z axis motor which
works in parallel with the main Z axis motor. In practice the up/down signals are sent to the main Z axis motor, but the idea remains that there are two sources of pulses,
the regular Mach generated Z axis trajectory pulses AND the THC pulses.

Mach can and does keep track of the main Z axis pulses but it cannot keep up with the overload axis. When you go do do a regular job the accumulated overload axis movement will offset
the Z axis. If you had Homed before then the accumulated overload offset would be accounted for and Mach would not dive into the table.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

Offline ROTM

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Re: Mach4 plasma acting weird, z commanded over soft limits
« Reply #2 on: October 28, 2022, 12:12:35 AM »
Thanks...probably the homing would help...but today..

I was cutting some aluminium sheet and had to take 0.0010 out...spindle running and I jogged with the increment buttons and the machine moved about 1" went into a metal plate holder.

I had sparks flying all around and side kicked the emergency stop button lol.
l checked and nothing seemed out of the ordinary. (The Avid aluminium bit survived..so I'll be buying more of those.)

I was doing some other operation just after homing...and again the machine moved 1" instead the 0.0010".
I changed the increments and worked again normal.

Now every time I change the bit I turn off the vfd since I do not want to find out that this will turn on its own :/

Are there any fix to this?

Thank you!

Re: Mach4 plasma acting weird, z commanded over soft limits
« Reply #3 on: October 28, 2022, 05:32:21 PM »
Hi,

Quote
I was cutting some aluminium sheet and had to take 0.0010 out...spindle running and I jogged with the increment buttons and the machine moved about 1" went into a metal plate holder.

That is a completely different subject., and sounds like somehow Mach is screwing up its jog increments.

Quote
Now every time I change the bit I turn off the vfd since I do not want to find out that this will turn on its own :/

I never turn my machine off unless I'm doing some maintenance or alterations that invovle 230VAC, or except in those rare occasions where the mains
supply shuts off. My machine, including the VFD, has been permanently powered for the last three months since I installed my new fourth axis. I've never had the VFD switch on unexpectedly
and I don't know how many thousands of times I've manually changed tools.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'