Arcok, who's that?   

Ok, I'm hoping to get some time tomorrow to pull that code apart and do some tests.

If it went
M03
M05

I guess that is the absolute shortest bite it can give?

Is there a delay in going from pilot to main arc?
I mean, if the metal is clean, the torch is at pierce height and then fired, surely the delay is microscopic and of little relevance. Does it not move to main arc as soon as the pilot arc touches the sheet and current starts to flow?

If the cycle time is so short, does it even get a chance to transfer to main arc?

Will do some tests on this.

Thanks

If it went
M03
M05

I guess that is the absolute shortest bite it can give?

Whatever a "bite" is.

Is there a delay in going from pilot to main arc?
I mean, if the metal is clean, the torch is at pierce height and then fired, surely the delay is microscopic and of little relevance. Does it not move to main arc as soon as the pilot arc touches the sheet and current starts to flow?

Your...

M3
M5

keeps the torch on signal active for 0.1 seconds (here). So let's look at what you "hope" will happen in that 1/10th of a second.

Your THC see's the (torch on) signal go active, it turns on the relay (so mechanical), the plasma cutter fires the pilot arc and opens the solenoid valve (mechanical again and even slower than a relay) that allows the air to flow. The air blows the pilot arc out of the nozzle, the arc touches the metal, the plasma cutter detects the circuit and switches from pilot to cutting arc, only NOW does it even START to "bite" PLUS "some" time to "bite" to whatever extent you'd like it to. What do you reckon? - all in a tenth of a second?

So how the hell long does all this nonesense REALLY take?

The answer is, you don't give a toss. You WAIT for arcok - that's when it's just started to "bite". That's why the nice people who make THCs (or THC interfaces) give you an arcok signal - because it's really useful. Once you determine your timings from this you're home and dry.

(and DON'T call me Shirley)

Very interesting stuff, so without an arcok system, a straight M03-M05 should be so fast as to not give any action at all? Probably just make a relay quiver somewhere.

Ok, so we switch on, wait for arcok, then switch off, is that the correct internal sequence?
Inside Mach there is a loop following the M03 that waits to see an arcok signal BEFORE processing the next command which in my case is M05, but I guess could just as easily be a move etc?

If that is so, then yes there is a long loop involved in getting that signal, in my THC it's created from a Hall effect trigger on the plasma ground lead so the current has to build to trigger point before it's sent, and as you said there are gas valves, relays, even the blowback start cartridge in the torch.

This all explains why a zero pierce delay is never really zero I guess.

Thanks for all this by the way, it's much appreciated.

The correct sequence is to switch on, wait for arcok, introduce any required delay then do whatever... which may be drop from pierce to cut height as in a "regular" cutting process or in your "drill" marking - switch off.

However - there's a Mach bug which makes this more tedious to implement than needs be. For a discussion of this, see the thread you linked to earlier in reply 13.
 

Thanks, just re-read that thread again.

So, if I were to set a realistic delay (longer than the electromechanical delays in the system combined) say 1sec then I would likely see stable timings in the G4 but because my zero delay request is far shorter than the inherent delays (allied with the mach bug)  then I am seeing seemingly random timings possibly caused by the arc ok arriving later for the first fire or some other micro variable delay?

I think that makes sense.?

I see you had some vb code for the M3 that might help but, as you said then, it could cause cause an infinite loop if the arc never arrives which is possible so I think I will leave that alone for the present.

I'll have a play as soon as I get some quiet time.

Results are in.

made a job that was just 4 pierces in a row, first test was no pierce delay
This set the code to a straight M03/Mo5 and I get one good mark and three where there was not enough loop time to actually fire the torch.

second test i set a 0.5s delay between each M03/M05
This time I got one deeper mark and three good ones

reduced to 0.4s delay
Result was slightly less depth than the previous test.

Then i realised the there was another factor at play - after the first pierce the torch air was still on its post-flow stage

The next test i made each pierce one at a time, allowing the air flow to stop between each firing
result - 4 perfectly equal marks.

Conclusion - there is a cumulative loop delay required of about 0.4s to get a reliable arc start on the torch PLUS if the air is still flowing then  the pierces WILL be quicker.

Summary - Not a lot i can do about that really, there is no way to stop the post-flow and no way to pre-trigger the air flow so the 1st pierce will always be longer.

Damn interesting test though and thanks for all the help.

My conclusion only applies to using the torch as a drill though, where there is no movement code following the M03, for normal cutting it will not fail to fire but it wll give a longer pierce dwell on the first cut providing the cuts are close enough together to be started with post-flow still running.

None of this would matter if you base your timings on arcok. I know I'm sounding like a scratched record but there it is.

None of this would matter if you base your timings on arcok. I know I'm sounding like a scratched record but there it is.

Yes possibly but what if the arcok is delayed on the first pierce but arrives faster when the post-flow air is on?

Surely the result would be as it is now - were waiting for a signal that arrives at varying time periods??

No real way to tell without some serious measuring equipment I think.

But I do now know that Mach IS consistent and that the pierces WILL vary if post flow is on.

Without a method of triggering the air earlier I doubt there's much can be done, but at least I have a reason now.

Thanks for all the discussion.

Yes possibly but what if the arcok is delayed on the first pierce but arrives faster when the post-flow air is on?

Surely the result would be as it is now - were waiting for a signal that arrives at varying time periods??

AAAAAGGGGGHHHHH!!!!  

Maybe I'm just crap at getting my point over but here's one last shot then I'll get back in my box.

It's the LENGTH of time the cutting arc is ON that matters NOT when it STARTS. arcok signals the time cutting STARTS. It matters not one jot If it takes one second or half a second to establish arcok. It's ONLY when you get arcok that metal is starting to melt.