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Pierce delay for plasma
« on: February 10, 2011, 07:17:21 AM »
Afternoon,

I have just changed my plasma cutter to one which has a arc ok signal on it, it seems to activate this signal as soon as the arc has transferred not once the plate has been penetrated, this means that when i have the thc mode set on in mach as soon as the arc transfers the machine starts to move but the arc hasnt penetrated the plate, i need to get some kind of a pause in there so i modified my sheetcam post processor to have a pause at the right time but mach seems to ignore it and as soon as it sees the arc ok signal it goes to the next line which has a machine move in it, any ideas why this happens? or if not any ideas on how i can get round it??

Help would be greatly appreciated

Matt

Offline stirling

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Re: Pierce delay for plasma
« Reply #1 on: February 10, 2011, 07:48:08 AM »
Hi Matt

it seems to activate this signal as soon as the arc has transferred not once the plate has been penetrated
This is correct behaviour.

this means that when i have the thc mode set on in mach as soon as the arc transfers the machine starts to move but the arc hasnt penetrated the plate, i need to get some kind of a pause in there so i modified my sheetcam post processor to have a pause at the right time but mach seems to ignore it and as soon as it sees the arc ok signal it goes to the next line which has a machine move in it, any ideas why this happens? or if not any ideas on how i can get round it??
This is normal procedure. i.e. go to pierce height, fire, wait while pierce, drop to cut height, start motion. Which Sheetcam POST are you using and can you post the few lines of gcode you use at the moment please.

Ian
Re: Pierce delay for plasma
« Reply #2 on: February 10, 2011, 08:36:29 AM »
Thanks for the reply,

I dont have the code to hand but i goes along the lines of

g28.1 z3.0
G92 z0.0
G00 z9.4
G92 z0.0
g00 z6.0
M03
P (any number i want to put in)
z3.0
x.........y.......

Im using the mp 1000thc delay fan on pierce count post.

Mach seems to observe the p.... when not using the thc function but not with it, is that correct?

Matt
Re: Pierce delay for plasma
« Reply #3 on: February 10, 2011, 09:04:03 AM »
The code for a pause would be...

G4 PX

X would be in either seconds or miliseconds depending on how you have mach3 set.  On the general config screen you can select seconds or miliseconds.  If you select miliseconds in mach then use seconds in you code, the effect will be almost like there is no delay.

That said, I've noticed the same behavior where the G4PX is completely ignored.  It only happens on the first G4 in the program, but it doesn't happen on every program.  It's odd because I use the same Sheetcam post to generate all code.

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Re: Pierce delay for plasma
« Reply #4 on: February 10, 2011, 09:20:44 AM »
Beat me to it about the G4 and the delay either being in ms or s  :)

Matt - is that just your memory - or have you actually missed out the G4 in your code.

Also - what do you have in your M3 macro?

This is pretty standard floating head IHS by homing stuff and should work fine. Can't comment on the behaviour of your particular THC as I've never used that one.

Ian
Re: Pierce delay for plasma
« Reply #5 on: February 11, 2011, 05:00:43 PM »
Afternoon,

I have just changed my plasma cutter to one which has a arc ok signal on it, it seems to activate this signal as soon as the arc has transferred not once the plate has been penetrated, this means that when i have the thc mode set on in mach as soon as the arc transfers the machine starts to move but the arc hasnt penetrated the plate, i need to get some kind of a pause in there so i modified my sheetcam post processor to have a pause at the right time but mach seems to ignore it and as soon as it sees the arc ok signal it goes to the next line which has a machine move in it, any ideas why this happens? or if not any ideas on how i can get round it??

Help would be greatly appreciated

Matt

Matt I may be wrong(I'm not at my machine) but I think there is a setting inside Sheetcam for pierce delay when setting up your your torch. It gets written into the gcode automattically. I'll take a look over the weekend

Mike
Re: Pierce delay for plasma
« Reply #6 on: February 12, 2011, 02:56:06 AM »
Hi,

Mach seems t ignore the pierce delay that you set in sheetcam when you use the thc function to recognise the arc ok signal before moving, is there another way of using the signal?? I have simply instaled mach 3 plasma and when i press the thc button on the signal is used when it is off the pierce delay is used.

Im not totally sure if there is a G4 in my code but all i know is the delay works with the thc button off and is ignored with it on, when i get a moment i will try using a different post or something.

Matt

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Re: Pierce delay for plasma
« Reply #7 on: February 13, 2011, 06:59:57 AM »
Hi Matt - after having a play, I think you're absolutely right - in a way...

It seems that regarless of whether you're using THC, Mach executes the M3 and THEN executes the G4 dwell. However, IF you're using THC Mach will THEN wait, AFTER the dwell for ArcOK (if it has to). The reason I (and I suspect a lot of others) have never noticed this is that IF the M3 is very quick in turning on your torch AND the ArcOK is very quick and between them the time is MUCH shorter than the dwell, then everything APPEARS to work as it should. BUT - IF the time it takes to turn on the torch and to return the ArcOK signal is pretty close to the G4 dwell time OR worse LONGER than the G4 dwell then there is effectively NO delay. i.e. it's allready done the G4 BEFORE it even got the ArcOK.

This IMHO is clearly wrong and I would regard it as a Mach bug. What Mach SHOULD do of course is execute the M3 and then wait for ArcOK BEFORE it does the G4 dwell.

In reality, the only gcode commands that Mach will not execute if ArcOK is not there (and THC is on) are MOVEMENT commands.

Hope that all makes sense. You can test the above out by doing a "silly" long G4 and you'll see it IS being executed and not skipped.
One make do solution I guess is to add the time it takes the torch to come on + the time it takes it raise ArcOK + the actual pierce delay you need and code G4 for that. Alternatively I guess some suplemental VB in M3 to do a wait for ArcOK - something like:

'untested and crude - i.e. infinite loop if ArcOK never comes.
DoSpinCW
while not isActive(THCON) 'yes annoying isn't it, Mach's signal name for ArcOK is THCON for gawds sake.
wend  

Incidentally, a tip: I don't use DoSpinCW - it's slooooooooow, instead I use activateSignal(OUTPUT1) - it's waaaaaay faster to respond.

Ian
« Last Edit: February 13, 2011, 12:20:31 PM by stirling »

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Re: Pierce delay for plasma
« Reply #8 on: February 17, 2011, 03:53:54 AM »
Matt - don't know if you're still interested in this but I asked Brian if he thought it should be corrected and it seems he doesn't... so the test for ArcOK in the m3 macro appears to be the only way to do this.

Ian
Re: Pierce delay for plasma
« Reply #9 on: February 17, 2011, 08:25:37 AM »
Ian,

Thanks for your efforts, i will take your m3 macro addition and try it out, i was hoping for a simple fire the torch, wait for the arc to transfer and then pause for the pierce delay interval then move, hopefully adapting the m3 macro will sort this out.

Thanks again

Matt