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Author Topic: Controlling THC?  (Read 16567 times)

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Offline Davek0974

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Re: Controlling THC?
« Reply #10 on: April 25, 2014, 01:17:04 PM »
Sorry, your answer was a little contradictory, you said you could turn the THC on or off whenever you liked, but also said it would only work smoothly at certain points I.e. When not in CV.

Better to have said you can only turn it on/off at these points without upsetting motion, it's not the same as being able to do it whenever you want :)

As for the code being three arcs, it is something to do with sheetcam, les newel over there is looking into now as he was baffled too,.

I have found that my machine is less impressed with holes sub 20mm but also know now it is connected with acceleration and CV so I will be going back to the basics next week and retuning the axes from scratch to see if I can get her singing a better tune, then I can forget about flipping the THC off and on.

Anyway, my foot is intact and I've learnt a little more, as always thanks for your help, it really is appreciated.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: Controlling THC?
« Reply #11 on: April 25, 2014, 06:55:05 PM »
Dave do yourself a favor and stop fiddling with the thcon/off on arcs.

Stirling is doing his best to help you (;-) try not to bite the hand that feeds you.


You do NOT needed it 99% of the time. Mach3 will compensate on the slow down in the arc BY ITSELF. Everytime you add the Macros for the THC on/off you are monkeying with MACH3 ability to do a SMOOTH CV. AND a smooth CV it the KEY to a good Plasma cut.

Leave the CV setting to the STOCK mach 3 settings do NOT turn on any values for CV let the internal settings HANDLE the toolpath. THEN learn to set up proper cut parameters of power/speed/cut height for a good cut.

IF it does not work correctly after that you have a problem with table /drive mechanics and Vel and accel problems. Mach3 WILL work correctly if you table is built correctly and tuned correctly.

But that is just based on about 100 zillion cut inches with plasma and Mach3,  your mileage may vary.

(;-) TP

Offline Davek0974

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Re: Controlling THC?
« Reply #12 on: April 26, 2014, 03:34:13 AM »
Please believe me when I say I really am not biting anyone's hand off, I'm not moaning or criticising anyone, I am just trying to learn as much as I can, and unfortunately that means asking questions.

I really do appreciate all the help that has been offered here, it's been most helpful, really. :)

I do know now that I need to retune my acceleration parameters and will do so this week, the CV stuff I think is all bog-standard (I think), I use G64 at the start of a program and I think the no-cv angle is set at 89 degrees in config, I don't know if that should come out though?

The other cv settings are all blank.

Once again, thanks to you guys,and if I come across as hand biting then I apologise.
;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline stirling

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Re: Controlling THC?
« Reply #13 on: April 26, 2014, 04:59:45 AM »
Dave - Before we do the group hug I'll just get this out of the way ok.

Sorry, your answer was a little contradictory, you said you could turn the THC on or off whenever you liked, but also said it would only work smoothly at certain points I.e. When not in CV.

Better to have said you can only turn it on/off at these points without upsetting motion, it's not the same as being able to do it whenever you want :)

IMHO Terry is THE plasma guru here but for whatever reason it looks like you're generally stuck with me at the moment. However, I'm not your hired help. If you're going to chip at me and even advise me on how I should phrase things I'll just call it a day here.

Now... onwards...

Yes - CV (and therefore accel and therefore rigidity) are the keys to happiness. I'm pretty sure Terry and I have said this already. I'm think I've also said that you shouldn't need to "tune" CV at all - maybe it was to someone else.

With ref. to No CV on angles > 89: NO - don't do this. You don't want to restrict CV at all.
« Last Edit: April 26, 2014, 05:06:16 AM by stirling »
Re: Controlling THC?
« Reply #14 on: April 26, 2014, 06:57:41 AM »
i use the m10 m11 macro to turn off and on the thc with the cutting rules in sheetcam.i use a dpdt relay that allows the thc to be used with a joystick for manual control , ei oxyacet flame cutting or auto for plasma. the thc control is a lcthc from candcnc.added activatesignal(output2) to m10   and deactivatesignal(output2) to m11.no hesitation in the disabling of the thc when cutting even at speeds of 240 ipm. i set up the cutting rules to slow at angles of +45 degrees and .5"
and m10. .25" out of the corner to turn on thc with m11.the relay is stopping signal to mach inputs when turned on.

Offline Davek0974

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Re: Controlling THC?
« Reply #15 on: April 26, 2014, 07:04:39 AM »
Dave - Before we do the group hug I'll just get this out of the way ok.

Sorry, your answer was a little contradictory, you said you could turn the THC on or off whenever you liked, but also said it would only work smoothly at certain points I.e. When not in CV.

Better to have said you can only turn it on/off at these points without upsetting motion, it's not the same as being able to do it whenever you want :)

IMHO Terry is THE plasma guru here but for whatever reason it looks like you're generally stuck with me at the moment. However, I'm not your hired help. If you're going to chip at me and even advise me on how I should phrase things I'll just call it a day here.

Now... onwards...

Yes - CV (and therefore accel and therefore rigidity) are the keys to happiness. I'm pretty sure Terry and I have said this already. I'm think I've also said that you shouldn't need to "tune" CV at all - maybe it was to someone else.

With ref. to No CV on angles > 89: NO - don't do this. You don't want to restrict CV at all.


It wasn't meant as a chip Stirling, that's why I put the smiley face on it, I was trying to explain how I misunderstood it that was all.

Re the CV angle I will certainly clear that on Monday and then retune my machine.

Thanks
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: Controlling THC?
« Reply #16 on: April 26, 2014, 05:20:20 PM »
Dave the important part is STOP fiddling with the THC ON/OFF macros,  for most of your cutting you do NOT need it.

Even on small circles here I do NOT use it, don't need to, mach3 will cut just fine. The anti dive will take care of it.

(;-) TP

Offline Davek0974

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Re: Controlling THC?
« Reply #17 on: April 27, 2014, 03:40:40 AM »
Point taken, I need to stop over complicating matters, my fault entirely but valuable lessons learnt.

Many thanks for putting up with me :)

I really feel a full and proper instruction manual would benefit many users setting out, but I am fully aware that creating one would be a mammoth task. I know there are a few on the 'net but none fully explain stuff like CV, THC, side effects of low acceleration settings etc.


BTW, if I need a small hole in thick material, it needs to slow down, I have found 70% seems to work but as that is programmed in sheetcam! how does anti-dive deal with that?

As far as I know there are no hidden auto-slowdown features in Mach, it just does what it's told.
Just wondering.
« Last Edit: April 27, 2014, 03:44:01 AM by Davek0974 »
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Offline stirling

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Re: Controlling THC?
« Reply #18 on: April 27, 2014, 07:38:51 AM »
BTW, if I need a small hole in thick material, it needs to slow down, I have found 70% seems to work but as that is programmed in sheetcam! how does anti-dive deal with that?

IMHO THC has pretty much no value on small holes - in fact in my experience it causes more problems than it ever solves. Remember THC is there to cope with the changing height of the metal. Almost by definition - small holes - don't cover enough metal to see any particular change in height. Add to that the fact that THICK metal is going to be even LESS prone to changes in height over short distances and it becomes clear that THC brings little if anything to the party.

Offline Davek0974

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Re: Controlling THC?
« Reply #19 on: April 27, 2014, 10:31:24 AM »
Yes, I can fully understand that, but what if you have a job with small holes plus large cut areas too?

My guess is that I would separate the holes into another layer in sheetcam, do the THC off and speed reduction business and then do the other features as a standard cut at normal speed with THC.

That I think is correct, but falls apart when you get a job like the dumbbell shape I was messing with, a long straight where I guess you want THC that then blends directly into small near-circles - you can't turn the THC off for the circles without a macro glitch but as it needs to be slowed down to cut, the anti-dive will not function?

These are the questions that cause me to pose questions because I can't answer it :)
« Last Edit: April 27, 2014, 10:33:03 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives