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Author Topic: Controlling THC?  (Read 16556 times)

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Offline stirling

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Re: Controlling THC?
« Reply #20 on: April 27, 2014, 11:14:22 AM »
No particular need for a separate layer for small holes. Remember turning THC ON/OFF BETWEEN cuts is not an issue. Turning THC ON/OFF DURING a cut usually IS an issue.

LOL - yes your long dumbbell with small circular ends could pose that problem. You don't maybe think you think too much do you Dave?

Of course when you have that great accel this sort of problem will magically disappear anyway. (hopefully  ::);D

Ian

Offline Davek0974

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Re: Controlling THC?
« Reply #21 on: April 27, 2014, 11:49:21 AM »
Of course, yes, got it now.

Lol! Yes I do tend to think a lot, it's just the way I am, when faced with a new task-plasma CNC for instance, I like to try and gain answers before getting into a situation where that answer is needed.  At least you too can see how a dumbbell shape or similar could be an issue :)

Hopefully I can significantly improve things by tuning ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline stirling

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Re: Controlling THC?
« Reply #22 on: April 27, 2014, 12:08:38 PM »
Remember your dumbbell shape is not "awkward" because it's particularly special in having small circles, it's just an example of a shape with tightish turns. ANY shape that requires sharp direction changes is going to need good accel. I know I keep harping on about the accel but it truly is the key.

Poor accel causes larger changes in cut speed. ANY change in cut speed will change the voltage across the arc. That change in voltage will be interpreted by your THC as a HEIGHT change. That's what causes dive. That's just how it works. Yes THCs use various methods to try to mitigate this but the plain fact is that you're better off not taxing them too much in the first place.

Offline Davek0974

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Re: Controlling THC?
« Reply #23 on: April 27, 2014, 12:39:20 PM »
Thanks again, I will tune for as much acceleration as possible without losing steps or shaking the table to bits ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: Controlling THC?
« Reply #24 on: April 27, 2014, 04:36:38 PM »
Dave somewhere in your brain is STUCK "You have to slow down on small arcs"  WRONG Cutting with a plasma is dependant on consistant cut speeds and heights.  When you slow down you are altering those constants.  

NOW a fact to remember . Mach3 most times cannot maintain constant feedrates on short arcs. It is a Physical problem with the drives accelleration rates not being able to keep up with the required acceleration between 2 or more short points. There is physically not enough room to do it at the Drives ability to do so. SO now mach3 has automatically slowed down compared to the called feedrate. THAT is where antidive kicks in. WHEN it does slow below requested feedrate MACH3 will shut OFF the THC to prevent torch dive. When the System gets back up to speed it will cut the THC back on.

NOW you talk about cutting small circles in thick plate. THE same applies lets say you are cutting 1/2 thick steel plate. I cut it here at 30Ipm @ 60amps AND I cut everything at that feedrate as THAT is what the torch wants for a smooth cut in that material. NOW a smooth cut is a smooth cut reguardless if it is a straight line or an arc. NOW if the machine can match the accel needed for a particular arc then it cuts the same. IF it gets too short for the machine to maintain a consitant rate then the machine rate will be lower as it just cannot physically do it. SO mach3 slows down and that will change the cut parameter and cause the torch to dive. AND that is where the anti dive kicks in and stop it from diving too low. The quality of the cut will be slighty different in those arc because ONE of the parameters has changed, "Speed".

It will ONLY Be a minor change and it is what it is . UNLESS you have a high END plasma that can auto control machine speed AND torch parameters ON THE FLY you will have what you have.

I spent a LONG time automating an older Plasma torch to have auto control over the power and air settings. Controlled it all automatically from mach3. It would compensate everything on the fly. In the end the overall cut quality 95% of the time was NOT a bit better than NOT having it on. It was a waste of time and energy for "WHAT" we are cutting (Fun doing it though).

SO I suggest you set your max Vel to something reasonable and LEAVE IT ALONE. Then tune the Accell for as FAST as it can react without loss of steps. THEN spend the time to develope a parameters table for your cutting based on YOUR MACHINE. Keep lots of notes. Soon you will find the sweetspot for YOUR machine. AND you will laugh at yourself for worrying about so much.

Then you can have fun at what your plasma can do for you as it is only limited by you imagination to create something to cut. AND that world is EXTREMELY large as to what you can get into and have fun at the same time.

Just another thought is with MACH3  using the THC control thru Mach3 it is NOT fast enough to keep up at HIGH speeds anyway so there is NO need to go there (;-)

Just some thoughts, (;-) TP





« Last Edit: April 27, 2014, 04:41:46 PM by BR549 »

Offline BR549

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Re: Controlling THC?
« Reply #25 on: April 27, 2014, 04:37:57 PM »
Got 2 posts for the price of one,(;-) TP

Offline Davek0974

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Re: Controlling THC?
« Reply #26 on: April 27, 2014, 04:48:20 PM »
Fantastic, now that really made sense.

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

Offline Val

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Re: Controlling THC?
« Reply #27 on: September 06, 2014, 05:09:56 AM »
I'm still using SCam 4.0.19 and I can turn THC on/off whenever I like with no pauses during cutting. YMMV.
How do you do that? Please do share. Sheetcam allows you to use rules. In their cutting rules tutorial on youtube looks very simple but in real life doesn't work. All I got is a jerk in movement right where the THC should go off. And on for that matter. They use M998 and M999. What is the code? M101/102 work? Do you have to write a macro for them? How do you do it whenever you want?
Thank you

Offline Davek0974

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Re: Controlling THC?
« Reply #28 on: September 06, 2014, 05:51:51 AM »
Since this thread I have upgraded to a better THC from CandCNC and it's way better at controlling things. Turning on and off during a cut is simple and has no effect on motion.

Also as mentioned, get the acceleration up, way up, push it as hard as it can take and things become much simpler.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Val

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Re: Controlling THC?
« Reply #29 on: September 06, 2014, 06:41:01 AM »
Since this thread I have upgraded to a better THC from CandCNC and it's way better at controlling things. Turning on and off during a cut is simple and has no effect on motion.

Also as mentioned, get the acceleration up, way up, push it as hard as it can take and things become much simpler.

I"am happy is simple to you, to me is something I don't know how to do. Can you explain haow you did it?