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Question on Plasma THC control to users of this facility
« on: November 23, 2016, 05:06:23 PM »
Mods if in the wrong place please move.

I am home brewing gear so sorry of the questions seem to be dumb, this is all new to me.

When using torch height control is there normally a 'dead' range that the head will not go up or down, hysteresis I guess it is called?  So  if you have your magic cutting height providing say 120 Volts into the controller, how many volts either side do you have before the controllers say move up or down?

I assume there is a hysteresis in controllers otherwise the Z axis would be constantly adjusting it self for even a minute variation.

I also assume that without the THCON input even if there is an input on Up or down the Z axis will not move until THCON is active?

If the last point is correct is there a requirement to send the X axis to a cutting height from pierce, or can this be left to THC control.

Cheers

Adrian
« Last Edit: November 25, 2016, 04:06:39 PM by RICH »
Re: Question on Plasma THC control to users of this facility
« Reply #1 on: November 23, 2016, 06:58:38 PM »
Sorry the Topic should read
Question on Plasma THC control to users of this facility

I must have left it to long since posting and can not edit it now.

Adrian

Offline Davek0974

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Re: Question on Plasma THC control to users of this facility
« Reply #2 on: November 24, 2016, 02:17:32 AM »
Usually something like 2-4v hysteresis or dead-band.

Generally Z axis is the height (you mention X ) and no it should not move on inputs if THC is off, providing it is all programmed to behave that way - you can set movements even if THC is off in ports & pins i believe.
« Last Edit: November 25, 2016, 04:10:09 PM by RICH »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: Question on Plasma THC control to users of this facility
« Reply #3 on: November 24, 2016, 02:33:52 AM »
Thanks Dave for the feedback, yes should be Z I talk about not X was getting late.

Also thanks for the 2 to 4 volts dead band, that was an uncertainty for me.  I guess it could be adjustable on some.

Adrian
« Last Edit: November 25, 2016, 04:10:29 PM by RICH »

Offline Davek0974

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Re: Question on Plasma THC control to users of this facility
« Reply #4 on: November 24, 2016, 03:10:25 AM »
Usually is adjustable, even on the cheap Proma THC's there is a setting for it.
« Last Edit: November 25, 2016, 04:10:46 PM by RICH »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: Question on Plasma THC control to users of this facility
« Reply #5 on: November 24, 2016, 03:50:46 PM »
Hi again Dave;

I have figured a way to change the dead band on what I am trying, quite easy when I stopped trying to think to hard.

I will explain what I am trying to do in very simplistic terms and please do not laugh as my set-up is purely as a hobby, keeping the grey cells active and a bit of fun.

I picked up one of the Chinese Cut40 plasma cutters, It is still at the limit of the mains supply in my garage and as my hobby is general metalwork I could not really justify a lot of hard earned.

After a few months I built a CNC frame for it, got a straight torch head for around £30 and started to have fun, the whole lot including plasma cutter probably cost me less than £500 and a far bit of time.

But I use it as a drag head across the metal, the Z axis has a floating section and the weight of the head keeps the drag tip on the work, but this slows every thing down, acceleration and top speed etc.  It also means it will show any slop or flex in movement, my circles are not perfect circles etc.

So I have started to think how to improve it and the only way I could think of was to lift the tip off the work piece and for that I need THC, so ultra cheap THC control using a 4 input Voltage comparator project has started.

It would be ludicrous to go out and buy a £200 plus THC controller to work with a £180 Plasma cutter!

Adrian
« Last Edit: November 25, 2016, 04:11:02 PM by RICH »

Offline Davek0974

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Re: Question on Plasma THC control to users of this facility
« Reply #6 on: November 24, 2016, 04:03:43 PM »
Sounds like your'e having fun, thats what matters :)

I guess you will have to start the cut as a drag then lift to move?

« Last Edit: November 25, 2016, 04:11:12 PM by RICH »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: Question on Plasma THC control to users of this facility
« Reply #7 on: November 24, 2016, 04:27:22 PM »
I can pierce off the metal, only by a mm, two at most, so I tend to do that then drop after delay to in theory be 2mm under the top of the metal!

That way if the metal drops by up to 2mm it is still in contact, if the metal rises more then the torch floats up with it, but as I say at a cost.

thanks for your input it us appreciated.

Adrian
« Last Edit: November 25, 2016, 04:09:37 PM by RICH »

Offline beefy

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Re: Question on Plasma THC control to users of this facility
« Reply #8 on: November 25, 2016, 06:45:20 AM »
The dead band on my old Candcnc MP3000 is normally set at 0.5 volt for Finecut consumables or 1v for 40 amps and above nozzles. Have not had any issues with these settings and while watching the Z rotation during cutting you can observe it not rotating while it's in the dead band. So even 0.5 volts does not seem too sensitive, at least for my system.

However, the dead band is inter-related with the THC Correction Speed. If this speed is high then a small dead band allows the Z axis to "shoot straight through" the dead band. Then it corrects in the opposite direction, and on and on. Thus you get Z jack hammering. To get rid of that, you either reduce your THC Correction Speed or increase the Dead Band, or a mixture of the two.

I don't know if you've considered any sort of filtering of the measured voltage. The arc is not a nice smooth DC signal.

Paying $200 for a decent THC is not ludicrous if you put any value on your time. Unless the whole idea of doing everything as cheap as possible is worth more than $200 then go for it, but I wouldn't personally get locked into thinking that just because I got part A cheap, then I MUST also get part B cheap. Just a thought.
« Last Edit: November 25, 2016, 04:09:20 PM by RICH »
Re: Question on Plasma THC control to users of this facility
« Reply #9 on: November 25, 2016, 02:23:28 PM »
Hi beefy;

I guess I like to play electronics, time is cheaper than money and I seem to learn a lot in the process.  None of my stuff is for profit, just to help me make more things.

If at some point in the future I had a commercial thing to do it would be a different matter.  I have a simple way to change my dead band, my travel speed is slow circa 900mm per min at the moment possibly up to 1200 or 1500 if I get this to work, still very slow in comparison to commercial equipment.

I enjoy the challenge also semi retirement helps.

If I get it to work I will try to do a video.


Adrian
« Last Edit: November 25, 2016, 04:08:40 PM by RICH »