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Author Topic: Physical buttons for plasma  (Read 88261 times)

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Offline beefy

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Re: Physical buttons for plasma
« Reply #70 on: January 23, 2016, 04:42:28 PM »
+1 to what Terry said.

Some setups have automatic voltage setting. The gcode sets up the proper cut height (the important bit) and the THC is switched off. Now, assuming your plate is nice and flat and parallel with your XY rails, the cut begins at that precise cut height, and doesn't care what the voltage is. The system takes multiple samples of the voltage for a certain time then averages those readings to give the SET VOLTS. It then passes that voltage to the THC, effectively saying, "At this cut height, feedrate, airflow, amps, etc, etc, THIS is the voltage you need to maintain your proper cut height".

That's also why the voltage can change when the electrode hafnium starts eroding away with use. This effectively increases the arc distance and hence the voltage. So as your electrode wears you need a higher arc voltage to maintain the same torch to work distance.

Another method of getting the correct voltage is to do a test cut with THC off and simply note the cut voltage. The feedrates, etc can be tweaked and the voltages noted at each test run, and the parameters from the best cut are what is used. But once again you must have a flat sheet laying parallel with your XY rails (no lumps of slag on the slats, lifting up the sheet) for these tests to be accurate.

So at the end of the day the arc volts is ONLY a representation of the cut height, which is the critical factor that Hypertherm for instance base their best quality cuts on.

If a different cut height to the cut charts gives you a better quality cut, then leave me out of that one, that's something to argue with Hypertherm, etc  ;D

Keith.
« Last Edit: January 23, 2016, 04:53:52 PM by beefy »

Offline BR549

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Re: Physical buttons for plasma
« Reply #71 on: January 23, 2016, 05:12:31 PM »
(;-) When cutting I normally adjust to BEST cut and that does not always agree with HTs chart data. Remember that that data was derived from LAB data not real world cutting where the variable conditions can be  a lot different.

NOW most times the data is  close but sometimes NOT so close. (;-)

(;-) TP

Offline beefy

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Re: Physical buttons for plasma
« Reply #72 on: January 23, 2016, 06:53:42 PM »
I mustn't forget that Terry.

In the days when I was learning all this stuff, one guy who cut regularly said he could use exactly the same parameters as he used on a previous day and yet the cut would not always be the same.

Temperature of the electronics changing measurement accuracy, air density/temperature, stars not aligned, who knows.

Keith.
Re: Physical buttons for plasma
« Reply #73 on: January 24, 2016, 05:19:47 AM »
Yup, agree 100% lab conditions... Don't forget cutting in an in temperature regulated shed without slowly preconditioning whatever you are cutting will also result in a different cut as the material will be slightly warmer or colder relative to the plasma gas temperature (aerospace industry they precondition materials to very close temperature tolerance before machining)

The main thing is with some machines there are no cut tables so at least you have a starting point

Here is another interesting read here about controlling the cutting current whilst inhibiting z-axis motion for corners (Jim colt and tom caudle

http://www.plasmaspider.com/viewtopic.php?t=16534
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Physical buttons for plasma
« Reply #74 on: January 24, 2016, 05:35:12 AM »
Terry, if you reread my post again you will note that I was talking about machines without any cut tables published, and tried to give a bit of guidance as to how you may use a good tested and published table of cut speeds for a machine without a table of cut speeds

Zero, no tables....  Nothing ... What would you use as a starting point....

I live very much in the real world... And there are way more machines being sold without any published information than those that have good detailed manuals.... Should they be purchased... NO... But people do... And then put them on a home built CNC... Why because they are cost effective to their objectives.
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline Hood

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Re: Physical buttons for plasma
« Reply #75 on: January 24, 2016, 10:21:59 AM »
Hoping Hood's choice works out very well and is equally, or better detailed and supportive.  :)
Russ

Well Russ, didnt reply earlier as I had no idea what the manual was like, I never read the bloody things unless something is wroong :D

Anyway went down to the workshop today to find it, still in the poly bag that the machine was wrapped in :D
As I suspected it is very basic, few specs, info on what the buttons/switches do and thats about it. It was the same with my Tig from them, just the basics but it works great and easy to figure out in seconds.

Maybe hooking to the CNC Table will provide some issues but absolutely none so far.

Hauled off the cover and took some snaps of the internals, I am thinking the CNC interface may actually be there and all that is missing is the connector, will have a study of the pics in a wee while and see if my initial thoughts are correct or more likely post some pics and see if the clever plasma people here  think they are :D

Hood

Offline Hood

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Re: Physical buttons for plasma
« Reply #76 on: January 24, 2016, 11:24:05 AM »
Ok first pic shows section from manual about the interface.
Next pic shows what I suspect is the Arc Ok signal board, the grey wire that wraps around the board is connected to the cap at one end and goes to the work lead clamp at the other, third pic.
The circuit board seems to have missing connections on the output side of it which I think likely are for the CNC plug, 4th pic

Offline Hood

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Re: Physical buttons for plasma
« Reply #77 on: January 24, 2016, 11:29:11 AM »
Never took a thought to see if there are wires directly connecting the circuit board to the arc voltage, all I have in the pics I took are wires from the cap to the board (pink and grey on one terminal white on other), not sure if that would be the raw arc voltage which then get divided, any thoughts?

Will likely give TecArc an email tomorrow and see what they say, in the mean time back to filling in my tax return :(

Hood

Offline BR549

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Re: Physical buttons for plasma
« Reply #78 on: January 24, 2016, 01:33:43 PM »
hIYA Robert if you have looked at some of the "others" cut values you will see MOST are not even close to HT specs (;-) And that is bascially a design issue because MOST of them are using old technology. It is simply BEST to do as Keith suggested and do a simple test cut to determene a good setting as far as height and set volts . You can figure it out in one or two simple test cuts.

Also if there are ZERO values published then the Manf does not really care about its customers (;-)

And YES I am a Loyal HT fan. And THEY have earned every bit of that respect over the years. Their HARD WORK has made my job a LOT easier and has put a LOT of money in my pocket. (;-)

IF I ever run into a weird problem I can simply call Jim and ask him about it. So far I have always gotten an answer. NOT always what I WANTED to hear but an honest answer all the same.

(;-) TP
Re: Physical buttons for plasma
« Reply #79 on: January 26, 2016, 02:38:51 AM »
Agreed Terry, I'm also a loyal ht fan. (13 years now).

Ever done anything with the rs485 on the 65 and 85?
Seem to have limited themselves there providing only one board running modbus ASCII.  Asked ht Europe last week and was given a short shift answer... First time been unimpressed... Reverse engineering may be required with an arduino rtu to ASCII bridge.  ... Long term project for me maybe ...
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”