Messages

31

General Mach Discussion / Re: Physical buttons for plasma

« on: January 26, 2016, 05:27:23 PM »

It deals with it simply be having the THC RATE set a lot lower than the rapid speed. I think my THC RATE is set at 15 percent.

A lot of people don't seem to understand that the Z axis design is also very important for faster THC speeds (with Mach3 and no accel/decel on the Z). You want as little inertia (weight) as possible so that the stepper is moving as little weight as possible. Linear bearings want to be very free moving, no stickiness. A weight counteract spring for the UP movements should help. At the end of the day you are telling the Z axis to move UP then having a change of mind and saying now go down, all as fast as possible. A heavy Z axis won't fare as well like that.

I'd hazard a guess a servo motor may help matters a little because I THINK they allow for some error from commanded movement to actual movement and will increase the current in an attempt to make the motor catch up. Not so with a stepper, try and make it do too much too quickly and it just squeals and stalls.

Keith.

32

General Mach Discussion / Re: Physical buttons for plasma

« on: January 26, 2016, 05:08:27 PM »

The Modbus in the THC is just a way of getting the Up/Down. Arc Ok etc to/from Mach instead of going via the parallel port or  motion controllers I/O.

As said I asked about it as it would have been an easy hook up but the guy said it wasn't that fast and not really suitable for thin material, so I never investigated it further.
Hood

I asked Jim Colt about sampling / THC signaling rate and he said most good THCs sample at least 25 times per second. I'm guessing you'd have to use a brain or macro pump with Mach3 to use Modbus so that limits the sample rate to a max of 10 times a second I believe, much slower than what Jim said. I'm working on my own THC and I have the sample rate at 32 times/sec which I could make a lot faster if I wanted. That doesn't seem fast in the world of electronics and microprocessors but at the end of the day the UP/DOWN output is controlling a mechanical device (Z axis) so it's own weight / inertia will limit it's reaction time. I hooked up the output to a terminal window and when you see the volt readings spewing on the screen at 32 times/second, and you imagine your Z axis ATTEMPTING to change direction at that rate, I don't think you need any faster.

My guess would be that the important bit would be once your system receives the THC UP or THC DOWN signal, how fast can it move. Mach is a problem there because the THC moves have no acceleration / deceleration in them so your THC RATE  setting is only a percentage of your Z rapid speed.
Keith.

33

General Mach Discussion / Re: Physical buttons for plasma

« on: January 26, 2016, 04:53:48 PM »

Terry,

I remember you posted some time ago about having an "automated potentiometer" on your plasma cutter and you had it reducing the current at corners, etc. You said about 95% of the time it made no difference to the cut. I've often had problem on outside corners on thicker steel, and also where a lead out crosses over a lead in. I get tabs left. When the lead out crosses the lead in the arc "jumps" over to the steel on the other side of the lead in, leaving an uncut tab. Outside right angle corners have had it too, but it's more weird because the arc "RE-PIERCES" around the corner, again leaving a tab.

I was wondering if slowing down at corners may help this and by reducing the current a little bit it won't blow the kerf out noticeably wider.

Rob,

thanks for that info. I've downloaded from that link plus downloaded the other two pdfs on the protocol.

Keith.

34

General Mach Discussion / Re: Physical buttons for plasma

« on: January 26, 2016, 06:41:51 AM »

So Rob,

what did you ask HT and what response did they give.

I'm curious about the reaction time of their current control. I wonder if they publish figures like that. So from gcode to HT current adjustment via their ASCII modbus interface there will be some delay. Some of that is under our control but once the HT receives the ASCII value I wonder how long it takes for the cut current to adjust.

Keith.

35

General Mach Discussion / Re: Physical buttons for plasma

« 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.

36

General Mach Discussion / Re: Physical buttons for plasma

« 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 

Keith.

37

General Mach Discussion / Re: Long motion pause after M3 - Candcnc plasma system

« on: January 12, 2016, 01:53:35 PM »

Thanks Fixittt,

checked that one already, and all set at zero.

The plugin has a settings box and a tick box "Use Mach3 THC Delay". I ticked that and it stopped the problem. It's all rather vague & confusing because the Mach3 THC Delay is to ignore the THC Up/Down inputs, whereas the plugin delay is called "Fault Delay" and is supposed to ignore the fault conditions the plugin monitors, such as over/under voltage, etc. So they are two different beasts. When I first got my MP3000 the story was the two delays run side by side and the Fault Delay should be set slightly longer than Mach3 THC Delay. Information and recommendations seemed to change in the early days of these systems as various bugs were found.

Keith.

38

General Mach Discussion / Re: Understanding Mach3 Plasma, ARC OK, halting motion

« on: January 11, 2016, 02:06:06 PM »

It never really got fixed Terry. I've hardly used my table the last couple of years and when I have it's been on thicker steel with a leadin so the delay in motion was just a slight nuisance during a pierce.

This time I've been given 2mm metal and I've nested the cut so tight I was using edge starts (won't be doing anything fancy like that again). Of course the motion delay just blows a big hole at the edge.

The other day I never got to the point of putting one of the delays to zero and testing that because Mach3 seems to also have gone wonky in the process. I've got a day off today so I'll re-install Mach3 and the MP3000 software and put the Mach3 THC DELAY to zero and do some test pierces.

Keith.

39

General Mach Discussion / Re: Understanding Mach3 Plasma, ARC OK, halting motion

« on: January 11, 2016, 02:27:11 AM »

Thanks guys.

No dwell in gcode.

Spindle spinups all at zero.

I'm actually going to uninstall & reinstall Mach3 because it seems to have gone nuts on me during this little cut. So that will give a fresh install then I only have to check the command in the M3.

Candcnc told me there's "a bug in Mach3" that causes their plugin to "fight" with Machs THC DELAY and convert it to a pause in motion 

I think their more modern systems have put a lot of functions into the electronics because the plugin and Mach3 just didn't do what was intended.

Keith

40

General Mach Discussion / Re: FEED HOLD

« on: January 11, 2016, 02:17:16 AM »

I bet it's Mach3 version dependent.

Heard plenty stories about how something works in one version but not in another, and users are often told to use an older version to get a particular feature working.

As dodgy as Mach3 is, I have quite a soft spot for it. I must be mad LOL.

Keith.