Another plasma component...

rodw wrote:

phillc54 wrote: Yes, I did comment out that line if thats what you mean. It made no difference. I did report back here at the time.

Yes, I saw that but I posted a later request.
Could you please try this:
In plasmac_buttons.glade change line 4 with a text editor from:

Code:

<requires lib="gtk+" version="2.24"/>

to:

Code:

<requires lib="gtk+" version="2.18"/>

Cheers, Phill.

Got it! I thank you guys for your patience.

What's the +- tolerance or how close does the calculated voltage need to be to the raw arc voltage for a good cut?

You only need the two voltages to be as close as possible to each other if you are using the voltage from a factory cut chart to set the THC height.

Cheers, Phill.

What I mean to ask is how far off can the actual arc voltage be from the optimal arc voltage before it noticeably effects cut quality?

[edit]
I think I found the answer I was looking for: +- 1 volt

John,

The electronics...and sometimes the mechanics of the torch height control can probably achieve 1/4 volt resolution (rule of thumb, 1 volt change in arc voltage is approx equal to .004"....although that varies with different processes)....but if you can hold arc voltage to plus or minus 1 volt....you will have a very good system.

Arc voltage THC from 10 years ago had a plus or minus 5 volt deadband....so the height could vary as much as .040"....todays plasma systems need accuracy in the plus or minus .010" range or plus or minus a little over a volt for best performance. Since minute variations in cut speed, surface condition, material content, plasma gas flow/pressure, and when a cloud passes under the moon all affect the arc voltage/torch height relationship......there really is not a good reason to try to get much better than 1 volt.

Many really nice arc voltage THC's end up getting "detuned" a bit to minimize torch z axis oscilation!

Jim

www.cnczone.com/forums/general-waterjet/...c-voltage-range.html

I'm just asking because I'm guessing my scaled up error from before is about +-0.5 volts.

I will have to defer to the cutters for this. I would attempt to get it as close as possible. I guess the amount of noise you get would be the limiting factor.

Cheers, Phill.

AgentWD40 wrote: Got it! I thank you guys for your patience.

What's the +- tolerance or how close does the calculated voltage need to be to the raw arc voltage for a good cut?

Well, here is another quote from Jim Colt from Hypertherm. The rule of thumb is that volts change at a rate of about 10 volts per mm.

jimcolt » Sat May 09, 2015 8:30 am
Most height controls accurately control arc voltage to plus or minus about 2-3 volts. For every volt you will see roughly a .004"(0.1mm) change in height (this varies a bit with thickness and power levels). Controlling the arc voltage tighter than this usually creates some oscillation in the z axis, which will show as striations (roughness) in the cut edge.

I think it is funny when THC manufacturers advertise .5 volts accuracy......because the arc voltage itself fluctuates more than this (due to the moving cathode attachment).....which means the height control will oscillate rapidly up/down to try to compensate. In all cases when the edge gets rough because of this oscillation, you need to slow down the z axis speed or deaden the THC reaction time, which ultimately loosens up the voltage deadband to at least the 2-3 volt range. In reality controlling to plus or minus 5 volts is ok on materials thicker than .125".

One of the overlooked components in a THC is the mechanical tightness as well as the lack of "overshoot" of the z axis lifter. A loose lifter requires that the voltage range (deadband) is loosened up, a lifter that does not instantly stop (braking) will do the same. The z axis lifter, properly designed will be the most costly part of any THC.

In my tests sampling bout 16000 readings with hal sampler showed my Everlast changed linearly at 7.53 volts per mm and this variation had very high correlation (>99.5% confidence on the linear regression). I think the other thing going for the THCAD config is that the voltage to frequency algorithm used on the board results in a averaging of the conversion which is improved with the 1/32 frequency division as the THCAD has more time to get a good result.

I really thin LinuxCNC combined with external offsers and THCAD sampling the way Phill has tied it together achives a far better result than Jim describes in this quote.