Perforated material -- torch starts but goes out immediatelu

I need help cutting perforated sheet metal. My setup is a Hypertherm Powermax 45XP on a 2x4’ Avid CNC plasma table controlled by Mach4. I realize the answer to my question might be in either the Mach 4/ESS settings or with SheetCam but I thought of asking here.

My design is a simple rectangle. The torch drops down, ignites and then stops immediately. The Hypertherm generator does otherwise work with non-contiguous surface (keeps the flame alive), I have cut mesh before. I use the plasma CNC infrequently and do not have a great understanding of the intricacies of the system plus the software seems to have changed (updates?), and I don’t remember prior settings.

The error message is potentially interesting but don’t know what to change:

These are the SheetCam settings:

And the default rule:

Thank you all for any suggestion.

This really depends on the material which is suspiciously missing in the images you posted.

Just how big are the holes?

24 gauge sheet metal, the holes are about 2.5mm in diameter. There is plenty of material.

Is there some Mach 4 adjustment I need to make, perhaps in the THC?

Is your ground directly to the sheet?

The 45xp manual says you have to keep the speed really high to keep the pilot arc lit. So cut faster than whatever you are and make sure you have the ground directly to the sheet.

Some people think it’s ok to ground the table or the slats but that isn’t what the manual tells you.

Yea the ground and the THC are both directly on the material.

I thought the problem is that the arc, once established, cannot sustain due to some material features, such as a nearby hole, etc. So I put a small piece of scrap, and that allowed the arc to maintain itself, and then the gantry starting moving at the factory recommended speed (I did not speed it up) and the cut came out perfect. I decided to post this just in case someone else has the same problem in the future.

@DesertRider , That one has me scratching my head. I cut perforated stainless a quite small number of times each year (a few examples, below) and I’ve not run into the problem we are seeing here. I’ve cut 16Ga all the way down to 0.050

All the perforated material cutting here has been carried out with standard consumables, not fine cut. The tip voltage (78V), in the Mach-4 screen shot, is in the range for fine cut consumables but it seems pretty far off of the recomended settings for 24gauge material in the Hypertherm manual? It would appear that at that voltage the arc would start and errode all material available to it away extremely fast and go back out. Did the pierce locations appear exageratedly large? My guess (just a guess) is that by putting the extra scrap of material there to start on is making the material effectivly “thicker” or giving more material to errode away during the pierce, so the torch doesn’t go out.

I would turn off the THC. See if that makes a difference. But I think you already did that.

I cut a lot of the pref sheet and expanded sheet using fine-cut consumables. The only problems I have are with dirty ground clamp or going to slow.

I do agree that there seems to be too much energy and that blows through the material; your analysis of the scrap thickening up is exactly what I thought. I have my tools and materials programmed into SheetCAM using the Hypertherm manual, which I checked again, and my settings were “correct” as in following the book. The Hypertherm manual recommends 78 volts for FineCut in mild steel. What changes is the cut speed, and a modest reduction in Amps (from 45 to 40) for 20Ga and thinner; for the record I am using 40A.

I have measured my material to make sure I am not grossly off.

tried 60V and the arc started then the motion began and completed 1/12th of a circle then I got the same error as above. Tried 39 volts (half recommended) and got the same. Will try some more and report back.

Even though I completed the project at hand, I am trying to find a more definitive fix for this problem. Playing with a test contour, the error I am getting is
ESS: Arc Okay (THC ON) WENT OUT! Activating feed hold now.

After more experimentation, I found that reducing settings to 30A and 60V (from the 40A and 78V respectively recommended in the manual) works just great. In the future I will experiment with test cuts to define the lowest power that cuts the material reliably. Turning off THC is not the way to go as thin sheet is often warped.

Thank you.

Worked some crazy hours yesterday and didn’t have time to sit down and write a coherent response at the end of the day yesterday.

Looking at it now, I observe where our disconnect on the amperage setting comes from. I was talking about Stainless Steel and when I looked at the photo, I miss-took that to be stainless, and of course you were talking mild steel. With that realization, we are in good agreement.

The data that you captured here is super useful to a lot of people, so I quite appreciate that you have taken the time to share the results of the experimentation, thank you.

It does make me wonder about having to run with settings different than those recommended in the Hypertherm reference manual. Of course those are recommendations that one is to use a a guideline, however Hypertherm puts a lot of testing in to make sure those starting point values are pretty accurate for the common use case. In the back of my mind, I have the nagging question. The Hypertherm power head puts out an arc-okay signal. The value carried by that signal comes back to the AVID box, gets inserted into Ethernet via the ESS, makes its way back to Mach-4, through the windows OS and Ethernet IRQs, etc, to tell it good to go, either dwell now (for thicker materials) or start moving now! (Depending on the next lines of G-Code. Basically the signal is a “ready to move on to the next line of G-Code” indicator. As we go to thinner and thinner steel, the amount of time to receive that signal decreases substantially. The quandary in the back of my mind is whether the delays incurred with ESS and OS (that may be dealing with other Ethernet traffic depending on what else is connected on that port) and Mach-4’s response time, all closing that loop is above the minimum amount of time required.

I’m completely speculating, in the paragraph above, sort of thining out loud, but that adds credence to the idea that turning the current down below that recommended by hypertherm is working here. Just taking longer to errode all that material so the arc still has something to conduct to while the message gets back to Mach-4 and the machine starts moving…

I experimented some more, and noticed my system got out of sync from different updates. So I tried to bring all the software versions into sync.

One of the problems I had was that Avid introduced a new parameter in their toolset, named AD1 Delay After Arc OK time and mine (a previous gen Avid download) did not update and instead the new value was created but was set to 0.8s for all tools, regardless of material thickness, metal type, or cutting tool/nozzle. When I downloaded the fresh toolset from Avid, this AD1 delay got populated with different values as intended. So if anyone is running into trouble with their setup it is worth checking this parameter.

As for thin material, I experimented with cutting 24Ga non-perforated sheet with factory settings and it did work OK. It is only with mesh-like material that one has to reduce the energy or add a sacrificial starting scrap.

And to your point about times to receive Arc OK signal getting shorter with thinner material, that might have contributed to my problem: I run VNC on the Intel NUC PC that operates Mach4 so I can remote from my Mac, and wonder if VNC might have stolen enough cycles to mess up the ESS. So I close VNC when cutting.