Halllppppp!! DTHC diving into plate

[BensPlasmaAu]

Hi again, so wish I could post more happy things. This time aroundmy machine WAS working so well. Turn it on and there is no way i can cut with the DTHC turned on, and the cuts it gives me without are attrocious.

It does the touch off, goes to pierce height, pauses on pierce, and then drops to cut height, and beyond. The Z used to go to 1.5mm and run beautifully, but this time around it drops all the way to 0.4220mm. Which when cutting 12mm hits on the pierce puddle slag and causes the z microswitch to activate and e-stops the machine 5mm into the cut.

I have changed the voltage required recently in the tool and it has worked brilliant so far. I have checked the gcode and nowhere does to tell the z to drop this far. It only sends it to 1.5mm i believe that it might habe something to do with the DTHC card/system but after checking everything i can think of physically and via software settings i am at a loss.

Any ideas?? I have 4 jobs waiting to get cut and i jave to have the machine going this week.

I see a JD2 Mad plasma table in my very near future.........

Thanks in advance everyone!! You are all a brilliant source of diagnosis and help.

Ben

[Simko]

Mig spatter spray will keep the metal from forming a pile around the pierce. Works great for me

[sphurley]

Ben, when its cutting, DTHC active, does the voltage on the screen match what you setup in sheetcam? Too high of a voltage reading would cause it to lower the Z axis to match your setting in G-code. You should not be having all these issues, you have a first rate setup.

[BensPlasmaAu]

Thanks Steves.

I’ll have another look when I get to the workshop tomorrow. It really is baffling as to why it is doing it. I have made the initial enquiry to JD2 about their table as well. I think for me it will be a good move. While my table does do the job, I feel I need to go for some better reliability with an off the shelf unit.

[beefy]

Ben,

seeing as it's a Candcnc system, I'd ask Tom on his forum.

Something interesting is that you say it immediately drops below 1.5 mm. How long do you have your THC Delay setting. Is it long enough that it allows time for the pierce to complete, plus the torch to move down to the cut height, and the voltage to stabilise at cut height, before allowing THC control to take over.

Have you also tried single stepping your gcode with THC disabled and plasma cutter turned off. If single stepping through the gcode shows the machine is doing exactly what it should, then the problem may be related to the THC control. But as said in the previous paragraph, THC control should be delayed by your THC Delay setting, so that THC control only starts once the cut has progressed a short distance at cut height.

Keith.

[acourtjester]

I had the same problem for some reason SheetCam will not keep my tools saved and I find that the delay for the DTHC reverts back to blank. I find about a 1.5 second delay in the G-code for the DTHC to turn on is needed to stop the torch from diving.

problem.JPG

[steel 35]

I would manually raise the amps with the up arrow, 1 at a time, 2-3 times Max. testing each time.
If Z drops when the delay ends, raise the amps; opposite if Z raises.

Hope its that simple. Works on my DTHC IV

[tcaudle]

Amps? How about volts.... Remember " the higher the torch the higher the volts" You cannot tell the plasma what volts to cut at (constant volts) you set a constant AMPs value and the type material, feed rate and consumables and the arc gap , define wht voltage the torch is at. Once you understand the relationship of the arc gap to the voltage (directly proportional to) then you understand how every Arc voltage THC works. The very first step in troubleshooting a diving problem is to run a base line test cut (long straight line) with the DTHC off and to note the Torch volts as it cuts at the right height by the manual/ The voltage shoul dbe close to the book voltage from the chart and on a flat piece of material only vary a few volts.

[SeanP]

I would be using a 4.5 second dthc delay time for 12mm steel, give it plenty time to settle down, it won't have travelled that far from the pierce in that time with PM45.

What I do especially on thicker stuff and going straight into a straight line cut is:
Set it off cutting with thc button off, watch what the torch volts readout says and as it settles after the pierce (4.5sec)
quickly adjust torch volts preset and then switch on thc button.

[steel 35]

Amps? How about volts.... Remember " the higher the torch the higher the volts"

Yep I am sure that what the arrow says

Glad I am just there to push buttons.