[firemaker]

Hi, I'm hoping someone can help with the following:

I have the issues below with my new (new to me) CNC plasma with Hypertherm Powermax 45:

- using the recommended THC voltage from the Hypertherm manual results in a cutting height of around 5mm rather than a sensible 1.5mm. For example I set the THC to 97 (should be nearer to 120 according to the manual) in order to keep the torch down when cutting 3mm stainless steel – see the attached photo for the result.

- the torch sometimes needs several attempts to pierce before making a cut – see photo of nozzle and failed pierce.

- running the feed rate lower than that recommended in the manual is sometimes necessary for a successful cut.


These are my tool setting in Sheetcam for 3mm stainless used to cut the part in the photo:

Feed - 3500mm/min
Pierce height – 3.8mm
Cut height – 1.5mm
Pierce delay – 0.35s

I’ve tried replacing all the consumables several times, including swirl ring. I'm using 45A shielded consumables.
I can’t see any issue with the airline up to the plasma unit. I drain the compressor and filter daily. The pressure light remains green when cutting.
I’ve hammered a 10mm stainless steel grounding rod 6’ into the earth and connected the bed and the plasma earth to it.

Any suggestions welcome, thanks!

[urbnsr]

I didn't notice what THC you are using. I would cut a few straight lines at an actual height of 1.5mm without the THC on and note the voltage. I would use that voltage reading for the THC. Changing the feed rate will effect the voltage. I would check the grounding of your system if you are not getting book-spec results. I also suspect that you're not getting good results if the torch is cutting at the wrong height.

Hope this helps until someone who really knows their stuff comes along.
Paul

[firemaker]

Thanks Paul

I had a look at the Torch Control PCB and it says - Digital Torch Height Controller | Torch Height Controller | Torch Height Control | DTHC | THC | Mach3 THC | THC for Mach3 | plasma THC DTHC V1.3 2014.

I tried cutting some lines with the height control off with interesting results! It would go to the pierce height ok at 3.8mm but then drop down to zero whilst cutting. I tried setting the cut height to 2mm, 2.5mm, 3mm but it still dropped down to zero when cutting. I thought this might be Sheetcam not registering the changes I made to the cutting height, so I rebooted the software and set up a new Sheetcam tool but the results were the same.

[Torchhead]

Not mentioned was anything about intial height sensing (touch-off) Bottom line is if you cannot setup on flat material with the THC off, and make a decent cut, then a THC proabably won't help. The table vendor should be your source for support and be able to explain why it drops to zero witht he THC turned off. It should drop to 1.5mm and make the cut at that height

[urbnsr]

If you are piercing at a measured 3.8mm, then I assume your torch can be programmed to go to 1.5mm for the cut. Would you be interested in posting a bit of your gcode to see what is asked of the setup? Other things may be an offset that needs cleared and how about mechanical play somewhere with your Z axis?

Sorry - Missed the initial post comment on your grounding.

[firemaker]

I've just run the following G-code (pierce at 3.8mm and cut at 2mm):

N0010 (Filename: test line.tap)
N0020 (Post processor: Redline cnc plasma.scpost)
N0030 (Date: 05/11/2015)
N0040 G21 (Units: Metric)
N0050 G53 G90 G40
N0060 F1
N0070 (Part: test line)
N0080 (Process: Outside Offset, 0, T8: 3mm stainless)
N0090 M06 T8 F3500 (3mm stainless)
N0100 G00 Z10.0000
N0110 X18.8400 Y-4.5900
N0120 G28.1 Z10.00
N0130 G92 Z0.0
N0140 G00 Z1.2000
N0150 G92 Z0.0
N0160 G00 Z3.8000
N0170 M03
N0180 G04 P0.35
N0190 G01 Z2.0000 F900.0
N0200 G03 X15.0000 Y-0.7500 I-3.8400 J0.0000 F3500.0
N0210 G01 X0.0000
N0220 G02 X-0.7500 Y0.0000 I0.0000 J0.7500
N0230 G01 Y300.0000
N0240 G02 X0.0000 Y300.7500 I0.7500 J0.0000
N0250 G01 X15.0000
N0260 G02 X15.7500 Y300.0000 I0.0000 J-0.7500
N0270 G01 Y0.0000
N0280 M05
N0290 G00 Z10.0000
N0300 X0.0000
N0310 M05 M30

With the torch height control off it pierces at the correct height but then drops down and drags the nozzle along the work piece to do the cut.
Switching the THC on keeps the torch above the work piece but using the recommenced voltage in the manual results in a cut height of a bout 5mm.

I can't detect any excessive play or 'stickyness' in the Z-axis and I had a look at the 'touch-off' and that seems to be spot on.

[firemaker]

Further info..... I just tried the following:

I set the nozzle at 1.5mm above the work. I then disconnected the Z stepper motor so the z axis can't go anywhere! I then cut a line just by jogging in Mach 3. At the end of the cut the nozzle was still at 1.5mm but according to Mach3 the nozzle had dropped by 6mm.

THC was turned off and I got sensible readings from the voltage during the cut.

[firemaker]

Further experiments have lead me to conclude that the THC on/off button isn't doing anything and the THC remains on regardless. Any ideas on how to rectify that? Many thanks

[urbnsr]

Yeah - Seems something is up with Mach or a macro. I'm not a Mach user so I can't help. Sri.