View Full Version : Plasma arc's look faceted when cut, not sure why?

05-03-2016, 12:37 AM

I'm cutting out the letter 'a' (arial font) in 3mm as test forms with my Thermal Dynamics plasma cutter. Letter size, approx 80mm x 50mm.

I've exported a dxf from Vectric Aspire using the fit curves to selected vectors (arcs) command. I brought the dfx info Sheetcam and cut using Mach 3.

Something isn't right, with the inner curves, they appear faceted and i'm not sure if its a problem with original vector file, (attached as the exported dxf) or, for example a velocity /acceleration and CV issue in Mach3. I'm currently using a velocity of 17,500 and an acceleration of 1750 in Mach3, perhaps an issue?

In Mach3 I currently have CV feedrate override turned off. CV is on, exact stop therefore off.

Its a process of elimination and i'm guessing its a vector file issue or Mach 3 feeds and speeds. 178221782317824

I'm all ears for solutions,


Web Goblin
05-03-2016, 08:56 AM
Unless you have some mechanical issues with your machine then I would say that this letter was drawn as a polyline.
Most post processors really don't like polylines. What they do is break them down in to short arcs or lines and then create the code for them leaving you with either a crap contour, a very long program or both. When drawing in cad for cutting the best things to use are lines, arcs and circles. Your post processor will easily understand them and create the correct code. I have seen straight lines drawn as polylines broken down into hundreds of lines of code and industrial controllers struggling to run them correctly. You could try saving the dxf as a v12 dxf and then try it again to see if that helps.

05-03-2016, 10:37 AM
Post the G-code file and lets see the code.

05-03-2016, 10:50 AM
Unless you have some mechanical issues with your machine then I would say that this letter was drawn as a polyline.

Thanks for thoughts. I suppose what i should do is run a file which is exported as dxf 12 to confirm or eliminate that. On that letter 'a' it appears to do some of the curves fine but is cutting corner on some of the tighter radius. This could be a mechanical issue, as the x axis is extended quite some way and something is causing a harmonic micro wobble, for want of a better description. I'd certainly be interested to hear back about my Mach3 settings as they might be an issue.

05-03-2016, 11:18 AM
N0010 (Filename: Big A3.tap)
N0020 (Post processor: Mach3 plasma THC with scriber and backlash compensation.scpost)
N0030 (Date: 05/03/2016)
N0040 G21 (Units: Metric)
N0050 F1
N0060 G53 G90 G40
N0070 (Part: Big A3)
N0080 (Operation: Outside Offset, LAYER_1, T3: Plasma 3mm-30A-850mm-1.58mm cut height)
N0090 G00 X15.6144 Y12.5939
N0100 G28.1 Z20.00 F500.0
N0110 G92 Z0.0
N0120 G00 Z1.5000
N0130 G92 Z0.0
N0140 G00 Z4.0000
N0150 M03
N0160 G04 P0.6
N0170 G01 Z2.8000 F150.0
N0180 X16.6791 Y10.0961 F850.0
N0190 X19.8560 Y9.0754
N0200 X22.8081 Y8.5534 F510.0
N0210 X23.2751 Y8.0316
N0220 Y5.0316
N0230 Y3.0000 F850.0
N0240 X23.2752 Y0.0000 F510.0
N0250 X23.1118 Y-0.3806
N0260 X22.7234 Y-0.5243
N0270 X19.7256 Y-0.4140
N0280 X19.5250 Y-0.4096 F850.0
N0290 X16.2684 Y-0.1946
N0300 X12.9140 Y0.4530
N0310 X9.7047 Y1.6244
N0320 X6.9448 Y3.1894
N0330 X4.4943 Y5.2049
N0340 X1.9916 Y8.3236
N0350 X0.3023 Y11.9481
N0360 X-0.4768 Y15.8702
N0370 X-0.3009 Y19.8651
N0380 X0.8199 Y23.7036
N0390 X2.7076 Y27.1242
N0400 X5.2379 Y30.1008
N0410 X8.3099 Y32.5146
N0420 X11.8006 Y34.2690
N0430 X17.0636 Y35.9060
N0440 X22.4926 Y36.8574
N0450 X41.8802 Y40.3266
N0460 X41.7476 Y44.9323
N0470 X41.5397 Y46.6742
N0480 X39.3169 Y50.6968
N0490 X33.8596 Y53.7325
N0500 X26.2101 Y54.6128
N0510 X19.4976 Y53.1823
N0520 X15.4249 Y49.6995
N0530 X13.5327 Y46.0347
N0540 X12.4418 Y43.2411 F510.0
N0550 X11.8739 Y42.8903
N0560 X8.9014 Y43.2956
N0570 X4.7687 Y43.8592 F850.0
N0580 X1.7962 Y44.2645 F510.0
N0590 X1.4233 Y44.5043
N0600 X1.3669 Y44.9440
N0610 X2.2191 Y47.8202
N0620 X2.2266 Y47.8476 F850.0
N0630 X3.2325 Y50.7950
N0640 X5.2232 Y54.4048
N0650 X7.9755 Y57.4738
N0660 X11.6546 Y60.1211
N0670 X15.7954 Y61.9647
N0680 X21.6148 Y63.4567
N0690 X27.5792 Y64.1762
N0700 X33.5864 Y64.1110
N0710 X39.1003 Y63.1710
N0720 X44.3471 Y61.2326
N0730 X46.9075 Y59.6615
N0740 X49.0885 Y57.5957
N0750 X50.7961 Y55.1243
N0760 X51.9568 Y52.3536
N0770 X52.8822 Y48.3915
N0780 X53.2996 Y44.3442
N0790 X53.3356 Y22.7635
N0800 X53.7209 Y11.2433
N0810 X54.3125 Y8.2339
N0820 X55.5566 Y4.3315
N0830 X56.5823 Y1.5125 F510.0
N0840 X56.5247 Y1.0271
N0850 X56.0921 Y0.7996
N0860 X53.0921
N0870 X48.3272 F850.0
N0880 X45.3272 F510.0
N0890 X44.8286 Y1.1602
N0900 X43.9445 Y4.0268
N0910 X43.6966 Y4.9088 F850.0
N0920 X42.9361 Y7.9071
N0930 X41.6861 Y6.9167
N0940 X39.7115 Y5.4403
N0950 X35.0065 Y2.8267
N0960 X29.9713 Y0.8867
N0970 X27.1101 Y-0.0142 F510.0
N0980 X26.6484 Y0.0702
N0990 X26.4386 Y0.4900
N1000 Y3.4900
N1010 Y5.2831 F850.0
N1020 X26.4385 Y8.2831 F510.0
N1030 X26.8227 Y8.7889
N1040 X29.6832 Y9.6912
N1050 X33.2111 Y11.1111 F850.0
N1060 X36.5363 Y13.1807
N1070 X39.7573 Y17.0997
N1080 X41.2449 Y21.9495
N1090 X41.8613 Y31.1315
N1100 X39.1532 Y30.2866
N1110 X35.6880 Y29.2892
N1120 X28.6139 Y27.9105
N1130 X21.5887 Y26.7631
N1140 X15.3494 Y24.4012
N1150 X13.0505 Y22.3261
N1160 X11.7379 Y19.5211
N1170 X11.6177 Y16.4265
N1180 X13.3167 Y12.5964
N1190 X16.6791 Y10.0961
N1200 X18.3443 Y10.8059
N1210 M05
N1220 G00 Z20.0000
N1230 X0.0000 Y0.0000
N1240 M05 M30

Web Goblin
05-03-2016, 12:37 PM
This isn't perfect but give it a try to see if its any better.

05-03-2016, 06:26 PM
I've posted the gcode below, thanks

05-03-2016, 06:49 PM
I loaded that into Mach3 and zooming in (not too far either) in the toolpath window on the toolpath tab it looked more like a series of straight lines than curves

- Nick

05-03-2016, 07:02 PM
Wow, your right! I rarely open the Mach3 toolpath window and its most definitely reading it as a series of straight lines. The question is why?

05-03-2016, 07:28 PM
I'm guessing that your Post Processor isn't outputting code that's compatible with your Mach3 configuration.
Sadly my expertise on these is limited to my own system but I'm sure someone with greater wisdom will enlighten us ;-)

05-03-2016, 07:41 PM
I just imported the dxf kindly uploaded by Web Goblin directly into Mach3, getting mach3 to generate the code. No segments, nice and smooth?

Indeed Hopfully someone with greater wisdom will enlighten us ;-)


05-03-2016, 08:46 PM
A quick look at the gcode immediately shows that it's a series of line segments - there's a G1 near the beginning, then just a series of coordinates thereafter which will also use the implied G1. Not a G2/G3 in sight.

My guess is that the DXF you are exporting, for some reason, is using straight line approximations and not curves or arcs. I've had that problem exporting from Adobe Illustrator and it turned out to be that I was not using the latest available DXF format. Can you explore that?

Web Goblin
05-03-2016, 08:56 PM
I had a quick look at the original dxf and it is made from polylines. Most post processors cant understand them and break them down into loads of little lines. That way you get the kind of effect your are getting with it. Curves end up being made from straight lines. This also causes machines to stutter when trying to process the code also prevents them from reaching top cutting speed due to the amount of code they are trying to load and run.
Take your original drawing and then draw over it in cad using lines and arcs only. Then save it as a dxf and post process it again and try the results. Hopefully you will get a nice smooth contour.

05-03-2016, 10:06 PM
One more thought - not sure about Aspire as I use VCarve, but in VCarve there is a "convert to curves" tool. Letters seem to be created as a series of line segments but you can use the "convert to curves" tool to, presumably, convert to curves... I have just done a quick trial but the CAM post-processor in VCarve itself seems to give straight line segments in the gcode in either case. However, it might be that the dxf written out is different which might help with a different CAM processor.

Robin Hewitt
05-03-2016, 10:32 PM
Convert to curves usually means throwing away details of character and font so you are left with a fixed outline. If the outline is too steppy, look to see if there are any parameters you can tweak in the Convert to Curves command.

06-03-2016, 02:27 PM
Sorry been busy but like been said Clearly there are no G2/3 arc moves only G1 so it's the code not machine or Mach3.

Doesn't matter if you convert to Arc's in CAD or CAM if the post can't process them. Often if standard Post can't deal with Arcs there'll be separate post which does.

Robin Hewitt
06-03-2016, 06:33 PM
Maybe you can sue them for deformation of character? :very_drunk:

06-03-2016, 06:53 PM
Maybe you can sue them for deformation of character? :very_drunk:


06-03-2016, 09:52 PM
Maybe you can sue them for deformation of character? :very_drunk:

You sir should be awarded a prize for that one! :D

07-03-2016, 01:59 AM
I just imported the dxf kindly uploaded by Web Goblin directly into Mach3, getting mach3 to generate the code. No segments, nice and smooth?

That points the finger firmly at the software you're using to generate your dxf files, stop using it and use something people who don't have the issue use.

07-03-2016, 10:29 PM
Pleased to report back that after changing the Sheetcam postprocessor from Mach3 plasma with THC and backlash compensation to Mach3 plasma with THC in the Sheetcam options the curve now cuts as a smooth line. Even the 6, 8 10mm holes are better.

Thanks all :)