Node Reduction- DXF vs SVG and SheetCam

[The-Meerkat]

I recently watched a YouTube video called “ The Secret to Fixing DXF Files for CNC Project Success!” by IDC Woodcraft. I know it’s primarily for CNC Routing but the premise apples to all CNC using DXF and SVG files. So it’s very much related to Plasma issues too.
The video got me thinking, so I ran a couple tests.

When prepping to import a drawing into SheetCam, I always optimize the design I’m working on to reduce as many nodes as possible. I use Lightburn most of the time for that. However, after watching the video, I found after optimizing and saving a file as a DXF, if I import the optimized DXF file back into Lightburn, I have the same node count as I did before optimizing. On the other hand, if I optimize the design and save it as an SVG file, close that saved SVG file and reopen it again in Lightburn, the optimized (drastically lower nodes) count has been successfully saved in the file. So it’s probable that I’ve been cutting designs with way more nodes than I previously thought. That’s huge. It would explain why my THC sometimes fails to keep the torch high under control on intricate cuts for no apparent reason.

In light of my little tests, what are your methods or steps do you do for node optimization and do you save your files as DXF or SVG or what before importing into SheetCam?

All the best,

Scott

[adbuch]

In general, the dxf will have a higher node count than the svg for the same drawing. But it does depend on the particular drawing. I sometimes go back and forth several times between Inkscape and Design Edge when editing a vector file. After the last import of the dxf into Inkscape, often there are many more nodes than before - so I use the "Path, Simplify" tool to "optimize" the drawing file.

David

[adbuch]

I recently watched a YouTube video called “ The Secret to Fixing DXF Files for CNC Project Success!” by IDC Woodcraft. I know it’s primarily for CNC Routing but the premise apples to all CNC using DXF and SVG files. So it’s very much related to Plasma issues too.
The video got me thinking, so I ran a couple tests.

When prepping to import a drawing into SheetCam, I always optimize the design I’m working on to reduce as many nodes as possible. I use Lightburn most of the time for that. However, after watching the video, I found after optimizing and saving a file as a DXF, if I import the optimized DXF file back into Lightburn, I have the same node count as I did before optimizing. On the other hand, if I optimize the design and save it as an SVG file, close that saved SVG file and reopen it again in Lightburn, the optimized (drastically lower nodes) count has been successfully saved in the file. So it’s probable that I’ve been cutting designs with way more nodes than I previously thought. That’s huge. It would explain why my THC sometimes fails to keep the torch high under control on intricate cuts for no apparent reason.

In light of my little tests, what are your methods or steps do you do for node optimization and do you save your files as DXF or SVG or what before importing into SheetCam?

All the best,

Scott

[adbuch]

Here is an example. If you are using SheetCam, then this can be a good method to use if you feel you need to reduce node count before importing your vector file to SheetCam for cam/post processing.

However, if you happen to be using a program like Design Edge - this will be of no benefit since Design Edge will only import/export files in dxf format. It doesn't have the ability to work with svg format. Design Edge does all of the cad/cam/post processing in a single program.

David

[adbuch]

Here is an example of a simple drawing I created with Inkscape. I saved in both svg and dxf formats, imported each to SheetCam for cam/post processing. The g-code for the svg version actually as more lines of code than the corresponding g-code from the dxf version. I will let you draw your own conclusions.

David

shape.dxf

(19.33 KiB) Not downloaded yet

shape.dxf

(19.33 KiB) Not downloaded yet

shape.svg

(5.84 KiB) Not downloaded yet

shape.svg

(5.84 KiB) Not downloaded yet

https://drive.google.com/file/d/1-8CDKj ... sp=sharing
https://drive.google.com/file/d/1nruNIZ ... sp=sharing

[The-Meerkat]

David,
That’s a great example. It illustrates what I’m trying to say much better than just words. Thanks for that. I’m going to change up my routine and start saving files as SVG after optimizing nodes. I’m using CommandCNC these days and can monitor torch height a volts live. That’s something new for me. I’ll run optimized SVG files that way for a month or so and keep a sharp eye on my torch height on the CommandCNC display. If my torch height scoots along closer to the set cut height and my volts stay close to the setting, I’ll know for sure switching file types is right.

Now I’m wondering where I got the notion that DXF was better for Plasma. Till now, I only used SVG for CO2 Laser cutting and engraving. Oh well…

Again, great illustration!

[adbuch]

Either file type is fine for cnc plasma cutting, cnc wood routing, cnc laser cutting, etc. I see no particular reason why node count should affect your torch height control.

David

[The-Meerkat]

I just figured out today that saving my work as DXF has been completely negating my node reduction efforts on complex art designs. So when I thought I had 1000 nodes in the test, I actually had over 2000 nodes. In Lightburn, I always save my work as a .lbn (Lightburn file). Then I export and save it again as a DXF to import into SheetCam. Until today I had never even thought to double check the DXF by importing it back into Lightburn and checking the node count in the Optimizer. I was shocked. Thats why I’m going to test saving as a SVG for awhile and that’s all I was originally trying to put out there. If I’m seeing this issue for the 1st time clearly, I figure others that have crash issues from time to time might want to do the test also. I’m also looking forward to hearing from folks that have experienced the issue too. I do disagree about nodes not causing crashes. If enough nodes are crammed into a tight area with lots of twists and turns, the motion will slow, the THC won’t respond fast enough and the torch will take a dive. Yes, I have the ability to tune my THC settings, but it works just fine in AUTO mode 90% of the time. That 10% where it fails is always in an area where there is a tight, extended run of intricate art like scrolls, swirls, extra fancy script lettering,etc. I know now that’s where DXF has failed me because it’s not truly removing the nodes I thought were deleted. I’ll try on a project or two where it’s failed before and report my findings. I’m not inventing anything new here or looking to reinvent anything, Like I said at the beginning, I just saw a guy in a video on YouTube that explained how DXF reverts back to the original nodes count when you save the file. I thought “oh hell no” and tested it and found it to be very plausible.

All the best.

[adbuch]

I suppose it all depends on your control program and particular thc. For Plasmacam, there is no option to import in svg format - so we work with dxf files. We do have a smooth tool which can often be successfully used to reduce node count without affecting the fidelity of the drawing. We also have the option to adjust corner acceleration which can be particularly handy for cutting intricate shapes and help avoid unwanted torch dive. I really have never had a problem with the torch crashing because of too many nodes (or otherwise).

I'm not sure if SheetCam has this ability to reduce corner acceleration. I know there is a "rule" for slow on circles. But I don't use SheetCam for anything other then demo purposes.

Let us know how your testing goes.

David