polyline vs spline

[tomloewen]

I'm hoping someone can help explain something to me. When you guys plasma cut, does it matter if the item, or file you're cutting out is made up of polylines or splines? And is there a general preference?
Thanks,
Tom

[little blue choo]

Hey Tom, really don't know the difference but when I went to Arclight to train they told me to use polyline and it has always worked well. Maybe I'll try to change up one day and see what difference it makes. If I ever find the time to experiment.

Rick

[WyoGreen]

Tom, I always convert files to Polylines before processing them in SheetCam. It's been my experience that SheetCam has an easier time with Polylines. Don't know why, it just seems to be that way, at least for me.

Steve

[tomloewen]

Tom, I always convert files to Polylines before processing them in SheetCam. It's been my experience that SheetCam has an easier time with Polylines. Don't know why, it just seems to be that way, at least for me.

Steve

Thanks for the info. I don't cut out files, I just draw them. I do a lot of freehand work, (basically using the mouse as a pencil) and I've found polylines are easier to work with, simply cause I can do more with them, so I'll stick to polylines.

But I downloaded a file from this site and it had a WHACK of nodes. So I used inkscape to reduce the nodes but when I saved the cleaned up file, and reopened it in Draftsight, the polylines and changed to splines, and Draftsight has no command to change splines into polylines. And can't seem to find an inexpensive program that can do that. You mentioned you convert files to Polylines before processing them in SheetCam. What software do you use for that?
Thanks,
Tom

[tomloewen]

Hey Tom, really don't know the difference but when I went to Arclight to train they told me to use polyline and it has always worked well. Maybe I'll try to change up one day and see what difference it makes. If I ever find the time to experiment.

Rick

Hi Rick, I'm not sure of the difference either. I know little about the technical side of dxf files but I'm thinking it may have something to do with node count, or controlling the amount of nodes . . . not sure

[urbnsr]

A couple of years ago I looked into this. I use SheetCAM and I assume your CAM program is going to make the biggest difference on how it works with either one.. SheetCAM will take both a polyline and spline through an arc detection. I believe there is not much difference in the two. There is a difference in cut quality if you have a true circle and a circle made up of either a polyline or a spline. A circle (G02 or G03) will look better. I think the spline was introduced after the polyline so I don't know if that means the spline offers something more the the polyline or not.

Paul

[urbnsr]

Assuming you saved the inkscape file as a DXF, if you save that DXF in draftsight using version R12 DXF, quit the file and reopen, the splines will be polylines (splines were introduced after R12).

I use both poly and splines and don't notice a resulting difference out of SheetCAM.
HTH
Paul

[tomloewen]

Assuming you saved the inkscape file as a DXF, if you save that DXF in draftsight using version R12 DXF, quit the file and reopen, the splines will be polylines (splines were introduced after R12).

I use both poly and splines and don't notice a resulting difference out of SheetCAM.
HTH
Paul

THANKS FOR THAT ONE Paul!! It worked great! only one problem, it's got a WHACK of nodes again. The file size went from 374kb to 1.81mb. So now the question is, does an over abundent amount nodes truly effect the cutting process?

[urbnsr]

You're welcome, Tom. I believe the greater number of nodes, the larger the GCode file. SheetCAM's import settings will probably play into the actual outcome along with controller program settings like constant velocity, etc. I still think the "cleaner" the code, the better cut. That's just my opinion and haven't tested it.

[tomloewen]

You're welcome, Tom. I believe the greater number of nodes, the larger the GCode file. SheetCAM's import settings will probably play into the actual outcome along with controller program settings like constant velocity, etc. I still think the "cleaner" the code, the better cut. That's just my opinion and haven't tested it.

Ok that helps. Next time when I need to choose between polylines with a whack of nodes, or splines with few nodes, I'll pick the splines.
Thanks.

[tnbndr]

and Draftsight has no command to change splines into polylines.

I don't use Draftsight but it is similar to Autocad from what I am told. You can change a spline to a pline in Autocad by choosing the Modify menu, spline, and typing "P" (look at the command line it should say convert to Polyline), select spline to edit and click enter. Do a properties check and it should have changed to a polyline.
The method I have always used is Modify, Polyline, select object, it then prompts you that "object is not a polyline do you want to make it one", type "Y" for yes and then follow the command line for other options.

I only use polylines, lines and arc for tracing and drawing. Programs I have used in the past for processing G-code do not like splines for some reason.

[Bigdogbro1]

I believe that polylines are straight line segments connected at each node. Normally polylines are straight lines between nodes but can be arc'd to create curves.

A spline is a number of nodes which are then connected together with a curved line which tries to intersect each of those nodes. The CAD software will sometimes not intersect each node but come as close as possible to create the curve. Thus you may have some unconnected nodes. Some draw programs will attempt to connect to the unconnected nodes if they are within a predetermined distance setup in the import settings but it's not guaranteed.

Recommended you stick with polylines in your mechanical CAD designs (.DXF) or go with creating .SVG vector files which is my choice for all artwork.