Experienced CNC users who have imported third-party vector designs from a DXF file format, have seen large numbers of vector nodes. Does this present a problem for the CNC wood machine?
What is the DXF File Format?
DXF is short for Drawing Exchange Format or Drawing Interchange Format. It's an open-source format for 2D and 3D drawings created by Autodesk back in 1982. It is a type of vector file.
The purpose of the DXF format was to make it easy for designers and engineers to share drawings between different CAD software applications. As a result, it quickly became popular.
The Problem with DXF File Format Designs
I've used the Vectric Aspire software in the vector design below to create two circles. Both are the same size. I made the one on the left using Bezier Curves. The circle on the right uses a more significant number of small, straight lines to create the circle shape.
The Bezier Curves are what I refer to as the blue-colored smooth nodes. It has handles on either side (white-colored nodes), which you can move to adjust the curve.
The black-colored nodes on the right are straight lines. Therefore, moving them will adjust the angle only.
DXF format files typically look like the circle on the right because they contain many black-colored straight nodes.
The problem can be even worse than the example I've fabricated above. The example below shows a design I downloaded from a popular DXF vector file-sharing site.
In this design, the vector nodes are so frequent that it appears drawn by a thick line. As a result, you see the individual nodes once you zoom in.
So what exactly is the problem with having this many nodes in your design?
Most CNC machines use G-Code to replicate the digital vector design onto wood or other materials. In addition, most software for CNC machines has a CAM, Computer Aided Manufacturing component in addition to the drawing side, i.e., CAD or Computer Aided Design.
Not all CNC software and machines work the same, but there is an essential process. This process involves the CAM side of the software translating the drawing vectors into G-Code for the CNC machine to understand and operate.
Typically, this happens by translating each vector node from the drawing into a corresponding line of G-Code to be processed by the machine. This logic forms the core of the problem with excessive vector nodes. You could end up with more lines of G-Code than necessary for the CNC machine to operate efficiently.
I'm not a G-Code expert, but the CNC software can send G-Code instructions to create an arc of a certain radius rather than multiple instructions for short, straight-line segments. These more accurate G-Codes allow the machine to process instructions faster and cover more distance on the material.
Not all CNC machines work the same, but a CNC machine could "stutter" due to the excessive nodes or even produce non-smooth edges.
DXF File Format Generated G-Code
I created a simple profile toolpath for each circle above to test the theory of excessive vector nodes. I limited the depth of the cut to one pass only. I calculated each toolpath and saved the resulting G-Code to a text file.
Looking at the two text files below, it does hold that the vector with more nodes generated more G-Code instructions. Based on the row counts, there is more than four times the number of lines with the short-line nodes.
Are DXF Files a Cause for Concern?
I've watched many YouTube videos on how to use the Vectric Aspire CNC software. However, most professional vector designers who have done this for a while create their vectors using fewer nodes.
The problems begin when you download DXF format files from various websites offering free designs. Someone created these vector designs in ways, and with software, you don't know.
Raster image tracing can also be a source of excessive nodes. This tracing is a process by which image pixels convert to vectors.
Typically the source issue with improperly formatted DXF files is how a drawing software exports the DXF file. There are options for creating the vector design export, but it uses the default options.
I typically download the drawing's SVG (Scalable Vector Graphics) format if I have a choice. SVG is newer and tends to be cleaner, with fewer nodes.
I would only clean up the DXF nodes after trying it first on my CNC wood machine. After that, if it works fine, then I would leave it alone.
The problem is if you want to node edit the DXF vectors to change the design. This editing is only possible by first cleaning and reducing the number of vector nodes.
Vectric does offer tools to make this cleanup of nodes automatic. It could be better, but close enough in most cases.
Open vectors and vector intersections are a much bigger problem, especially if you plan to V-Carve your design.
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