Segmentation Issues for Laser Cutting


#1

So here is the situation.

I draw a circle with a radius of 6".
I set the segments to 6.
I make it into a component.
I set style so that edge color matches material.
I assign a color of red to the circle.
I save the file.
I click file - Export - 3D Model - Save as DWG (Edges Only)

I then import the file with different programs:

In SU2017 Pro: i get 96 segments, 72" radius, black colored outline only.

In Autodesk DWG Trueview 2018:
2D wireframe View: I get no segmentation (or infinite segmentation) with a radius of 6 without a unit of measure such as inches or feet. The color of the outline is red.
Wireframe View: I get what appears to be 48 segments. Radius of 6. Red outline
Shaded View: Again 48 segments. Radius of 6. Red outline.

In Autodesk A360 Online Viewer: I get no segmentation. Radius of 6". Red outline.

So my question is this: if i send the circle to a laser cutter then how many segments will the cut circle have?

Furthermore, if i export the DWG file with the Faces Only option then i get the same shaded 6" circle with 6 segments in all the programs mentioned above. The only issue is that in SU the line segments are divided. Instead of clicking on one to select all i have to select all of them individually. Assuming the faces only option when exporting can be sent to the laser cutter, something i have read not to do in this forum in another post, then my second question is would the detachment of the line segments making up the circle have an effect on the continuous movement of the laser cutting? In other words, would it be properly cut or would the initial square tile still be stuck to the 6 segments of the circle?

Note: I’m new to laser cutting so any feedback on these questions or anything important that i should know about SU and laser cutting would be greatly appreciated.

Thank you.


#2

Circles and Arcs exported as ‘2d’ are segmented at the default.
But when in 3d they should be true ACAD Circles/Arcs - i.e. no segmentation.
Although the ACAD settings can display such things as if they are segmented - a graphics-memory saving trick.

However, if you have used a Circle/Arc to extrude a 3d shape in SketchUp then the edges sharing it will effectively segment them.
Exporting Faces only will force this.
Why not export edges only ?
What function do the faces have in your CAD/CNC ?

Wouldn’t you be better to export a single 2d face as a 3d CAD file ?
That way the Circles/Arcs remain true.
Is there any need for actual 3d geometry for the CNC ?

What color have you set for Layer0 in the SKP ?
This will b reflected in the CAD version…


#3

Thanks for the info TIG.

I get it now. I kind of had an idea that exporting to 3D Model with Edges Only produces true circles and arcs, but got confused by Autodesk DWG Trueviews segmentation for graphics memory saving trick.

But i do have two questions remaining. Perhaps you or someone knowledgeable would be able to answer my questions.

1 - I heard somewhere that the laser cutters need the lines, circles, and arcs of the 2D model to be a specific thickness to cut properly. Is this true? I’m guessing it isn’t because there is no option to set the thickness like 2D export when exporting to 3D. But i have to ask in case i have to import the DWG file into a different program to set the thickness.

2 - If the DWG exported file only uses the colors from layer0, then how can i create a file with more than one color since layer0 can only be one color? The reason i’m asking is because the red color is for laser cutting, the blue color is for vector engraving, and the black color is for raster engraving, which means if one needed to carry out a combination of these laser operations on a single DWG file then it would be impossible to do it with sketchup alone. This means i would have to somehow open up the DWG file in another program to set the different colors of each edge.


#4

in the past I have used layers with set colors to differentiate between cuts and etching…

to make sure it matched their machine I had them send me an example dxf and imported that into SU and saved it as a Template…

it had 32 layers, but I only used three…

all geometry on Layer0

group containing cuts on ‘red’

group containing etching on ‘green’

I turned on colour by layer

exported dxf as 3d in top view PP and all worked well…

john


#5

Thanks John, Layers seems to be the key.

However for the time being i will only be laser cutting, but while i was in the territory i had to ask in case i planed on using etching and engraving further down the road.

But i do have one question that remains unanswered.

If the segments to a circle are not welded, if they are divided, then does that make a difference on the laser cutting when compared to the same circle with welded segments?

EDIT: Never mind. The answer to the question is obviously no, there is no difference. I think the logic is that so long as the segments are connected the laser will run the cut continuously.

However i do have to note, for anybody who cares, modifying arcs and circles in the slightest way converts them into segmented lines. Also, taking an arc and a line that connects them, exporting them to a 3D model in DWG or DXF format, and using the edges only option keeps the arc as a true arc. But if you weld them together, with a welding extension in SU, then they become segmented.

So its all a very delicate process that has to be carefully examined by importing the DWG/DXF files into one or two other programs to verify that the arcs and circles remain true.


#6

There is a plugin the will restore the circle/arc as long as the segment sizes are still all the same.


#7

It works.

I can create an arc, divide the segments, remove a segment, and then apply the plugin and it becomes a true arc again.

However, strangely, with a circle, if i divide the segments, then erase one of them, then apply the plugin it will re-close the circle to produce a true circle.

But that is where the ‘weld’ plugin comes in handy. If i first weld the circle with the missing segment, then apply the plugin you just gave me, then the circle becomes a true arc.

Thanks for the plugin Box. Maybe i should call you ‘arc’ from now on. lol.


#8

Question:

Does combining lines into a group or component have an effect on the workload for the laser operator and or the way the laser follows an outline during a cut?

For instance, in the following photo i have 3 combinations to choose from.
1 - Keep all lines detached.
2 - Make into a group or component all the lines that connect.
3 - Make all the lines into one group or component.

My thinking is that option 2 is the one that makes the most amount of sense since when laser cutting the operator will have to choose which connected lines have to be cut first. This means that having all of the lines detached means more time to select the individual lines, while having all the lines combined into a group or component would also require extra steps that come about from editing the group or component.

Furthermore, i am not sure anymore if detached lines will produce a continuous cut during laser cutting, which again means option 2 would make the most amount of sense.

This is my thinking. And quite frankly i am not sure if i am right.

If anyone has any experience or knowledge about what option i should take or if there is even a difference between the three then i’m all ears.

Thank you.


#9

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