I’ve got a real simple Sketchup drawing - just a 2D oval shape - that I need to export to DXF to provide to a shop that will be cutting out a table top on a CNC router. The shop said to keep it as simple as possible, so no 3D elements, labels, dimensions, etc. They can take .skp, .pdf, or .dxf files, but said the .dxf would be best.
I see that I can do this by selecting either 3D Model or 2D Graphic on the File->Export menu. I’ve tried both and get a successful export, but the file sizes are different. Are there any best practices on which to choose for a 2D shape going to CNC?
I also saw a comment on an older thread about always drawing curves in the counter-clockwise direction, and never using the flip tool for best results. Does this imply that the CNC machine will actually follow the curve in the direction I’ve drawn it? Any suggestions will be appreciated!
I would suggest that you copy the table top to a separate file. Set the camera to Parallel Projection and the appropriate standard view. Then use the 3D DXF export option. The 3D DXF exporter will represent the curves as smooth curves instead of individual straight segments.
Thanks, Dave. I do have it in a separate file, with parallel top view as you suggested. Good to know that the exporter will generate smooth curves - I had set all my curves to the highest segment counts that SU would allow, so maybe that step wasn’t necessary. Right now my drawing is just the outline of the curve (i.e. 600 edges but no faces). I’m wondering if I need to add the one bounded face back into the model. I’m sure it all depends on what the CNC machine requires in order to make the cut. I guess I’ll find out tomorrow when I send it over. Just trying to be proactive and avoid a lot of back & forth.
No, I think from memory adding a face will give you double edges that become confusing.
And as Dave noted 600 is overkill, even 360 is one segment per degree, but essentially the default 24 segments will export as a true curve this way.
But only if your arcs and circles are recognised as such in entity info, a ‘curve’ will be segmented.
I would agree that 600 edges is excessive, but I was under the assumption that they would be exported as straight edges so the router would follow them exactly - giving a faceted cut that would need to be smoothed with a sander. The edges all belong to “curves” as shown in Entity Info, but they’re not circular arcs. I originally drew them as circular arcs (inscribed within a 40" square), but then I used the Scale tool to stretch the overall shape to its final dimensions (different x and y dimensions).
Now that I know the curves will be converted into actual smooth curves by the exporter, I can easily go back and re-draw using 24 segments each. But I don’t expect it will really matter to the exporter.
Any ideas about needing to draw the curves in a certain direction (i.e. counter-clockwise)?
I remember there was some talk about that some time back, but wasn’t of much interest to me. I haven’t needed to use .dxf for a long time so my memory of the inticacies is foggy.
I use .svg for laser work.
Well, go figure. I sent the 3D export to the shop this morning, but they said it wouldn’t even load. So I sent the 2D export, and it loaded fine and produced a beautiful cut. No segmenting/facets whatsoever. FYI, the piece being cut was edge-glued white oak, about 1 5/8" thick, and they cut it in seven passes (about 1/4" per pass).
Thanks all for your input and suggestions!
Yes, Sketchup has long had this capability of exporting 2D arcs and circles in .dxf. There are two pathways being discussed in this thread, one is the native function that leverages the stored metadata for arcs and circles using the export 3D function and paralel projection, that method is outlined here:
The second is a newer development using the very good extension OpenCutList which uses a different method of recognizing and building DXF and DWG arcs and curves by recognizing collections of edges and converting them. The advantage of this is that the curves need not be circles or strict arcs in Sketchup. I use this extension too and find it works well as long as there are enough segments to your arc to be recognized.
Which method you use I think depends greatly on the complexity and frequency of the files you need to output. I have used the first method for years, but use a combination of both.
I would begin with the native export, it’s simple enough and understanding that is a good foundation. Don’t forget to set the export options correctly, export edges only, not faces.
I have figured this out through the very comprehensive documentation. This has only been a problem a few times when working with large sets of compound curves, sometimes multiple intersecting tangent curves will end up splitting a curve and leaving only 3 or 4 segments behind, this is hard to see until export. Generally 5 is a good number and I understand the line needs to be drawn somewhere, but I have wished it could be adjustable.
