Sketchup File Export Question - DXF file format

[Warren E. Johnson]

I am designing a piece that I would like to use a CNC router to locate about 144 holes. I have a source with a CNC router that is large enough to handle a 4X8 sheet of plywood but he need the data to be in a DXF file format. I have the drawing in Sketchup. Is there a plug in that will convert the Sketchup file to a DXF file?

Warren

[Dave Richards]

Not that I know of. I did a quick search to see if perhaps I'd missed one but didn't find anything useful. Get the pro version of SketchUp. It'll do it. Or get a CAD application that can import SKP files and make the conversion there.

Maybe he can read a point cloud text file. You could export the centers or the holes as a txt file and go from there. Or you could find someone who has the pro version of SketchUp and ask them nicely if they would make the export for you.

[Mark Bolton]

I know Dave is the Guru but will this not work?
http://www.guitar-list.com/download-software/convert-sketchup-skp-files-dxf-or-stl

** Additioinal Info ** - I had the above link and this video http://www.youtube.com/watch?v=kei0gmOwZ5Q in my bookmarks

[Dave Richards]

Might work depending upon the SketchUp version the OP has.

Good find.

[Mark Bolton]

Might work depending upon the SketchUp version the OP has.

Good find.


I remember reading/seeing that the main issue with exporting from the free version is with regards to polygons (circles) in that the free exports will only export curves as poly lines and will of course be machined that way. I dont have the pro version but I think its suppose to address this.

[Dave Richards]

the pro version uses a real exporter while plugins are sort of cheating it. The same applies for importers--there are several of them that I am aware of but they all seem to fall short in one way or another.

[Art Mann]

I remember reading/seeing that the main issue with exporting from the free version is with regards to polygons (circles) in that the free exports will only export curves as poly lines and will of course be machined that way. I dont have the pro version but I think its suppose to address this.

You are right about circles and the free version of Sketchup. If the design has circles, the they need to be composed of many - say 360 - polylines so that the circle will be round and not angular. Sketchup allows you to choose the number of lines used to make the circle when you first select the circle tool. Just type it into the input box in the lower right hand corner of the display.

[Mark Bolton]

You are right about circles and the free version of Sketchup. If the design has circles, the they need to be composed of many - say 360 - polylines so that the circle will be round and not angular. Sketchup allows you to choose the number of lines used to make the circle when you first select the circle tool. Just type it into the input box in the lower right hand corner of the display.

RIght, but isnt it true that true exporters (somehow) smooth these lines automatically into a smooth circle? Simply shortening the length of the poly line will never make a true circle. That said, I dont know that high end cad exports do that either.

Its a given that with a very short poly line the polygon would be imperceptible but I can only imagine there are some shortcomings with sketchup free. Hopefully the plugin will be usable measure for the OP. Most everything I would ever export to a CNC shop would incoporate polygons so I tend to give them a rendering with dimensions and then bear the cost of them getting it into the software they use in house.

[Bob Lang]

Circles in either version of SketchUp are many sided polygons. The default number of sides is 24, but you can change that if you like. Arcs are the same way, and this doesn't change during a DXF export. It's been a while since I've done anything with CNC, but my understanding is that the G-code that runs the machine thinks the same way – curves look like curves because there are a zillion short lines. Whether or not the holes look like holes will depend on their size, the size of the cutter in the machine, and the way that particular machine works.

The DXF export function is a feature of the Pro version of SketchUp, and one of the good reasons for upgrading. It might be wise to ask this question on the CNC forum here at Sawmill Creek.

Bob Lang

[Mark Bolton]

Circles in either version of SketchUp are many sided polygons. The default number of sides is 24, but you can change that if you like. Arcs are the same way, and this doesn't change during a DXF export. It's been a while since I've done anything with CNC, but my understanding is that the G-code that runs the machine thinks the same way – curves look like curves because there are a zillion short lines. Whether or not the holes look like holes will depend on their size, the size of the cutter in the machine, and the way that particular machine works.

The DXF export function is a feature of the Pro version of SketchUp, and one of the good reasons for upgrading. It might be wise to ask this question on the CNC forum here at Sawmill Creek.

Bob Lang


Bob, this was what I was getting at. I didnt know if other programs had some sort of default function for polygons that smoothed them. Given a 3, 4, or 5 axis, machine your talking polygons at some scale. It just always seems to me when you have to hand the file over to someone else there is going to be some inherent tweaking on their part based on their knowledge of their equipment.

[Dave Richards]

Bob beat me to it but as he says, the thing with faceted circles is not unique to the free version of SketchUp.

Mark, I think you are correct about the tweaking thing.

[Warren E. Johnson]

Thank you for all of the replies. Fortunately I am just drilling holes for 1/4 inch dowels so the faceted circles should not be a problem. Are there other things I should know about the conversion?

Warren

[Dave Richards]

At what precision did you work when you drew the holes in SketchUp? In other words, what was Precision set to in Window>Model Info>Units?

[Grant Wilkinson]

It may depend on the working software of your CNC machine, too. We have tried unsuccessfully to export DXF files from the Pro version of Sketchup to Biesseworks, which is the operatiing system for a commercial sized CNC router. We have tried for several months, on and off, and never managed to get it to work. On some Biesse forums, we found that we were not alone.

[Bob Lang]

One issue may be the point of view of the SketchUp model when you export. There are only two dimensions in a DXF, not three as in SketchUp. Most of what I do these days is exporting to Adobe Illustrator and curves can be an issue. For CNC work I would do the export from a standard view with parallel projection. That should produce the same (or at least very similar) output to what you would have from a DXF file created in AutoCAD. The other issue could be that lines that are on top of each other in SketchUp might all be present in the exported DXF. Most CNC machines that I'm aware of have a program that reads the DXF file to create the paths for the machine and the issues may be at that stage of the game.

Bob Lang

[lowell holmes]

Warren,

I have AutoCad. Check your personal messages.