DXF export for CNC

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Permalink Reply by chris on August 23, 2010 at 8:46pm

I'm unsure what you need for CNC or if it's flat parts, but for unrolling flat parts (for boats, done out of alluminium) you need to silhuette the flattened panel and export the curves. There are settings that you can adjust in the export toolbar.

My workflow is to:
-Unroll panel - (checking to see that there's no shrinkage),
-Explode panel into seperate surfaces
-Silhuette from the top view
-Join the edges of the part into a closed poly curve. Put any etching/fold marks you want onto a different layer and group all of the lines for each part.
-Once all your panels are 'pulled' we export to autocad and save the dxf from there. Sometimes we notice that the entities 'jump'. That is, they sometimes cut corners or round out sharp edges which you can see when you put into autocad.


Hope this helps.

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Permalink Reply by Schuyler Greenawalt on August 25, 2010 at 5:44pm

Thomas -

I'm going to assume from your post that you're trying to export 2D linework for CNC cutting - is that correct? I do a lot of designing in Rhino for parts that I have CNC waterjetted out of flat stock, so maybe I can help. I typically setup my export settings to the 2004 Polylines setting, but really that depends on what system the people have who are doing the cutting. The important thing is to properly set the curve parameters. When you go to export, click on "Edit schemes..." On the page that comes up, you can select your dxf file type - I use ACAD 2004. The "curves" tab is the one you want to play with. In the AutoCAD objects drop downs, I set everything to Polylines, except Arcs, which I set to Arcs. This means even if you have a curve (in Rhino speak) it will break it down into a polyline. HOW it does that depends on your Tessellation Parameters. Check the "Maximum Angle" box. This determines how much the curve can deviate before it breaks it into a unique segment. So you will be representing smooth curves with small straight lines, and this parameter is the one that really matters. I typically set it anywhere between 2 and 4 degrees. You may be tempted to set it smaller than that, but here's why you might not want to - if you make it too small, the segments become really tiny, and they might choke the CNC. Make sense?

-Sky

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Permalink Reply by Will Tait on August 25, 2010 at 8:33pm

Greetings Schuyler,

I do a lot of CNC work and am writing a short article for a trade group to bring about some awareness of issues on both sides, that is those who want to have contract CNC work done and those who do CNC work. May I use your statement thread as a quote in my article? If so how would you want me to acknowledge it. This is not something I am being paid for, I am simply trying to facilitate communication around the various issues people have.

My e-mail address is willt@mcn.org

Thank you,

Will Tait

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Permalink Reply by Will Tait on August 26, 2010 at 3:00pm

Hi Thomas,
I am writing a short article on CNC for a trade group. May I use your post iun that article to help highlight some of the issues people run into when thay want to have CNC work done?

Thanks,

Will Tait
willt@mcn.org

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