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DWG export for CNC alters art/path

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I tried to export a DWG file for a CNC vendor and the artwork changes to a point where the shapes change and shift off the material template boarder. I am going from VWX2010 and exporting back to 2007/2008/2009 by the vendors request.

Has anyone else had this issue, and more importantly, how can I keep the line work accurate? Registration is critical. Help

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I had a couple curves go bad. In VWX they started as 3 vertex splines where the middle vertex was pulled to create non arc curves between corner points at ends. Curves were then converted to arcs with Polysmoothing in Arc mode. The export to DWG caused a distortion. I reworked with more points and the new export was fine.

A few things -

Lots of CAD/CAM software can only interpret circular arcs and straight lines. Check with your operator, but you may need to convert everything to arcs.

Always send a 1:1 scale file. Include a scale object in each file with some text describing the dimension - I often use a 10"x1" rectangle with text "Scale check - do not cut", and a phone conversation to verify that this is a guide object.

Port out to dwg or dxf and port back into a new vwx file. Compare to your original. And/or open the dwg in Draftsite or other native dwg software before you transmit it to the cnc shop. You might catch any problems before they get expensive.

Try to be at the CNC shop looking at their screen with the operator when they open your files, especially the first few times. Take a laptop and be ready to revise as needed. Or at least send pdf so the operator has something to compare. Ask for and approve pdf confirmation drawings of the cutting paths before they do the work.

Sometimes a hidden segment of a polygon will export as part of the path. Watch for these in the reimport.

Sometimes a vwx straight path will export as a curve with infinite radius. Delete and redraw.

It takes some work with each new cnc shop and machine. But ultimately, the process creates perfect parts from the cnc work.

Good luck!

-B

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Thanks for the tips. I think converting to arcs might help, If i can figure it out for these shapes.

I wish I could be on site to work this out, but that the way of the internet. It allows you to work thousands of miles away, but you have to do a little more coordination.

I have a call with the vendor on Monday, so we'll see what happens. I think I may send a test file ahead of time.

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You don't indicate your vwx version. Please click the My Stuff tab near top of this techboard window and create a profile signature with your OS info and Vectorworks version.

If you are unfamiliar with the process, and your setup is fairly recent, here is a method to convert the vertices in a selected object to arcs:

Select the object.

Modify menu>PolySmoothing>Arc Smoothing

Vectorworks will read the curves, convert any curve vertices to arc vertices, and add new arc vertices to maintain tangency/continuity. It's not perfect, though. Corner vertices in polylines remain corners, corners in polygons are converted to arcs.

Do a smoothing test in a new file. Draw a polyline with some corner points and some non arc curves. Also put in one of your curved paths. For each path duplicate it in place, run the polysmoothing command. Change the color of the converted paths, zoom in, and navigate along the paths to see where and how much they vary from the originals below.

HTH

-B

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