Warning: DWG export degraded my curves too much :|

A little heads up, tagging you here @pascal and @wim.

I just got informed that the DWG I delivered to a customer came back from the waterjet all wrong… We are working on an art project and unfortunately the file I worked on was in Meters (I usually make all 2Ds in mm) but I figured it would work just fine. BUT when I exported I used the default 2007 flavour and that has “Simplify lines and arcs” on with 0.01 as default setting… resulting in all the curves being wrong and wonky within that 1cm tolerance… Which is obviously way too much for welding.
So now that stuff has to discarded and new panels has to be cut. Costly and annoying.

So PLEASE, to avoid this happening to others, turn off the simplify curve option as the default Rhino setting. Or at least check file unit size and lower that tolerance to 0.001 if the unit size is large.

Exporting what you have should always be the go-to standard. Modifying stuff with out telling, or at least asking, the user is a big no-no IMO.

Obviously my fault though, for not checking the file after exporting, prior to shipping it off.

I am not familiar with former context.
But directly sending the DWG to fabrication without checking it is really bad habit.

Always import back your DWG file into Rhino, or open it in AutoCAD, and check if the result DWG is right.

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Hi Holo,

Yes, this is always a problem when going from Rhino to CNC cutting. It’s not really a failure of Rhino. it’s more a case of making sure that your exported file matches the tolerances of the CNC.

We have three CNC cutters here and each one has its own idiosyncrasies (one only accepts polylines for example). To add to the fun, each controller software has its own customizable tolerances which can bugger up the accuracy.

To solve this, we’ve got a series of saved DXF export schemes that are tweaked for each offending machine.

When we were testing we’d export from Rhino and then run the file through the appropriate controller and capture the outputted GCode or HPGL with viewer software. Then overlay it and compare that to the original file in Rhino. Tweak a bit, repeat, tweak etc etc etc until a happy balance of accuracy and point density was achieved.
Tedious but effective - and you only need to do it once.

If you are outsourcing the cutting then exporting and then importing that file back in to compare is, as Deer suggests, essential.

Hope that helps, Steve

Thanks, yes I do actually know, this was my fault of course.
The “problem” is just that I have exported DWG’s for many years, and always in mm, and all was good, until I messed up and exported in Meters and I trusted my experience. Only to now then that the default is simplifying all curves with a tolerance of 0.01.

And for anybody working in Meters (landscape architects) then 1mm is OK, but 1cm is too much of a deviation.

Thus the plea for updating that tolerance and even better setting simplifying to OFF :slight_smile:

Hope that makes sense.

This seems to be a crapshoot … DWG apparently can include units but may not be ALWAYS consistent depending on the importing application … in other words, the importing application may not be reading the correct units from the file?
If the file format does not have internal units (ie, DXF), it is easy enough to add “mm” or “in” to the file name to alert the user to make the adjustment (scaling) on import (knowing that DXF does not have an internal units specification.)
But if the importing application doesn’t read the correct units from the DWG, and if you are NOT confirming the dimensions after import in the app you customer is using, who would know if the units are NOT correct?

For comparison, when exporting STP from SolidWorks, STP usually always import at correct size regardless of applications used.

I often deal with manufacturers who request DWG (or sometimes DXF) format for 2d drawings but they have all sorts of problems importing relating to scale, lines that didn’t import, etc. I try to work with them to establish a format of DWG that will be reliable for them, but they often are not really able to handle this. So my solution has been to also export to PDF and always include both files. The project managers can always open the PDF, and if the PDF does not agree with the DWG their tech dept shows them at least they are alerted to a problem and will contact me to clear this up.


And I agree with @Holo, please turn default simplifying curves off. Seems like a land mine waiting for someone to step on.