Visual double line edges, how to fix?

Hi all Rhino experts!!

As you can see in the picture, when you zoom the left corner of the hinge area of the model into certain point, you start to see the double lines. The middle set of shorter curves are Boolean by another object but they all originally come from the same straight extrusion.

How can I get rid of the double line situation here?


visual double line question.3dm (479.6 KB)

You have to zoom in really close to see that. I mean really close! When I could first see the double line I took a distance across my entire viewport and it was not even measurable. Since your object checks as a closed polysurface is it really necessary to zoom microscopically?


Hi Dan, thanks for your reply! I didn’t notice that until a CNC/Wire Cutting tech told me that since he was trying to pull DXF out of this and get confused when he saw the double line edges there.

According to him, it would make a difference at the wire cutting stage?

Hi Wen,

How big is this thing going to be? At the moment it’s around 2.8mm wide which isn’t far from the width of a wire cutter… If it’s going to be scaled up it will still fall within tolerance of a wire cutter etc.

The easiest thing to do is DupFaceBorder and extrude another version and draw a cylinder to boolean the other sections to keep it clean.


My guess is that the CNC guy is talking about the fact that you. have several surfaces that are split in two pieces instead of being just one single surface. On those surfaces there are twice as many edges as there should.

What the CNC guy would probably like to see is a model like this:
No_Double.3dm (423.9 KB)

My advice to you is don’t use booleans when modeling stuff like this. You will be likely to discover if you build your solids using the surfacing tools, without using booleans, you will have a lot less trouble when exporting to other solid modeling CAD applications.

Thanks Jim. How did you achieve the clean look in your attached 3DM?

I probably should mention that I did the Boolean in Grasshopper as the Solid Difference, I did try the MergeAllFaces after baked the object out, but it still has the center line running through the whole piece…

Your model has the same errors, Jim. I think it’s a render mesh issue?

You can only merge faces of planar surfaces, sadly.

visual double line question-1.3dm (663.7 KB)

Same as what? Dan already explained the double lines are visible only if you zoom in farther than an electron microscope can zoom[quote=“wenJ, post:6, topic:41116”]
How did you achieve the clean look in your attached 3DM

To make a set of rwo surfaces into one, first extract both surfaces (extractsrf command) then use Untrim and extendsrf
on one of the surfaces and delete the other. Then use trim and join to make it back to a solid use the rest of the solid as the trimming object. Do that 3 times to each of the sets of double surfaces.

I also used ShrinkTrimmedSrf before untrimming on the 2 sets of surfaces that had a huge amount of extra surface beyond the trim boundaries. That step isn’t necessary bot it makes the file smaller.

The same as the model that was presented in the first instance, Jim. The changes that you made still present the double line (of sorts) that the technician was seeing with the dxf.

As Dan pointed out it’s only visible when you zoom in so far. So it’s probably a render mesh issue and won’t make any difference to the output CNC or otherwise.

The boolean option works really well in this instance, horses for courses I guess.

Hi Wen

I went trough this before with wire cutting guys while cutting different gauges. What I think he wants is a planar closed curve such as the red outline in the first picture. I don’t think it matters which one, but you could supply the one you used for your extrusion. At that point no matter what your call-outs for perpendicularity (or parallelism) are, they are only as good as the tolerance his machine can keep.

I too tried to measure that difference and I believe it is not measurable within the scope of this software. Rhino simply would not want to display anything in the dimension line and the number in the picture is produce by using “measure distance”.

Good luck

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Also, it will help a lot if you filleted your piece, so it reduces your cutting time. In fact the bottom corner will need a radius that is at the very least equal to the the radius of the wire he is using.

Yes, that is what I should do! We kinda of have a middle guy between me and the wire cutting guy so I didn’t think about providing the extrusion outline. That is a much better way to avoid future confusion.

Thanks for your help, Costel!

I recently discovered ShrinkTrimmedSrf too and it has been a great help on certain models!