Adding a simple loop to an extruded surface

Hi everyone. I’m new to Rhino. I come from Maya and Softimage modeling back in the day. How do I add a simple edge loop to the center? e.g. add a loop that goes all around the surface in the middle. I thought about add control points and a knot, but I’m not sure. Having to re-learn the approach from my past experience. Thanks in advance.

Hello- it looks like what you have there is a polysurface, correct? and not a SubD object… the way surfaces work is completely diffferent from SubD, if that is where your experience lies… You could make this as a SubD in Rhino and then tools like InsertEdge, Inset and others that the SubD gods know about, can be used.


Thanks for the quick reply. Yes…this is a polysurface. I love Sub-D but I’m concerned I won’t get the exact accuracy in Rhino. If I extrude something say 1.75 inches thick or do a neck pocket at 5/8" deep, I need to know it’s the exact measurements. I know from my previous experience using Sub-D, the accuracy was not there. So I guess I’m saying, how accurate is Rhino Sub D? Thanks again. -Jer

Hi Jeremy - Rhino SubD are subject to all the vagaries of SubD in general - if you are making your part from surfaces, though, which is fine (and BTW, you can combine shapes made as SubD with surfaces at the end of the process, so both may be useful for different parts of your design - the more mechanical bits as surfaces and the wigglier parts as SubD - in the end the combination will be a polysurface however ) you need to go about it completely differently.


rebuild that surface to be degree 2 where it is currently degree 1.

run the changedegree command on that surface.

fwiw- here is a video about making a guitar shape in subd.

That’s what I was looking for!


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Thank you both!

Is there a way to set the degree while you’re extruding a surface? -Jer

no, extrusions are always deg 1 because it does not have any info other than translate to set the 2nd direction.

if you extrude a curve along a curve, now you have two pieces of info which then sets both the u and v degree based on the input curves.

Excellent. Thanks. I just discovered that a degree of 5 will keep the geometry the same. Degree of 2 alters the curve.

Anything 3 and higher will keep the shape.

Thanks again. Sorry for all the questions. I’ve also noticed that you can’t trim certain surfaces until they are exploded. I’ve had to explode the neck pocket area in order to trim the extruded body around the pocket.