SubDFriendly circles

I would like to use circles as shape curves in SubDLoft and SubDSweep1 commands to make SubD surfaces. How do I draw SubDFriendly circles?


My understanding is that it’s mathematically impossible to draw a SubD friendly circle. It will always be an approximation. _MakeSubDFriendly will generate this approximation.

circle on the left – _MakeSubDFriendly on the right

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Really simple, rebuild the curve to degree 3 with a larger number of control points. More control points equal more segments and closer to true round. A degree3 with 8 control points has 0.04mm deviation from true round.

Degree3 with 12 control points has 0.008mm deviation from true round.

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This is probably a good time to review this:

– Dale


I forgot this command and I could not find it in the Rhino documentation. (It is not mentioned in Rhino 7 documentation.) By the way, Rebuild command has Make SubD friendly option.

Hi Andrew -

The YT item for this command has not yet been completed - I’ve given it a nudge…

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Added, sorry for the delay.

A SubD face or cylinder that is a perfect octagon in box mode will yield a curve that has a diameter that varies from perfectly circular by about 0.125%.

Below 8 sides, I can start to see the divergence from round if I look closely, and I bet a lot of other designers can too. At 6 sides, the divergence from round is 0.417%. At five sides you can really start to see the points of the pentagon reflected in the subD faces.

And above 8 sides you start to get somewhat diminishing returns: 10 sides is 0.045% out of round, an improvement on .125% at 8 sides but probably not significant for anyone who isn’t engineering machinery or something similarly finicky.

So when we get an update for the Fatten component in GH and for SubDMultiPipe that doubles the number of faces around the mesh, it’ll probably be good enough for almost everybody. Would 12 or 16 faces be necessary for anyone who’s using SubD? I’m curious to know. I wouldn’t need it.

I agree with you that in terms of accuracy 8 faces is enough for most uses. However it may not be enough to capture the features or details you need. I have been playing with even multiples to capture design intent and symmetry and end up somewhere between 8 and 12 faces around. I try to keep round profiles to 8 if I can but sometimes I und up with edgeloops that go up the cyclinder therefore requiring more than 8 around.

It’s possible, I just need to get better at working with the topology, but that is where I’m at at the moment.

I could not find the MakeSubDFriendly command in the list of new commands:

…and I could not find it in the list of all commands:

I have an SOP list to follow when adding new commands to Help, I won’t miss adding them to these two pages. You didn’t see them because Amazon CloudFront caches web pages on a webserver near your location. I can force CloudFront to update the cache, but I don’t usually do that.

Your web browser also caches web pages on your computer. If you use Chrome, you can force Chrome to update the caches on your computer by press F12, right-click the Reload button, and select Empty cache and hard refresh,

The caches will automatically update on CloudFront servers and your computer a few hours later if they are not forced.


I use Chrome browser. Right-clicking the Reload button does nothing. F12 displays source code. When I updated Chrome to latest version, the MakeSubDFriendly command appared in the list of new commands, but not in the list of all commands.

more info about empty cache and hard reload:

Right-clicking the reload button only works when the source code is displayed.