Problem with seamless joining

Hi all,

I am fairly new with Rhino and trying hard to learn as much as i can with tutorials etc.

I’ve modeled half a ‘u-rack’ and then mirrored it and tried a lot of ways to join it seamlessly.
Unfortunately I am not succeeding and hope you guys can help me out a bit.
off course i can just start from the beginning and make the rack out of one piece so i don’t get edge but there must be another way right?

Best regards,


urack edges.3dm (340.5 KB)

Hoi Gunnar
You could extract the surfaces and run MergeSrf on them.
The question is, though, why do you need these to be one surface?

Also, I recommend turning on the CheckNewObjects command - the bottom parts of the surfaces that you want to merge are bad objects. Do you know how these were created?

Hey Wim,

Thanks for the quick reply!
I’ve already tried to extract the surfaces and merge them but i didn’t succeed.
I wanted it to be as smooth as possible and the rack normally is not made from 2 halves.

This command is new for me but i will start using it from now on, thanks.

I created the bottom with a polyline followed by the pipe command.
Is it because of the ‘bad objects’ that the merge srf does not work?

Best regards,


Technically, it’s because the trimmed edge of the surfaces cannot be merged but because it is a bad object you can’t shrink the surface so that there isn’t a trimmed edge in that location.

I wasn’t able to create a bad object by running Pipe on polyline so if you have a way to reproduce that, please let us know!

Hi Gunnar- the two halves are capped at the plane of symmetry -


If you ExtractSrf the two coincident end caps there and delete them, you can then Join the two halves. You’ll need to just ignore the ‘Break History’ warning.


Maybe it has to do with the upper part of the model, the slimming down from the larger pipe to the hook was done in another way but i am not really sure which method i used for that…

@wim @pascal Now that i tried working with ‘check new objects’ on i found that when using extractsrf to remove the cap that i get the notification ‘The “ExtractSrf” command created 2 bad objects.’.

The way i solved my issue for now was by making the bigger maintube out of one piece and adding the ‘hooks’ on top afterwards. But i am still curious why drawing half of my object, mirroring and then al the various ways i tried to make it one seamless object didn’t succeed.

Best regards,