Movement of surface after splitting



Does anyone know why when I split my object, it moves the surface which distorts my model and therefore I won’t be able to print it properly? If you compare the top right pictures before and after they have been split, the bottom of the circular opening has moved. Do you know what I can do, and if so, what details I need to enter, to stop this from happening?


I’m sorry to have to tell you this but the reason is that your model is a complete mess. You have lots of bad objects and many edges where surfaces connect that are way out of tolerance.

The reason you should avoid bad objects and out of tolerance surface joins is because they cause the very problems that you are experiencing. There is no magic fix.

The only good way to fix your model is going to be using Rhino’s surface modeling tools. You will need to take most of the individual surfaces apart and discard the ones that don’t need to be there, and then untrim and properly trim and join the others so that they all fit and join together properly and accurately.

You should have learned to use Rhino’s surface modeling tool’s from the beginning and ignored Rhino’s solid modeling tools. By learning to do this with Rhino’s solid modeling tools all you did was learn how to bring a rope to your own hanging.

To Jim,
I had hoped that when my son put a comment on this forum that the response that he would receive would not be as unkindly worded as yours. He is just starting to learn this program and is asking for help. I am a Teacher and if I had spoken to one of my pupils in the way that you have addressed my son then I would have been out of a job!!! And also considering that my husband’s cousin actually hanged himself yesterday, I don’t think that the terminology is appropriate either!!! Perhaps, Rhino should have advised to use the surface modelling tools from the beginning too. Perhaps just advice on how to deal with the program instead of the additional comments would have been better from yourself. I now have a very distressed son who has been trying his best for over a month now. I am sure that he will sort it out but your comment has certainly put him off asking for help on this forum again!
from one very unhappy mother

Trust me, I could have worded that unkindly if I was intending to be unkind. I understand that he is learning and what I am saying is that he is being taught Rhino very badly.

If your son wants to learn Rhino he would be well advised to consider my advice to do this without using the solid modeling tools. He will learn not just how to model this but also why what he is doing now is failing. And that will put him ahead of most of the people reading this.

That is not the intent. The intent is to get him to try doing this without the solid modeling tools. If he is willing to do that, he can ask all the questions he wants and I will be happy to help him complete this today.


I agree 100%. By teaching the solid modeling tools to new users who have no grasp of how to use Rhino without them they are just learning how to fail.

Hi Kyran - using ‘solid’ modeling tools in Rhino is just fine - in your example, the problems were almost certainly caused by the use of JoinEdge (Please see Help on this tool) and not from using the solid based tools. As I demonstrated in my simple example above that uses only solids and Boolean operations. What is true is that Rhino is a surface modeler though, and surfaces have properties that is it just as well not to get to understand, and I think that is what is getting in the way here for you. I continue to recommend having a look through the tutorials on the Rhino learning page, in particular the Level 1 and Level 2 training material linked there,


If he had been taught to use the surface modeling tools and avoided Rhino’s solid tools, he would not have spent a month struggling with this model. There is nothing at all fine about endless failure.

From what I have observed most user who are taught at the beginning to use booleans end up struggling forever and often quitting.

Hi jim - I daresay if this user had been taught anything about how to use Rhino, the month would have been better spent. It’s my impression Kyran has been left to spin her wheels, making it up as she goes. I’d say using solids based tools is perfectly appropriate for this project, but here, as always, it is not the only workflow available if the user understands just a little about surfaces, a point I’ve made more than once in these threads. In any case, I see no advantage in being a purist about methods, myself - there are lots of tools and workflows that are perfectly valid.


I’d say your dead wrong, but I won’t argue that point because its a red herring. Whether or not the model the user wants can be made with just the solid tools isn’t the issue.

The relevant issue is that if new users learn to model without booleans they will then have the power to know for themselves whether or when a boolean might be appropriate.