Full Version: Splitting Cylinder

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Hi Sun, you will need to form each of those cutters to be a surface and then you will be able to use the surfaces as cutting objects in boolean difference to slice your cylinder up.

Since your shape is not planar you will need to use either the Sweep or Network surface construction methods to build the surfaces. To do that select the twisted rectangles and then use Edit > Separate to break them apart into 4 separate individual curves. Now build one surface at a time using either Network (where you can select 4 boundary curves at once) or sweep (start by selecting the top and bottom pieces for the sweep profile and then the other 2 longer ones for the rails). Once you have created 2 surfaces like that those surfaces will divide the solid and use Boolean difference on the solid with those surfaces as the cutting objects.

I've attached an example file where I've done this process using Network to build some cutting surfaces - if you load the attached file you will see that there are 3 objects in it, the cylinder and 2 cutting surfaces which were constructed from your curves (after using Edit > Separate to break them into 4 pieces each).

Select the cylidner, then run Construct > Boolean > Difference, and pick the 2 cutting surfaces (using area selection where you click initially in empty space and drag a window is easiest for selecting things submerged within others) as the cutting objects, and then the cylinder will be divided into sections, go in there and select the little piece between the cutting objects and delete it:





Also sometimes with things like this it is easiest to pick the big pieces first and then invert the selection to then get the little things selected and then you delete. You can invert the selection by Select > Invert on the side pane or it's also useful to set up a keyboard shortcut, to do that go to Options > Shortcut keys, and push the Add button, for the Key put in I and for the command part paste in the following: script: /* Invert selection */ moi.geometryDatabase.invertSelection();

Then anytime you push I the selection will invert.

Hope this helps!

- Michael

Attachments:
seg_boundaries_02_v4_moied_02_new.3dm

Image Attachments:
sun_boolean1.jpg  sun_boolean2.jpg 

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So basically if you need a very simple straight cut all the way through an object in one direction you can just draw in a 2D curve and use the curve directly in the boolean.

But when you want something that's more customized than that like here you want something that's not just a straight-direction extruded cut and also it's limited to a certain area and not all the way through, then you need to build a surface or solid for the cutting object instead of just a curve.

You don't have to have a solid for the cutter - a surface that fully crosses the solid and so divides it can also be used as a cutting object in the booleans.

In order to construct a custom swoopy surface you'll usually be using Sweep or Network and they want to be able to identify the individual cross-section curves so you will usually give them individual curves and not just a single all-together connected piece like you had before. But if your piece is all planar then it is ok to make it all one joined piece and then in that case you can use Construct > Planar to build a surface through a planar closed shape like that.

- Michael

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Thanks for the quick reply Michael! I'll try what you suggested.

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That worked very well. Thanks again Michael. I love MOI. Dang Rhino can't seem to do this. I've been trying to automate the creation of this thing using Grasshopper & Rhino, and it seems that it's impossible to cut solids with surfaces in Rhino. I'm going to have to think of a different approach.

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