# Can't figure out why my brep isn't fully merging in grasshopper

Hey! I have been working on making a fast changeable lattice structure for school research, and I have been stuck trying to figure out why I can’t get my breps to fully merge and notice that there are edges in the places that I circled. I have tried a number of things and can fix this in Rhino with booleanunion and then mergeallcoplanarfaces, but I am trying to add concave based fillets so I can actually cut these out on a machine. Could anyone possibly have an idea of how to get past this in grasshopper?

(Sorry my program is all over the place, this is my first real application of grasshopper)

First go.3dm (2.4 MB)
First go.gh (21.6 KB)

Hi,

as a beginner, it is always helpful to model a shape manually first, and then try to parameterize it with Grasshopper. The pattern, shown here, doesn’t need any Grasshopper at all!

The outline should always be clean and closed. If your curve references are already messy, you just increase the error later in the process. You can always draw a cell and then array and transform it using Grasshopper if you fail to build a clean cell with Grasshopper. But as I said, you can also use the Rhino ‘Transform’ toolbox for this. Step by step, you can convert more and more to a Grasshopper definition.

Hey Tom!
I initially made this in Rhino a number of different ways and fully understand how easy it can be made in there, so thank you for trying to lead me in that direction. I don’t believe that will be useful for my research though. As I will be testing material properties of 2d lattices in real life, I need to be able to make a huge variety of these lattices, using a 3-line system as I did. Where I can control the length of the vertical leg, 2 side legs, angles and arch of the side legs, extrusion length, thickness, and the number of times the pattern repeats in the x and y. I tried to break it down so I can quickly make any simple lattice structure with the variations of those variables. I just thought since it possible in Rhino to just merge it correctly, grasshopper too could do such a thing without having to break down what I have made too far. Thanks again though.

The way you created the parts is complicated and something is certainly messed up in your tree structure. But the breps do union after culling duplicates. Even some of the fillets can be added with Grasshopper. However if you want to do all fillets in Grasshopper I’d suggest a different approach.

First go.gh (35.1 KB)

Gosh, that looks like a very complicated solution. Is there something wrong with this one?

hexgrid-bb1.gh (6.0 KB)

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Thanks for check this out and helping! I realize that this is overly clunky and not ideal, it is my first time using the software and have been hopping all over the place to figure out how to control every variable I needed to be able to control. The end goal was to be able to machine all of these lattices and I thought this would be the fastest way.

So while that would be awesome if I was only doing Hexgrids, I am also doing all the lattices from the picture above, so I believe I am in of need of a bit more complicated of a program. Also I was told to work on it through using 3 lines as shown by the red lines. Thank you though!

Here’s an example for you. A very simple way to get offsets in both directions is by creating a pipe and then getting the intersection curve between the brep and a plane.

pipe_section_extrude_fillet.gh (14.3 KB)