Boolean Difference Problems

I'm using Rhino 5 and Grasshopper .9.007

I trying to create a solid (that represents a plywood board). I want to drill holes in the board. So I create cylinders that go through the board. Then, I do a Solid Difference in Grasshopper to remove the cylinders from the board. But it's not working the way I expect. When done and baked into Rhino, the board shows the circles for the holes, but there is still material in there. You can see this in the attached image Undesired.jpg.

Interestingly, if I bake the board and cylinders into Rhino. Then BooleanDifference the cylinders from the board, I get the holes that I am looking for. You can see this in the attached image Desired.jpg.

My questions. Is Grasshopper/SolidDiff the same as Rhino/BooleanDifference? What method should I use in Grasshopper to get the desired result?

I have attached the Grasshopper file. Apologies for the extraneous elements. The two pieces in question have preview set to on.

Thanks!

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Permalink Reply by AB on March 11, 2014 at 10:05pm

Scott,

The Boolean Difference in GH is working fine right now... you were just creating lots of different overlapping copies of your "plywood board" that happened to have only a single column of holes removed. To avoid problems like this getting a good grasp of data trees is essential. This is where the learning curve gets a little steeper, but it is where much of the power of GH comes from (IMHO).

As others have suggested... this is a good place to start for anybody looking to tackle data trees

http://lab.modecollective.nu/lab/working-w-data-trees/

As a quick fix, you could just flatten the input of your Boolean Difference and this will give you the resulting sheet you are looking for... it is not the "correct" solution though as you could remove tons of the redundant components "upstream" by understanding data tree logic.

There are certainly lots others on the forum that could tackle your definition better than I... and clean it up considerably.

I may be giving you more information than you are looking for... but without a good working knowledge of data trees Gh is only a fraction as powerful as it is designed to be.

As far as the workbench goes, it looks good... lot of holes for clamping!