Sdiff with boundary surfaces..................now this is odd

Hi all,

I am trying to generate a 150x150 EAx10 surface, from two discrete surfaces within the same YZ plane.

Create 1st rectangle 150x 150
Create a closed boundary surface
Create 2nd rectangle 140 x 140: 10mm is the plate thickness, using relative coord 0,10,10 in the yz plane
Create a second closed boundary surface
Under intersect/sape/solid diff create the angle ready for baking

numerically the numbers are well, odd

Any help appreciated, i have been using all my fingers and toes to determine that the result thus far is pretty rubbish. I am sure there is a moderately simple explanation.

Oh if its really obvious please be gentle, I w=thought that this was a 2 minute def :(

regards

kenyon

Attachments:

Sdiff.gh, 10 KB

Replies to This Discussion

Permalink Reply by Joseph Oster on December 25, 2015 at 5:10pm

"Sdiff with boundary surfaces"? 'SDiff' wants closed Breps, not surfaces. I don't understand all that code you have and the 140 x 140 surface. Isn't this what you want?

Attachments:

ext_2015_Dec25a.gh, 10 KB

Permalink Reply by Kenyon Graham on December 25, 2015 at 5:54pm

Hi Joseph,

Thanks for replying, Not quite.

I'm trying to subtract the smaller rectangular surface from the larger rectangular surface to make a "L" shaped surface. Ie. The remainder of the 150 x 150 minus the 140 x 140. The 140 origin is translated in the YZ 0, 10, 10.

The L shaped surface is 150 x 150 x 10 mm (my dims are metres). I thought I was being quite clever. The alternative is awkward coordinate geometry. My idea is to use basic (primitive) surfaces to get more complex surfaces, which I'll then extrude etc.

Is my boundary surface not a planar brep ?

Rgds

Kenyon

Permalink Reply by Joseph Oster on December 25, 2015 at 6:28pm

Ah, now I understand... Still, 'SDiff' is for "solids" with volume, and though it will work, you really want to use 'RDiff' instead:

When using such very small values, it seems to be important that your Rhino file be set to the correct units; meters in this case.

Attachments:

RDiff_2015_Dec25a.gh, 11 KB
SDiff_2015_Dec25a.gh, 11 KB

Permalink Reply by Kenyon Graham on December 25, 2015 at 7:18pm

Thanks Joseph,

I started with Rdiff but desparetly tried sdiff.

I think that the origins of the rectangles/curves require to be coincident also which would relate the geometry.

thanks for your help, its been driving me bonkers.

Kenyon

Permalink Reply by Kenyon Graham on December 25, 2015 at 7:25pm

Sorry Joseph, the tolerance in Rhino was crucial ...great spot.

Permalink Reply by Joseph Oster on December 25, 2015 at 8:01pm

The rectangles/curves do NOT need to be coincident:

But that precision issue just bit me again and I was perplexed for awhile. It seems that changing the Rhino units has no effect until you adjust a slider!?