Why Can't I Boolean Join these?

I really don’t know what to ask except why can’t I Boolean union the these two solids.
I’m really not having much luck with Rhino.CanNotBooleanJoin.3dm (149.0 KB)
Thanks for any help.

Hi David,

I had a go at it and couldn’t get it to boolean either so I redrew it and got it to work. It is something to do with the amount of points in the surface of the upright solid. I drew it (a bit shoddily mind you, but you get the idea) with a curve with only 7 points and then sweep 1 rail to get the shape. The surface doesnt have the same isocurves as the previous version and it booleans together. Someone with more technical knowledge might be able to explain exactly why. Anyone? File attached CanNotBooleanJoin.3dm (3.1 MB)

Everytime my booleans fail, it is something wrong with the initial geometry. I could not get yours to work either. I duped edges and lofted, exploded, joined and several methods I’ve used on my own work recently. No go. Someone more advanced than me will have to help.

it doesn’t work because the faces are coincident:

if you first use Split :

then you can delet those coincident surfaces and make the booleanunion

also you can split this surfaces horizontally to avoid meshing problems


Thanks Nickpledge. Your model confirms Diego Krause’s post below that, as you have removed the coincident edges. This is all very curious.

Thanks Diego
Your reply has helped encourage me to persevere with Rhino. I kind of remember that my BricsCAD 3D couldn’t Boolean these either so it’s not the software, it’s to do with coincident surfaces. I’ve been trying for months on and off to make this thing.

Hi David,
I often undersize one of the parts by a bees dick and then boolean. It works although I never knew exactly why. Now I do.

How many RCHs is a bee’s dick?
Do you have a conversion factor?

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Could someone define “coincident” in simple terms, or with visuals. I’ve read a few definitions but it’s still not clear. I know it’s why some of my attempts to process objects don’t work, and I too also resize elements a minute amount to make operations work. But is that quality modeling? Perhaps if I understood the term I’d understand how to avoid it.

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is where two surfaces are overlaping or they are in the same place, the math underneath boolean operations use the intersection curves to make each split. when you have coincident surfaces, the intersection curve is multiple and in most cases, a few closed curves and others are open curves and that’s the problem, when you have open curves as intersection between objects.
I would say that in 99.99% of the cases, Rhino doesn’t like coincidences, if they intersect, make sure they do with a reasonable margin.

You made me do research…

The world scale of Units and Measurement has been thrown into disarray after it has been discovered that the variation of length of a Bee’s Dick differs from country to country.

Dr. Capalano from the world scales of measurement has discovered that the Africa Honey Bee is hung like a March Fly, whilst the Asian Bumblebee is hung slightly smaller than a Mosquito.

To add further confusion to what should be a standard form of measurement, the American Bee’s Dick is an Imperial measurement and the Australian is Metric.

At present 1 Australian Bees’s Dick is approximately 1.8 American Bee’s Dicks. Furthermore the Australian Bee’s dick in general is the largest variation of the Bee measurement.

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