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Negative part subtraction, or how to retain cavities?

laird_broadfieldlaird_broadfield Member Posts: 42 ✭✭
1. Novice user; novice CADder.  2. Actually thought I had solved my problem and was just looking for improved methods -- until I put together a document for sharing, and realized I haven't quite solved all of my main problem.

I'm trying to create a reusable mating/self-aligning feature, principally for 3D printing use.  So, I created a truncated, rounded pyramid:

I extended the bottom a bit, 

to accomodate a hollow for a 2mmx6mm neodymium magnet:

That's the male side of the part.

I then duplicated the top of the male part, 7% larger, to be the female cavity, and added a cylinder cavity for this side's magnet, and connected the two with a tiny pillar, so they'd stay one part and be easy to manipulate, derive, etc.  My plan is to subtract this part from my component body

Tiny pillar: 

And there's my first question: Is there a better way to do the keeping-together other than with the tiny pillar?

So, as I mentioned at the top, I thought I was complete at that point.  However, when I unioned/subtracted with my demo cubes, my female part did the right thing:

but on the male part I lost the sunken portion of the magnet cavity.  I get why it happened; the gray cube occupied that space, and it got kept.

...and I suppose I could leave the male pyramid solid, and bring in another part (magnet cavity) and subtract that -- but that seems inelegant compared to having male pyramid and male-pyramid-magnet-cavity all in one.


Document here: https://cad.onshape.com/documents/976b3e05d7cfba5fa841c3a3/w/9a4ba8750dbc29b3c09dcd3f


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    laird_broadfieldlaird_broadfield Member Posts: 42 ✭✭
    Got it; thanks to both Narayan_K and chris_8.

    (Incidentally, if anyone is thinking of reusing these, I printed these on a benchtop FDM printer last evening, and at 1:1 scale, I need a little more than the current clearance.  Also, the magnet void needs a little more room as well.  Might be better to increase the clearance on the female, also increase the taper on the pyramid, and move the magnet out down to the base part.  It'd be nice to have it all-in-one, but the pyramid has to be pretty bulky to accomodate the magnet.)
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