Inersecting holes in a solid not working correctly


#1

Note: I’ve attached the file below, if it works correctly…

So, I’ve drawn a cube, drawn circles on top of the cube, and push/pulled the circles down to the opposite face, thereby making holes through the cube.

Next, I go to another face on the cube, and draw the exact same holes, and then push/pull them through the cube to the opposite face. I get the leftover ‘chunk’ in the middle. Click on it, select ‘intersect faces - with model’.

The above step I believe is not working correctly - it creates the intersection, but joins the side face of one of the holes, to the face of the chunk that was in the middle. So when I select the faces of that chunk, and delete it, it will also delete the face of one of my holes. No matter what order I do it in, if I intersect with selections or context, or whatever - I can’t get it to just delete the chunk in the middle, and make two holes through the cube.

I tried doing it in a fresh file, with the exact same dimensions, and it works fine. But in my real drawing, it freaks out.

Any advice?

CNC Mockup16.skp (886.8 KB)


#2

Is this what you are trying to accomplish?

After extruding the holes through the block, select the cylinder walls, right click on one of them and choose Intersect Faces>With Selection. Then select the parts of the hole walls that are waste and delete them. It worked as expected for me, anyway.


#4

It does behave badly for me. 3 out of 4 times it bugsplatts when opening.
The holes you are trying to intersect are right down at the point where the tiny face issue almost guarantees they will fail.


#5

DaveR - I am trying that now, but it still isn’t working correctly for some reason… Do you have yours configures so that circles are more ‘circular’ ie have more little segments than I do? Could that have something to do with it?

And sdmitch - what do you mean by ‘overlapping sections’?


#6

Aha! Sort of… I tried your method DaveR, on the left set of holes, and it worked flawlessly. On the right set it freaks out. I suspect I have some sort of messy geometry in my right set of holes. Now if I can figure out how to delete those holes to make that side a perfect solid again (any suggestions here?) I will redraw that half, and see if it behaves better.


#7

Nope, that didn’t work either… I deleted all geometry and guides associated with the right set of holes, redrew everything, tried intersecting my faces again, and then deleting, and then splat. Why on earth does it work on the left set of holes, but not the right. This has been killing me for over an hour now. Ugh.

Any ideas?


#8

I didn’t do anything to your model other than open the group for editing.

I suspect that the problem you are having on the ones on the right is that they weren’t drawn on axis. The guidelines passing through the center of the circle should also pass through vertices on the edges. This circle on the front as well as the one on the top, aren’t aligned properly.

The ones on the left are properly aligned.

This sloppiness in drawing those circles would certainly cause problems.


#9

Alright, here it is again, uploaded, redrawn. The left set of holes is correct, the right set, you can double check, are drawn on axis, using guides. If it behaves for you and doesn’t for me I may conclude that sketchup just hates me or something.

CNC Mockup16.skp (898.8 KB)


#10

The top one on the right is still off axis.


#11

There is something wrong with the group, it won’t select correctly.


#12

Delete the guide lines and try selecting it. There’s a guideline inside the group.


#13

Ok, the horizontal guides are in the group. I rarely bother with guides.
Scale still seems to be an issue to me.


#14

DaveR you nailed it. I didn’t’ realize that the vertices of all the little segments which make up a ‘circle’ in sketchup need to line up, for them to ‘push/pull’ and ‘intersect’ correctly. Makes me wonder what would happen if you started getting circles intersecting at angles, off axis, different sizes, etc. I wish sketchup would just work with perfect circles (are there any plugins or anything which achieve this?) - I have to convert this stuff to CNC friendly formats, which all the little line segments definitely isn’t.

In any case, this is working for now - thanks!


#15

Nope. No plugins to make “perfect” circles. You can increase the number of sides in a circle up to a point (dependent on the radius) to make smoother looking circles but they’ll still be made of straight lines.

If you make 3D DWG or DXF exports, the circles get read as circles instead of polygons.


#16

I agree. I got some missing facelets inside (about 0.8mm in size) until I made the group a component and scaled it up before doing the pushpull + intersect + cleanup.


#17

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