Unable to solid subtract and maintain solid

Hey there.

I realized a model I made was a bit too tall on one portion. I want to remove the bottom 10mm from this model. (It’s scaled 10:1 because I’ve run into SketchUp having problems with small scales).

Unfortunately as I am still learning SketchUp I seem to have created some geometry issues. I believe that I have two circles (with 96 sides) which are rotated a bit so the sides do not properly align. It has caused no issues when printing and I still have a solid object but I am unable to subtract from the bottom without causing the object to no longer be a solid.

I have tried creating a cylinder of height 10, grouping it, and moving it down to the appropriate height, then solid subtracting. This leaves me with errors Solid Inspector cannot fix and none of my manual attempts to fix them have been successful. I’ve attached pictures for clarification.

Also attached is my project file. I’m not sure how to proceed here short of redoing the entire thing and being more careful about my geometry which I will in the future, but seems like overkill for such a small operation.

Signal_Light.skp (2.2 MB)

Am I right in assuming you want to reduce the height of the plain middle cylinder by 10mm?

Just window select round the bottom ‘fatter’ section, then Move up on blue 10mm (or scaled up, move 100mm).

Here’s the result of doing that:
Signal_Light shortened.skp (2.2 MB)

If you want to shorten the ‘fatter’ shaped section, then it’s less clear what you want to shorten.

Change the view to Camera/Parallel projection.

Change to Xray mode - View/Face Style/Xray.

Then window select round the geometry you want to move (I just selected round the bottom edges), and Move up on blue axis 10mm.

Like this:

Signal_Light bottom shortened.skp (2.2 MB)

Another way of doing it:
Draw a flat face at the height you want to reduce the bottom to - 10mm up from the base - in the context of editing the component.

Select the face, then Edit/Intersect faces/With model

Use a crossing select, also in parallel projection, front view, to delete the bottom parts below the plane.

Delete the edges of the plane.

Result should be the same as above.

In theory, you could just push pull down the elements of the bottom face one at a time, but it isn’t cleanly enough drawn for that to work - some sub-faces won’t pushpull.

Should have been more clear about the scale, I really only want to remove 1mm in real life, which is 10mm in the model. :slight_smile:

Either way your method worked for me and I was able to move up that larger cylindrical portion without compromising any of the important features.

Yes my very first attempt was to push/pull the bottom of the model but as you found out because it’s not very cleanly done this was impossible.

Anyway, thanks a bunch.

Which was the move you wanted? I think, looking back at your image, it was to take 10mm off the bottom (the top in the inverted view you posted) in the scaled model.

Please mark the relevant one of my posts as ‘Solution’.

Yeah sorry spoke too soon there. The first method doesn’t actually help as I’m not concerned with reducing the height of the entire model, but removing the bottom 1mm (10mm in SketchUp).

I am trying the second method you mentioned with the intersecting plane but am unable to delete all the geometry below the plane without causing more solid issues.

That may be another symptom of the model being not quite cleanly drawn.

Is moving the whole of the bottom face(s) and edges not the right thing to do, as in my second suggestion?

If it isn’t, then you might consider adapting the model into subcomponents - a top outer cylinder, middle cylinder, and bottom outer cylinder; then one or more subcomponents for the indented sections of the inner top and bottom segments.

And maybe work at an even larger scale - x 100 or x1000 even (use metres for mm)

for example, these pieces (highlighted)
should be components, to ensure they all stay the same, keeping their geometry separate from the rest. It’s really hard to model cleanly if all your geometry is connected together.

I see that you have used the 3Dprinting template. It’s largely useless, and just bloats your file size by over 1MB. Use Purge Unused to get rid of it. Just know the maximum print volume of your 3D printer, and stay within it, or draw a simple box to represent it.

Next time, start with a simple Construction Documentation template in metres, and scale the result down x 1000 before printing, to get mm instead. Or use cm, and scale down by x10.

If you are going to print this object, have you allowed offsets for the thickness of your extruded filament? I’ve found on my printer that the print head centreline follows the model edges, so it fills in on either side by half the nozzle diameter - in my case, that’s a diameter of 0.5mm, and offset 0.25 mm.

So if you want an exact finished size, you need to offset inwards by 0.25mm (or whatever half of your nozzle size is) for any outer or inner edges, and outwards by 0.25mm round openings to get the solid you want.

And a small extra offset to get the kind of fit you want, from loose drop in to tight press fit. I found that adding an additional 0.05 to 0.1mm from nominal dimension of holes gave me a drop-in fit, and reducing the opening by the same amount led to gentle or hard push fit.

I also found that any small extrusions less than the nozzle width just don’t get sliced, and hence don’t print.

PS. One last observation. You don’t need 96 segment circles for the small holes - all that does is overload SU with edges too small to be seen in the finished print. Try 12 or 16 at most for those small holes.

96 segments is probably a bit more than you really need even for the 70mm diam outer circles too, but not excessively so to get a smooth print. 48 would probably do just as well.

There’s another thread of the forum giving a method of calculating how many segments make sense, depending on the maximum difference you want to tolerate between a true circle and a segmented one, and the size of the circle. I can’t find it at the moment, though I know I have seen it here.

Thanks for all the advice. Next time I’m working on a model I’ll skip the 3D printing template.

I’ve only recently learned about components, and will start using them going forward.

To clarify, it’s an issue that 1mm needs to be shaved off the bottom. You can see grooves running along the inside of the cylinder. Small tabs on another component (also pictured at the top of my model) interlock into those. My measurements were apparently a bit off and while it works it’s a very tight fit.

I’ve actually already printed one of these and it fit very well except for the bottom section. I have to really force it to be able to turn and lock it into position. If it were were just a bit shorter it’d be much easier. Hence why I want to “shave” off a bit of the bottom. Moving the bottom section up does not help with this issue because it’s caused by the grooves being a bit too far from the bottom of the model, not by the bottom part being too long.

I ran the plugin CleanUp3 to merge coplanar faces. That makes the bottom into a single face.

Then I tried yet another way - to push pull the bottom face up by 1mm. It wouldn’t, until I used the Ctrl key to allow it to move past the existing face.

But when I do that, and trim off the bottom 10mm in the scaled up model, it loses the inside faces of the notched sections - shaded blue-gray below.


So one more try.

Just select the cleanedp-up single bottom face, and Move up 10mm. Then you get what I think you want:

Signal_Light bottom face moved up.skp (809.8 KB)

If that ISN’T what you want, then you may have to redraw the bottom.

PS. There was a stray edge or two left to delete.

And I think this should have had the same effect as my first suggestion, of using a window select to get all the separate pieces of the bottom face and move them up 10mm.

OOPS. Now the result isn’t solid:

Solid Inspector 2 says there’s a hole in the surface, and here it is highlighted in red. Probably again a combination of very slightly ‘off’ geometry and small edges problem.

Thought I’d managed to fix that by copying round the missing faces from another notch of the same size, but Solid Inspector says no - still has missing surface borders.

At this point, it’s probably quicker to redraw the bottom.

Select the bottom, move it up 10mm then delete the unwanted edge that gets formed due to strange geometry.

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