Problem with slicers filling model beyond original design

Hello everyone, I’m new here and to 3D modelling and printing and having a bit of problem with my first model.

It’s just a simple bracket to hold something but the slicers are filling the bottom of it past the specifications in my design on sketchup. This is the second time I drew the object after the first time I got the measurements slightly wrong and oddly, the first drawing did this on one side but not the other. Now the second drawing is doing it on both sides. I have loaded the file into both Cura and Slic3r and both programmes are doing the same thing so it isn’t just one programme having a whoopsy.

Both original drawings were absolutely identical in this part of the object and I have compared, checked, double checked and triple checked everything between them and there is no difference whatsoever, so I’m at an absolute loss as to why one drawing would succesfully slice on one side and overfill the other whilst the other drawing overfills on both sides.

Here are some pictures to help me explain

This is an inside view of the part of the model which is overfilling. As you can clearly see from the picture, the measurement from the centre of the cutout to the top of the inside is 8mm. The slicers are completely fillling this gap between so the hollow inside of the model is level with the top of the cutout, making the inside hollow 8mm shorter, as you will see in the next photo.

The photo above shows the inside of the walls on sketchup. The walls are all 2.45mm thick the whole way round. The part of the drawing showed in the picture is where it is going wrong. The measurement clearly shows 2.45mm, this is in fact getting filled to 10.45mm with a sort of crosshatched/honeycombed pattern.

Above is a photo from outside, just in case an external visual will be any help.

I’m hoping there is a schoolboy error here somewhere and an easy fix, but as already said I’m at a loss as to how this is happening and can’t find a way to stop it.

Thanks in advance for any help or advice!

You probably have “print with support” turned on, and that part of the model may not be printable without it. 3D printers build from the ground up. They don’t do sharp flat overhangs well at all. Think of it this way. If you wanted to print a statue of someone with their arm outstreached at different angles, there are some angles that you could print and some that you couldn’t. If you printed a person with their arm pointing straight up towards the sky, that would print fine. If they moved their arm down at a 45 degree angle that would still be fine because each layer up would only be a little further out than the last. If you tried to print that same person with their arm level at a 0 degree angle to the horizon, it would fail because the plastic would go out to the finger tips, find nothing to anchor to, and then drop away as a gloopy mess. unless you used a supporting layer.

If you tried to print someone with their arm outstreached towards the ground, that would also fail but for a different reason without support. The fingers would be printed before the hand or arm existed for them to attach to.

The other possibility you may be running into here if it isn’t support enabled, is a non manifold object. lets say you have a cube. As long as all 8 surfaces of that cube exist and are connected at the edges to the other surfaces, the 3d printer slicing program sees it as a cube. But if you had an error in one of the faces where a piece of it was missing, the slicing program doesn’t know what to do and will generate a crazy path. You might not have an extrusion joined properly or you might have a geometry error. Loading the stl file into the free version of netfabb and then seeing if it wants a repair is a good way to check for that.

You could also post the stl file here if you wanted to and we could take a look at it for you.

Have you checked that the part is manifold / watertight? Sometimes slicers try to “heal” non-manifold objects. I use the “Solid Inspector” plugin / extensions for Sketchup.

Post the STL or SKP…

Thanks for the quick replies.

It does need support material on one bit of it which arches, it is printed upside down to the sketchup photo’s so that the closed side was at the bottom with the open side at the top.

Since posting this I redrew the whole bracket, making almost every measurement larger. It still had the same problem. I then tried exporting the STL from each different rotation to no avail. All measurements and joins were again checked three times over, everything linked together perfectly, every line was straight, everything was where it should be. Oddly, Cura would read the drawing perfectly as it should when it was lying flat horizontally on the bed, however that was a non starter to print as support material would be needed inside the bracket and it would be near impossible to get it out. I then tried drawing faces actually inside the parts walls again to no avail.

Finally I tried Solid Inspector, it told me something about inverted faces, I pressed fix, some of the white faces turned gray and vice-versa… Bam, perfect.

I didn’t quite understand what it was telling me but I assume it had something to do with which way/from which view I drew the final line which ultimately decided which side was the true face once all points were linked, if that makes sense? And that some were facing the wrong way essentially making them invisible…

Thanks again to you both for taking the time to offer your suggestions and ultimately solving my problem.

I’m not exactly sure what the reverse faces mean ( a flat face is a flat face, right? :slight_smile:). They seem to be interior faces which has been revealed somehow through manipulation of the exterior face (non-reversed face or normal) within the drawing. Often a result of “pushing” on a normal (exterior) face into the project… resulting in the once exterior (normal face) becoming a face in a cavity and the opposite side becoming exposed to the exterior. Again, I’m no expert just reporting observations in my design efforts… I’m sure there is a better explanation out there.

While a flat face is a flat face, this does affect slicing programs. Often times in SketchUp, reversed faces are a darker shade of grey (or slighlty darker shade of the chosen color for the face)… and sometimes difficult to see. Orbit around the project a few times and they become more apparent.

Solid Inspector comes in a second flavor which can identify and help “fix” common problems. There is also a tool from Fredo6 which checks for face alignment… helpful when the project has a lot of small triangles.