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I have an object that has cutouts in it (alignment pins fit in the cutouts). The shape of the hole is a right triangle with the point clipped off to create a flat surface in the deep part of the hole.

When I print the object in vertical orientation the wall in the deepest part of the cutout is printed properly. But when I print the same object laying down flat on the build plate, the internal wall is not printed and I can see the infill grid through the hole where the wall is supposed to be.

I sliced the object with a slicer based off a recent Cura version. I'm using the same STL to print the object vertically and horizontally.

Why is this occurring? Is there anything I can do about it other than printing vertically? (Because I have a need to print the real part horizontally. The part shown here is just a thin test piece.) Thank you Same object showing vertical / horizontal printing orientations The horizontal print position does not print the inner wall of the hole

Here is a picture showing what the (Cura-derived) slicer does with the model in horizontally-printed position. I checked the layer display in the vertically-printed instance, and the missing wall was correctly rendered and visible.

I guess this is some kind of a slicer bug.

Layer view showing the missing back wall

Here is a large-scale picture of what the cutout shape looks like. This picture is of the protrusion tab that fits into the hole. But the same shape was used to cut the hole in the object.

The shape used to cut the hole

Here is another instance of the same problem. This time, I made up a simple block component, a simple cylinder component, aligned the cylinder into the block volume, and did a combine/cut operation in Fusion to cut a hole in the block (visible in the STL file). As you can see from the (Cura-derived) slicer layer image below, the same problem exists - no wall at the back of the cut when printing in the horizontal position. If I draw a sketch on the block and extrude/cut into the block, I get the same results. I also tried cutting the cylindrical hole, creating a "tin can" shell cylinder with an explicit bottom-of-the-can surface, sliding the open can into the cut hole, and joining the can to the block. Same results. The explicit bottom 0.5 mm surface of the can disappears in the horizontal slicing position. Strange.

Simple cylinder component used as a cutting tool to cut into a block shows the same missing back wall problem.

UPDATE:

The test object is just a simple block with a cylinder extruded into the block as a cutout. As simple as simple can be. I have determined that Cura 3.5.0 works properly (Cura v3.6.0 is available).

I am using the Qidi slicer v5.0.7 latest, which uses an earlier version of Cura (I don't know which one; I have sent them an email to find out).

I have determined that the Qidi slicer behaves properly if the cutout cylinder diameter is 6mm or larger. But at 5mm, the slicer will not generate a back wall in the cut. The square/triangular cutouts in the example objects below are all 5 mm or less. My installed Cura 3.5.0 generates a proper back wall even at 5 mm. Therefore, it must be a bug in the Qidi slicer, which uses an older version of Cura.

As a workaround, I will increase the size of my cutouts to 6 mm. When Qidi updates to a newer version of Cura (they are currently using 3.3), the problem should go away.

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    $\begingroup$ You state you are using "the same G-code" to print horizontally as vertically. I'd suggest this isn't so. G-code is a string of commands which tells the printer, "go from point a to point b putting out this much filament". In order to print in one orientation, the G-code is going to be completely different than what you have going on in the other orientation. Maybe you mean something else? $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Dec 24 '18 at 21:01
  • $\begingroup$ Yes, of course, you are exactly right. I realized while I was out driving I meant the STL file, not the gcode, which as you point out, must be totally different. My apologies. $\endgroup$ – Kevin Dec 25 '18 at 0:51
  • $\begingroup$ Please try to slice the part in non-expert mode and see what the slice looks like. This must be a slicer problem, not a Fusion one. Which Ultimaker Cura version is used? Please update to the latest. $\endgroup$ – 0scar Dec 25 '18 at 9:09
  • $\begingroup$ I would like to check it with my Cura settings - could you provide the STL or at least the relevant part of it? $\endgroup$ – Trish Dec 25 '18 at 13:57
  • $\begingroup$ Thank you all for your attention to this problem. As soon as you suggested checking it with Cura, I realized that I could do that and save everyone some time. Cura 3.5.0 works properly. See the UPDATE in the original post. I have a work around now. $\endgroup$ – Kevin Dec 26 '18 at 17:55
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I think this is caused by the shape of the hole. The shape is parabolic or circular, this means that if you slice it as in the green part, the slicer determines the placing of the layers along the curvature. If it has a shallow curvature, and slicing layer height is relatively thick, the curvature of the object cannot be followed. But, if you have more than 1 top layer, this usually should not be visible. I don't think that you have a single layer, so this is a pretty odd anomaly that I have not seen yet (that you look at the infill without top layers).

You could get past this by using a local different infill, e.g. 100 % infill. You can look at this answer of the question: "Different infill in the same part". This should help you out printing in your preferred orientation.

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  • $\begingroup$ The shape of the hole is a right triangle with the point clipped off to create a flat surface in the deep part of the hole (so I can use a joint origin in Fusion 360). So, this should mean the slicer should create a 2 or 3-layer "top" surface on both the downward-facing hole and the upward-facing hole, yes? There are alignment holes on both sides of the object. The object is thick enough to allow for some infill between the deepest parts of the holes. Slicing layer thickness is the default 0.2 mm. The angle on the hole is 45 degrees. The flat part in the hole is 2.8 x 4.8 mm. $\endgroup$ – Kevin Dec 25 '18 at 0:56
  • $\begingroup$ thank you for the link reference - I never knew that was possible! That's a great tip for special infill situations. I'm not so sure it would help in my case, since when I set my infill to Grid, 100%, I still did not get a layer on the back wall of the hole in the layer display. I got a finer grid like shown in the new image above, but no back wall. $\endgroup$ – Kevin Dec 25 '18 at 1:12
  • $\begingroup$ @Kevin If you post the STL somewhere, e.g. Thingiverse, I'll take a closer look for you. $\endgroup$ – 0scar Dec 25 '18 at 8:48
  • $\begingroup$ Thank you to you and Trish for volunteering to check it out. You both inspired me to check it with Cura myself. I found the problem. The Qidi slicer v5.0.7 (based on an earlier version of Cura) will not generate a back wall of 5 mm in size (6 mm works fine). Cura 3.5.0 generates a back wall of 5 mm properly. Best regards, Kevin $\endgroup$ – Kevin Dec 26 '18 at 17:58
  • $\begingroup$ @Kevin No problem, usage of a more recent version of a slicer is always a good idea. Anyways, my suggested solution with 100 % infill should also work. $\endgroup$ – 0scar Dec 26 '18 at 18:10
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I found the answer with the help and inspiration of other people above. Their words reminded me that I could check Cura too, to see if it had the problem. Cura v 3.5.0 did not have the problem. The Qidi slicer v5.0.7 (based on Cura 3.3) correctly generated a back wall if the cutout was 6 mm or larger. At 5 mm, the Qidi/Cura slicer did not generate a back wall. I entered a ticket with Qidi about the problem. I expect the problem will be resolved in their next version. Thank you to everyone for your help.

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