Bug report - v3.0.2 Generate Automatic Supports

[pcman]

In my attempts to find a workaround for another issue I am having, I noticed what appears to be a bug with the 'Generate Automatic Supports' function. I have searched the forum and did not find a prior report of it.

When one object is placed on top of another and automatic supports are generated, supports will be created for the upper object as if the lower object was not there. If both objects are to be printed by the same extruder, it's not a real problem because the supports will not be generated by the slicer. If the objects are to be printed by different extruders, it can be a problem.

The behaviour can be replicated as follows:

1. Start a new project and import a 20mm cube.
2. Duplicate the cube and stack one squarely on top of the other using the numeric inputs.
3. Run the dual-extrusion wizard but deselect the option 'Group and align models'.
4. Manually group the two cubes and rotate them 45 degrees on the Z axis.
5. Generate automatic supports with parameters of 4mm and 45 degrees.
6. Examine in the g-code preview.

This is obviously just for demonstration as no supports would actually be needed in the example. The problem came to light when I had a model with areas that did require supports and S3D created hundreds of extra supports unnecessarily. These would have required a lot of work to remove manually one at a time.

[CompoundCarl]

Any supports for the second object that overlap with the first are automatically removed. There's no need to do it manually.

I'm not sure why the rotate 45 degrees step was necessary, but you may also want to try slightly smaller support pillar resolutions. In my case, I was using a 20mm cube, so a 4mm support pillar is pretty big. 1-2mm is much better for small objects like that.

[pcman]

No, they are not entirely removed if the upper cube is being printed with a different extruder to the lower cube. That is my point.

The 45 degree rotation was just to make the cubes off-square to the supports so the supports are visible. The size of the supports isn't relevant. I picked those parameters because they are the default and I knew they would illustrate the problem. 1mm supports still produce the same problem. Again, this was just for demonstration. In reality, I would pick support sizes appropriate to the areas that needed them, not the upper 20mm cube that shouldn't require any at all.

[CompoundCarl]

Let me say this differently. I followed your instructions exactly, and there is nothing wrong with the gcode file that is produced after slicing. Even though the support pillars in the preview overlap with the other model, those overlapping areas are automatically removed when slicing. So it looks like it works exactly as I would expect.

If you still disagree, why don't you post your factory file that produces the overlapping gcode when slicing

[pcman]

@CompoundCarl: Thank you for your interest in this issue. I have attached the factory file as you requested and I look forward to hearing your thoughts.

[CompoundCarl]

I looked at your file. There is no overlap. The gcode is correct and would print just fine.

Read the posts above. Even though it may look like there is overlap when you are placing the support pillars, it is automatically removed when it is sliced so it won't be present in the gcode (or the preview). I posted a picture of the preview to illustrate. The gray extrusions are support material. Note how there is no gray color inside the part. It was removed.

As I said earlier, if you don't want the extra bits of support on the outside (the tiny gray specs around the border), then use a smaller pillar resolution. Yours is far too big for this small part.

[pcman]

@CompoundCarl: Thank you once again for your reply. I've read through a lot of posts in this forum and it is obvious that you are a very knowledgeable and helpful contributor, and I certainly appreciate your insight on this issue. I cannot agree that this is acceptable behaviour though. Perhaps my QA expectations are too high. I write software in an industry where bugs could potentially kill people.

You are correct that the remnants don't cause a problem in my example but, as I have tried to make clear, the cubes were just for a quick illustration. I chose them because I assumed that just about everyone would have a 20mm calibration cube available. Tweaking the support resolution does not solve the problem. If the software worked as would seem reasonable to expect, no supports would be generated at all in the example because none are needed. The fact that unnecessary supports are generated is clearly undesirable (i.e., a bug) and because there is no marquee selection tool to allow removal of supports en masse, it makes cleaning up larger and more complex models a really tedious task.

[pcman]

I eventually found a workaround for this bug that I would like to share. It worked well for me in my particular case but I can't promise it will solve the problem every time. Depending on your circumstances, it might save a great deal of work.

After you have run the dual extrusion wizard with group and align models selected, select the created group and click Edit > Ungroup Selection. You may then select each model individually and the support generation tool will only affect the selected model(s). Then, to stop the slicer creating all the unnecessary supports automatically for the remaining models, edit the process and on the Support tab, set Support Pillar Resolution to a very high value. I used 1000mm.