Internal support for deep holes

[PCLoadPLA 0]

I'm making a drill-bit holder with deep, blind holes as shown in the picture.

 

The problem is that the bore and the bottom of the holes are treated as "walls" by the slicer; this means there's no way to print them regardless of the orientation of the model while printing, because the "hole" is sort of sticking into space. I need support under the "holes" in order to print them, but if I turn on support, Cura will not add internal support to support internal structures like this.

 

In the picture of the slice preview you can see the bottom of the smaller holes starts to print in mid-air, which will never work. One option would be to increase infill to perhaps 5mm between lines, but then print time goes to 24 hours vs. 4, and cost of course goes up by 10x or something too. 

 

Is there any Cura option to support these internal, deep holes, or other workaround I can try in modeling it?

[Smithy 1,144]

I am not sure if I understand it, so please upload the STL if possible.

Is the holder closed at the bottom? Because when you print it in normal orientation like on the first picture, there should be infill inside of the object. 

[PCLoadPLA 0]

I will upload a wireframe and STL later.

 

When sliced like the picture, yes it will be full of infill, but I don't want infill in this case. It's not needed for strength and it adds print cost. Also, unless I use like 60% infill or more, I still can't print the smaller holes because they will end up between the infill lines, where is still no support underneath them, and you can't extrude plastic into thin air. 

 

The holder is closed at the bottom. It's a big block with blind holes punched in the top for the drill bits to sit in. The problem is that the drill bits don't go all the way through the block. So no matter what orientation you put the block in, the holes are impossible to print because it's basically a cylinder sticking into space. And there's no way to put support underneath the holes because Cura won't put support inside the model, only outside of it. 

 

 

[Smithy 1,144]

Ok, got it - thanks! 

 

Check if the setting "Infill Support" is doing what you want.

[PCLoadPLA 0]

Infill support is already enabled, but it doesn't help the problem. There is a "top" over the whole model, so with Infill support enabled, it simply generates infill everywhere, because everywhere has a top. In other words, the bottom of the holes and the top of the block are both "top" as far as Cura is concerned. But unless the infill lines are less than 4mm apart, there will still be print failure on the smaller holes. 

If the holes were outside the model then support would be generated in the normal way and it would work fine. What is needed is a way to generate support for them inside the model. I can also build in a solution into my model, but I'm actually not sure how to modify my model to fix this problem either. 

Edited December 11, 2020 by PCLoadPLA

[GregValiant 1,264]

Have you tried a support blocker?

Place a support blocker (Mesh Modifier) under the blind holes.  Use Non-uniform scaling and set the height, width, and length.  Move the block so all the holes will be supported and check that the Z is at 0.  With the Mesh Modifier selected:  From "Per Model Settings" select the "Modify Settings for Overlaps" tool.  Use Select Settings and pick Infill Density.  Set it to something that will allow the bottoms of the holes some support.

All of your model around the Mesh Modifier will have the infill you set in the main settings, and the Mesh Modifier will have the higher density support for the holes.