How to add holes to bottom of model?

[pozzello 0]

I've got a model of a shoe that printed nicely in clear PLA with 10% lightning infill on my CR10v3.    I'd like to add a hole in the bottom (that sits on the build plate at Z=0) so I can set it over an LED tea light.   I added a disk and set per-model settings/modify-setting-for-overlaps to 'cutting mesh', with 'wall thickness', 'top/bottom thickness' and 'infill density' all set to 0.  Slicing results in a hollow where the disk is placed inside the shoe, but it has top & bottom layers, thus not a hole.  See attached image. 

 

If I scale the disk vertically up through the top, it does make a cavity all the way down, but it still has a 'floor' printed.  How do I get rid of the printed floor and ceiling where the cutting object intersects/overlaps with the main model?     The model is too big to import into Tinkercad and I'm hopeless with any other 3d design software, so looking for a way to do this in the slicer.   Seems like it should be do-able...

 

TIA,  Paul

Cura 5.1.0 (and 5.2.1) on Windows 10.

[pozzello 0]

Getting closer...  I found that setting the cutting mesh 'Bottom layer' COUNT (not 'top/bottom THICKNESS') to 0 does remove the first layer floor (see attached,) but I still get a top layer as in the image posted with the OP above.  I'm guessing that's really a bottom layer for the main model (raised above the build plate due to the cutting mesh below) but not having any luck removing that to leave the entire disk cross-section as an opening into the model cavity...

 

I could just drill a hole into that layer to allow the 'flame' part of the tea light into the body, but will require putting that layer at just the right height for these specific lights, so still not optimal...

[pozzello 0]

Success (maybe)    the solution presented here sort of does the trick: 

 

I added another 'cutting mesh' encompassing the entire object just few mm off the base.  (see attached)

 

I'm still trying to get my head around WHY this works, but there it is...

 

BUT I seem to have lost the lightning infill I need to get this print.  Always something...

 

Edited November 28, 2022 by pozzello
edit: adding 10% lightning infill to the large cutting mesh and I'm back in business... Still makes my head spin tho.

[GregValiant 1,408]

This is all about "Definitions".

Remember that your model is solid through-and-through.  When you add a Cutting Mesh configured with no walls, no top or bottom it creates a "cavity" in the solid model, not a "hole" into an open area within the interior because there is no open area in the interior.  When it slices it looks open because of your settings (Lightning infill), but it ain't.  if you change the Infill Pattern to Grid you'll see what I mean.

The model is set to have walls and bottom layers so Cura puts walls around the cavity and bottom layers (of the model) on the top of the cavity because that is now a "floor" within the model.

 

You could set it up like you have and with that cutting mesh taller than the thickness of your Bottom Layers.  Slice the model and print it.  As a post-process finishing step - cut the top out of the cavity with a drill, dremel tool, or a hobby knife.

 

You can take that big cutting mesh and just set the "bottom layers" to 0 and move it up off the build plate.  That would leave the sole of the shoe but keep bottom layers from forming over the cavity.

 

This is option 2.  The cavity mesh is 3mm tall and the big cutting mesh is 2mm off the build plate.  So it interferes with the floor of the cavity but not the floor of the shoe itself.

(The light may show the Lightning Infill as shadows within the model.)

 

 

 

Edited November 29, 2022 by GregValiant