Print 2 models intefering so one subtracts from the other

[mastory 44]

I did this once before.  There is a way to "modify settings for overlap with other models" and/or "modify settings for infill of other models" (in per model settings) that results in one of the models (overlapping the other) having basically 0 wall, 0 infill and 0 skin, and effectively performing a boolean subtract within the slicer.

 

Can someone remind me of the specifics of this method?

 

Thanks

[geert_2 557]

As far as I understood, slicers don't do boolean math on the STL-files. They rather "count walls", sort of. The first wall it encounters, it switches material on. The second wall = material off. Third wall = material on, fourth wall = off, etc... So any objects totally enclosed by another, will automatically be subtracted and become hollow upon slicing and printing. (But correct me if I am wrong on this.)

 

At least, this is how I make hollow watermarks. In the beginning, I made complex subtract-operations in DesignSpark Mechanical on my CAD models, to get these hollows. But this made subsequent editing difficult, because these hollows are hard to reach. Now I don't: I just move the watermark logo and text inside the main model, without subtracting. So they are "solid blocks inside of other solid blocks". Upon exporting to STL, it makes triangles of those watermark-surfaces. An STL-file just consists of surface-triangles, as far as I understood. No colors, no materials, no solid/hollow-definitions, no dimensions; just triangles... And these triangles are then automatically sliced and printed correctly, using the "wall-count" method.

 

Not sure how it would/should handle models that partially overlap each other, if it should do the exact same, or throw an error?

 

A few examples of watermarks done in this way. Most of the watermark text is 3.5mm high, character-legs are 0.5mm wide, and they are sitting 0.5...1mm below the surface. Obviously, this requires transparent or translucid filament.

 

 

 

 

 

 

 

 

[mastory 44]

Thanks for your thoughts Geert.  I have created empty voids by subtraction in CAD, but never by placing an STL inside another.

 

What I'm referring to is actually very similar to the support blocker function.  Although I don't know if the support blockers are made up of STL files..  Those can be partially interfering a support and/or the printed model.  Any portion that interferes the model is ignored, but the interfered support is effectively cut away.

 

I can tell you that I've done the practice in question in the past few months.  I just don't remember the exact steps.  It is an unintended function in Cura.  I'm not sure which versions.  To me it worked without qualification like a boolean subtract in CAD.  Given that, I think it could fairly easily be added as an intended function.

 

The project at hand is a hand held topographical map of a ski area.  My primary model was extracted as grey scale from a topographic map.  This PNG file was imported into CURA like a lithophane with the model thickness relative to grey scale.   This makes a model that is an accurate topo model, but it has sharp corners.  Not a friendly shape for carrying in your pocket.  I don't know a way to easily apply chamfers and radii to an existing STL model.  What I can do easily, is model a subtract solid in Solidworks and export that to STL.  In this case, the subtraction STL is shaped like a picture frame with an contoured inside edge.  The shape cuts the exterior of the map with large radii.  A cylinder was placed in the subtract model to create a lanyard hole in the map.

 

 

Edited January 28, 2020 by mastory
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[mastory 44]

I figured it out.

 

Select the model you want to use as a subtract solid.

 

Set the "modify settings for overlapping models" for this solid.  Then pick "select settings".  You can then set whatever slice settings you want for this piece.  If you set wall thickness, top/bottom and infill to 0, the piece will be regarded as a subtract from the other models.

 

 

[mastory 44]

Actually the settings that worked out are:

 

 

 

Edited January 28, 2020 by mastory

[geert_2 557]

Glad you found a solution.

 

I like the idea of printing topographical maps. Where did you find good quality images?

 

Another question: do I understand it correctly that the main purpose of this procedure is to round the 4 corners of the image (but not the mountains themself)? Like a plastic bank card? And to "drill" a hole in it?

 

If so, couldn't the same be achieved in Photoshop by changing the black and white levels of the image, and adding a black or white border around it? (Depending on whether black or white is zero height?) And then import it in Cura and set the base to zero, so that this black border is not printed? Then you could do everything in a graphic editor, and just export a JPG-file. Maybe this might add more flexibility, and you could more easily add logos and stuff?

 

I did a quick concept-test, and with a bit of trial and error this seems to work in an older Cura version, but I don't know in the newest. Edited in Photoshop from a (too) low-resolution image. I set the base thickness to zero, so the black border would not be printed, and the dark grey Rhone-valley is now the lowest part that would be printed.

 

 

 

 

Edit: cutting off 0.1mm from the bottom improves the view in (my version of) Cura.

 

Edited January 28, 2020 by geert_2

[mastory 44]

There are actually quite a few ways to create an stl from a topo map.  This site works ok, but the cropping and manipulation of the map pre download is awkward and kind of imprecise in my opinion.  No control over the aspect ratio.  http://jthatch.com/Terrain2STL/

 

This site works good.  I think it's been tweaked for the good since my last attempt.

https://touchterrain.geol.iastate.edu/

 

I am importing the gray scales into Cura 4.3.0 and using the import utility to generate the STL.  I am not sure where I got the map I am currently using.  Maybe from Google.  The map you tested looks alot like the one I used.

 

My subtract solid adds radii on the 4 rectangular corners and vertically all around in a sweep.