Cura 2.3.1 merge models problem

[jazzychad 1]

I am having some trouble with merged models in Cura 3.2.1 (Mac 10.11.5) - using Ultimaker 3

By way of example, here is what I'm doing:

I am printing some letter tiles. I have several .stl files, but the main process for each tile is:

- add Tile.stl to the build plate

- add {Letter}.stl to the build plate

- select the Letter and change the Per Model Setting to Blue PLA (2nd extruder head)

- select the Letter and the blank Tile and right click -> Merge Models

- Cmd-click the Letter inside the merged model and change the Z position to be correct (so Letter is raised above tile: Tile is 5mm tall, Letter is 3mm tall, but set Z position to 4 so 1mm is 'inside' Tile and 2mm stick up)

Repeat for each letter, and you get something like this:

Now, normally when things are merged correctly the slicing will result in the dual extrusion interface to be printed starting at layer 18 (as seen in next screenshot) - except that sometimes it doesn't! This can be seen in the 2nd column of tiles which only show printing the triangular infill

More curiously, it looks like both extruders are printing in all the layers where the 2 models overlap for the 1mm inside the tile, the screenshot below shows what would be the top layer of the tile, and the 2nd column is again different from the 1st and 3rd column of tiles.

Sometimes if I just move the merged model around the build plate enough it will magically slice it correctly. I haven't found any pattern or steps to reliably reproduce this behavior. It seems like a bug to me, but maybe I am misunderstanding something or am adding too many separate models to the plate..?

Another clue that they aren't quite merged together correctly:

- If I select a correctly merged model and press Backspace/Delete key, it will remove the model from the build plate.

- If I select an incorreclty merged model and press Backspace/Delete key, it will NOT remove the model from the build plate... but if I right click and select Delete Model, only ONE of the pieces of the merged model is deleted, and the other remains on the build plate.

So, it is acting as if the two models are just existing in the same space, and are somehow grouped together b/c I can move them around as a group, but they are not being sliced as if they are a merged model.

Edited December 19, 2016 by Guest

[ultiarjan 1,223]

Do i understand you correctly that you try to merge a blank tile (with no letter cut out) with a letter? I think it's logical that in this case cura will print double on the overlap.

I think the best and most accurate way to do this thing is to create 2 stl's for each tile, one with the letter and one with the tile that has the letter cut out. Set the right depth and position already in CAD, so you don't need to fiddle with the Z height in Cura, this way you get consistent quality.

[nallath 1,124]

Merging a model will only set their origins to be "shared" and then group them.