I have a small Keychain, created with Printmon on Makerworld. Is it possible to put a small cylinder inside the Model so basically in the infill so that i can put a small magnet inside the modell?
Right-click the model, Add Negative Part, Disc, Scale Disc to size, Move Disc to correct location.
Put the cavity at the surface if the magnet will be glued in place, or just a couple layers from the surface if you wish to enclose the magnet.
To completely embed the magnet, after slicing, adjust the vertical slider on the right to the first layer which bridges over the cavity, right-click and add a Pause.
Are you sure you have added the cylinder as a negative part? I tried my own instructions from the earlier post to add a negative 3x3x5 cylinder to a cube and the cavity is not filled. Maybe you can compare this example to your project and spot the difference: Cube.3mf (36.6 KB)
Is there a Setting where I can say I don´t want to have tree support inside this modell? Because my Model automatically creates support, even if the support setting is turned off. But here you can see that it generates support where I want to put my magnet in: