Both objects Letters + Base must be solid !
Letters must overflow inside >Base for not have some problems! :)

Hi Bodo-Lutz, one issue is that there is an area inside your model where the "wall thicknesss" is pinched down to 0, that may cause some problems with volume operations:



- Michael

Hi Bodo-Lutz, please try with this attached version it should boolean union ok now.

I used Edit > Separate and Edit > Join to get rid of the naked edges in the model to make it a solid (although there is still the 0 thickness "pinch point" which may be a problem for other things down the line) and also stretched out the text so that it pushed a little distance down through the model instead of skimming right along it.

- Michael

Hi Michael,
Many thanks for your help
Good night!
Bodo-Lutz