Problem with join/booleanunion of objects

Hey guys,
I have a problem bringing these objects into a single one. We have a project at uni, where we have to 3DPrint our models, but most of websites have declined my model and I think its because it is not a single object.

ModelCAD.3dm (3.3 MB)

Hello - please start with the help file page - there is information on how Boolean operations work and what causes them to fail -


I have union problems at 2 places, the points describe it as Surface Intersection Error. Do you know how can I correct this?

you have several problems, naked edges ( green in the image)
coincident surfaces
flipped objects ( dark red in the image) manily because they are open
and also you have selfintersecting objects ( red circle)
try to make booleans by pairs, then you will find sequentially each problem.

Thanks, I tried to make booleans by pair and now everything is connected except the 2 green naked edges at the right side and the A and the O. I been seeing some youtube videos on how to fix naked edges but I cant explode my tubes cause they are just one surface. Do u know how can I fix those?