Posts: 1,409
Thanks: 63180 in 116 Posts
26 Achievements
View My Journal
When you create new parts like your cylinder, if you have "autosmooth" un-checkmarked they have no normals and will appear black.
The normals are what tells the game which direction the light will reflect from the surface of your mesh. No normals means no reflected light, so it will always look black.
But if you have "autosmooth" checkmarked, your entire mesh will get it's normals re-aligned and this can create other problems such as visible seams and strange shadows.
The solution is to save your mesh before creating the new part as a .ms3d file.
Then create the new part and bring it into position as you want it.
Now delete all the original mesh groups except your new part.
Select it, then use "Smooth All" on the menu. It should turn from black to silver-grey.
Export this as an .obj file.
Now open your saved .ms3d file, then import your new .obj file to bring it back with proper normals.
Now you can uv_map it and assign all it's vertices, then regroup it into one of the original groups.