A week is long enough to suffer and this hopefully will cover me for my good deed of the day.
You need to do two things before baking,
- Add some lamps to illuminate your object.
- Add a new Image Texture in the node editor for each of your two textures.
This new image will be the image that they will both bake to.
- First change the Preview Mode to Render.
- Add a Point Light to your scene and position it a little above and in front of the object.
- Open the lamp tab.
- Increase the Power value until the front of the object is appropriately illuminated.
- Copy ( Shift + D ) the Lamp and position it somewhere behind and to the side of the object. Make a second copy and position to the other side of the object. (See the screenshot below). Play with the Power values of these new lights as needed.
Adding an Image to bake to :
- In object mode Select the object.
- Open the materials tab.
- Select the first material (White paint).
- In the Node editor Add a new Image texture.
9b. Click on the New field and we will give it the name Bake. Notice that this new "Bake" image node is highlighted in white, indicating that it is selected.
Repeat the above for the second material (Brass)..... Add a new Image texture then click on the little image icon and select the same "bake" image from the list.(see screen_shot below).
The same image "Bake" because both materials will be baked to this one image. Notice that this image texture node is also highlighted again indicating that it is selected.
To bake both materials to the same image ("Bake") it is very imported that in each of the two material node setups that the "Bake" image node is selected and only that node in each material. Having this image node selected is telling Blender which image to bake to when we hit that Bake button in the next step.
Open up the Bake sub-menu and enable Direct and Indirect lighting.
Now hit the bake button. If all is well the new bake image will appear in the UV editor window. From here you can save the new image texture.
As you probably know already it is the number of Render Samples in the Sampling menu that will effect the quality of the bake.
It is not often that the first bake is the one you will be happy with and you may find that you have to go back and play with the lights etc and then try more bakes. If you have a slow machine it is often a good idea to reduce the number of Render Samples to something like 32 or 64 for these test bakes then when happy increase the value to 128 or more for the final Bake.
Just some observations:
To get a shiny brass texture you will have to play with the Metalic, Specular, and Roughness values in the Pricipal BSDF shader. Also for the finish on the cylinder.
Your cylinder object has like 100 (200 even) times to much geometry than the object actually needs. The Geometry is so dense it is hard to say if you have used used smooth shading or not ! before your next project check out some tutorials on creating game assets. :)
Perhaps consider joining the "Wheel" object to the Cylinder object and find space in the UV map for the Wheels's UV's.
You have quite alot of unused space on your UV map so consider scaling up the Brass material UV's so that this material occupies a larger area in the UV space. A larger area equals more pixels for the material, equals higher resolution.