3D Computer Graphics Using Blender 2.80 - Modelling Methods, Principles & Practice

          Blender Tutorials: Machined Metal Gear- part 2

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Creating and Texturing a Gear - Part 2

Preparing the UV Layout

The process of laying out a 2D representation of all the 3D faces is called UV unwrapping. Fortunately Blender contains some very powerful tools to unwrap a mesh and I strongly recommend you check the Blender Wiki and do some of the many unwrapping tutorials to see its full capabilities.

Before you unwrap a mesh you need to have some understanding of how you will create the 2D image to use as the texture and where most of the detail needs to be.

Creating the textures for a machined metal surface needs to take into account the direction of cut that created the profile.

On our gear model we have three distinct areas as detailed on the coloured gear opposite.
Areas of texture
A gear like this would normally be machined from either a casting that is generally the correct profile with a little bit of surplus metal in the areas that need to be machined, or from a metal disk cut from a bar. This gear is machined from a casting

Because the gear is made from a casting the recessed area of the gear represented by  the red area would be left as cast with a fairly rough sand cast finish. The face and bore of the gear would be turned on a lathe giving radial tool marks around the gear, represented by the yellow area. The gear teeth would be cut on a gear hob and the key-way broached out of the bore, both using a linear cutting stroke represented by the blue colour.

Because there is such a distinct difference between the machined and as cast surface, texturing is best done using two different methods. The texture of the sand cast area can easily be recreated using Blenders procedural textures, whereas the machined regions are more suited to image based textures. As we are employing two different texture types we need to use two different materials. Applying different materials to areas of the same mesh is done using the Editing Context buttons in the Link and Materials panel.

Because the gear doesn't have a material yet, press the New button indicated, the material indices will change from 0 Mat 0  to 1 Mat 1 and a default grey material will appear to the left of the Material indices. Click New again and the numbers will change to 2 Mat 2.
Link & Materials
We now have two materials associated with the gear but only the first one is assigned to the gears faces. If you now go to the Shading context, Material sub context buttons and  in the material panel change the colour to red. Then go back to the Edit buttons Link and Material panel, the material displayed to the left of the Material Indices should now be Red. 

Paint select faces If you click the arrow to the left of 2 Mat 2 the numbers will change to 2 Mat 1 and the red material change to grey. The numbers 2 Mat 1 mean two materials are assigned to the gear and you have material 1 selected. We now need to assign the second (red) material to the cast area of the gear.
Paint select BB the faces in the recessed section on both sides of the gear and then in the Link and materials panel click the right arrow next to the 2 Mat 1 to select the red material. Press the Assign button, this will assign the second material to the selected faces, which will now turn red. 2nd Material Applied
We will later changes this red material to give the appearance of a sand cast, iron surface.

Before we start to unwrap the gear we need to open a UV/Image Editor window. If you still have a Scripts window open you can change this to the UV/Image Editor.

With the faces of the cast selection still selected go into front view and wire frame Z and Box select the top and bottom face vertices, include the vertices on the centre of the bevelled edge.

Go back to face select mode and paint deselect BB-MMB the faces of the bore and key-way.
Select faces to unwrap

With all the faces now selected, go into top view and scale the view SW so the gear occupies approximately half of the view. Pan the gear Ctrl MMB so it sits towards the bottom left corner of the view.
UV Unwrap - Project from view
Press U to open the UV Calculation menu and select Project From View. This takes the selected faces and lays them out as they appear in the 3D view.

In the UV/Image Editor window you will now have a 2D layout of the selected faces. The top face is stacked on top of the bottom face.
UV Calculation
You can use blender manipulation commands, RMB to select, Grab, and Scale on the UV points in the UV/Image Editor window. Once you know the commands in one window they usually carry over to all the others, 

The gear teeth are a little more tricky to layout because we can't get all the teeth parallel to the view.

To enable us to use some of Blenders automatic unwrapping tools we need to mark the mesh at the points where the unwrap can split the UV layout into sections, rather than making a single skin which would be very stretched and distorted.

Alt-RMB select the loop of vertices in the centre of the bevel between the top face and gear teeth. Press Ctrl-E to bring up the Edge Specials menu and select Mark Seam. The seam will get an orange highlight. Do the same on the bottom face seam.
Select Loop

Select Gear Tooth Edge We now need to mark a seam on the one side of each of the gear teeth.

Select the three edges to the side of a gear tooth so you have a seam touching the marked seams we have created in the centre of the top and bottom face bevels.  Again press Ctrl-E and Mark Seam.

Repeat this on all the gear teeth.
What we have created is a group of faces for each gear tooth. The groups will be individually laid out in the UV/Image Editor Marked Seam

Select the four edge loops Shift-Alt-RMB that form the gear teeth and half the bevel.

Press U to open the UV Calculation menu and this time select Unwrap.

Blenders unwrap tool will layout each gear tooth as a ladder frame of vertices in the UV window. As we are going to create an image texture for the grain of the metal that is very fine, we can stack each tooth on top of each other to gain the most detail from the image. The teeth will need an image texture with the grain running vertically.
Generated UV Layout As mentioned above most of Blenders commands are also used in the UV window.

You will need to straighten up the vertical edges of each tooth by Box selecting the top two rows of vertices and moving them G on the X-axis.
Link Select
You can select all the vertices of a gear tooth by Link selecting. In the UV/Image Editor Link select will deselect all the other vertices that are not part of the linked group.

Stack teeth in top right Link select each gear tooth, straighten the verticals, scale it to approximately the same size as the tooth in the top left corner, then move it over the top tooth.

The teeth with the faces stacked vertically will need to be Rotated 90 degrees

You should end up with all the teeth stacked up in the top left corner. They don't need to be exactly on top of each other, just all roughly the same size and in that area. Sll teeth Scaled and stacked

Mark Seam's of Bore Select the top and bottom edges of the bore (edge select mode) and key-way and the vertical edges between the bore and key-way as indicated, then Ctrl-E Mark Seam.

Paint select the face of the bore BB (not the key-way faces) and  Unwrap
Paint Select Bore

Blender will unwrap the bore into a row of faces across the UV/Image Editor

Unwrapped Bore

You will need to rotate the faces into the vertical plane because we are going to set the image texture with a vertical grain, which must run around the bore of the gear.

Before rotating the faces you will need to re-align the vertical edges as we did with the gear teeth.
Stack vertically

Select Keyway Finally select the faces of the key-way and Unwrap them. Straighten up the faces and scale them to approximately the same height as the gear teeth.

Move them into the top right corner of the UV/Image Window.
Unwrap Keyway

If you now select All in the 3D view all the gears faces will be represented in the UV/Image Editor.

The layout isn't making the best use of the available area at the moment, but we now have four distinctive parts that can be easily selected and scaled to suit the image texture we create.
Initial UV Layout

In Part 3 we will move away from Blender and make an image texture of the surface grain and machining scratch marks using Gimp.

<< Gear Part 1 Modelling the Gear
Gear Part 3 Image Texture >>

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