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          Blender Tutorials: V-Roller Guide - part 3











Part 3 Detailed Thread Profile




Before we can model the thread we need to understand the thread form. ISO Metric threads come with a Standard profile and as the V-Roller axle will use an M6 thread, I will describe the set-up of this size.

Layout of a Metric Thread





Thread Layout




Key:


D Major Diameter
P Pitch
H Thread Height





The ISO Metric thread profile is a fairly simple shape to construct in Blender and with the screw tool only one instance of the thread profile is required. As a model engineer I am not going to discuss thread tolerances or fits in any detail. You should however be aware that the finished male thread profile (bolt) should be kept below the bold blue line of the diagram above and the finished female thread profile should be kept above the bold blue line, otherwise the two won't fit together. If you need them tolerance classes are defined in ISO 965-1.

For this exercise we will make the thread to the nominal profile above. To construct the thread only two pieces of information are required the Major Diameter and the Pitch. A few of the more common sizes are detailed in the table below.





Major Diameter 3 4 5 6 8 10 12 16
Pitch 0.5 0.7 0.8 1 1.25 1.5 1.75 2





Append Axle We will build the thread around the V-Roller axle. Open a new Blender project and go into front view NumPad 1. Append the V-RollerAxle into the scene Shift-F1 
navigate to V-Roller.blend and select Object>V-RollerAxle. The axle will appear facing you in the front view. The screw tool spins a profile around the Z-axis so the profile needs to be created and the screw operation performed in front view. The Axle needs to be rotated so it is vertical in the front view. Rotate X -90.
Rotate Axle
Tab into edit mode and Shift-RMB select the 7 vertices making up the left-hand profile of the threaded section.
Select Profile

Copy these vertices Shift-D then Esc to leave them in place. Separate the copied vertices from the Object P. Its easier to work on the separated profile rather than the complete axle.





Copy & Part Profile add edge Tab into Object Mode and select the profile. Tab back into Edit Mode.

We now need to work out the Thread height. It could be done with trigonometry given that the pitch is 1mm and the thread angle is 60 degrees. But I find it easier to do in Blender.

De-select All vertices then to the left of the axle Ctrl-LMB click to add a new vertex.
Extrude this vertex on the X-axis 1mm. The thread form is an equilateral triangle so the sides of the thread triangle will be the same length as the pitch. Link select both vertices of the edge and copy them Shift-D on the Z-axis 1mm (the thread pitch).

Select the top left vertex of the two edges and snap the cursor to it Shift-s Cursor>selection.
Rotate from Cursor

Then select the vertex on the other end of the edge and with the Pivot set to 3D Cursor Rotate it 30 degrees.





Rotate other edge Snap the cursor to the bottom left vertex and Rotate this -30 degrees.

Select All and remove doubles W.


Select the centre vertex and Extrude it on the X-axis then scale it to the cursor Scale X 0.
In the Mesh Tools 1 panel press Edge Length and select the centre edge. The Edge Length shown is the Thread Height.
Thread Height




Position Therad Delete X the vertex on the left-hand side of the central edge. Select the three vertices of the thread profile and move G them towards the undercut at the bottom of the thread.

If you haven't already got one open split the 3D view and open the Outliner. Click the eye icon for the axle to remove it from view.

1/8 Height
Select the vertex on the major diameter of the thread and Extrude it on the X-axis -0.108mm (1/8 H)
Snap Thread
We can now use the snap tool to position the thread V profile.

Click on the magnet Icon on the view header. Select the 3 vertices of the V and move them G, whilst moving hold down Ctrl and move the cursor towards the end vertex. The V will snap into position.





Snap Thread
We now need to add reference geometry to allow us to cut new vertices on the major and minor diameters.


E
xtrude vertex A on the X-axis


Extrude Reference Edges
Extrude vertex B on the Z-axis as detailed, then Extrude this X -0.216mm (1/4 H) then Extrude again on the -Z-axis ensuring the edge crosses the V.

To finish the reference edges, extrude a vertex from the major diameter across the v.
Extrude Major Diameter





Cut Major Diameter Vertex Select the three vertices of the V and cut Knife (Exact), snapping the cut Ctrl-LMB to the vertices of the major diameter.

Repeat the cut snapping the knife to the vertices of the minor diameter.
Cut Root Diameter Vertices
Delete the reference vertices, but ensure the top chamfered edge of the thread is not deleted, as this will be used to locate the cursor when we spin the thread.
Top Chamfer

Thread Form Vertices





Add Edges Add Edges F to the vertices of the major and minor diameter. Threads usually have a radius at the root of the thread so we will add a fillet.

Select the vertex at the bottom of the minor diameter and snap the cursor to it Shift-S Cursor>Selection.

Shift-RMB Select both vertices of the minor diameter and copy them Shift-D, then Esc to leave them in place. With the Pivot in 3D Cursor Rotate the edge -30 degrees.
Rotate Edge





Rotate Other Edge Select the vertex at the top of the minor diameter and snap the cursor to it Shift-S Cursor>Selection.


Again Shift-RMB Select both vertices of the minor diameter and copy them Shift-D, then Esc to leave them in place. This time Rotate the edge 30 degrees.

Where the two edges cross is the centre point for the bottom fillet. Cut a vertex on the intersect Knife (Exact) and using Ctrl-LMB to snap the cut to the rotated edge.
Cut Centre Vertex





Prepare to Spin Snap the cursor to the intersect and Delete the reference vertices.

Select the vertex at the top of the major diameter and in the Mesh Tools panel set Degr:120 and Steps:4  Press Spin and the profile for one pitch of the thread will be created.

Select All and Remove Doubles W.
Thread Form





Prepare to Screw Select the vertex on the thread centreline (right hand vertex on the top chamfer profile) and snap the cursor to it.

De-select All vertices, then Link select the thread profile.

We need the thread to continue past the chamfer so we can later combine the chamfer detail to the thread. Counting the grid squares we will need 10 turns.


Screw
In the Mesh Tools panel set Degr: 360 Steps:32 and Turns:10 Make Sure Clockwise is not selected Press Screw and the thread will be formed.
Delete Chamfer

Go into top view NumPad 7. De-select All then Link select the centre and chamfer vertices. Delete these X. Select All and Remove Doubles W.





Join Mesh
Tab into Object Mode and in the outliner open the eye icon for the axle,
Reference Edges
bringing it back into view. If necessary move the thread in the Z-axis to align with the axle. Close the eye for the thread.

We now need to prepare the axle to accept the thread.
Go back into front view and select the axle. Tab into Edit Mode and select the top right vertex of the chamfer and copy it Shift-D moving it to the right of the axle on the X-axis. Extrude this vertex on the X-axis to the left of the axle. Repeat this on the bottom vertex loop of the thread section.
Paint Select

Go into edge select mode and paint a selection B B across the straight section of the thread.


Delete these X (edges).

Go back into vertex select mode.





Delete Edges Tab into Object Mode and in the Outliner bring the thread
back into view. RMB select the thread then Shift-RMB select the axle. Press Ctrl-J to join them into one mesh. 
Cut Thread Top & Bottom
Tab into Edit Mode and De-select All then Link select the thread. With the Knife tool, cut two rows of vertices across the thread, Knife (Exact) and snapped Ctrl-LMB to the reference edges.
Delete
De-select All then Box select the vertices below the bottom reference edge. Zoom in MW to make sure all the vertices below the edge are selected (not the vertices on the edge) Delete these vertices X.





Thread Hight Box select the vertices above the top reference edge and delete these. Select the two reference edges and delete them.

The thread is now the correct length for the axle but there is still more to do. We must join the base of the thread to the under-cut and the top of the thread to the chamfer.

If you zoom in on the base of the thread you will see the flange that was originally on the axle sticking out past the edge of the thread (highlighted in green below).





Merge Vertices To correct this we need to manually merge the vertices of the original axle flange onto the corresponding vertex of the thread.

RMB Select a vertex on the flange then Shift-RMB select the corresponding vertex on the thread.
Press Alt-M to merge the vertices and choose "At Last" from the popup menu.

Repeat this around the circumference of the axle. 
Merge Vertices





The intersect between the top chamfer and the thread is a much more complicated detail. Because the intersect doesn't occur on a set plane there are no vertices on the line of intersection. Therefore we cannot simply merge vertices to obtain the correct profile. The first part of combining the thread and chamfer will be to create a line of vertices on the intersect between the two sets of faces.

Face Select Go into face select mode and box select the top section of thread and chamfer. Press Shift-H to hide all the other vertices.

We can now use another of the python scripts to cut the vertices on the intersect of the faces. Split the 3D view and open a Script Window (detailed description in 608-4). With all the faces still selected, in the Script window click on Scripts>Mesh>Geom Tool and from the popup menu click on "intersect: face(s) (cut)". A new loop of vertices will be created on the intersect between the faces. Go back into vertex select mode, select All and Remove Doubles W.

The Geom Tool script isn't bundled with Blender but can be downloaded from the Blender Website. http://wiki.blender.org/index.php/Scripts/Catalog
A description for loading the script is also available from this page.

Geom Tool





Edge on Intersect With the new edge created on the intersect its now simply a matter of deleting the vertices, edges or faces that are not required. It sounds simple but this will test your patience and call on many of the editing techniques you have learned.

Only delete X a few vertices at a time, if necessary  Ctrl-Z will undo the change. In 
places you may need to merge vertices Alt-M and other places you will need to add new faces F. Its also worth noting on one side of the axle the thread intersects the chamfer in two places.
As a new user this may take a fair amount of time, but as your experience grows this will only take a few minutes and the end result is well worth the effort.
Delete





Chamfered Thread

Once complete press Alt-H to bring back all the hidden vertices. Select All, Remove Doubles W and Set Smooth W.

That completes the top thread. Rather than repeating all that work on the bottom thread we can simply copy the top one and reposition the copy to complete the axle.
Top Thread





Copy

Set Cursor

In front view Box select the thread vertices, then loop select Shift-Alt-
RMB
the inner loop of vertices on the undercut next to the main body of the axle.

Copy these Shift-D and move them to the side.


In front view Rotate the copied vertices 180 degrees.

Separate the copied thread from the axle P. Tab into Object Mode, Select the copied thread and then Tab back into Edit Mode.

Select the top row of vertices and snap the cursor to them Shift-S Cursor>Selection.
Centre Cursor

Tab into Object mode and in the Mesh panel click the Centre Cursor button. This will move the object centre to the centre of the top row of vertices.





Delete
Select the axle and delete the vertices of the bottom thread.

Alt-RMB select the inner loop of vertices where the under cut was.
Set Cursor
Snap the cursor to the centre of these vertices.

Tab back into Object Mode and select the thread.
Snap the thread to the cursor Shift-S Selection>
Cursor.

Selection>Cursor





Completed Axle With the thread still selected Shift-RMB select the axle and joine the two objects into one Ctrl-J.

Tab
back into Edit Mode, select All and Remove Doubles W. to complete the axle.

This axle will have 7274 vertices, compared to 1418 vertices of the axle without the detailed thread.

You may also want to set up a camera and lights and render an image of the shaft as detailed in 608-9.


Tab into Object Mode and save your work.





In the next section we will do a dimensioned drawing of the V-Roller components.





<< V-Roller Part 2 The Axle Tutorials V-Roller Part 4 The Drawing Layout >>












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