1. Create a ‘Helix’ spline object from the create panel. Make sure there are plenty of turns in it and that both radii are the same.
2. Add an extrude modifier and adjust the amount so it just about reaches the next coil, get it as close as possible but don’t don’t spend ages doing it as step 4 will sort it out.
5. Now, add an 'Edit Poly' modifier and go into 'Edge' sub-object mode, then select one edge travelling the length of the tube and hit 'Ring' (Alt+R) to select the entire helix.
6. Click the small grey box next to 'Connect' in the modify panel and give the selection 1 edge segment. You will now have two spirals travelling the length of the tube. (I forgot to t o do an image of this stage :) 7. Select one edge of one spiral and click 'Loop' (Alt+L) in the modify panel to select the entire spiral. Then click the 'Scale' tool (R) and drag the web connecting the two width axes for the tube (shown in yellow in the image below), this will create your thread depth.
8. Now, if your thread is too t oo spaced out or too close together select all vertices or edges (Ctrl+A) and scale them using only the axis that travels the length of the screw. screw. Doing this non-uniform scaling scaling in sub-object mode will eradicate any problems in distortion during animation later on (if applicable) and you will not need to reset the xform.
9. Now we will move move on to cleaning up the end on the thread. Add a 'Slice' modifier, then click the modifier itself in the stack to enable editing of its gizmo, then rotate it to face down the length of the thread (see image below), then click either 'Remove Top' or 'Remove Bottom' depending on which comes out right for you then move the gizmo so it chops just the first thread off on the screw and you end up with a flat f lat end.
10. A little housekeeping housekeeping is needed here to aid you further down the line. You will see that the thread fades out in two t wo opposite places on the end of the thread and you need to do a little target welding to tidy it up. In the picture below, ‘Target Weld’ the two red vertices to the green vertex.
11. Go into 'Border' sub-object mode and select the end hole then check the area just below the modifier stack to see how many edges have been selected (on my mesh there exactly 40 edges).
12. Then create an 'Ngon' spline object with the amount of sides you just had selected (40 for me) and align it slightly away from f rom the end of the screw but dead central from side side to side and top top to bottom. Make this Ngon about as small as the hole running through the screw (if seen from the end) this stage creates the chamfered end to the screw, you could just select the hole and bevel it but you will find its not central and its not circular so this is much nicer if a little more work
13. Select the screw object again and add the Ngon to it via 'Attach' 'At tach' (you may need to flip the normal of the new end face ifif its facing the the wrong way). way). You will then have something something like the image below. Then go into 'Border' subsubobject mode and select both borders as detailed in red below.
14. Next, click on 'Bridge' in the modify panel to join the two borders together, this is where knowing the exact amount of edges the original hole had comes in very useful as you end up with a very clean mesh, (see image below)
15. I then scaled and move the end face about a bit to give it a more correct size and distance from the end of the thread.
Here’s what I did with a little litt le more work. The thread in the render below is very oversized and should be scaled down quite a bit for a realistic realistic screw/bolt. This is just for demonstration demonstration purposes.
