Screw Thread Tutorial

Color Chart:
Grey - Construction Line/Surface
Red - Current Object in Step
Cyan - Thread Pitch Profile Line
Blue - Thread Pitch Helix

  1. Layout bolt cylinder diameter and profile
  2. Insert a line to establish the pitch length and draw your thread profile. Make sure that your thread profile extends beyond the bolt diameter line. Move the thread profile so that the middle of the minor diameter lines up with the start of your bolt profile.
  3. Create the thread helix to match your TPI (threads per inch) specifications.
  4. Copy your thread helix from end to end (this is so that you can create your disappearing thread curve).
  5. Take the copied helix and scale it up (in all three axes) by 1.25. Then create a cutting plane and place it approximately 1/2 turn into the scaled helix curve.
  6. Trim back the helix to the cutting plane.
  7. You now have the thread curves required to sweep your thread profile curves. Do not join the thread curves or helixes.
  8. Taking two of the thread curves (shown in cyan), use the "Sweep 1 Rail" command using the helix as the path. When prompted, choose the "Right Side" preview and select OK.
  9. Taking the last thread curve, again use the "Sweep 1 Rail" command using the connecting minor diameter curve of the thread surface you just created in Step 8. When promted, choose the "Follow Curve" preview and select "OK". Once completed, you can join all 3 surfaces together into 1 (this will close off the edges, assuring your thread surface won't have any bad edges to deal with).
  10. Repeat the same process as used in Steps 8 & 9 to create the disappearing thread surfaces.
  11. Taking the surfaces created in Steps 8 through 11, explode and then rejoin them into 1 surface. You now have your thread profile/cutting surface.
  12. Using your bolt profile you created in Step 1, rotate your bolt diameter circle 90 degrees on the Y axis.
  13. Move the rotated bolt diameter circle in the X axis -1/4 inch and create a 1" long cylinder using the "Solid - Extrude Planar Curve" command in the X axis.
  14. Using the "Solid - Differnece" command, subtract the thread profile/cutting surface from the bolt diameter cylinder.
  15. You should end up with a 3/8" dia. x 1" lg. stud with a 3/4" lg. thread length.

Bolt diameter cylinder can not be Booleaned if bolt cylinder end extends beyond the thread profile/cutting surface. The thread pitch helix curves can be joined to make a longer threads. For All-Thread studs, the stud diameter cylinder must remain smaller than the thread profile/cutting surface.

- Tom Rhino Newsgroup

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