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Why is my helix larger than the diameter of the circle I used to draw it?

Question asked by Justin Roskowske on Jul 12, 2018
Latest reply on Jul 12, 2018 by Justin Roskowske

EDIT: It appears this is just an appearance error and not an error on the model. The problem I'm experiencing is related to the thread profile.


I'm attempting to draw a model that uses buttress threads. I normally just do cosmetic threads, but the machinists have asked that I actually model these to help them with their lead-in / lead-out on the threads since they are so much larger than a normal thread.


The problem I'm having is related to the helix. When I draw a circle the same diameter as an extrusion and make a helix from it, the helix diameter appears to be larger than the diameter of the extrusion. I think it could be what's causing an error for me in modeling my threads since the profile isn't actually connected to the model.


See screenshots below.


Extrusion: This extrusion is the same size as the minor diameter of the threads.



Circle for Helix: You'll see that this is the same diameter as the extrusion which is the minor diameter of the threads.



Helix: Here are my settings for creating the helix.



Helix Error: You can see that the helix diameter is correct, but appears to be outside of the extrusion which is the same diameter.

helix error.PNG