Why naked edges in this sweep on helix?

Rhino Rhino for Windows
1

Hi,
V5

Helix 2BA thread naked edges
Helix 2BA thread naked edges904×612 111 KB

I have been oh so careful. drawn the thread profile dark blue.
drawn the helix with correct pitch entered as a number and dragged out radius to snap to profile tip.
drawn a second helix to act as second rail, as one rail saw wierd effects.

sweep2

and result has naked edges.

Not sure how to fix them.

the profile is a perfect match to all the theoretical lines for the thread.

help !

I then intend to trim the ends with the two sheets.
Its a boolean difference cutter and no need to have the thread feather in as a bolt would have.

2BA Female Thread naked edge.3dm (3.6 MB)

I try for a single ‘lap’ then copy move it, run intersect, and its not quite complete, but why ?
2BA Female Thread naked edge try suss.3dm (577.4 KB)

what is wrong with the helix command ?

Steve

2

Nothing

Solution:
Split the thread surface using the outer helix curve
Join the two parts
Result is a single polysurface with not internal naked edges

3

Hi David,

Many Thanks.
Thats solved it.
Why was it that there was a naked edge there ?

Steve

4

The cause appears to be: an edge of an object cannot be joined to an edge of the same object.