Hi V5,
how to sweep a helix inward during its next 360 deg rotation ?
What method does this ?
If one has a helix, how is the last rotation taken progressively inwards during the 360deg rotation of it.
Such that any triangle thread on it vanishes into the inner solid its sitting around.
Steve
Project it on to an appropriately designed cone?
Hi,
FANTASTIC AND MANY THANKSâŚI CAN NOW PROGRESS. 
Now thats a neat trick, do some maths and establish cone angle. It needs to depart the helix tangentially and that would do so as well.
Now someone needs to add that into a bolt thread making video !
Steve
Spiral command Rhinoceros Help - Spiral | Rhino 3-D modeling (mcneel.com)
As @davidcockey said, itâs called a Spiral. See the Help for details on how to use it.
Hi,
Thanks guys, so spiral would also do it. enter same pitch etc as helix and create the last turn.
Which in theory is the easier to construct, the project to cone or the spiral matching the pitch and so on of the helix ?
Cheers
Steve
Spiral IMOâŚ
Probably what Mitch said - especially after youâve done half a dozen or so.
Why not try both and let us know what you think?
Project does not work.
Spiral Steve.3dm (2.0 MB)
Creating a rectangular surface with a diagonal line, then flowing the diagonal line onto the cone also works. Result is essentially the same as Spiral.
Spiral Flow Steve.3dm (2.0 MB)
Of course you are right. I spoke too soon. I was imagining âprojectingâ parallel to the coneâs base (perpendicular to its axis). But as you show thatâs not how the project command (or, for that matter the pull command) works
in its one rotation?
In its own rotation you mean?
Hi Steve,
If you are talking about the final turn of a thread on a bolt, I believe you will find that the helix radius stays constant to the end. The reason that a casual glance leads you to think the final turn spirals in is that the end of the bolt has a chamfer that progressively cuts away more of the top of the V as you get closer to the end.
So to get the effect, make a solid bolt, then make a cutter by boolean differencing a cone from a cylinder and then boolean difference the cutter from the bolt.
Regards
Jeremy
Hi Jeremy,
aha !
I have seen videos of folk sweeping the curve in
an apparent Rhino tutor ?
and took that as to be the need, and theur method was criticised but no mention of the fact that it wasnt needed at all. However what you show makes such as they do unnecessary.
My brain says if metal moves inwards the helix would remain out in space, however your image shows that as not the case.
I must do what you show to see it for myself.
we need a definitive guide to bolt thread making !
I then look at the other end of the thread and see they have milled around the thread and it simple gets milled or ground/turned, whatever one would call it, out of existence without going inwards.
My item has the thread vanishing just before the slope starts, or perhaps its a tad up the slope, so a bit of experimentation moving the slope up and down is needed.
Steve
Try and find a large bolt such as an M20, then use your vernier (assuming the edges are sufficiently feathered) to measure the diameter at the base of the thread at several points along the length, including near the very end and you should see it remains pretty constant.
You should also see a video on how a thread is created in a thread turning operation on any CNC machine. To me, moving the helix in, while aesthetically âcorrectâ, breaks the reality of how your underlying geometry definition is produced. Even on a proper higbee thread, the tool that turns or thread rolls the helix doesnât just âbite downâ at the end. Infact, they often taper outwards (at the screw/bolt head end), the opposite of what the modelling strategy may be by crushing the helix.
That is a fictitious feature of thread making.
Havenât you ever successfully shortened a fastener and properly deburred it to function correctly?
âSpiraling the helix inwardsâ has nothing to do with it, and is completely unnecessary.
1.) no.
Hb which theory is correct?
Music to my ears 
Finally someone who knows 
