Helix extrusion for multiple thread

[MarcusWolschon]

I am designing a double-start thread.
So my sketch designs both sides of the axis and then I do a helical extrusion.
Somehow the helical extrusion tool creates geometry below the start of my thread and one thread ends early at the end.

PS:
My Alibre version is 2018.0.1 [build 19033] because I'm using the removed mesh functions a lot.
Consequently I don't know if this bug still exists in current versions.

 

[bigseb]

I would guess that since a helix is not that different to a sweep that the one sketch figure is doing an extra half turn so that the two end faces coincide.

Either separate the two sketch figures and create two separate helical features or lower the current sketch and then trim the feature.

 

[MarcusWolschon]

Yes. That's a workaround.
But as I see it, that's not how the helix-extrusion tool SHOULD behave.
Can anyone test if current versions of Alibre Design still behave this way?

Workaround:
Since dimensions are given in diameter, I made one side a reference.
Then made another sketch projecting the first and making it no longer a reference.
Then a second helix extrusion.
(I could also have used the rotary pattern of the feature, count=2 degrees=180.)

Sad that I can't export a collection of multiple features as one catalog-feature (and no helix extrusions anyway),
so I can't have the entire connector as a catalog feature to use serveral times.

 

[HaroldL]

However Alibre is repositioning the sketches it looks like it still creates the 2-start thread. After some trimming on the start end it shows the two starts opposite each other.





And if you remove one of the threads...



I don't think you need any "work arounds" but a little clean up on the ends, but that depends on how you want the ends to look.

 

[MarcusWolschon]

Thanks for testing this in a current version.

"a little clean up at the end" doesn't cut it because the second thread doesn't start with a vertical face like it should.
(Well, it does but pitch/2 below the proper location.)
I actually tried that as my first workaround.

However, in this thread, the start faces gets a well defined chamfer.
(It's a modified Luer Lock outside thread.)

So a rotary pattern seems to be the easiest workaround for this misbehavior and also allows for 3x and more threads.