Hi Michael,

Following on from your example on how to do a screw thread, I've seem to have found a problem?
I've included the file for you to see.

I first created a Helix of 6 twists to test, but couldn't get it to sweep? (centre at X0, Y0)
I then created another the same in reverse, but it also wouldn't sweep?

I then decided to try moving the starting point for where the Profile would start & it worked??
I also tried a couple of different amount of twists & they worked??
I then redid the 6 twist, but with the start point rotated away from the Profile & now it works??

So is this just me or is this one of those "oddball" situations or a bug???

regards Colin

Hi Colin, thanks for reporting this - it is definitely a bug with sweep.

It's triggered specifically by a 6 loop helix (or I suppose any multiple of 6 like 12, 18, 24, etc..).

What happens is the sweep is doing one phase of work checking for things at 7 different stations along the rail, like 0, 1/6, 1/3, 1/2, 2/3, 5/6, 1 - and it gets messed up if the profiles at all of these stations are all completely lined up with one another in one straight line.

I should be able to fix it up, but I'm kind of worried about altering the way sweep does its calculations just immediately before the v1 release. I think that to be safe (to make sure there aren't adverse side effects from changing it), I should probably wait to apply this fix a little bit later instead.

There is a workaround you can use to make sweep work for this case of a 6 / 12 / 18 / 24 loop helix: select the triangle and use Transform / Array / Curve, and then select the helix as the path curve. Set Rotation: Flat (this is the same kind of thing as Twist in sweep), and set the Item count to some number that will distribute some profiles in such a way that they are not completely lined up vertically, for example Item count = 5. That will give you this:



Now select all those 5 triangles and then do Sweep - it should now work with the profiles arranged like this, or basically with any kind of non-single-column vertically stacked arrangement.

Thanks for posting the example file! I have saved that off and put a note on my todo list to implement the fix a bit later.

- Michael

Hi Michael,

Thanks for explaining that & giving us a work around.

This isn't really a big problem, it's just that at first I couldn't figure out why it wouldn't work?
I agree with you that this oddity with Sweep & a certain amount of twists on a Helix can wait till after V1.
Just like with the Fillet tool, we now all know it's limitations & how to work around it in the meanwhile.

Also just for anyone else's reference, you need to create your Helix in a vertical Z position to do the Sweep.
I first made the mistake of trying to do it with the Helix in a horizontal Z & at first couldn't get the Sweep to work correctly.
I was just about to report another possible bug, but after rereading your example, I realised what I was doing wrong.

regards Colin