Sweep with taper?

[Bruce Kieffer]

Can this be done? Take a look at the screw threads I created by sweeping a line and adding a pitch (see the attachment). I want the threads at the tip to follow at diminishing radius.

[Benson Shaw]

Bruce - I keep running in to this, too, but always end up solving it with diminish "by hand". I don't think there is a way with sweeps or helixes, or others. The tools allow change of radius, or change of rotation, or other, but no combos of these for the diminishing thread you are asking for. Please, someone, prove me wrong!

Here is my solution with a loft (what else would it be from me?):

Make the 2d shapes of the thread, but four times as many (mine repeat in sets of 4 - black, blue, green, yellow, . . .). Scale and relocate the diminished ones at each end of the screw profile.

Convert them to NURBS and rotate them in color sets around the axis - Black ones stay in place, 90? for the blues, 180? for the greens, 270? yellows. Select Similar tool helps here.

Then loft - round and round you go from bottom to top hitting each color in turn on each layer. The loft here is a separate object from the base screw shape (a sweep), but one could probably make a solid addition of the two shapes.

-B

[img:left]http://techboard.vectorworks.net/ubbthreads.php?ubb=download&Number=8886&filename=ThreaddLoft.png[/img]

Edited April 2, 2013 by Benson Shaw

[Kizza]

Could you not develop the diminishing thread of the screw by a solid subtraction?

[Bruce Kieffer]

Benson,

Very nice!

Kizza,

I tried subtracting a solid from the sweep, but VW can't figure the math.

[Benson Shaw]

I don't think subtracting can make the thread wrap the point. Subtraction just truncates the thread, leaving a nail-like point.

Take a close look at a bugle head (aka sheetrock screw) or other screw to see the threads wrapping all the way to the point. The threads start low at the head end, "grow" to full height along most of the screw, then diminish in height as they wrap the point.

All that detail is probably unnecessary in a screw symbol placed in a drawing, but it is an interesting drawing/modeling challenge. Someone does same detailing when a screw is designed for mfg!

-B